Disease and Pest Control

Major Symptoms & Possible Causes

Sometimes the cause of a garden problem is easy to identify. Fan shaped mounds of soil littering a lawn are obviously the work of a pocket gopher; slime trials leading to plants with large, ragged holes in the leaves can only mean slugs or snails.

A bigger challenge is deducing the source of trouble when many explanations are possible. Leaf yellowing and wilting, for example, may be due to insects, nematodes, diseases, or improper watering. If you can’t find clear evidence of a pest, the best course is to assume that growing conditions are at fault, then to focus on improving them. If you’re convinced a pest or disease is the villain, check the rogues’ gallery for a likely candidate but be sure all the evidence fits before placing blame.

Your Disease and Pest Control Experts

For help in solving problems you can’t identify on your own, consult your Cooperative Extension office or a reputable local nursery.

 

Symptoms Possible Causes Notes
Leaf yellowing Spider mites
Insects
Nematodes
Root rot diseases
Viral diseases
Over watering
Nutrient deficiencies
Soil chemistry
Old age
Usually pinpoint yellowing
Especially bark borers
Wilting also occurs
Older leaves affected firstOlder leaves affect first
Leaf mottling Viral diseases
Pesticide damage
Natural on some plants
Genetic variegation
Leaf spots DiseasesInsects
Spider mites
Air pollution
Pesticide damage
Nutrient deficiencies
Soil chemistry
Leaf malformations Sucking pests
Viral diseases
Peach leaf curl
Lack of water
Nutrient deficiencies
Pesticide damage
On peaches and nectarinesEspecially from certain weed killers
Holes in leaves Chewing pests
Birds
Leaf drop Diseases
Bark borers
Improper watering
Improper light
Air pollution
Nitrogen deficiency
Soil chemistry
Natural on some plants
Deciduous plants
Cankers(sunken lesions) DiseasesInsects
Root stress
Sunburn
Mechanical wounds
Especially borersFrom lawn mowers, pruner, and other equipment
Branch dieback DiseasesInsectsNematodes
Root stress
Soil chemistry
Especially vascular diseases such as firelight and verticillium wilt
Severe infestation by root or foliar pests or twig girdlers
Root rot Diseases
Over watering
Root stress
Soil chemistry
Usually fungal
Discolored tissue inside roots and stem Wilt diseases
Fertilizer damage
Root malformations Nematodes
Diseases
Girdled roots
Natural on some plants
Crown gall, for example
Formed in container
Nitrogen-fixing nodules on legumes
Poor germination Old Seeds
Uneven irrigation
Incorrect planting depth
Damping-off disease
Soil crusting
Insects
Birds
Root maggots, wireworms
Wilting Lack of water
Insects
Nematodes
Diseases
Especially borers and root feedersRoot rots and wilt diseases

 

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