Still others cause general wilting which may eventually lead to plant death. Occasionally, leaves may have holes as a result of damaged tissue that has dried, become brittle and fallen from the leaf. Because these pests do not consume any of the plant surface, stomach poisons on the surfaces of plants don't work very well. In this case a systemic pesticide, one that enters the plant system so the insect picks up the pesticide as it feeds or a contact insecticide may work best. Insecticidal soaps have contact activity but must be come in contact with the pest because they have no residual activity.
Some insects are capable of transmitting diseases from infected to uninfected plants.
The most important ones here are leafhoppers and aphids. The aster leafhopper is the primary vector of aster yellows disease. It does not overwinter here, but migrates from more southern regions each season. The amount of aster yellows is related to the disease incidence occurring in the southern United States at the time if migration. Thus, disease levels can vary from year to year.