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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

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?

Cercospora leaf spot

Tan spots, may have yellow haloes.

Cercospora leaf spot cont’d

Spots may be smaller or may show rings

Alternaria leaf spot

Definite rings. Alamo turnip pictured.

Anthracnose

Small lesions

Anthracnose cont’d

Lesions on stems and veins are diagnostic

Anthracnose cont’d

Downy mildew

Diffuse yellow spots. May advance to necrotic.

Downy mildew cont’d

White tufts of spores may be seen on the undersides of lesions. Can be difficult to see.

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.

Powdery mildew

Southern Giant Curled mustard and Alamo turnip growing side-by-side. Mildew very light on turnip.

Southern Giant Curled mustard

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

Bacterial leaf spots Symptoms vary. Easier to see lesions on undersides of leaves.

Bacterial leaf spots Can resemble nutritional problems or fungal diseases

Both of these are bacterial leaf spot diseases.

Bacterial leaf spots cont’d

Vein necrosis distinguishes them from fungal diseases, but often not seen.

Black rot Bacteria become systemic in plant.

V-shaped lesions

Black rot cont’d Bacteria spread rapidly by rain splash.

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.

Pythium root rot. Don’t grow

transplants in float beds.

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

Downy mildew trial, Highland

Rim REC, Springfield, TN

Fall, 2011

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.

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.

Scenes from a garden center.

Garden center suppliers must be held

accountable for diseased transplants.

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.