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Disease Control in Leafy Brassica Greens
Steve Bost Extension Plant Pathologist
University of Tennessee
Presented at 28th Annual Southeast Vegetable & Fruit Expo December 4, 2013 Myrtle Beach, SC
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Tennessee has some large leafy greens operations. Most plantings are small scale, hand-harvested.
What are the major diseases of brassica leafy greens? How to identify them? How to control them?
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Cercospora leaf spot
Tan spots, may have yellow haloes.
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Cercospora leaf spot cont’d
Spots may be smaller or may show rings
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Alternaria leaf spot
Definite rings. Alamo turnip pictured.
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Anthracnose
Small lesions
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Anthracnose cont’d
Lesions on stems and veins are diagnostic
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Anthracnose cont’d
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Downy mildew
Diffuse yellow spots. May advance to necrotic.
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Downy mildew cont’d
White tufts of spores may be seen on the undersides of lesions. Can be difficult to see.
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Downy mildew cont’d
Spores on undersides may appear gray, such as on these collards.
Diseased leaves may remain in canopy, causing a quality problem in harvested product.
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Powdery mildew
Southern Giant Curled mustard and Alamo turnip growing side-by-side. Mildew very light on turnip.
Southern Giant Curled mustard
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Bacterial diseases
Black rot Xanthomonas campestris pv. campestris
Leaf spots Xanthomonas campestris pv. campestris
Xanthomonas campestris pv. armoraciae
Pseudomonas syringae pv. maculicola
Pseudomonas syringae pv. alisalensis
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Bacterial leaf spots Symptoms vary. Easier to see lesions on undersides of leaves.
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Bacterial leaf spots Can resemble nutritional problems or fungal diseases
Both of these are bacterial leaf spot diseases.
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Bacterial leaf spots cont’d
Vein necrosis distinguishes them from fungal diseases, but often not seen.
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Black rot Bacteria become systemic in plant.
V-shaped lesions
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Black rot cont’d Bacteria spread rapidly by rain splash.
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Bacterial disease control
Sources of infestation are contaminated seeds and infected weeds. So:
• Treat seeds. Hot water seed treatment kills internal and external bacteria, whereas disinfestants such as bleach and trisodium phosphate only kill surface bacteria. Seed company service preferred to do-it-yourself.
• Control cruciferous weeds in and around field.
If disease is found:
• Copper and/or Actigard sprays may suppress the severity of the disease, but often do not suppress incidence, i.e. the number of diseased leaves.
• Incorporation of post-harvest crop debris into soil will hasten decline of bacterial populations.
• Long crop rotations are not necessary, but cole crops should be limited to one crop per year. Longer rotations may be needed if other diseases are a problem or if cruciferous weeds persist.
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Pythium root rot. Don’t grow
transplants in float beds.
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Fungicide Trial, Highland Rim REC, Springfield, TN Spring, 2013
Product, rate/acre (application number)
Cercospora leaf spot (% leaf area affected)
Turnip Mustard
Check 35.0 a 30.0 a
Quadris, 6 fl oz (1,3); Kocide 3000, 0.5 lb (2) 16.5 b 7.5 b
Fontelis, 1 pt (1-3) 2.8 c 1.8 c
Fontelis, 1.5 pt (1-3) 4.3 c 1.5 c
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Downy mildew trial, Highland
Rim REC, Springfield, TN
Fall, 2011
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Fungicide Trial, Highland Rim REC, Springfield, TN Fall, 2011
Product, rate/acre Leaf area affected (%)*
Check 16.3 a
Fontelis, 1 pt 22.5 a
Fontelis, 1.5 pt 20.8 a
Endura, 8 oz 15.8 a
Quadris, 6 fl oz 4.5 b
* Primarily downy mildew, some Cercospora.
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Controls Chemical
Caution: Be careful where you get your information! Every product used must be registered with EPA!
The Southeastern US Vegetable Crop Handbook http://www.thegrower.com/south-east-vegetable-guide/
Cultural
Plow-down crop debris at end of year.
Rotate with non-cruciferous crops.
Control cruciferous weeds*.
Use treated seed and buy transplants from trusted source*.
* Particularly important for bacterial disease control.
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Scenes from a garden center.
Garden center suppliers must be held
accountable for diseased transplants.
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Anth Cercos Downy Powd Bacter Collard Kale Mustd Turn grns Turnip
Actigard X X X X X X X
copper X X X X X X X X
Forum X X X X X
Presidio X X X X
Ranman X X X X X
Reason X X X X
Revus X X X X
Ridomil X X X X X
Zampro X X X X
Endura X X X X
Fontelis X X X X X X X X
Inspire Super X X X X X X X
Quadris X X X X X X X
Quadris Top X X X X X X X
Cabrio X X X X
Switch X X X X X X
Procure X X X X X
sulfur X X X X X X
tebuconazole X X X X X X
Flint/Gem X X X X
Partial list of registered products. X = Registered for use.