Plant Health Problems
See Perennials for a detailed discussion of problems that may occur and are common to most herbaceous ornamentals.
Diseases caused by Fungi:
Powdery mildew, Erysiphe, Sphaerotheca.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, sulfur, potassium bicarbonate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Diseases caused by Phytoplasmas:
Yellows, phytoplasma.Symptoms consist of a yellowing or clearing of the veins in newly infected leaves, shortening of the internodes of the main stem, and production of long axillary breaks which create a yellowish witches' broom. If plants are infected young, they remain stunted, and if flowers are produced, they are small, abnormal, and exhibit phyllody, a condition in which flower parts revert to green tissues. Symptoms do not always appear on the entire plant, but may show on only one stalk, depending on the time of infection. This phytoplasma is transmitted by leafhoppers. Since the pathogen infects many plants (e.g., daisies, chrysanthemums, plaintain, echinacea, and rudbeckia), gaillardia may become infected from neighboring plants.
Strategies for control include promptly roguing and removing diseased plants as well as control of the leafhopper vectors.
Leafhopper, Macrosteles fascifrons.
The adults of this leafhopper are grayish and 1/8" long. They spread aster yellows disease. Apply carbaryl, which is among the compounds registered for control of this pest in Connecticut, when leafhoppers are troublesome. Imidacloprid applied as a systemic to be taken up by the roots will also provide season-long control. Consult the label for dosage rates and safety precautions.
Fourlined plant bug, Poecilocapsus lineatus.
This bug lays eggs in the soft stems. They hatch about the middle of May and the young bugs suck the sap from the tender leaves. They molt five times and when mature, about the middle of June, they have wings and are nearly 1/3" long. The insect body is yellow, marked lengthwise on the wings with four black stripes alternating with three green stripes. The injury to the leaves consists of sunken areas around the punctures. These areas later appear as circular transparent spots and finally as circular holes. This insect injures the new leaves of many different kinds of annual and perennial plants and shrubs. There is one generation each year. The nymphs can be managed by spraying with ultrafine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for control of this pest in Connecticut. Imidacloprid, applied as a soil drench, will provide season-long systemic control. Consult the label for dosage rates, safety precautions, and preharvest intervals.