Plant Symptoms and Their Causes

Plant Symptoms and Causes

California’s soil is generally rich in minerals plants need. Unhealthy looking plants show similar signs to common diseases, no matter what soil they grow in. Here are some common signs and their causes.

Problem looks like: Possible cause Controls or treatments
Low fruit yeild, 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.

read the next article: Raised Bed Gardening



Mike was one of the founding members of the garden, author of this website and first chairman of the garden. Mike helped create the Antonio Garden which in turn has spawned more gardens throughout the county and across the country. The latest garden that used our model is in Iowa.
Mike Taylor is a best-selling author, Sr. Editor at Newswire, publisher, broadcaster, business strategist and coach. Mike works from Southern California offices and helps businesses and professionals across the country. Mike's work has been seen on major media sites including ABC, CBS, CNN, FOX, NBC, Yahoo Finance, the Sacramento Bee, the Wall Street Journal and Reuters as well as local TV and newspapers. Visit his Amazon author page here or connect on LinkedIn or Google+.


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