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Cucurbits- Major Diseases and Management for the Southeastern U.S Mathews Paret Stephen Olson, Gary Vallad, Shaoun Zhang, Pamela Roberts, David Langston Tri-State Watermelon-Cucurbit meeting, Feb 3, 2011 IFAS-Extension, Jackson County Ag Conference Center


Priority Diseases 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Gummy stem blight (GSB) Powdery mildew (PM) Downy mildew (DM) Fusarium wilt Phytophthora crown/root/fruit rot Bacterial fruit blotch Papaya Ringspot Virus type W: Aphid- South FL Zucchini Yellow Mosaic: Aphid- South FL Watermelon Mosaic Virus: Aphid- Central FL + Northwards Squash Vein Yellowing Virus- Whitefly- South + Central FL


GSB: Didymella bryoniae/ Phoma cucurbitacearum Most destructive on watermelon (>50% yield losses in ideal conditions for spread of GSB) Can infect muskmelon, cucumber, pumpkin, and squash


• GSB-resistant varieties: not available in cucurbits • One of the primary sources of GSB inoculum is the seed • Seeds/transplants can be infested without expressing symptoms


• GSB at the seedling stage (a sure case of infected seed/unclean trays): necrotic areas on the margin of the leaves


• GSB at the seedling stage: water-soaked regions on the stem, gummy ooze from the stem.


• Second source of GSB inoculum is the organic debris from previous cucurbit crops with a history of GSB incidence 2 1

3


• Third source of GSB inoculum are volunteer cucurbits, wild citrons, and balsam pear

Balsam Pear/Bitter melon - Momordica charantia


GSB: Symptoms


GSB

GSB/inadequate soil liming/ other reasons

GSB

GSB/inadequate soil liming/ other reasons


GSB: confirmatory diagnosis


GSB: epidemiology • IDEAL WEATHER CONDITIONS FOR INFECTION Temperatures: 68-75F Peak ascospore dispersal: after rain, and dew periods at night 1 hr leaf wetness required for infection, and further leaf wetness aids in lesion expansion


GSB Management: Step I • Use of healthy/ certified seeds from fields with no history of GSB • Seed treatment necessary if not previously treated. • Disinfectants as solutions more effective than dry dust. • Regular inspection of transplants in greenhouses. • Remove infected plants • Whenever possible, avoid using healthy-looking seedlings from trays with infected plants


GSB Management: Step II • Rotation of non-cucurbit crops • Duration of rotation: >2 years after a single cucurbit crop with an outbreak of GSB • Remove volunteer cucurbits, other host plants from fields prior to planting during crop growth


Step III (Fungicide program)

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Trt 1 2 3 4 5 6 7 8

Untreated Luna Privilege (6.84 fl oz/A) Inspire (7 fl oz/A) Folicur (8 fl oz/A) Bravo (2 pt/A) Topsin (10 fl oz/A) Endura (6.5 oz/A) Quadris (12.4 fl oz)


GSB Management: Step III • • • • • • • •

Bravo, Inspire Super/Revus, Topsin rotation works great Bravo and Folicur gives good value Inspire Super works great, but costly Luna works good: no label available. Resistance to Quadris (azoxystrobin) and Endura (Boscalid) Rotate, Rotate, Rotate……..available chemistries Preventative sprays important. Be ahead of GSB Bravo: Follow label instructions on watermelon after fruit set. Do not apply for mature watermelons under dry, hot, and other stressful conditions.


GSB/Black rot

• Rarely noticed (only when infection is severe) • Can be post-harvest • Avoid wounding fruits during harvest, and store fruits at 4550F to prevent postharvest black rot.


PM: Sphaerotheca fuliginea/ Erysiphe cichoracearum • Talcum-like symptoms on the upper and lower side of the leaves. • First symptoms: Older leaves, or shaded lower leaves.


• The PM fungi are obligate parasites • Primary source of inoculum include conidia dispersed over long distances, from greenhouse cucurbits, and alternate hosts (mostly other cucurbits) • Conidia viable for 7-8 days


• Large number of spores are produced in 3-7 days • Favorable conditions: Dense plant growth Low intensity light • High R.H is favorable for infection and conidial survival • Infection can also occur at <50% R.H. • Dry conditions favor colonization, sporulation, and dispersal


• Optimum condition for PM development: 68-80F • Reduced yield by decreased size of fruit/ length of crop harvest • Fruit infection: Rare; however, when foliage is lost, greater chances of sunscald


PM: Management • • • •

Resistant varieties Reducing plant density Adjust planting dates Destroy volunteer plants

• Increase in PM incidence in cucurbits (1996: 1st report of PM on watermelon in U.S.) • Fungicide resistance and/or development of new PM pathotype. • S. fuliginea and E. cichoracearum are the commonly reported PM pathogens. • Other genera and species have been reported, and a shift in pre-dominant PM fungus might have happened.


Trt 1 2 3 4

Untreated (Torino+Procure) alt (Procure) (Torino) alt (Procure) (Quintec) alt (Rally)


Trt 1 2 3 4 6 9 10 11 12 13

Untreated Procure 480SC, 8 oz (2,4 w) Regalia 1% v/v (1-4 w) Actinovate, 3 oz (1-4 w) Companion, 32 fl oz (1-4 w) Quintec, 6 fl oz/100 gal (1,3 w) and Procure 480SC, 8 oz (2,4 w) Luna Sensation, 5 oz (1-3 w) Luna Sensation, 5 oz (1-4 w) Luna Privilege, 6.84 oz (drip 1,3 w) Pristine 38 WG, 18.5 oz (1,3 w) and Procure 480SC, 8 oz (2,4 w)


PM Management • • • • • •

Torino alternated with Procure works excellent Quintec alternated with Procure also is good Pristine alternated with Procure also works Torino: not labeled Luna sensation: not labeled Luna Privelege: not labeled


DM: Pseudoperonospora cubensis â&#x20AC;˘ DM infects leaves only; rare case of sporulation on fruits and flowers

New sporangia are produced within 4-12 days from infection sites


â&#x20AC;˘ The DM fungus is an obligate parasite. Needs a cucurbit host â&#x20AC;˘ During winter season, the fungus survives on cucurbit production in south FL


• Primary inoculum: Air-borne sporangia from infected cucurbits • Secondary inoculum: air currents, rain splash, contact by workers and tools • Favorable weather conditions: 59-77 F, 6-12 h leaf wetness and 100% R.H (sporulation)

1. 2. 3. 4. 5. 6. 7.

Cucumber ‘Straight Eight’ (DM susceptible) Cucumber ‘Poinsett 76’ (DM tolerant) Cantaloupe ‘Athena’ Acorn squash ‘Table Queen’ Pumpkin ‘Big Max’ Watermelon ‘Mickey Lee’ Butternut squash ‘Dickinson’


Trt 1 7 8 9 10 12 13 14 15

Untreated Ranman (2.75 fl oz; 1,3,5,7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w) Pristine 38WG (18.5 oz; 1,3,5,7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w) Presidio 4SC (4 oz; 1,3,5,7 w) Penncozeb 75DF (2 lb; 1-7 w) Curzate 60DF, 3.2 oz (1,3,5,7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w) Catamaran (4 pt; 1-7 w) Forum/Acrobat (6 oz; 1,3,5,7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w) Revus 2.08 SC (4 oz; 1,3,5,7 w) Bravo WeatherStik 6SC (2 pt; 1-7 w)


Fungicide application against DM • Once you hear of DM in your region, apply preventative fungicides • Apply fungicides at first sign of DM - the longer you wait, the harder it is to control • Rotate with fungicides with different modes of action: it is important to prevent resistance • Include a protectant in every application: chlorothalonil & mancozeb are good options


Interactions of cucurbit hosts with pathotypes of P. cubensis Pathotype Host

1

2

3

4

5

Cucumber (Cucumis sativus)

+

+

+

+

+

Netted melon (C. melo var. reticulatus)

+

+

+

+

+

Pickling melon (C. melo var. conomon)

-

+

+

+

+

Bitter melon (C. melo var. acidulous)

-

-

+

+

+

Watermelon (Citrullus lanatus)

-

-

-

+

+

Squash & pumpkin (Cucurbita spp.)

-

-

-

-

+

+ = Highly compatible or susceptible interaction - = Incompatible or very slightly compatible interaction Thomas, C. E. 1998. In: Compendium of cucurbit diseases. APS Press, St. Paul, MN


Thank You

Cucurbit meeting  

Cucurbits in the southeast