AZ Master Gardener Manual: Key to Specific Vegetables (Pepper and Potato)

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Plant Pathology

PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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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

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

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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