Spots & Rots

Craig H. Canaday Dept. of Entomology & Plant Pathology The University of Tennessee – WTREC

Jackson, Tennessee

(Common pumpkin diseases, their

identification, and control)

Powdery and Downy Mildew Disease Cycle

Powdery mildew is easily spread under dry conditions.

Downy mildew requires wet or very moist conditions.

Spores are blown-in from far away.

Both are caused by obligate pathogens.

Heavily infected plants wither and die.

Spores land on a plant, germinate, infect the plant, and produce millions of new spores.

The appearance of foliage infected with these two diseases is very different.

Powdery Mildew

Powdery Mildew Control

Resistant varieties Fungicides

chlorothalonil (Bravo Weather Stik; Equus 720) wettable sulfur quinoxyfen (Quintec) azoxystrobin (Quadris) myclobutanil (Rally, Nova 40W) triflumizole (Procure 50WP) pyraclostrobin + boscalid (Pristine 38WG) azoxystrobin + chlorothalonil (Quadris Opti 5.5SC)

– Apply chlorothalonil every 7- to 10-days – Thorough coverage is critical with chlorothalonil and sulfur – Do not apply sulfur if temperatures exceed 90 F – Add other fungicides if needed for extra PM control – Always read the label (e.g., Procure has plant back restrictions)

Powdery Mildew Resistance Differences

Variety

Powdery mildew (%)

Source 2008 2009 Magician 4 A* 3 A* Harris Moran Camaro 1 A 3 A Hollar

Magic Wand 0 A 3 A Harris

Corvette 4 A 4 A Hollar

Warlock 5 A 5 A Harris Moran

Gladiator 2 A 18 B Harris Moran

Magic Lantern 1A 23 B Harris Moran

Sorcerer 28 B 54 D Siegers

King Midas 29 B 59 D Siegers

Howden 30 B 80 E Seedway

*Values in the same column followed by the same letter are not significantly different.

The Fungicide Resistance Action Committee (FRAC) is an industry group reporting to Crop Life International. Its purpose is to identify potential and existing resistance problems, evaluate scientific data and knowledge, and provide fungicide resistance management guidelines and education to prolong the effectiveness of fungicides and limit crop losses should resistance occur. They developed the FRAC coding system used to identify the mode(s) of action of particular fungicides.

Fungicide resistance management strategies are based around the FRAC codes, good agronomic practice, optimum fungicide timing, the use of appropriate dose rates, and optimizing the use of alternative modes of action in fungicide programs.

The Fungicide Resistance Action Committee

GROUP 4 FUNGICIDES GROUPO 4 M5 FUNGICIDES

Fungicide Resistance Pathogen resistance to several frequently used fungicides is

becoming common – Ridomil Gold – Quadris

Rotation of fungicides to different “mode of action groups”

(FRAC codes) is essential to prevent resistance development Some fungicides are called “protectants”

– Multiple modes of action (FRAC ‘M’#) – Resistance development is very rare or unknown – Rotation is not needed – Examples of protectant fungicides:

- chlorothalonil - mancozeb - fixed copper - sulfur

– Through plant coverage is needed

(FRAC 4) (FRAC 11)

Downy Mildew

Photos courtesy of Dr. Steve Bost

Downy Mildew Control

Fungicides chlorothalonil (Bravo Weather Stik, Echo, Equus , etc.) copper, fixed (Kocide, Champ, Nu Cop, etc.) mancozeb (Dithane DF Rainshield, Manzate, Penncozeb, etc.) pyraclostrobin (Cabrio) trifloxystrobin (Flint) azoxystrobin (Quadris, Amistar) cyazofamid (Ranman) fenamidone (Reason) pyraclostrobin + boscalid (Pristine) famoxadone + cymoxanil (Tanos)

– Apply protectant fungicides every 7- to 10-days – Thorough coverage is critical – Add other fungicides if needed for extra DM control – Always read the label

Resistant varieties – For a few cucurbit varieties (not available for pumpkins)

Plectosporium Blight

Photos courtesy of Dr. Steve Bost

Plectosporium Blight Control

Fungicides chlorothalonil (Bravo Weather Stik, Equus 720, etc.) maneb or mancozeb (Dithane DF Rainshield, Manzate, etc.) pyraclostrobin (Cabrio) trifloxystrobin (Flint)

– Apply chlorothalonil or maneb or mancozeb every 7- to 10-days – Thorough coverage is critical – Alternate pyraclostrobin and trifloxystrobin with protectant

fungicides – Always read the label

The Difference with & without Disease Control

Cucurbit Yellow Vine Disease Control

Is caused by a phloem-limited bacterium Is transmitted by the squash bug

– Remove egg-infested vines Apply insecticides for control

– Apply after squash bugs appear

Photos courtesy of Dr. Steve Bost and Dr. Annette Wszelaki

Other Diseases and Problems

Viral diseases

Insect and rodent damage

Phytophthora blight

Bacterial diseases

Rodent damage

Summary

There are over a dozen diseases of cucurbit crops that are common on Tennessee pumpkins.

Powdery mildew and downy mildew are obligate pathogens, come into Tennessee from other areas, and are relatively common.

Both “mildews” can spread very fast - powdery mildew without rainfall; downy mildew with rain.

If diseases are not controlled, loss of yield and fruit quality can be expected.

Control is possible! Fungicides are applied on a preventive schedule. Resistant varieties are available for many diseases.

• The Southeastern US Vegetable Crop Handbook www.ces.ncsu.edu/fletcher/information-andbooks/2011_SEVG.pdf • UT Commercial Vegetable Crop Disease Control Guide http://utextension.tennessee.edu/publications/Documents/W141.pdf

Sources for More Information

Which disease is seen here?

Plectosporium Blight

Questions?

Contact: Steve Bost: 615-835-4573; email: scbost@utk.edu

Craig Canaday: 731-425-4746; email: ccanaday@utk.edu

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