Weed, Insect, and Disease Control for Turfgrass Producers Preview

Weed, Insect, and Disease Control FOR TURFGRASS PRODUCERS

FIRST EDITION, 2022

Editor

Casey Reynolds, PhD. Executive Director, Turfgrass Producers International

Authors

Matthew Elmore, PhD. Assistant Extension Specialist, Weed Science. Rutgers University

Gerald (Lee) Miller, PhD. Associate Professor, Turfgrass Pathology. University of Missouri

Aaron Patton, PhD. Professor, Turfgrass Extension Specialist. Purdue University

Doug Richmond, PhD. Professor and Extension Specialist, Turfgrass Entomology and Applied Ecology. Purdue University

Casey Reynolds, PhD. Executive Director, Turfgrass Producers International

Manuel Roman Chavarria Sanchez, PhD. Lead Research Scientist. Prairie Turfgrass Research Centre, Alberta Canada

Acknowledgements

April N. Grummer, Undergraduate Student, Department of Entomology. Purdue University

Daniel Earlywine, Research Assistant, Turfgrass Pathology. University of Missouri

This free publication is created and mailed annually to members of Turfgrass Producers International. For more information on this and other TPI member benefts, please visit www.TurfgrassSod.org.

Diseases

Plant Growth Regulators

What’s New for 2022

New Herbicides

✔ Celsius Xtra (thiencarbazone-methyl + iodosulfuron + halosulfuron). The sister product “Celsius” contains thiencarbazonemethyl + iodosulfuron + dicamba. The substitution of halosulfuron for dicamba means Celsius Xtra will control or suppress sedge species.

✔ Sublime (triclopyr + dicamba + mesotrione)

New trade names of herbicides with previously registered active ingredients and/or previously registered combinations of ingredients include:

• Acquit (sulfentrazone)

• Addax (asulam)

• Antik EC (carfentrazone)

• Aquesta 4F (sulfentrazone)

• Biscayne (bentazon)

• Cheetah Pro (glufosinate)

• Daikon (halosulfuron + dicamba)

• Doleac DMA (dicamba)

• Dolerity DGA (dicamba)

• Empero (halosulfuron) – not in OR or WA

• Finale XL T&O (glufosinate)

• Flumioxazin 51WDG Select (fumioxazin)

• Meso 4SC Select (mesotrione)

• Metallis (S-metolachlor)

• Q-Ball (quinclorac)

• Quintessential (quinclorac)

• Semera 51WDG (fumioxazin)

• Semera SC (fumioxazin)

• Sertay (sulfosuluron)

• SlipStream (mesotrione) – not in AZ

• Stadia (halosulfuron) – not in OR or WA

• Torocity (mesotrione)

• Triad QC Select (2,4-D + quinclorac + dicamba)

• Triad T Select (2,4-D + MCPA + triclopyr + dicamba)

New trade names of plant growth regulators with previously registered active ingredients include:

✔ Pramaxis MEC (trinexapac-ethyl)

The U.S. Environmental Protection Agency (EPA) has proposed the following changes to oxadiazon in sod production. TPI is working with EPA on these changes and will share the results of the Final Decision when they occur. Proposed changes include:

✔ Use on turfgrass will be limited to golf course fairways and sod farms only

✔ Yearly maximum use rate to be reduced from 8 lb ai/A to 6 lb ai/A

✔ The single maximum application rate reduced from 4 lb ai/A to 3 lb ai/A

✔ Applications are limited to 2 per year –spring and fall

✔ Liquid applications will be limited to 1 per year

✔ There must be a 120-day retreatment interval between applications

✔ Application to sports felds is prohibited, included at planting/new construction

New Insecticides

✔ Fipronil 0.0143G, Fipronil 0.1G (fpronil)

✔ Suprado (novaluron)

✔ Alucion 35WG (dinotefuron + alpha-cypermethrin)

New Fungicide

✔ Serata (picarbutrazox): Only efective against Pythium diseases such as damping of, root rot, root dysfunction and blight.

Weeds

Weed management in turfgrass production

Weeds in turfgrass production felds increase production costs (e.g. equipment, herbicide, and labor costs) and reduce the inventory of marketable sod due to contamination (lost production ground) and lack of turfgrass uniformity (poor quality). All managed turfgrass systems (athletic, lawn, golf, sod) have weed problems, but production felds typically have diferent weed problems. While some common weeds are the same (crabgrass, nutsedge, spurge), often turfgrass production felds receive additional weed pressure from surrounding farm felds, open drainage ditches, fence rows, or previous crops. As such, controlling weeds in nearby fence rows and open drainage ditches is essential to keeping these problematic weeds out of production areas. Additionally, good sanitation (i.e. cleaning of equipment) can help prevent weeds from being introduced.

Turfgrass farms typically sufer more from annual weed problems than perennial weeds, with rhizome producing perennial grasses and nutsedge being exceptions. Annual weeds invade after harvest, germinating in bare soil left behind (Figure 1). Annual weeds are often easily controlled, particularly broadleaf weeds that invade shortly after harvest or planting. Many of these annual weeds are controlled simply through proper cultural practices of regular mowing while others may require the use of herbicides. Perennial grassy weeds with rhizomes, such as common bermudagrass, smooth brome, or quackgrass, are the most problematic and have the biggest impact on harvestable acreage. Additionally, of-types of the desirable crop, such as common bermudagrass in a hybrid bermudagrass crop, are only removable through non-selective herbicide applications. Substantial efort should be placed towards the eradication of these perennial grassy weeds.

Protecting the Crop

Most modern herbicides that can be safely used on established turf can also be safely used in production felds. Some herbicides; however, can inhibit root or rhizome development which could run the risk of reducing sod tensile strength or reducing the rate that a crop flls-in after planting. Several herbicides may cause injury or impact sod tensile strength, but three specifc herbicide modes of action should be used cautiously: WSSA Group 3 (HRAC K1), WSSA Group 5 (HRAC C1) and indazifam, a WSSA group 29 (HRAC L) herbicide (Table 2).

Herbicides that inhibit microtubule assembly (WSSA Group 3, HRAC K1) and indaziflam reduce the ability of stolons and sprigs to root into the soil. This is most problematic when these herbicides are applied after harvest as recovery from sod ribbons can be reduced. As such, these herbicides are used less often in turfgrass production because of their potential to reduce rooting and establishment from either sprigs or stolons. Oxadiazon (Ronstar), a WSSA Group 14 (HRAC E) herbicide, is a potential alternative in sprigged bermudagrass or zoysiagrass. When seeding cool-season grasses such as tall fescue or Kentucky bluegrass, mesotrione (Tenacity; WSSA group 27, HRAC F2) is one of the few herbicides that can be applied to provide residual weed control without inhibiting seedling development.

Commonly used WSSA Group 5 (HRAC C1) herbicides include atrazine and simazine. These herbicides provide excellent weed control but can injure certain tolerant warmseason grass species such as hybrid bermudagrass. Injury often occurs when applied to immature sprigs and this can result in reduced sod tensile strength when herbicides are used at high label rates. Further, some cultivars may be less tolerant. Growers are advised to test the safety of these herbicides on new cultivars before treating large areas.

Figure 1. Bare soil between sod ribbons, such as in this zoysiagrass (Zoysia japonica) production feld, provide a perfect opportunity for the invasion of annual weeds.

Table 5. Postemergence herbicides for selective weed control in turfgrasses

HRAC, Trade name labeled for WSSA Common name (Product/A) application Weeds controlled Comments group

2,4-D

Hardball (1–1.75 qt)

Weedar 64 (1-1.5 qt)

Others

Turfgrasses

Cool-season: All major species

Warm-season: BA, BE, CE, Z

Broadleaf weeds

Do not apply to St. Augustinegrass. Can be applied to centipedegrass and bentgrass on sod farms only. Short-term stunting may result from application to centipedegrass and bentgrass, especially at higher rates. Many products permit application to bentgrass only as a spot treatment.

Do not apply to newly seeded turfgrass until it has been mowed at least twice. Do not seed into treated area until at least 30 days after application.

Many broadleaf weeds are not controlled by 2,4-D alone. For more broad-spectrum control, combine with other active ingredients such as dicamba, triclopyr, or furoxypyr. Rates and recommended turf species difer for sod.

2,4-D + dicamba

2,4-D + dichlorprop

On Deck (1-4 qt) Patron 170 (3.5 qt)

Cool-season: CBG, KB, PR, TF

Warm-season: BA, BE, CE, BU, SS, Z

Cool-season: All major species

Warm-season: BE, BU, CE, SA, Z

Broadleaf weeds

Control a broader spectrum of weeds than 2,4-D alone. Do not apply more than 1.5 pt/A to warm-season turfgrass. For use on creeping bentgrass only as a spot treatment.

2,4-D + clopyralid + dicamba

Millennium Ultra 2 (1.5–3 pt)

Cool-season: All major species

Warm-season: BA, BE, Z

Many broadleaf weeds

Controls a broader spectrum of weeds than 2,4-D alone.

2,4-D + dicamba + quincloraz

2DQ (1–4 pt)

Cool-season: All major species except FF

Warm-season: BA, BE, CE, SA, Z

Many broadleaf weeds

Provides broad-spectrum broadleaf weed control. Provides excellent white clover and Canada thistle control.

Specifcally for common bermudagrass; use on hybrid bermudagrass not specifed. Short-term injury may occur after application to creeping bentgrass where lower rates are specifed on the label.

2,4-D ester + mecoprop + dicamba + pyrafufen-ethyl

2,4-D ester + triclopyr ester + dicamba + pyrafufen-ethyl

Redzone 2 (1.8–4 pt)

Cool-season: All major species

Warm-season: BA, BE, Z

Many broadleaf weeds

Provides broad-spectrum broadleaf weed control. Use lower rates in warm-season turfgrass. Short-term injury may result after application to Centipedegrass or St. Augustinegrass especially if applied during spring greenup.

Higher rates (up to 4 pt/A) can be used in cool-season turfgrass sod production.

Many broadleaf weeds

Some hybrid bermudagrass varieties may be sensitive. Use lower rates in creeping bentgrass to prevent injury.

4 Speed XT (1.8–4 pt)

Cool-season: All major species

Warm-season: BA, BE, Z

Many broadleaf weeds

Some hybrid bermudagrass varieties may be sensitive. Use lower rates in creeping bentgrass to prevent injury.

7 continued. Nonsynthetic auxin herbicides for postemergence broadleaf weed control in turfgrasses

Turfgrasses HRAC, Trade name labeled for WSSA Common name (Product/A) application Weeds controlled Comments group

sulfentrazone + carfentrazone

Dismiss NXT (5.1 to 15.2 oz)

Spartan Charge (5.1 to 10.2 oz)

Most cool- and warm-season grasses (see label).

Broadleaf weeds, sedges/kyllingas

Spartan Charge is labeled for sod production only. Primarily functions as a contact herbicide. Tank-mix with systemic herbicides to control perennial or mature annual weeds.

sulfentrazone + metsulfuron - methyl

Blindside (3.25–10 oz)

Cool-season: KB, TF, Warm-season: BE, BU, CE, SA, Z

Broadleaf weeds, some grasses, sedges

Provides good to excellent control of many broadleaf weed species.

A systemic herbicide with some soil residual. Use caution around trees and ornamental plants. See label for more information.

Sulfentrazone results in injury symptoms visible within 48 hours, compared to about 2 wk for metsulfuron-methyl alone.

thiencarbazone - methyl + iodosulfuron + dicamba

Celsius WG (2.5–4.9 oz)

Cool-season: None

Warm-season: BE, BU, CE, SA, Z

Broadleaf, grassy weeds

Controls many broadleaf weeds.

Two applications may be needed for difcult-to-control weeds such as dichondra, wild geranium, and Virginia buttonweed.

Nonselective herbicides for general weed control

Table 8. Nonselective herbicides for general weed control and/or turfgrass renovations

HRAC,

Trade name WSSA

Common name (Product/A) Comments group

dazomet

diquat

glufosinate

glyphosate

Basamid (218–525 lb)

Reward (1–2 pt)

Finale (3–6 qt)

RoundUp, Touchdown, many others (see label)

See label regarding site preparation, use rates, tarping and overhead irrigation after application. Tarping may improve efcacy. Restricted-use pesticide.

Quickly dries out green tissues. Adequate spray volume is essential to obtain leaf coverage and best control. A contact herbicide that does not translocate and therefore does not control perennial weeds.

Translocation more limited than that of glyphosate; thus, it is excellent for edging around desirable turfgrass. Can be applied to dormant bermudagrass.

Optimal for control of grasses and many broadleaf plants. At low rates, does not completely control legumes or Cyperaceae (sedges and kyllingas).

glyphosate + 2,4-D

pelargonic acid

Campaign (1.5 to 4.0 pt)

Scythe (see label)

Consider tank-mixing with additional glyphosate to control certain weeds. See label.

Dries out green tissues quickly. Spray volume must be adequate to obtain leaf coverage and best control. Does not translocate or control perennial weeds.

Z, 17

D, 22

H, 10

G, 9

G, 9 + 0, 4

Z, 17

Table

E, 14

E, 14 + B, 2

B, 2 + O, 4

Herbicides for commonly occurring weeds

Crabgrass Preemergence herbicides

Most preemergence herbicides in the section on preemergence herbicides for grassy and broadleaf weeds (table 3; beginning on page 9) provide acceptable crabgrass control when applied before crabgrass germination. However, most of these should not be applied to immature turf often present in sod production. See table 4, (intervals for preemergence herbicides application in sod production) for more information. Mesotrione is commonly used for annual weed control on immature seeded cool-season turfgrass species while oxadiazon is commonly used on immature sprigged warm-season species.

Crabgrass germination typically occurs in late winter to mid-spring (February to mid-May depending on location), but varies from year to year, based on temperature, rainfall, and location. Crabgrass germination usually begins when the soil temperature at a 2-inch depth reaches 55°F for at least 3 days in temperate climates. Germination may occur throughout the year in tropical climates.

The forsythia (Forsythia spp.) plant can be used to time preemergence herbicide application. Make preemergence applications when forsythia are in full bloom (since they are usually among the frst plants to bloom, their yellow fowers are easy to spot). Forsythia plants are most prevalent in the eastern United States.

Postemergence herbicides

These herbicides control crabgrass plants at various growth stages after germination. See the comments section and the product label for efcacy and application rates at various growth stages. Most products in table 9 control smooth (Digitaria ischaemum) and large (Digitaria sanguinalis) crabgrass. Control may vary for other crabgrass species, such as blanket (D. serotina), India (D. longifora), and tropical (D. bicomis) crabgrass.

If you apply herbicides early in the season in areas where the desirable turfgrass is thin and crabgrass infestations are severe, new crabgrass plants will germinate in the voids after the existing crabgrass plants are controlled. For residual control, consider tank-mixing a preemergence herbicide with the postemergence herbicides in table 9.

Large crabgrass (Digitaria sanguinalis) and common bermudagrass (Cynodon dacytlon) contamination of a zoysiagrass (Zoysia japonica) production feld. Repeated spot applications of glyphosate are needed to remove perennial weeds costing labor and chemical and resulting in reduced harvestable acreage. In this photo, the common bermudagrass was sprayed with glyphosate once already but additional applications are necessary for removal.

Insects

Arthropod pests of turfgrass

Although the small, multi-segmented animals found associated with turfgrass sod are often referred to collectively as insects, these organisms actually represent a larger, more diverse group of animals known as arthropods (insects, mites, spiders, centipedes, millipedes, crayfsh, etc.). Many diferent arthropods are associated with sod, but a handful of common species are responsible for the vast majority of damage.

A square yard of healthy turfgrass typically contains thousands of arthropods, most of which are benefcial. These animals perform a variety of important functions including decomposition of dead plant material necessary for proper nutrient cycling, soil aeration that enhances water and nutrient infltration, natural control of insect pests through predation or parasitism, and pollination of fowering plants and food crops. The primary challenge for turfgrass producers then, is striking a balance between the functional, aesthetic and economic requirements of the sod that make it harvestable and marketable, and maintaining an environment that is suitable for benefcial organisms and the stabilizing ecological services they provide.

Integrated pest management

Sound cultural practices that promote healthy, vigorous turfgrass capable of tolerating or quickly recovering from arthropod damage form the foundation of an approach called “integrated pest management” (IPM). The goal of IPM is not to eliminate arthropods, but to manage those few species that are pests in order to keep them below damaging levels. When properly implemented and aligned with user needs and expectations, IPM can achieve grower goals while minimizing pesticide use, reducing costs and environmental impacts, and increasing worker safety. Only when the balance between benefcial organisms and pests is disrupted are growers usually forced to take remedial action. Such actions often involve the use of biological or synthetic insecticides.

Because efcient insecticide use requires proper targeting, timing and product selection, some basic knowledge of pest identifcation and biology is useful. There are many resources available that provide this information including: county and state extension specialists, consultants, extension publications, textbooks, and videos. In order to efectively scout for pests and select an appropriate product for a specifc pest problem, growers should also think about pests in terms of the diferent regions of the sod profle where they are likely to be found. The location of the pest within this profle and the stage of development the pest has reached will determine the kinds of scouting approaches that are likely to reveal the pest and inform the grower’s choice of insecticide chemistry, formulation, and application techniques.

The target zone

For the purposes of scouting and applying insecticides, turfgrass arthropod pests can be categorized into two broad groups: surface-dwelling and soil-dwelling. Although this distinction can seem a bit artifcial for pests that spend portions of their life in both zones, the choice of target, adult vs larva for instance, can determine the utility of a given scouting procedure and the efcacy of a given insecticide application.

Surface-dwelling pests like billbug adults, cutworms, armyworms, chinch bugs and aphids are typically exposed to insecticide residues by ingesting or contacting treated surfaces (i.e., leaf tissue or thatch). A broad selection of insecticides are suitable for this kind of application as long as they adhere to material that the target pest will contact or ingest. Movement through the thatch and into the soil is not necessarily required for good efcacy and may in fact reduce the residual efcacy of the application by moving it away from the zone where the target pest is most active. However, uptake of systemic insecticides through the roots, and movement upward into above-ground tissues (translocation) can enhance and prolong the residual efcacy of some products (i.e., neonicotinoids and anthranilic diamides). Direct penetration of plant tissues by translaminar products can serve a similar purpose. Translocation or translaminar movement may in fact be essential when the target pest is located within plant tissues where it is not directly exposed to insecticide deposits on the treated surfaces (e.g., billbug larvae tunneling within plant stems). For arthropod pests like ants, that are active on the surface, but do not directly feed on plants, bait formulations may also be efective.

Soil-dwelling pests such as white grubs are typically exposed to insecticides only after the product has moved through the thatch and into the soil where the pest is active. “Sticky” materials, like pyrethroids, that bind tightly to organic matter at the soil surface rarely move into the soil in large enough amounts to be efective against such targets. Conversely, more water-soluble materials move readily into the soil where the pest is active. This process can be facilitated by precipitation or irrigation immediately following the application. Once in the soil, such materials may be taken up by the plant as a sort of self-protection, or simply contacted and ingested by the target pest.

Management decision guide

The following tables are provided to help turfgrass producers prioritize monitoring programs based on the frequency and damage potential of the arthropod, and select appropriate insecticides based on the target, mode of action, and the spectrum of activity of a particular formulation. These tables include only chemical insecticides registered for use in sod production. In order to prolong the useful lifespan of chemical insecticides, a rotation that includes multiple classes and modes of action is always the best practice.

bifenthrin

Insecticide Mode of Action (MOA) classifcation

Products containing a single active ingredient

No products currently registered for ground pearls, scales or yellow jackets on sod farms acephate

Acephate 90% Prills, Acephate 97 UP, Acephate 97 WDG, Bracket 97, Bracket 97 WDG, Orthene T-T&O WSP, Orthene T-T&O 97

Avalon Golf & Nursery, Bifen 2 AG Gold, Brigade 2EC, Capture LFR, Fanfare ES, Menace GC 7.9% F, Pro-Mate Bifenthrin, Sniper, Tailgunner, Talstar GC, Talstar S, Up-Star GC, Up-Star SC, Wisdom GC

Acetylcholinesterase inhibitors

Sodium channel modulators

turfgrass

carbaryl

chlorantraniliprole

chlorpyrifos

clothianidin

cyantraniliprole

deltamethrin

dicofol

dinotefuran

Carbaryl 4L, Sevin SL

Acelepryn SC, Acelepryn G

Chlorpyrifos 4E, Chlorpyrifos 4E-AG, Dursban 50W, Govern 4E, Hatchet, Lorsban 4E, Lorsban Advanced, Vulcan, Warhawk, Whirlwind, Yuma 4E

Arena 0.25 G, Arena 50 WDG

Ference SC

Deltagard GC

Dicofol 4E

Zylam Liquid, Zylam 20 SG

Acetylcholinesterase inhibitors

Ryanodine receptor modulators

Acetylcholinesterase inhibitors

Nicotinic acetylcholine receptor agonists

Ryanodine receptor modulators

Sodium channel modulators

Uncertain mode of action

Nicotinic acetylcholine receptor agonists

Dicofol

Neonicotinoids

continued on next page

Table 2. Mode of action classifcations of chemical1 insecticides and miticides registered for use in

production (Source: IRAC)

Table 1. Arthropod pests of turfgrass, target zones and relative importance in turfgrass production

Insecticides registered for use in turfgrass production

Table 3. Insecticides registered for control of Ants in turfgrass production

acephate Acephate 90% Prills

Mound drench treatment (see label) for fre and harvester ants only.

Acephate 97 UP Mound drench treatment (see label) for fre and harvester ants only.

Acephate 97 WDG Mound drench treatment (see label) for fre and harvester ants only.

Bracket 97 Mound drench treatment (see label) for fre and harvester ants only.

Bracket 97 WDG Mound drench treatment (see label) for fre and harvester ants only.

Orthene T-T&O WSP Drench (see label) and dry (1-2 tsp) mound treatments for imported fre and harvester ants only.

Orthene T-T&O

Mound drench treatment (see label) for fre and harvester ants only.

Larval (grub) and adult (weevil) stages of a billbug. At least 6 species are known to infest turfgrass sod. Billbug adults have a distinctive snout that is characteristics of weevils and is used for insertion and feeding in plant stems. However, damage from adults is rare and usually not signifcant. Most of the damage occurs as larvae (white, legless, with brown head capsule) feed on stems, crowns, roots, stolons and rhizomes resulting in spotty, brown patches of sod.

Table 6 continued. Insecticides registered for control of Billbugs in turfgrass production

* See label for detailed instructions.

(Pictured: Hunting Billbug Sphenophorus venatus)

Hunting Billbug Beak

Diseases

Turfgrass diseases

Infectious disease occurs when three factors integrate simultaneously – a susceptible host, a virulent pathogen, and a conducive environment. Like humans, turfgrasses are more susceptible to infection when not healthy and actively growing. Plants are more likely to contract a disease when continuously exposed to abiotic environmental stressors (i.e. heat, drought or fooded conditions, etc.), or stresses invoked by high or improper maintenance practices (i.e. low mowing height, lack or excessive fertility, overirrigation, etc.). Growing the right plant (turfgrass species and cultivar) in the right place under the right conditions will limit or prevent turfgrass disease occurrence.

Turfgrass management involves growing individuals of the same or similar genotype very close together, meaning pathogen dissemination and disease transmission is relatively easy and occurs quickly. Therefore, even under proper management, fungicides may be necessary and are recommended for protection of high amenity turfgrasses. Correct and judicious fungicide use requires knowledge of the biology of the pathogen, including where the pathogen infects the plant and the environmental conditions required for infection. These two factors greatly infuence the necessary methods for fungicide delivery and application timing to maximize disease control.

Fungicide Delivery: Diferent pathogens can infect diferent parts of the plant. Foliar pathogens cause diseases such as brown patch and pythium blight and infect leaves and sheaths. The location of infection for soilborne diseases such as spring dead spot or summer patch is stolons, rhizomes or roots. Fungicides must be efectively delivered to the location of infection. This is particularly crucial for soilborne diseases because most fungicides move upward in the plant, and will not move downward into the rootzone to a depth greater than they are applied. Therefore, fungicides targeting soilborne diseases must be either applied in higher carrier volumes

Table 1. Location of infection for turfgrass diseases

FOLIAR ROOTS, STOLONS, RHIZOMES

Anthracnose Fairy Ring

Brown Patch Nematodes

Dollar Spot Spring Dead Spot

Gray Leaf Spot Summer Patch

Large Patch

Leaf Spots/Melting Out

Microdochium Patch

Pythium Blight

Red Thread

Rust

Snow Molds

(3-5 gallons/1000 sq ft) or, perhaps more efectively, be watered in with at least 1/8 inch (3 mm) of postapplication irrigation.

Application Timing: Preventing disease and turfgrass loss often relies on applying fungicides not when symptoms occur, but earlier in the disease cycle when infection occurs. As with fungicide delivery, this is particularly true for control of many soilborne diseases which can infect and cause root loss prior to symptom development. For instance, the spring dead spot pathogen infects and inhibits the bermudagrass’ ability to overwinter in the fall before symptoms ever appear the following spring. Therefore, fall and not spring applied fungicides are necessary for efective control of this disease. Several foliar diseases, such as dollar spot and pythium blight, can cause symptoms rapidly, and are also most efectively controlled preventively. See each disease description for information regarding timing.

Fungicide Resistance: As with other pests, pathogen populations can develop resistance to fungicides when exposed to repeated applications. In many cases, the population doesn’t just contract resistance to the one fungicide active ingredient or product that’s been used, but will also acquire resistance to all the fungicides that are in that class or mode of action. Therefore, rotating fungicide classes for pathogens that are known to develop resistance is critical to a long-term control strategy. This being said, not all turfgrass pathogens have the same propensity to develop resistance. Take brown patch for instance. Despite repeated applications targeting this disease, no instances of fungicide control failure of brown patch have been observed due to fungicide resistance. Below is a table listing turfgrass pathogens and fungicide classes with known cases of fungicide resistance.

Disease

Chemical Class

Anthracnose Benzimidazoles

DMIs

Strobilurins (QoI)

Dollar Spot

Benzimidazoles

Dicarboximides

DMIs

SDHI

Gray Leaf Spot

Strobilurins (QoI)

Pythium Blight Phenylamides

Microdochium Patch Benzimidazoles

Dicarboximides

Table 2. Turfgrass diseases with known cases of fungicide resistance

Fungicide Mode of Action (MOA) classifcation

Table 3. Mode of action classifcations and mobility of fungicides registered for use in turfgrass production1 (Source: FRAC)

Fungicides registered for use in turfgrass production

Warm-season turfgrass diseases

Due to its increased metabolism in high temperatures, warm-season turfgrasses are subject to far fewer major diseases than cool-season turfgrasses. Symptoms mostly occur on warm-season turfgrasses in the fall and spring, particularly in regions where the plant either goes into or comes out of dormancy. Aside from “ultradwarf” varieties used on golf putting greens, the two most important diseases on warm-season turfgrasses are described below.

Large Patch

Pathogen: Rhizoctonia solani AG2-2 LP

Main Hosts: Zoysiagrass, Centipedegrass, Kikuyugrass, Bermudagrass, St. Augustinegrass

Description: Large patch occurs when warm-season turfgrass is growing slowly due to low temperatures, particularly in the fall or spring leading into or coming out of winter dormancy. Most severe disease outbreaks occur in the spring about two to eight weeks after spring green up. Symptoms occur as roughly round patches of tan or straw-colored turf that can range from a few to many feet/meters in diameter, hence the

name “large patch.” When the disease is active, bright orange leaves (also known as “fring” symptoms) are evident along patch margins. The pathogen infects at the leaf sheath, causing a basal rot and reddish brown to black lesions along lower leaf and sheath tissue. Bermudagrass can also be afected by large patch, but the disease is short-lived and recovery occurs more rapidly than in other warm-season species.

Control: Large patch is considerably more severe during periods of heavy rainfall/irrigation and saturated soil conditions. Providing good surface and subsurface drainage will reduce excessive soil wetness and humidity in the turf canopy and thus reduce large patch incidence. Several studies show that large patch severity is not afected or may even be slightly reduced by moderate spring nitrogen applications. Several fungicides are available for large patch control, but they must be applied preventively and sometimes several times in the fall or early spring to achieve complete control. Since the pathogen infects lower down on the leaf sheath, applying fungicide in higher water carrier volumes will result in more efective disease control.

FOLIAR

Large patch, caused by Rhizoctonia solani AG2-2 LP, results in stand decline of warm-season grasses when plant growth is slowed either going into or coming out of dormancy. The pathogen infects along the leaf sheath, causing an orange color to leaf blades prior to decline. Patches are light brown to straw colored and can range from a few inches to several feet in diameter. In conducive environmental conditions and disease expansion, patches may “fre” with brilliant yellow to orangish red coloration of infected leaves along the patch margins.

Table 4. Fungicides registered for Large Patch control in turfgrass production

1 Product amounts in f oz for liquid products and oz for granular products (unless specifed).