The first step to correcting a plant problem is to identify the problem. This can be a guessing game that is somewhat tricky, but if you can identify the symptoms and narrow down the possible causes, you will be well on your way. Symptoms of plant problems include eaten or distorted leaves, distorted stems, wilted or discolored leaves and deformities on leaves and stems.
Tiny notches in the leaf edges are most likely caused by root weevils, which are mainly found in Washington, Oregon and northern California. Leaves that are eaten and wilted indicate squash bugs, which lay a mass of hard brown eggs on the undersides of the leaves. Leaves with irregular holes may be caused by slugs, snails or oak moths.
Aphids distort new leaves. Thrips rasp soft plant tissues and drink plant juices, preventing leaves and flowers from opening normally. Leaves may take on a silvery or tan cast, with stippled puckerings on flower and leaf tissue and black varnish-like fecal pellets apparent on leaf undersides. Leaf rollers hide during the day by rolling leaves around themselves.
Galls are abnormal growths on plant leaves and stems caused by abnormal cell growth or reactions to infections from fungi, bacteria or viruses, or stimulated by sucking insects such as aphids.
Wilted leaves coated with white powder indicates that plant is affected by powdery mildew. Oak root fungus affects woody plants and begins with dull or yellowed leaves that eventually wilt, and whole branches that die. Verticillium wilt is a widespread plant disease that is extremely destructive. The fungus can stay in the soil for years, even in the absence of affected plants. It is indicated by wilting on one side of the plant. Leaf margins yellow and then progress inward until leaves turn brown and die.
Whiteflies lay eggs that appear as whitish speckles on leaf undersides. Mites create yellow stippling on leaves and fine webbing across leaves and around stems. Hold a paper under an affected leaf and rap on the plant stem to see if mites fall onto the paper. Nitrogen deficiency is indicated by yellowed leaves. Leaves that are yellow with green veins may be affected by iron deficiency, called chlorosis. Leaf spot may be red, brown, yellow or black, and severe infections may defoliate entire plants. Rust is indicated by colored pustules from spores on the undersides of plant leaves, with yellow mottling on top.
Deformities on Stems and Leaves
Scale is detected through bumps on stems and leaves created by their hard outer shells, which stick to the plant while they suck out the plant juices from underneath. Sticky honeydew secretions may also be present. Mealy bugs have soft, white, oval bodies, and they move around on the plant, sucking out the juices and leaving black, sooty mold on their honeydew secretions.