Progressive Crop Consultant - May - June 2016

Progressive

Crop Consultant The Leading Magazine For CA Ag Professionals

May - June 2016 Grapevine Red Blotch or Leafroll Disease Emerging Diseases Threatening the California Citrus Industry New IPM Solutions for Managing Insect Pests in California Strawberries Don’t Let NOW Monitoring Fall Off Your Radar

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In This Issue 6

Grapevine Red Blotch or Leafroll Disease Are these viruses having an impact in your vineyard?

Contributing Writers & Industry Support The Almond Board of CA Contributing Writer Larry Bettiga Viticulture Farm Advisor UCCE Monterey, San Benito and Santa Cruz Counties Surendra K. Dara Strawberry and Vegetable Crops Advisor, UCCE San Luis Obispo, Santa Barbara and Ventura Counties, and Affiliated IPM Advisor, UC Statewide IPM Program Steven J. Klosterman United States Department of Agriculture, Agricultural Research Service (USDA ARS) Mojtaba Mohammadi, Ph.D. CRB, Associate Science Editor

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Citrus Research Board

12

Spinach Downy Mildew

18

Almond Fertility Protocol

20

New IPM Solutions for Managing Insect Pests in California Strawberries

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Nitrogen Applications

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Don’t Let NOW Monitoring Fall Off Your Radar

Cecilia Parsons Contributing Writer Amy Witt CRB, Communication Assistant

UC Cooperative Extension Advisory Board Kevin Day

County Director and Pomology Advisor, Tulare/Kings County

David Doll

UC Farm Advisor, Merced County

Dr. Brent Holtz

County Director and Pomology Farm Advisor, San Joaquin County

Steven Koike

Threat, Prevention and Control

Revolutionizing How Growers Apply Nitrogen

Not Always Uniform in Vegetable Crops

Plant Pathology Farm Advisor

Emily Symmes

Integrated Pest Management Advisor, Sacramento Valley

Kris Tollerup

IPM Advisor, Parlier, CA

The articles, research, industry updates, company profiles, and advertisements in this publication are the professional opinions of writers and advertisers. Progressive Crop Consultant does not assume any responsibility for the opinions given in the publication.

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Emerging Diseases Threatening the California Citrus Industry

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Grapes

Grapevine Red Blotch or Leafroll Disease Are these viruses having an impact in your vineyard?

Larry Bettiga Viticulture Farm Advisor UCCE Monterey, San Benito and Santa Cruz Counties

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rapevine leafroll and red blotch disease are two virus-associated diseases that should be on the radar of all grape growers.

The following article will hopefully provide you an update on these virus diseases based on our current knowledge. Summer surveying of vineyards for visual leaf symptoms is a great time to assess vineyard blocks for the presence of disease.

Grapevine Leafroll Disease Leafroll is one of the more important virus diseases of grapevines. It occurs in every major grape growing area of the world.

There are five grapevine leafroll associated viruses (GLRaVs) that are serologically distinct. These single stranded RNA viruses are placed in a family called Closteroviridae. The majority of these are grouped in the genus Ampelovirus (GLRaV-1, -3, and -4), most of the viruses in this genus have been demonstrated to be vectored by mealybugs and scale insects in vineyards.

GLRav-2 is in the genus Closterovirus, and GLRaV-7 is in the genus Velarivirus, there is no known vector of these two genera.

These viruses can cause similar symptoms in infected grapevines. All the GLRaVs can be transmitted by vegetative propagation and grafting; GLRaVs in Ampelovirus can also be transmitted by the mealybugs and soft-scale insects in vineyards. GLRaV-3 is the predominant species Page 6

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found in most vineyards worldwide. Recent surveys in the north coast have shown 80% of symptomatic vines sampled were infected with GLRaV-3.

To further complicate matters there are variants that have been identified for given GLRaV species. For GLRaV-3 there are several distinct variants known to exist.

What needs to be better understood is the significance of these GLRaV-3 variants and their interactions with other viruses when multiple infections exist in a vine. For GLRaV-2 the “Red Globe” variant is known to cause graft incompatibility when grafted onto certain rootstocks (5BB, 5C, 3309C and 1103P) resulting in the decline and death of vines.

In the post-phylloxera infestation plantings that have occurred in coastal California during the past 20 years there has been an increased incidence of grapevine leafroll disease. The use of non-certified scion material has been a major contributor to this disease increase. The other issue has

been the spread of leafroll (primarily GLRaV-3) from infected vineyards to adjacent vineyards planted with California-certified stock. UC research documented the rapid spread of leafroll into a certified planting from an adjacent infected block. During the 5 years of observation the annual rate of increase in leafroll symptomatic vines was more than 10% in a Napa Valley site.

Recognizing Leafroll Leaf symptoms become visually apparent by early summer and generally intensify into midsummer and fall. Physical stresses to the vine may increase symptom severity and there are similar symptoms caused by other abiotic and biotic injuries. On affected vines, the margins of the leaf blades roll downward, starting with the basal leaf on the cane. Areas between the major veins turn yellow or red, depending on whether the cultivar produces white or red fruit.

In some cultivars, the area adjacent to the major veins remains green until late fall.

Leafroll disease on Pinot noir (left) showing burgundy red between green main leaf veins accompanied by downward rolling of the leaf margins; on Chardonnay (right) leaves show a more generalized chlorosis and downward rolling of the leaf margins in late fall.

May/June 2016

The most important effect of leafroll disease is a reduction in the yield and quality of fruit from infected vines. Yield losses of 10 to 20% are fairly typical. Because leafroll viruses damage the phloem of infected vines, sugar accumulation is delayed and color pigment production is reduced. Fruit from infected vines can be low in sugar, poorly colored, and late in ripening.

It is important to remember that the lack of symptoms in a grapevine does not guarantee freedom from infection by the viruses that are the causal agents of leafroll disease.

Lab Testing Leafroll viruses may be diagnosed using ELISA and RT-PCR tests. Virus titer levels are variable not only within the year, but also within the vine. Collect petioles in late summer and fall, or shoots/canes for cambium scrapings in fall and winter. PCR and ELISA tests are not available for all GLRaVs. Check with the commercial lab for their preferred sampling method and collection time prior to taking samples.

Mealybug Vectors The most common mealybug found in California vineyards is the grape mealybug (Pseudococcus maritimus). Obscure mealybug (P. viburni) is present in central coast vineyards but less common than the grape mealybug. The vine mealybug (Planococcus ficus) was introduced into California in 1994 and has now been found in most production area of the state. Less common is the long-tailed mealybug (P. longispinus) found primarily in the cooler areas of the south central coast. The Gill’s mealybug (Ferrisia gilli) is the fifth species found in California but is currently very limited in distribution with populations found in the Sierra foothills, in the northern coast (Lake County) and in the southern San Joaquin Valley.

All the above species are capable of being a vector for leafroll disease. Research has shown that mealybugs can become infective after one hour of feeding on a leafroll virus infected vine and can transmit the virus to a clean host after one hour of feeding. Although all female instars can transmit the virus once infected, the first instar is the most effective vector of the disease. The first instar or “crawler” moves to find a feeding spot and is considered to be the most common dispersal stage of a mealybug population. Wind, equipment, workers and infested nursery stock can also move mealybugs.

Management of Grapevine Leafroll Disease 1. Plant Material.

The first management strategy should be to plant certified vines that have been grown and produced by a nursery participating in the California Grapevine RegistraNature’s Energy Powering tion and Certification Soils for Enhanced: Program. Once virus infected a vine will • Biodiversity remain infected, there is no cure. Commercial • Fertility nurseries that produce • Fertilizer efficiency certified grapevines • Nutrient Uptake and participate in the California Grapevine • Sustainability R&C Program obtain their clean stock from the Foundation Plant Activate™ • Azomite • Mycorrhizae • Nature’s Solution™ Services at the University of California, Davis.

UC Davis has a foundaProducts by Natural Resources Group tion vineyard for grape cultivars and clones.

Before being planted in the foundation vineyard, all vines are tested across biological toms. Leafroll symptoms become visually indicators, and by ELISA and RT-PCR. apparent by early summer and generally The foundation vineyard is monitored by intensify into midsummer and fall as noted visual inspections in spring and fall, and a above. Symptoms can vary by leafroll speportion of it is retested every year by ELISA cies, multiple virus infections, and by cultiand RT-PCR for viruses known to spread var and rootstock combination. Symptoms naturally. This provides the highest level are generally more apparent in cultivars of confidence about the virus status of the producing red or black fruit than in white selections. fruiting cultivars. Remember that the lack of Both the fruiting scion and the rootstock symptoms in a grapevine does not guarantee need to come from certified mother plants. freedom from infection by the viruses that A very common spread of leafroll is the are the causal agents of leafroll disease. use of infected bud wood from commercial 3. Recognize and be aware of potential vineyards. The lack of symptoms in the leafroll vectors. As discussed above mealysource vineyard cannot be relied upon as bugs and scale insects are known vectors a guarantee that there is no virus; many of some species of GLRaVs. Monitor and of the major grapevine viruses show no be aware of which insect vectors may be in symptoms during some or all of the season. your vineyards. More information on these Particularly if wood is collected during insects is available in Grape Pest Managethe dormant season, it is unlikely that the ment UCANR publication 3343 or in the source vines will show distinct symptoms online UC IPM guideline for grapes, http:// of virus infection. Selected grapevines www.ipm.ucdavis.edu. Know which species should also be pre-tested for virus by a of mealybugs are present in your vineyards, competent diagnostic laboratory if this their population dynamics are different type of material is going to be used. Even and will influence the timing of any needed with vine testing, sourcing bud wood from control practices. European fruit lecanium established vineyards carries a risk of intro- scale (Parthenolecanium corni) is a comducing virus into a new planting.

Continued on Page 8 2. Learn to recognize leafroll symp-

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grape herbarium collection at UC Davis has shown one plant specimen collected

by Harold Olmo in 1940 from a Sonoma County vineyard to be positive for GRBaV, indicating this virus has been present in California for quite some time.

Recognizing Red Blotch In red wine cultivars, irregular red blotches form on the leaf blades on the basal parts of shoots. Veins on affected leaves can turn pink to red in color. Symptoms can vary between cultivars and the severity may also vary between years. In white cultivars the symptoms are not as dramatic.

Interveinal chlorosis is most common followed by irregular chlorotic blotches. These symptoms can begin to appear as early as July and as late as September. In comparing red blotch to leafroll disease, leafroll symptoms are generally more uniform across the leaf blade, the veins remain green, and there can be a downward rolling of the leaf margin. For more pictures of red blotch symptoms on different cultivars go to: http://cesonoma.ucanr.edu/viticulture717/ .

Late summer symptoms on Chardonnay, red blotch on the left and leafroll on the right.

Continued from Page 7 mon insect found in California vineyards, it and other scale insects have been shown to transmit some GLRaV species.

4. Be aware of potential spread from leafroll infected blocks. Leafroll infected blocks can be a source for vector and disease spread into adjacent clean plantings. Consider if plant removal is a viable option to reduce further spread for both the source and clean blocks. Vector control may be a management decision to consider.

Recent research suggests the rate of disease spread of GLRaV-3 is greater when higher mealybug population levels are present.

Treatment of virus source blocks should minimize the infective vectors leaving the block; the treatment of clean blocks should be targeted to kill infective vectors quickly upon entering the block and to reduce secondary spread to adjacent vines.

5. Area-wide management. When both mealybug populations and the virus causing leafroll disease are present in an area, Page 8

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cooperation between neighboring vineyard owners will be necessary to improve on reducing the spread of disease from infected source blocks to non-infected vineyards.

Grapevine leafroll disease is actively being studied both here in the US and internationally. Improvements in identification techniques and better understanding of disease epidemiology in vineyards will hopefully improve our ability to develop management practices to reduce economic impacts.

Red Blotch Disease Grapevine red blotch disease was suspected as a concern on vines growing in the Napa Valley in 2008. In 2011 a DNA virus was identified in independent studies in California and New York and shown to be associated with the symptoms on infected vines. Since the initial identification of Grapevine red blotch-associated virus (GRBaV), it has been found to be widespread in vineyard producing areas of the United States and Canada. A recent survey of a

May/June 2016

Lab Testing The identification of GRBaV can be difficult to determine by visual observation due to the similarity of the symptoms to leafroll disease and other nutrient deficiencies. This is especially true in the case of white cultivars. Co-infections with other viruses can also affect symptom expression.

Suspected infections should be confirmed by having samples assayed by a PCR test by a commercial diagnostic lab. Check with the commercial lab for their preferred sampling method and collection time prior to taking samples.

Disease Spread GRBaV is spread by the propagation of planting stock or grafting non-infected vines using infected budwood. The widespread occurrence of red blotch disease would suggest this type of spread has occurred. Since the identification of the virus and the availability of the PCR testing in 2012, grapevine nurseries have been testing their increase blocks and removing infected vines to eliminate this type of spread. The recently established Russell Ranch Foundation Vineyard at UC Davis has been tested and all vines are free from GRBaV. Each vine planted at the Russell Ranch has undergone extensive virus testing following a process known as Protocol 2010. For nurseries participating in the CDFA R&C

Feeding damage from three-cornered alfalfa treehopper can cause a reddening of shoots and leaves in red cultivars.

Arrows point to feeding sites that can result in a girdle.

Program this will provide a source for future increase blocks to supply certified vines for vineyard plantings.

GRBaV is a DNA virus and is closely related to a family of viruses called Geminiviridae. Insects such as leafhoppers and whiteflies can vector other virus diseases within this family. Researchers have been testing potential insect vectors of GRBaV. Although there was a report of Virginia creeper leafhopper being a vector in a greenhouse study other researchers have been unable to duplicate that study. Recently, the three-cornered alfalfa treehopper (Spissistilus festinus) has been shown to be a vector of GRBaV by Brian Bahder, Mysore Sudarshana and Frank Zalom from UC Davis. The three-cornered alfalfa treehopper is an occasional pest of grapevines being observed primarily in coastal and Sierra foothill vineyards. Grapes are not a preferred host of this treehopper which prefers grasses and legumes. On red cultivars when feeding punctures are concentrated around a petiole or shoot they can cause girdling which turns the leaf blades distal to the girdle red. This symptom is less obvious on white cultivars. This may not be the only vector that can spread GRBaV and researchers are continuing research on other potential species. This initial discovery does help to explain the vine to vine spread of red blotch disease reported to have occurred in vineyards. Additional research will be necessary to fully understand the impact and potential management strategies to deal with vector spread of red blotch disease.

Vine Effects Research has shown that when comparing GRBaV infected vines to ones that have no known GRBaV, leafroll-associated viruses, vitiviruses, or Nepoviruses that Brix were lower and malic acid in the juice were higher at harvest for Cabernet Sauvignon and Chardonnay but not Zinfandel.

For Chardonnay, yield was also reduced for infected vines. A study looking at the effect of dropping crop to improve quality on infected vines saw little beneficial effect from that practice. For most cultivars, there is a decrease in total phenols, tannins, and anthocyanins (for red wine cultivars) for vines infected with GRBaV. Management of Red Blotch Disease As with leafroll disease the first management strategy should be to use propagation material that is free from known viruses when establishing new vineyards or grafting existing sites. Meetings of the Grapevine Regulations Working Group have been recently conducted to discuss proposed changes to the Grapevine Registration & Certification Program with regards to red blotch disease. Until budwood increased from the Russell Ranch Foundation vineyard is available for use it is important that propagation material is tested to avoid virus disease.

If you have blocks that have leaf symptoms and have had delayed maturity or low crop yield have a virus panel run by a commercial lab to confirm which viruses are present. Remember symptoms are going to be more noticeable in red wine cultivars and less so with white cultivars. For confirmed GRBaV infected vineyards the management response may vary depending on the vine effects that are being observed.

The difference in sugar accumulation between infected and non-infected vines in some vineyards has been as much as 5 Brix. In vineyards with a combination of infected and non-infected vines this wide variation in maturity has resulted in selective harvests to improve fruit uniformity.

For infected sites that fail to meet yield and quality expectations vineyard removal is the best solution. If only a low percent of vines in a block are infected, then rogueing and replanting is an option. PCC

References Al Rwahnih, M., et al. 2013. Association of a DNA virus with Grapevines affected by Red Blotch disease in California. Phytopathology 103:1069-1076.

Daane, K. M. et al. 2012. Biology and management of mealybugs in vineyards. p. 271307. In: N. J. Bostanian et al. (eds.), Arthropod Management in Vineyards: Pests, Approaches and Future Directions. Springer. 505p Golino, D. A., et al. 2002. Grapevine leafroll disease can be spread by California mealybugs.

California Agriculture 56:196-201.

Golino, D. A., et al. 1992. Grapevine virus diseases. In: Bettiga, L, (ed.), Grape Pest Management, 3rd ed. Oakland: University of California Division of Agriculture and Natural Resources, Publication 3343, 157-173.

Golino, D. A., et al. 2008. Leafroll disease is spreading rapidly in a Napa Valley vineyard.

Calif. Agric. 62:156-160.

Krenz, B., Thompson, J., et al. 2012. Complete Genome Sequence of a New Circular DNA Virus from Grapevine. J. Virol. 86:7715.

Krenz, B., et al. 2014. Grapevine red blotchassociated virus is widespread in the United States. Phytopathology. First Look.

Oberholster, A., et al. 2015. Impact of red blotch disease on grape and wine composition and quality. American Society of Enology and Viticulture National Conference Technical Abstracts, p. 75. (2015).

Poojari, S., et al. 2013. A leafhopper transmissible DNA virus with novel evolutionary lineage in the family Geminiviridae implicated in grapevine redleaf disease by nextgeneration sequencing. Plos One 8:e64194.

Sharma, A. M. et al. 2011. Occurrence of grapevine leafroll-associated virus complex in Napa Valley. PLoS One 6(10): e26227.

Smith, R., et al. 2015. Effect of crop reduction of vines infected with grapevine red blotchassociated virus on fruit maturity. American Society of Enology and Viticulture National Conference Technical Abstracts, p. 136-137.

Sudarshana, M. and M. Fuchs. 2015. Grapevine red blotch In: Wilcox, W., et al, (eds.), Compendium of Grape Diseases, Disorders and Pests, 2nd ed. The American Phytopathological Society.122-123.

Tsai, C. W., et al. 2010. Mealybug transmission of grapevine leafroll viruses: Analysis of virus– vector specificity. Phytopathology 100:830-834.

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Citrus

Citrus Research Board

Emerging Diseases Threatening the California Citrus Industry

HLB-infected citrus tree with a significant fruit drop.

Mojtaba Mohammadi, Ph.D. CRB, Associate Science Editor Amy Witt CRB, Communication Assistant

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s the California citrus industry has been threatened by Huanglongbing (HLB) and Asian Citrus Psyllid (ACP), the importance of postharvest technologies and practices are increasing. As industry professionals unite, research and technology is directly focused on battling and conquering this issue through the allocation of resources. The California Citrus Research Board (CRB) is dedicated and determined in helping our industry succeed in conquering these foes.

Long before citrus became a viable commercial crop in California, Spanish missionaries who settled in southern California during the 1700s, were already cultivating citrus believed to have originated from southeast China thousands of years earlier.

With a thriving citrus industry, Page 10

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growers lobbied for the establishment of a research facility that would address production issues. On February 14, 1907, the first Citrus Experiment Station was established in Riverside which became the cornerstone of the UC campus to be born in 1954. The station has been in the forefront of citrus genetics, breeding, physiology and postharvest studies and introduced into the market new citrus varieties such as Ojai Pixie tangerine, Gold Nugget tangerine, Oroblanco grapefruit and Tango seedless mandarin.

The station celebrated its 100th anniversary in 2007. The UC Riverside Citrus Variety Collection holds more than a thousand different varieties from all over the world.

Today, the California citrus industry is valued at two billion dollars per year and produces fresh-market citrus such as navels, Valencia, lemons, grapefruit and tangerines (Figure 1, pg.11). Because of the rise in urbanization in southern California which used to be the state’s original belt for citrus production, the in-

May/June 2016

dustry has moved to San Joaquin Valley.

The California Citrus Research Board (CRB), located at 217 N. Encina, P.O. Box 230, Visalia, California 93279, is a non-profit organization that was established in 1968 to administer a research-based program on various aspects of citrus production and protection under the California Marketing Act of 1937.

The program is funded and directed by California citrus growers to sponsor and support needed scientific and technical research to further the goals of the California citrus industry. Although not formally a government agency, the CRB must follow rules and regulations that apply to commodity boards.

Currently, the biggest threat to the commercial citrus production in California is a deadly bacterial disease known as huanglongbing (or HLB) meaning yellow dragon disease in Chinese or simply citrus greening. The phloem-limited, fastidious bacterium that is associated with HLB is called “Candidatus Liberibacter asiaticus”. It is transmitted by the

Figure 1

Adult Asian Citrus Psyllid.

Photo Credit: J. Lewis

Asian citrus psyllid (ACP) (Diaphorina citri (Kuwayana) after feeding on leaves and stems of a citrus tree. The disease can also be spread by grafting an infected budwood or root stock onto another plant. The bacterium colonizes the phloem cells in the diseased plant and plugs off the sieve tubes blocking the flow of water, minerals and nutrients into the roots and other parts of the plant. As a result, the plant suffers from nutrient deficiency such as phosphorus and gradually declines within a few years. HLB is a century-old disease endemic to Asia. The disease was first discovered in Florida in 2005 and in Los Angeles County, California in 2012. In Florida, where HLB is prevalent, citrus production has been decreasing at an alarming rate.

The infected tree remains symptomless for at least a year and hence can serve as a source of bacterial inoculum for transmission by ACP to healthy trees if not identified and subsequently removed.

Symptoms include blotchy mottled leaves, miniscule and lopsided fruits, premature fruit drop, reduced acidity in the juice and a bitter taste. Currently, there is no cure for HLB. Almost all citrus cultivars and hybrids including some relatives are susceptible to HLB. The three-prong approach to mitigate the disease includes: a) removal of infected trees, b) use of disease-free nursery stocks and c) use of insecticide sprays to suppress ACP populations. Other coordinated actions already in place in California include establishment of quarantines to ensure that people are not moving around infested or infected plant material and increased public awareness and education through effective outreach programs. These programs will continue into the future as long as HLB poses a threat.

Through the Citrus Research Board, California citrus growers have invested

substantial amounts of money on ACP/ HLB research projects over the years hoping to find short-term and long-term solutions to this devastating disease that could pose a major threat to the citrus industry in California. The CRB also funds research projects dealing with pre- and post-harvest diseases of citrus in California. One such project is evaluating new fungicides prior to harvest for control of postharvest decays in citrus. Further, a survey is conducted to determine the prevalence of postharvest decays affecting mandarins in the California Central Valley, particularly those caused by Botrytis cinerea (gray mold) and Mucor spp. (Mucor rot). Fungicides are being evaluated to control these post-harvest diseases as well. Another project has been evaluating a new bio fungicide (Exp-13) to control post-harvest diseases such as green mold and sour rot. These projects also study fungicide resistance among various strains of fungi causing

post-harvest decays. Septoria spot in oranges, caused by Septoria citri, is another pre- and post-harvest fungal disease in California that can affect citrus exports to Asia. Research is being carried out to manage the disease through developing and validating a forecasting and risk assessment model using pre-harvest fungicides.

HLB could potentially devastate the citrus industry. With collaborative efforts from many other organizations and individuals, the CRB is committed to not allowing this to happen. As professionals in the industry, we must work together to problem-solve and take on one of the biggest challenges the citrus industry has ever looked in the face.

On October 19th, the CRB will be hosting the California Citrus Conference.

This one-day event is geared toward hearing from the best of the best scientific researchers within the citrus industry. The event will be held at the Exeter Veterans Memorial Building in Exeter, California. There will be no admission or registration fee and lunch will be provided. For information or to sponsor the event, please contact Amy Witt at amy@ citrusresearch.org. PCC Mojtaba Mohammadi, Ph.D. is the Associate Science Editor for the CRB and the CRB’s publication, Citrograph. Amy Witt is the Communication Assistant for the CRB and the CRB’s publication, Citrograph.

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Spinach

Spinach Downy Mildew Threat, Prevention and Control

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May/June 2016

Steven J. Klosterman United States Department of Agriculture, Agricultural Research Service (USDA ARS)

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Photo Credit: Steven J. Klosterman

ntroduction – disease symptoms and the spinach downy mildew pathogen Downy mildew diseases of crops can be very difficult to control, especially when synthetic chemical fungicides are not available, or their usage is not allowed, as in organic production. As in the case with most other crops damaged by downy mildews, spinach downy mildew disease culminates in the field with yellow spots on the leaves (chlorosis) as shown in Figure 1A. Examination of the underside of the diseased spinach leaf reveals gray downy masses (Fig. 1B) of microscopic spores (also known as sporangia, plural) that are borne on structures known as sporangiophores (Fig. 2A). Sometimes the fuzzy mat of sporangia and sporangiophores appears purplish and can also form on the top leaf surface, though less commonly. Microscopic sporangia can readily become air-

A

B

Photo Credit: Steven J. Klosterman

Figure 1. Typical symptoms and signs of downy mildew on spinach. A) Top of an infected leaf revealing chlorotic spots; B) The underside of the same leaf exhibiting gray-brownish masses of sporulation from the downy mildew pathogen.

A

B

Figure 2. Asexual and sexual spores formed by Peronospora effusa, the cause of downy mildew on spinach. A) A single oval-shaped sporangium and the typical branching pattern of the sporangiophore on which the sporangia are borne; B) An oospore of the spinach downy mildew pathogen derived from a commercial spinach lot in 2014. The asexual sporangium and sexual oospore are microscopic, and each type is approximately 30 micrometers in diameter.

borne, and there may be thousands of these spores per leaf, each capable of causing another downy mildew infection on a nearby, or downwind, spinach plant.

Spinach downy mildew disease is caused by the pathogen Peronospora effusa, a scientific name abbreviated simply as P. effusa. The scientific name of the organism for the causal agent of spinach downy mildew has undergone changes over the last 150 years, and therefore, when scanning the literature on the topic of spinach downy mildew, these changes are important to keep in mind. For a period of about 50 years, until very recently, the pathogen was most commonly referred to in the scientific literature as Peronospora farinosa f. sp. spinaciae. The “f. sp.” refers to a form species of P. farinosa, that infects spinach, “spinaciae”. However, the available morphological and genetic data indicate that like other Peronospora species, P. effusa is distinct, requiring a name change to the original scientific name of Peronospora effusa.

Peronospora effusa belongs to a group of organisms known collectively as the oomycetes, which derive their name from the sexual structures, or the oospores, that they form. Oospores enable the oomycetes to survive 2-3 or more years, and therefore to potentially be transported long distances on seed and even survive long periods in the soil. The microscopic oospores of P. effusa have a very distinctive smooth, round wall (Fig. 2B) lacking spikes or other ornamentation found on the walls of the oospores of some oomycete species. For mating and the production of oospores to occur, available evidence indicates a requirement of two different mating types, borne on separate thalli (or bodies of two separate strains).

Peronospora effusa also has a very limited or narrow host range. Unlike some other related pathogens, or even many fungal pathogens, there is no evidence that P. effusa infects other crops and weedy plants found near spinach production areas. Rather, a series of pathogen cross-inocu-

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Continued from Page 13 lation tests dating back to the 1930s have repeatedly shown that P. effusa only infects spinach, and not related plants, even those within the same plant family (Amaranthaceae).

Like other downy mildews, P. effusa infection requires some leaf wetness, and the disease is also favored under cooler conditions.

Widespread use of overhead irrigation and dense spinach plantings in California and Arizona, where approximately 90 % of the U.S. fresh market spinach is produced, ensure that moisture levels are conducive for the disease.

Spinach Downy Mildew -- threat to organic spinach production There has been a dramatic increase in the amount of organic spinach produced over the last two decades in the U.S. Today, some estimates indicate as much as 30 % of all fresh market spinach is produced for the organic market. In the last ten years there has been mounting concern that the pathogen will be unstoppable due to a lack of durable resistance, especially for organic spinach production, where fungicides are not available to effectively control downy mildew. In fact, at an industry-sponsored meeting held in Seaside, California, in mid-2014, the alarm was evident, with some growers suggesting that organic production of spinach may cease within ten years in the U.S., due to losses caused by downy mildew. Thus, there is especially a need to establish downy mildew disease control measures or management methods that can be adopted for organic spinach.

Deploying spinach cultivars that are bred to resist downy mildew has been deemed the most effective strategy for managing this disease, at least for organically grown spinach. Just as plant breeders are able to breed spinach plants through natural genetic crosses, and select for particular traits, such as disease resistance, the pathogen populations also change and adapt very quickly to overcome this resistance. One of the reasons for the quick adaptation of the pathogen is the short lifecycle, Page 14

Progressive Crop Consultant

which produces thousands of offspring from a single leaf. In situations where a single gene for resistance is naturally bred into spinach, the pathogen has rapidly adapted and overcome this type of resistance.

Genetic variants, or different genotypes of the pathogen, with new pathogenic capabilities, may also arrive in a new area as oospores, like the one shown in Figure 2B. If these oospore populations contain new pathogenic traits, this could contribute to the breakdown of resistance. Durable (long-lasting) disease resistance is most desired, but takes additional effort over a longer period to breed for this type of resistance, which does not rely on one or two major genes. Inevitably this type of resistance will help to control downy mildew for conventional production as well, and even more cost-effectively with reductions in the use of fungicides.

While plant disease resistance has been the most important tool in the fight against downy mildew on spinach, spinach cultivars with resistance to all of the different pathogenic variants P. effusa have become increasingly scarce. In fact, no cultivar is currently resistant against all of the pathogenic variants. The spinach downy mildew pathogen populations in California and Arizona have demonstrated the remarkable ability to continuously overcome the genetic resistance to downy mildew that is bred into the spinach cultivars.

Hence, the threat to organic spinach production remains very real.

Short term solutions and preventative measures The United States Department of Agriculture, Agricultural Research Service (USDA ARS) in Salinas, California is currently leading collaborative efforts with University of California researchers to prevent pathogen introduction into cropping systems and to provide tools for growers and pest control advisors (PCAs) to diagnose the pathogen in the field early, before symptom development, to reduce or eliminate economic losses caused by spinach downy mildew. Aspects of this research are currently funded

May/June 2016

by both the California Leafy Greens Research Program and the California Department of Food and Agriculture Specialty Crop Block Grant Program.

Oospores, like the one shown in Figure 2B were recently identified in 13/82 (16%) of modern seed lots examined. This is disconcerting since oospores of this pathogen are predicted to survive 2-3 years in soil or on seed, based on what is known about similar organisms that produce oospores. The oospores can germinate and cause disease, as determined by a study conducted in Japan in the 1980s, and published in the journal Phytopathology. It is also the most likely explanation for the disease appearing on spinach fields “in the middle of nowhere” as one grower described it. Thus, the elimination or reduction of oospores arriving on spinach seed destined for organic production should be considered in protecting spinach crops against downy mildew.

In addition, early detection of Peronospora effusa using DNA-based techniques can be applied to determine whether leaves in a field are infected with the pathogen, but not yet showing symptoms. This can be a powerful advantage for the spinach industry. For organic production of spinach, such early detection tools can be valuable to cut losses and harvest the crop early. In many instances, there is still a chance to salvage the crop early, rather than having a devastating disease outbreak destroy the entire field.

For conventional spinach production, where synthetic fungicides can be applied for effective disease control, the new technology allowing early diagnosis in the field will enable the grower to determine whether to spray, thereby saving the rest of the crop from destruction.

Reducing overall fungicide usage also helps to reduce fungicide resistance in the pathogen populations.

Steve Koike (University of California Cooperative Extension, Monterey County) indicated that there are currently many effective fungicides available for preventative control of spinach downy mildew, if used properly. Some of these commonly

used products include Revus, Reason, Ranman, Presidio, and Aliette.

Another commonly applied fungicide for control of spinach downy mildew is Ridomil, which is applied at planting but not as a foliar application. So while there are many effective products to choose from, there are a multitude of other considerations about which fungicide to use, such as price and availability.

An additional consideration is P.H.I, or preharvest interval, since the field can be harvested more quickly with the use of certain fungicides with a shorter P.H.I. Currently, downy mildew disease forecasts and available models can be helpful, but even greater precision is required to guide those important decisions on the best timing for spray applications to maintain crop health. The research on this early detection approach in the field, in spinach leaves, involves replicate field studies, and should be completed within the next two years.

Research also conducted by the USDA ARS in Salinas, in collabo-

ration with the University of California, involves spore trapping, to detect airborne sporangia, like the oval-shaped one shown in Figure 2A. These efforts have led to a greater understanding of inoculum sources in the Salinas Valley of California, where a large portion of the U.S. fresh market spinach is produced between April and November. By monitoring the airborne spore traps using DNA-based techniques, the research revealed that a low level of the airborne pathogen is typical, as the pathogen DNA has been routinely detected, even in the winter months of December through March, when very little if any spinach is grown in the Valley. This makes timing spray applications based upon simple presence or absence of the pathogen impossible. However, the DNA assays from the spore trap samples are also quantitative. In other words, we know roughly how many spores are present (inoculum load) at a given time based upon the amount of DNA of the pathogen present. Thus, there is currently an ongoing effort by

USDA and University of California researchers to decipher how increases in local pathogen inoculum load in small areas of the Salinas Valley are impacted by various weather parameters for the purposes of disease forecasting. PCC The mentioning of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture (USDA). USDA is an equal opportunity provider and employer.

May/June 2016

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Page 15

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Photo Credit: Kathy Coatney

Almonds

Almond Fertility Protocol Revolutionizing How Growers Apply Nitrogen

The Almond Board of CA Contributing Writer

A

ccording to the new almond fertility protocol that is revolutionizing the way almond growers apply nitrogen fertilizers throughout the year, May is the time to make in-season adjustments to nitrogen budgets on the basis of April sampling results and adjusted yield predictions.

Under the new nitrogen (N) management protocol posted on the Almond Board website (note revised calculations on page 6 and 7) and discussed in previous issues of California Almonds Outlook, growers establish a preseason

Page 18

Progressive Crop Consultant

nitrogen fertilization plan based on predicted yields and all potential sources of N. From there, April tissue sampling results, along with early-season yield estimates, are used to fine-tune that nitrogen budget and make in-season adjustments.

By May, growers will have received lab results from April leaf tissue analysis, and can make adjustments in N rate through kernel fill according to those results.

In years of lower-than-expected yield with adequate April tissue N analysis, a reduction in mid-season N fertilization is suggested, while higher-than-expected yields might require an increase in N

May/June 2016

applications. Similar adjustments can be made in accordance with sampling results and scenarios, which are included in the protocol.

Lead researcher Patrick Brown (UC Davis, Pomology) has offered four basic scenarios for leaf tissue analysis and yield assessment, and basic strategies for those scenarios. The protocol lays out very simple formulas to make in-season nitrogen application rate adjustments based on whether tissue levels are adequate, low or high as determined by April sampling, and whether visual field estimates for yield in April and May differ from preliminary yield predictions. PCC

WHAT IS VITAZYME?

Vitazyme is a liquid concentrate microbially synthesized from plant materials, and then stabilized for long life. Powerful but natural biostimulants contained in the material greatly benefit plant growth and soil conditions to boost yields and profits for the farmer.

• Increase crop yields and profits • Improve crop quality • Reduce fertilizer nitrogen inputs and improve its utilization • Hasten germination and maturity • Improve soil structure and infiltration

BENEFITS TO SOIL

Soil structure is critical for air and water movement through the soil to facilitate root growth and nutrient uptake. This is improved by Vitazyme in at least four ways:

1 Increased root growth (more channels)

2 More polysaccharids to glue particles together 3 Improved mycorrhize activity (more sac-like structures) 4 More eathworms and their channels

BENEFITS TO YOU

• Inexpensive, very cost-effective

• Easy to use • Safe and nontoxic • Can be foliar or soil applied • Can be mixed with liquid fertilizers and pesticides

Doug Graham Certified Crop Advisor License #329563

Cell: 559-903-6007 | Tel: 559-686-3833 | Fax: 559-686-1453 doug@newerafarmservice.com | 2904 East Oakdale Ave., Tulare, CA 93274 May 2016

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Page 15

Strawberries Cosmetic damage to strawberry by lygus bug.

New IPM Solutions for Managing Insect Pests in California Strawberries Photo Credit: Surendra Dara

Surendra K. Dara Strawberry and Vegetable Crops Advisor, UCCE San Luis Obispo, Santa Barbara and Ventura Counties, and Affiliated IPM Advisor, UC Statewide IPM Program

W

estern tarnished plant bug (Lygus hesperus), also known as lygus bug, is a major pest of strawberries on the California Central Coast. Lygus bug feeding on developing berries causes fruit deformity.

Deformed or ‘cat-faced’ berries are not desirable for fresh market and lygus bug damage results in significant yield losses. Lygus bugs typically move into strawberry fields in early to mid-spring and thrive in fall-planted and summer-planted fields during the following months through multiple generations. Degree-day calculations and timing of treatments is difficult for lygus bug Page 20

Progressive Crop Consultant

management in strawberries due to multiple sources (wild and cultivated hosts) and continuous movement of populations among different hosts.

Conventional growers typically rely on pesticide applications and use of bug vacuums is gaining popularity in the recent years. Lygus bug management continues to be a challenge with these tools and emphasizes the need for IPM strategies that use several control options.

Studies conducted in 2012, 2013, and 2014 in commercial Santa Maria strawberry fields showed that non-chemical alternatives such as azadirachtin, entomopathogenic fungi, and bacteria-based pesticides can play an important role in managing lygus bug and other insect pests. Such botanical and microbial alternatives were also critical in managing twospotted spider mite,

May/June 2016

another major pest on strawberries. IPM approach beyond rotating chemicals among different modes of action groups is necessary for obtaining effective control, maintaining environmental sustainability, and reducing the risk of pesticide resistance.

An IPM study was conducted in 2015 at Sundance Berry Farms in the Santa Maria area using almost all management options available for controlling lygus bug. The following groups of options were used in different combinations and rotations and evaluated for their efficacy against lygus bug, western f lower thrips, and greenhouse whitef ly.

Chemical pesticides Pyrethrins (formulations proprietary and Brigade, IRAC mode of action group 3A – sodium channel

modulators), neonicotinoids [(formulation Assail 70 WP, IRAC group 4A), sulfoximines (formulation Sequoia, IRAC group 4C), and butenolides (formulation Sivanto, IRAC group 4D) – all of them are nocotinic acetylcholine receptor competitive modulators], f lonicamid (formulation Beleaf 50 SG, IRAC group 9C – modulators of chordotonal organs), and benzoylureas (formulation Rimon 0.83 EC, IRAC group 15 – inhibitors of chitin biosynthesis).

Botanical pesticides Different azadirachtin formulations were used (cold pressed neem, Neemix, AzaGuard, and Debug Turbo). Azadirachtin acts as an insecticide, insect growth regulator, antifeedant, and a repellent. Pyrethrum was present in two of the Beauveria bassiana formulations.

Entomopathogenic fungi Beauveria bassiana (formulation proprietary), Isaria fumosorosea (Pfr-97), and Metarhizium brunneum (Met 52 EC). Beauveria bassiana formulations had pyrethrum, azadirachtin or both.

Mechanical Vacuuming twice a week with one pass each time at a speed of 2 mph.

This study had 12 treatments that included an untreated control, Assail 70 WP alone, and vacuuming alone as grower standards. Treatments were administered on 26 August, 2 and 9 September, 2015 using a tractor-mounted sprayer. A spray volume of 100 gallons/ac was used for pesticide treatments. Each treatment had six 75’ long (4 row) beds and four replications distributed in a randomized complete block design.

Before the first treatment and 6 days after each treatment, 20 random plants from the middle two beds in each plot were sampled for insect pests and beneficial arthropods.

Number of young and old nymphs, and adult lygus bugs, thrips, adult whitef lies, big-eyed bugs, minute pirate bugs, lace wings, damsel bugs, ladybeetles, parasitic wasps, predatory thrips, predatory midge larvae, Continued on Page 22

Pre-treatment and post-treatment (average of three counts) numbers of lygus bug nymphs and adults in different treatments.

Percent change in lygus bug (all life stages) and various natural enemy (all species combined) populations after three spray applications compared to pre-treatment counts.

May/June 2016

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Page 21

Continued from Page 21 and spiders were counted from each sample plant. Data were subjected to ANOVA and significant means were separated using Tukey’s HSD test.

Lygus bug Lygus bug populations were very high during the study period (treatment threshold 1 nymph/20 plants) and control was difficult, in general. Sequoia/Sivanto/Beleaf rotation provided the highest control where there was a 29% reduction in all life stages compared to pre-treat-

ment numbers. Sivanto/Sivanto/ Vacuum treatment was the only other treatment that provided a 12% control. B. bassiana+pyrethrum/ Vacuum/Rimon+Brigade treatment prevented the population buildup and lygus numbers increased in all other treatments. The popular practice of vacuuming was ranked 6 th . Having two passes instead of one pass might increase the efficacy of vacuuming, but results emphasize that multiple tools need to be considered for managing lygus bugs in strawberries instead of relying on one or two options.

Ranking of the treatments based on percent change in lygus populations by the end of three spray applications.

Natural enemies Percent change post-treatment indicated that natural enemy populations were relatively higher in Pfr-97+Neemix/Pfr-97+Neemix/ Vacuum followed by Sequoia/Sivanto/Beleaf, and Sequoia/Sequoia/ Vacuum and B. bassiana+neem/B. bassiana+pyrethrum+neem/B. bassiana+pyrethrum.

Western f lower thrips Post-treatment counts showed that thrips populations were reduced only in Rimon+Brigade/Met52+Debug Turbo/Met52+AzaGuard and B. bassiana+neem/B. bassiana+pyrethrum+neem/B. bassiana+pyrethrum treatments.

Greenhouse whitef ly Adult whitef lies occurred at very low numbers during the study and population reduction from post-treatment counts was seen only in Vacuum/Sivanto+Debug Trubo/Rimon+Brigade, Sivanto/ Sivanto/Vacuum, and Rimon+Brigade/Met52+Debug Turbo/ Met52+AzaGuard treatments.

This study demonstrates the efficacy of various chemical and non-chemical tools in various combinations against lygus bug, western f lower thrips, and greenhouse whitef ly and growers can make appropriate treatment decisions based on these results.

Acknowledgements Thanks to Dave Murray for collaborations with this study, Ted Ponce for coordination, Sundance Berry Farms crew, Chris Martinez, Fritz Light, Tamas Zold, and Kristin Nicole Stegeman for their technical assistance, and industry partners for the supply of materials and/or financial support. PCC

Percent change in western flower thrips and adult greenhouse whitefly populations after three spray applications compared to pre-treatment counts.

Page 22

Progressive Crop Consultant

May/June 2016

Vegetables

Photo Credit: Michael Cahn

Nitrogen Applications Not Always Uniform in Vegetable Crops

Low flow (1/4 gph) pressure compensating drip emitters were used to collect samples of the irrigation water during the entire irrigation cycle Kathy Coatney Editor

A

major benefit of drip irrigation for vegetables is the application of fertilizer through the irrigation water.

This allows the crops to be spoon-feed nutrients like nitrogen (N), and avoid large applications of N fertilizer when the crop is small and uptake rates are low. This also minimizes losses of N through leaching.

Advantages of Drip Fertigation Drip fertigation has several advantages for managing N fertilizer, but it has to be well managed and use the best fertigation practices.

Drip systems with poor distribution uniformity may cause fertilizer to be unevenly distributed within a field, according to Michael Cahn, University of California Cooperative Extension (UCCE), irrigation and water resources advisor for Monterey County.

“One of the benefits with fertigating is you can also do smaller more frequent applications, so you don’t do large applications at once that would risk losing that nitrogen to leaching,” Cahn said, “But in some cases growers only do a few applications with the drip, too.”

Another advantage is the fertilizer can be applied later in the season when a tractor cannot get out there because Page 24

Progressive Crop Consultant

the canopy is too close together for any tillage, Cahn said. These later season applications give an extra boost in production, he added.

This also means less fertilizer is applied up front on the crop, and again, lessens the risk of it leaching into the groundwater.

How the fertilizer is injected into a drip system can affect the distribution of fertilizer to the crop. “Proper fertigation requires injecting at a steady rate,” Cahn said.

The fertilizer also needs to mix well with the water before it branches in the irrigation system, Cahn said. It’s important to use good procedures for good fertigating: • •

•

The drip system should be pressurized and most of the leaks fixed before fertilizing There should be enough time to flush out all the fertilizer, which can take 45 to 50 minutes to completely travel to the end of a 10 acre field A short irrigation is not going to provide enough time to clean out all of the fertilizer

There are some misconceptions, too, Cahn said. It is thought that if the fertilizer is injected quickly, it will go out quicker.

“That’s not true. It just depends on

May/June 2016

the flow rate in the drip tape,” Cahn said.

Reuse Vegetable growers on the central coast, retrieve the drip tape after each crop is harvested. The tape is repaired, and reused for eight to 12 crops. “This is the only way drip tape is affordable, Cahn said.

“Breaks and leaks in the tape are repaired using a splicing machine,” Cahn said.

“Splicing machines often do not fully repair leaks in tape, and emitters tend to plug over time unless the tape was adequately maintained by flushing and chemical treatment,” Cahn said.

Reusing drip tape can create issues, and one is uniformity of the drip system. Because the tape is reused for a number of crop cycles, leaks and poor uniformity of the tape definitely impacts the uniformity of the fertilizer application, Cahn said.

A major benefit of drip irrigation is the uniformity of irrigation and application of fertilizer, Cahn said.

“We never think about the uniformity of the fertilizer going out just like the uniformity of water. If some areas get less fertilizer than others, you’re going to have to put more fertilizer on just to Continued on Page 26

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May 2016

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Page 25

High Quality and Consistency in Sea-kelp AfriKelp - Improve the rooting, fruit set and retention, quality and quantity of agricultural crops.

www.afrikelpusa.com 1-877-AKUSA26 Continued from Page 24 keep the low areas at a sufficient level,” Cahn said.

Research In response to problems with fertilization uniformity, and with funding provided by the California Leafy Green Research Board, Cahn evaluated the uniformity of applied water and N fertilizer with drip.

Cahn conducted trials in 11 commercial lettuce fields irrigated by surface drip during the fall of 2012 and the spring of 2013.

All fields were planted with romaine or iceberg lettuce varieties on 40 or 80 inch wide beds. Field sizes ranged from eight to 20 acres, with maximum row lengths ranging from 600 to 1340 feet.

The drip tape was 7/8 inch in diameter, medium flow tape (0.34 gpm/100 feet), but it varied by manufacturer and age.

Irrigation, pressure, and fertilizer uniformity were evaluated at each site during a single irrigation event.

“Distribution uniformity of applied water for the 11 fields averaged Page 26

Progressive Crop Consultant

Splicing machines are used to repair leaks and breaks in drip tape.

73 percent and ranged from 38 to 88 percent. 100 percent represents perfect uniformity, and the industry standard for irrigation uniformity of surface drip is 85 percent. Fertilizer application uniformity averaged 67 percent and ranged from 46 to 82 percent in the 11 fields evaluated,” Cahn said.

One of the causes of poor distribution uniformity in some drip systems may have been related to pressure, Cahn continued.

“Pressure uniformity averaged 80 percent and ranged from 43 to 99 percent,” Cahn said adding some drip systems had very low pressures.

Cahn found a substantial percentage of emitters in some drip systems were plugged, which reduced the irrigation system uniformity. Leaks were also evaluated in five fields, and they ranged from one to five leaks per 1000 feet of tape.

“Significant leaks can potentially reduce drip uniformity by lowering the downstream pressure. Other limitations to good drip uniformity included: mixing different types of tape in the same field, fluctuating pressure during

May/June 2016

the irrigation, and row lengths longer than 800 feet,” Cahn said.

Conclusions Cahn found that the N fertilizer applied by drip had an average distribution uniformity of 77 percent when the injection was properly made.

“There were some operational errors,” Cahn said.

In general, most were injected correctly, but in one case the uniformity of the system was good, but there was a very poor distribution of fertilizer because the injection was not a sufficient distance for the fertilizer to mix with the water before it branched out into different beds, Cahn said.

Because of this, one side of the field got a lot more fertilizer than the other side, Cahn said.

The results also showed that the N fertilizer applied by drip irrigation was frequently distributed unevenly to fields because of poor uniformity in the drip systems, or because proper injection procedures were not followed. PCC

Field #

Lettuce Type

Bed width

Irrigation DU1

inches

-------------- % --------------

Pressure Uniformity

Plugged emitters

Average pressure

Tape leaks

%

psi

#/1000 ft

1

Romaine

40

58

54

82

5

7.2

--

2

Romaine

80

75

82

87

4

4.3

--

3

Romaine

80

81

73

62

1

8.3

--

4

Iceberg

40

80

75

89

2

13.8

--

5

Romaine

40

83

74

91

3

10.8

--

6

Romaine

80

46

66

79

16

4.6

--

7

Romaine

80

86

78

77

2

7.0

0.8

8

Iceberg

40

88

46

89

0

9.0

4.3

9

Romaine

80

38

32

43

2

3.5

0.4

10

Iceberg

80

81

80

86

3

7.2

3.4

11

Romaine

40

87

74

99

0

12.4

5.4

73

67

80

3

8.0

2.9

Average 1.

Fertilizer Uniformity

Distribution Uniformity of the lowest quarter

Lettuce Type

Field

Travel time

Irrigation time

Injection time

Flush time

Average row length

field size

-------------- hours:min ----------------

acres

Max row length

Injection location

------------- ft -------------

1

Romaine

1:04

5:20

0:23

4:30

8.0

610

620

well

2

Romaine

0:47

6:00

0:30

2:30

10.5

860

890

well

3

Romaine

0:40

7:00

0:20

4:20

20.2

940

1340

field, 2 valves

4

Iceberg

0:51

6:00

0:14

5:30

9.3

630

640

well

5

Romaine

0:22

6:00

0:13

5:00

8.7

530

640

field, 1 valve

6

Romaine

0:47

5:00

0:13

5:00

9.5

850

850

field, 1 valve

7

Romaine

0:40

6:00

0:22

3:00

8.5

600

675

field, 1 valve

8

Iceberg

0:41

5:20

0:19

2:30

10.6

685

800

field, 1 valve

9

Romaine

0:33

9:00

0:15

2:50

20.2

1030

1300

field, 2 valves

10

Iceberg

0:33

3:40

2:07

1:22

15.0

350

630

well

11

Romaine

0:47

5:00

0:13

5:00

18.3

575

600

field, 2 valves

0:42

5:50

0:28

3:46

12.6

696

817

Average

Tape Discharge Rate Field

Distribution Uniformity

Tape re-use

Wall thickness

%

# of crops

mil

Emitter spacing inches

Average pressure

Plugged emitters

Tape leaks

psi

%

#/1000 ft

measured

manufacturer

----- gpm/100 ft -----

1

58

15

8

8

7.2

5

--

0.28

0.34

2

75

>8

15

8

4.3

4

--

0.24

0.34

3

81

>3

10

12

8.3

1

--

0.34

0.34

4

80

10

10

8

13.8

2

--

0.42

0.34

5

83

10-11

10

8

10.8

3

--

0.41

0.34

6

46

4-5

10

8

4.6

16

--

0.24

0.34

7

86

3

10

8

7.0

2

0.8

0.31

0.34

8

88

12

10

8

9.0

0

4.3

0.39

0.34

9

38

2-3

9

12

3.5

2

0.4

0.23

0.34

10

81

4

8

12

7.2

3

3.4

0.23

0.34

11

87

3

10

12

12.4

0

5.4

0.43

0.34

8.0

3

2.9

0.32

0.34

Average

73

10

May/June 2016

www.progressivecrop.com

Page 27

Tree Nuts

Don’t Let NOW Monitoring Fall Off Your Radar

Pest control advisor Justin Nay checks a mummy nut baited wing trap in a Tulare County almond orchard. He counted nine females in the trap. Nay said the wing traps are preferred because they offer more access to NOW. Cecilia Parsons Contributing Writer

P

aying close attention to navel orangeworm (NOW) numbers as the growing season progresses could prevent unpleasant surprises at harvest for almond, pistachio and walnut growers.

Damage from this scavenger pest is more likely after mild winters and warm springs as populations can build quickly in the spring. Different growth stages in developing crops, orchard sanitation practices, and presence of biological control all play a part in developing a integrated pest management strategy for control of NOW. Season-long monitoring of NOW populations can be an effective tool in preventing crop damage.

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Progressive Crop Consultant

According to University of California Integrated Pest Management guidelines, NOW is a primary pest in almonds and has become significant in pistachio and walnut.

The value of these crops is driving growers and pest control advisors to become more vigilant in their assessment of pest numbers. Monitoring NOW numbers in orchards with lures and traps, counting NOW infested mummy nuts and assessing crop damage are essential for control decisions.

Kris Tollerup, a University of California IPM specialist at the Kearney Research Center in Parlier notes that monitoring for NOW is different from coddling moth or Oriental fruit moth because there is no diapause for NOW- “they can f ly when they please. If it is warm in

May/June 2016

January they will be active,” Tollerup said.

An important factor in year-to year NOW damage has to do with phenology- or the timing of seasonal changes in trees and insect populations. Earlier or later f lowering, and early or later maturity of the crop can play a part in NOW damage potential.

Crop damage occurs in almonds at hull split when NOW larvae bore through the shell and feed on the nut, producing large amounts of webbing and frass. Feeding also opens the nut to fungal infections that produce af latoxin. Walnuts and pistachios are vulnerable later in the season when NOW pressure may be higher due to multiple f lights.

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is important. Adult NOW moths have a snout-like projection in the front of the head and have irregular silver and black forewings and legs.

Newly hatched larvae are reddish orange and later vary from milky white to pink in color. The larvae of NOW can be distinguished from other moth larvae by reddish-brown head capsule and a pair of crescent shaped marks on the second segment behind the head. The larvae overwinter in mummy nuts in trees or on the ground.

As almond production in California was ramping up 30 years ago, Tollerup said two percent NOW damage was okay with growers and processors. Over time, growers have increased their management and understanding of orchard sanitation and have been able to drop

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damage to below one percent. With the growth in pistachio production, growers are realizing the potential for damage.

“There is a night and day difference between NOW in almond and pistachio,” said Tollerup. “There is more understanding, monitoring and management in almonds.”

Tollerup said the value of the almond crop and food safety concerns with af latoxin have driven efforts in NOW control in almonds. Pistachio growers face bigger challenges.

More nuts per tree present more opportunity for NOW damage. Due to the small size of pistachios, it is difficult to remove all the mummy nuts. They can be swept off the berms and windrowed, Tollerup Continued on Page 30

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Continued from Page 29 said, but f lailing tends to scatter rather than destroy the mummies.

Walnut damage due to NOW infestations is also on the rise.

Walnuts are most susceptible to damage at husk split, and as more generations of NOW per season are occurring, damage is more likely.

UC IPM guidelines recommend that split nuts on the ground be checked for NOW egg from the third generation. Samples of nuts at harvest should be assessed for NOW damage to determine NOW population levels.

Pest control advisor Justin Nay oversees both almond and pistachio orchards and said his company takes a season-long approach to NOW monitoring. They start with mummy nut inspection and larval infestation levels. Those findings will dictate their orchard sanitation practices, he said. In mid March he sets out traps to determine female NOW activity. The sticky wing traps he uses attract mated females and are different from the standard egg traps, which have been used for many years. With the wing traps, Nay said he only has to count the number of NOW females in the trap rather than egg numbers on the egg trap. A mesh bag filled with 90 percent pistachio mummies and 10 percent almond mummies attract the females NOW to the trap.

The traps are checked weekly, he said, and if a block averages more

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Progressive Crop Consultant

A standard egg trap. Female NOW lay eggs on the grooves. These traps were commonly used for many years to monitor NOW activity. than nine female NOW, he said it is reason to consider some type of control. Finding a large number of males in a trap baited with female NOW or a pheromone may not signal the same type of response, he explained, because males typically f ly in and leave.

Nay said he uses one trap for 150 acres in large blocks of trees.

Female trap numbers are at one per 50-70 acres. They like to place them soon after petal fall, Nay said, because there will be less f lower debris caught in the traps. Traps will go into pistachio blocks at the same time, he said, as they will catch NOW earlier in pistachios.

Nay said he is still working on understanding how trap num-

May/June 2016

bers correlate to populations and crop damage. There are also other factors in control decisions. The timing of the first f light of NOW last year missed hull split and pesticide application was not needed.

This year, he said they will overlap and although fewer NOW are being trapped he expects more problems.

Monitoring with traps, Nay said, helps them locate problems in block of trees and to gauge the biology of the moth and how it overlaps with the biology of the tree.

Agricultural Research Service scientist Chuck Burks said the goal with NOW lures and traps in nut crops is to have a cost effective device that consistently releases the pheromone. With lures in the $5-$7 range, he said while it is an expense, their use can save the cost of an insecticide application.

Between the commonly used delta and wing traps, Burks said the delta is less labor intensive. In his experience, he said most PCAs prefer the wing traps.

Burks, who works out of the USDA facility in Parlier, said there are two ways to use traps/lures for NOW. The objective of timing is to try and get pesticide applications placed earlier in cohorts so that the application residue will impact the maximum number of eggs or newly hatched larvae before they enter the nuts and become inaccessible.

In the spring, this would mean

getting a “May spray” out close to the beginning of heavy oviposition (often several weeks after males are consistently captured in pheromone traps). For an almond hullsplit application, this means balancing the beginning of the second f light (i.e., the first gravid females from the offspring of overwintered moths) with almond hullsplit and vulnerability.

Burks said one caveat for timing in general is that it usually takes several days to get insecticide applied with good coverage across a large block. A second caveat for NOW in particular is that, because they overwinter in various larval stages and emergence in spring is spread out over many weeks, their cohorts are not as synchronized as some lepidopteran pests. Achieving the best timing for applications contributes to effective pest management and is considered a best practice.

With thresholds as a focus in the trapping system, trap data are used to determine whether one of several possible insecticide applications will be made. Examples cited

by Burks include foregoing a spring treatment or with light numbers if a hull split treatment can be skipped.

The use of pheromone traps for thresholds places a higher demand that the number of males captured in traps should have a tightly correlated relationship with the local abundance of the pest.

In contrast, with timing, the number of insecticide treatments is decided early in the season, generally based on historic factors. For example, what was harvest damage last year? Over the last several years, has this block had heavier or lighter NOW damage? Another possible factor is whether there is evidence of unusually low or high overwintering mortality. In this case traps are used to determine when insecticide applications are made, rather than whether they are made.

Burks said the current lures used are better on timing and are an improvement over lures used four years ago. The challenge remains in determining threshold numbers. PCC

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