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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 11 - 12
[ Diagnostic Key: vegetables | specific vegetables; asparagus, bean, beet, carrot, cole crops, corn, cucurbits, eggplant, lettuce, onion, pea, pepper, potato, tomato | tree fruits| specific fruits; apple, stone, citrus | ornamentals | specific ornamentals; rose family, rose, palm, pine ]


KEYS TO PROBLEMS ON SPECIFIC VEGETABLES

ONION Top

SYMPTOMS CAUSES CONTROLS
Numerous small white flecks on leaves; leaves die from tips back and turn brown Botrytis blast • Use registered fungicide
• Downy mildew (fungal disease) • Use registered fungicide
• Onion thrips • Use registered insecticide
White flecks form on leaves and expand into elongated leaf lesions; white to purplish mold develops on spots during moist weather leaves drop over and dry up • Downy mildew (fungal disease) • Rotate; use registered fungicide
Leaves yellow and die back from tips; bulbs are soft and rotted • Fungal or bacterial bulb rot • Rotate; remove old plant debris; plant in well drained soil
Dark green or black smut up to 1 inch in diameter on bulb or neck • Smut (fungal disease) • Rotate; remove old plant debris; plant in well drained soil; plant disease-free onion sets
White streaks or blotches on leaves • Onion thrips • Use registered insecticide


PEA Top

SYMPTOMS CAUSES CONTROLS
Plants stop producing pods; leaves turn yellow, then brown and die • Hot weather • Peas are cool season vegetables: plant early in spring; plant heat resistant varieties
• Root rot (several fungi) • Rotate; plant in well drained soil; remove old plant debris
Fusarium wilt (fungal disease) • Resistant varieties; rotate; remove old plant debris
Plants stunted; lower leaves yellowed; internal stem tissue discolored brown Fusarium wilt • Resistant varieties; rotate; remove old plant debris
• Waterlogged soil • Improve drainage
White, powdery mold develops on upper and then lower surfaces of leaves; leaves and pods may be distorted • Powdery mildew (fungal disease) • Rotate; remove old plant debris
Brown spots on leaves, pods, stems • Fungal or bacterial disease • Submit sample for diagnosis
Yellowish areas on leaves; blister- like ridges on undersides of leaves and on pods; pod distortion • Pea enation mosaic virus • Resistant varieties; weed control; insect control; remove affected plants
Light-colored leaf veins; rosetting of shoot tips; plants stunted with poor pod set • Pea stunt virus • Weed control; insect control; remove affected plants

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