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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 9 - 11
[ 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

EGGPLANT Top

SYMPTOMS CAUSES CONTROLS
Blossoms drop; no fruit develops • Poor pollination due to unfavorable temperatures • Be patient; fruit will set when temperatures become more favorable
Plants wilt; bottom leaves may turn yellow • Dry soil • Supply water
Verticillium wilt (fungal disease) • Rotate; remove old plant debris; do not plant after tomatoes, potatoes, brambles, or strawberries
• Waterlogged soil • Improve drainage
• Root knot nematode • Check roots for knots, rotate; soil pasteurization
Circular or irregular brown spots on leaves and/or fruit • Fungal or bacterial disease • Submit sample for diagnosis
Leaves riddled with tiny holes • Flea beetles • Use registered insecticide
Large holes in leaves; caterpillars present • Tomato hornworm • Handpick; use registered insecticide or B. thuringiensis spores


LETTUCE Top

SYMPTOMS CAUSES CONTROLS
Bolting; may taste bitter • Weather too hot • Lettuce is a cool season crop; plant early or late
Sunken, water-soaked spots on lower leaves, which turn brown and slimy; head turns brown; hard black, pea-sized pellets of the fungus found in mold between dead leaves Rhizoctonia bottom rot (fungal disease) • Rotate; remove old plant debris; plant in well drained area
Sclerotinia drop (fungal disease) • Rotate planting area each year with deep plowing; fungicides are available for Sclerotinia disease
Stem and lower leaves rotted; dense, fuzzy gray mold on affected areas Botrytis gray mold • Rotate; remove old plant debris; plant in well drained and ventilated area
Yellow or light green blotches on upper leaf surfaces; white fuzzy mold on underside of blotches; spots eventually turn brown • Downy mildew (fungal disease) • Rotate; use registered fungicide
Plants stunted, yellowed; youngest leaves curled; head soft • Aster yellows (mycoplasma disease) • Remove affected plants; weed control; insect control
• Mosaic virus • Remove affected plants; weed control; insect control
• Nutrient deficiency • Amend soil as needed
Leaf veins and area adjacent to veins turns light yellow causing a "big vein" effect • Big vein (viroid disease) • Plant in well drained soil: viroid (virus-like particle) is spread by a soil fungus; remove affected plants; rotate out of area for 10 years
Leaves have holes, ragged appearance • Cabbage looper • Apply B. thuringiensis spores
Yellowish translucent areas near leaf margins which form an irregular brown border • Tipburn, caused by fluctuating water supply • Grow plants with a uniform moisture supply; avoid excess nitrogen fertilization

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