AZ Master Gardener Manual: Key to Specific Vegetables (Eggplant and Lettuce)

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Plant Pathology

PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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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

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

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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