AZ Master Gardener Manual: Key to Specific Vegetables (Beet, Carrot, and Cole Crops)

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Plant Pathology

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

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
Misshapen roots	• Lumpy soil	• Thin beets early

CARROT

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

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)
Heads soft and rotted	• 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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