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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 12 - 15
[ 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

PEPPER Top

SYMPTOMS CAUSES CONTROLS
Large, sunken, tan watersoaked spot develops on blossom end of fruit; spot turns black and mold may grow • Blossom end rot, caused by calcium deficiency to developing fruits • Calcium deficiency is a problem when developing fruits receive uneven moisture: supply water during dry periods; mulch
Thin, wrinkled tan areas develop on fruit and become white and papery • Sunscald • Control leaf diseases to prevent leaf drop which exposes fruit to sun
Dark brown, sunken spots develop on fruit (not restricted to blossom end) and leaves • Fungal or bacterial disease • Submit sample for diagnosis
Small tan to dark brown spots develop on leaves; small brown, dry raised spots appear on fruit • Bacterial spot • Use fixed copper bactericide (e.g. Kocide) if available; use chlorox-treated or western grown, hot water treated seed; avoid overhead watering
Tiny, brown specks with pale white haloes develop on fruit; fruit may be distorted around specks • Stink bug injury • Control weeds which may host stink bugs
Brown spots on leaves • Fungal or bacterial disease • Submit sample for diagnosis
Plants stunted; leaves curled with yellow and green mottle; fruit misshapen with brown streaks, rings, yellow, green, and red mottle • Virus disease (any of several) • Resistant varieties are available for some virus diseases of pepper; weed control; insect control; remove affected plants; remove old plant debris
Plants wilted; dark brown canker at base of stem • Fungal or bacterial disease • Submit sample for diagnosis
Plants wilt; lower leaves may turn yellow • Vascular wilt (fungal disease) • Rotate; remove old plant debris
• Dry soil • Supply water
• Waterlogged soil • Improve drainage
• Root rot (fungal disease) • Rotate; remove old plant debris; plant in well drained soil
Large holes in leaves; caterpillars present • Tomato hornworm • Handpick; spray with registered insecticide or B. thuringiensis spores


POTATO Top

SYMPTOMS CAUSES CONTROLS
Potato tuber is green • Exposure to sun • Mound soil up around plants; do not eat green part of potatoes
Brown spots on leaves and/or stems • Various fungal diseases • Submit sample for diagnosis
Plants wilt; bottom leaves may turn yellow • Dry soil • Supply water
• Vascular wilt (fungal disease) • Rotate; remove old plant debris
• Root rot (fungal disease) • Rotate; remove old plant debris; plant in well drained soil
• Root knot nematode • Check roots for knots; rotate; soil pasteurization if necessary
• Waterlogged soil • Improve drainage
Plants wilt; dark brown or black canker at base of stem • Fungal or bacterial disease • Submit sample for diagnosis
Plants stunted; leaves turn bronze to yellow color; plants wilt; tubers have raised, knotty areas • Root knot nematode • Rotate; soil pasteurization
Tubers show irregular white or brown cavities when cut open • Hollow heart, caused by plants growing too rapidly • Do not overfertilize or plant too far apart
Irregular brown discoloration inside tuber • Early frost  
• Drought • Supply water
• Virus disease (any of several) • Tolerant varieties; weed control; insect control
Tubers have slimy, smelly rot • Soft rot (bacterial disease) • Plant in well drained soil; hill plants to encourage water runoff; wait until vines turn yellow and die to dig; store properly
Leaves roll upward, turn light green to yellow and leathery; plants stunted • Leaf roll (virus disease) • Plant certified seed pieces; insect control; weed control
Leaves roll upward, turn purple or yellow; plants stunted; aerial tubers form • Aster yellows (mycoplasma disease) • Leafhopper control; weed control
Tunnels bored into tubers • Wireworm • Use a soil insecticide at planting time
Leaves chewed; fat red, humpbacked beetle grubs or orange beetles with black stripes present • Colorado potato beetle • Handpick beetles or use registered insecticide
Poor, uneven stands in spring; girdling on sprouts and stolons; black or brown sclerotia on tubers • Black scurf (Rhizoctonia) • Avoid planting in cold, wet soils; use disease-free seed pieces
Wilt; leaves turn pale green or yellow; vascular tissue of stems becomes brown Verticillium wilt • Rotate potatoes with cereals, grasses, or legumes; avoid rotation with tomatoes, peppers, or eggplant

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