Plant Symptoms and Their Causes

California’s soil is generally rich in the minerals that plants need for healthy, vigorous growth. Unhealthy looking plants show similar signs to common diseases, no matter what soil they grow in.

Many California soils are far from neutral – either acidic or alkaline. This may tie-up some minerals your plants need. Adding compost and organic materials to your soil helps neutralize it and release the minerals you need.

It is helpful to know the pH of your soil (7 is neutral) as this may account for some deficiencies. A home pH test key with tests for the major minerals costs $10 to $15 and is worth having. We’ll look at mineral deficiencies on another page…

Here are some common signs of stress in your garden and their causes.

Problem looks like:	Possible cause	Controls or treatments
Low fruit yield, small fruit with poor taste	Uneven Moisture	Water properly during dry periods
	Poor soil fertility	Add compost, manures
	improper temperature	Plant at the correct time of year
Plants grow slowly and have light green leaves	not enough light	Thin the plants, don’t plant in the shade
	weather too cool	protect with floating row covers, cloaches
	improper pH	Test the pH; if alkaline, add soil sulfur, aluminum sulfate, peat moss
	excess water	Don’t over water; improve drainage with amendments or plant in raised beds
Seedlings do not emerge	not enough soil moisture	Supply enough water; multiple applications may be needed in hot or windy conditions
	soil crusting	apply light layer of fine mulch; keep moist as above.
	damping-off	don’t over water; avoid spraying water on plants; plant treated seed
	improper planting depth	follow packet instruction; use gentle watering techniques
	slow germination due to weather	Cover beds in spring and fall to warm the soil (see note)
	root maggots	Use floating row covers to exclude insects; registered soil insecticide as last resort.
	old seed	Use seed marked for current year and season
Seedling wilt and fall over	soil too dry	Water properly
	damping-off (a fungus)	Don’t over-water or water from above; use sterile soil-less mix; use fungicide
	cutworms	Destroy crop residues; keep weed free, hand-pick a night with flashlight
	root maggots	Use floating row covers for exclusion; soil insecticide
	old seed	Use seed for current season
chewed seedlings, plants, fruit	birds, rodents, rabbits	Fence garden or beds, floating row covers, wire mesh, netting (or accept it and plant an additional row to share)
leaves covered with tiny white spots	spider mites	Use insecticidal soaps; registered miticides are available
	air pollution	Rinse off leaves
wilted plants	rot rot (fungal disease)	Don’t over water; remove affected plant materials; rotate your crops
	Vascular wilt – found primarily in tomato, potato, eggplant and peppers	Plant resistant varieties; solarize the soil; rotate to other crops.
	root knot nematodes	Plant resistant varieties; solarize the soil; rotate to other crops
	other root-feeding nematodes	Solarize soil; have the soil analyzed for nematodes if problem persists.
	water-logged soil	Improve drainage; use raised beds; correct watering practices.
yellow leaves, but not wilted	lack of one or more nutrients	Test soil; treat for deficiencies. This may include adjusting the pH
	Not enough light	Thin crowded plants
		Move to sunnier location
brown, shriveled leaf edges	soil is too dry	Correct watering practices
	salt water damage	Spa water can contain enogh salts to burn foliage. leak any areas where spas drain,
	Chemical fertilizer burn	Same as above – bagged fertilizers are concentrated salts. Wash these deeply into the soil to avoid concentrations.
	Potassium deficiency	Test soil first. Add compost, manure or other potassium bearing fertilizer
	Cold burn	Floating row covers trap the soils heat and cn protect from frost
White powdery growth on top of leaves	Powdery Mildew, a fungus	Some varieties are listed as resistant. Treat infected plants with Safer’s sulfur and a surfactant.
Leaves have spotted or mosaic-like discolored patterns, puckered leaves, runty plants	Various virus diseases	Remove infected plant materials – do not compost them Remove and compost nin-infect plant materials, control weeds, insects (See IPM listing in resources page)
Curled, pucked, distorted leaves	Herbicide injury	Herbicides drift on the slightest breeze. Be careful of neighbors dispensing herbicides upwind of you.
	Virus diseases	Remove infect plant materials – do not compost it. Remove and compost non-infected plant materials, control weeds, insects (See IPM listing in resources page)
	aphids	Soap-based sprays, dormant oil sprays – but only in heavily infested areas. Leave some areas untreated to act as a host crop for predatory insects. Control ants (they farm the aphids for their honeydew)

For more information on plant diseases and their symptoms, refer to the University of California’s IPM diseases web page.