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PLANT PATHOLOGY: DIAGNOSTIC KEY [continued]

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  MG Manual Reference
Ch. 4, pp. 5 - 7
[ 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

BEET Top

SYMPTOMS CAUSES CONTROLS
Small, circular spots with light centers and dark borders on leaves Cercospora leaf spot (fungal disease) • Pick off and destroy affected leaves; fungicides not warranted; use deep tillage of beet refuse
Roots cracked; black areas on surface and inside root; plants stunted • Boron deficiency • Amend soil as needed; maintain pH between 6 and 7; apply solution of household borax if necessary (1 T. household borax per 12 gal water per 100 ft row)
Leaf margins rolled upward; leaves brittle and puckered along veins; plants stunted • Curly top disease (virus) • Control leafhoppers that spread the disease; eliminate weed hosts; rogue infected plants
Misshapen roots • Overcrowding • Thin beets early
• Lumpy soil


CARROT Top

SYMPTOMS CAUSES CONTROLS
White powdery growth on leaves • Powdery mildew (fungal disease) • Use registered fungicide; remove old plant debris
Inner leaves yellow; outer leaves reddish-purple; roots stunted and bitter • Aster yellows (mycoplasma disease) • Remove affected plants; weed control; leafhopper control with registered insecticide
Root tops green • Root tops exposed to sunlight • Cover exposed roots with soil or mulch
Roots misshapen • Overcrowding • Thin carrots early
• Lumpy soil  
• Root knot nematode • Rotate; soil pasteurization
Plants stunted and yellowed; roots misshapen; small knots on fibrous roots • Root knot nematode • See control above


COLE CROPS Top

SYMPTOMS CAUSES CONTROLS
Cracking of heads • Excess water taken up by plant causes head to burst • Harvest heads as soon as mature
Poor heading • Overcrowding • Thin plants early
• Dry soil • Supply water
• High temperatures  
• Poor fertility • Amend soil as needed
• Root knot nematode • Check roots for knots; rotate; soil pasteurization
• Root rot (fungal disease) • Rotate; remove old plant debris; plant in well-drained soil
Discolored cauliflower heads • Exposure to sun • Tie leaves over head when heads form
Brown spots on leaves • Fungal or bacterial disease • Submit sample for diagnosis
Plants stunted and yellowed (esp. cabbage); roots not discolored • Dry soil • Supply water
• Poor fertility • Amend soil as needed
Fusarium yellows (fungal disease) • Resistant varieties; rotate
• Cabbage maggot • Dust with diatomaceous earth; work in a soil insecticide at planting time
Heads soft and rotted • Soft rot of broccoli (bacterial disease) • Grow broccoli varieties that shed water (conical head)
• Bottom rot of cabbage (fungal disease) • Rotate; plant in well drained soil
Rough, brown, raised areas on underside of leaves • Oedema, physiological problem due to uneven water supply • Water during dry periods
Leaves riddled with shotholes • Flea beetles • Use registered insecticide
Leaves chewed • Imported cabbage worm, cabbage looper, diamondback moth, or cross-striped cabbage worm, flea beetle • Identify insect; use registered insecticide or B. thuringiensis spores
Some leaves curled and yellowed; clusters of small gray or green insects • Aphids • Use registered insecticide or hard stream of soapy water

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