Like most garden problems,plant diseases are easiest to control if you catch them early. But unlike insect pests, pathogens are generally too small to see without magnification. In most cases, you won't know they've struck until your plants begin to suffer and display symptoms.Environmental and cultural problems, like frost injury, air pollution, or nutrient imbalances, can also be tricky to diagnose,since the conditions that cause them are seldom visible.
Step -By -Step Disease Diagnosis
1) Identify the plant. Although it sounds obvious, this one simple step can put you surprisingly close to an accurate diagnosis in just a few minutes. Many popular garden plants are commonly attacked by easy -to-identify diseases and disorders, like black spot on roses, powdery mildew on lilacs, smut on corn, or blossom end rot on tomatoes.If you're not sure what the plant is, ask a fellow gardener, a local nursery or botanical garden, or your local Co-op for help. Even if identifying the plant doesn't help you diagnose the disease, it can be important later on when you are deciding on a control measure. Some plants, for instance, are sensitive to soap- or oil based sprays, so you'd want to use a different type of control on these plants to avoid causing even more damage.
2) Take a good look. Jot down anything that you notice about the affected plant. What parts seem to be affected: The leaves, stems, flowers, or fruits? If the plant parts are spotted or discolored, notethe color, size, and general shape of the patches. If leaves are affected, is it the old or new leaves? Is the plant shorter than similar plants arounit? Was it recently planted,or has it been in your landscape for many years? Anything youknow or notice about the affected plant-no matter how minor-may help you or your consultant make or confirm a diagnosis of the problem.
3) Consider the environment. Extreme weather conditions, like strong wind, hail,and waterlogged or dry soils, can give plants an unhealthy appearance that resembles symptoms of plant disease. Make a note of any unusual weather conditions that you can remember. (Actually, it's smart to jot down weather occurences, like frosts,
heavy rains, or dry spells, as they happen so you'll have those notes to refer back to when a problem strikes.) Also consider whether your plants have been exposed to pollutants like acid rain,herbicide drift, or road salt.
4) Rule out insects pests. Some insects cause damage that resembles plant disease symptoms. When in doubt, use a magnifying lens to check for insect signs like webbing or droppings. Symptoms that are particularly unusual might mean that damage is the result of two or more pathogens or pests; open wounds from insects or other damage make convenient entrances for plant pathogens.
5) Do some research.Discuss problems with neighbors who have similar plants and check reference books in your local library.
6) Consult the experts. If a particular problem has you stumped, submit samples to your local or state plant disease diagnostic laboratory, or your local Co-op. Local botanical gardens and arboreta may also be willing to help you identify plant problems.