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, Sphaerotheca.
This is the most common disease of veronica in Connecticut. 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.
Downy mildew, Peronospora.
Early symptoms of infection often go unnoticed and appear as slightly chlorotic areas on the upper leaf surface. Diagnostic symptoms develop as the fungus grows and breaks through the lower leaf surface and appears as a purplish-gray, fuzzy growth. When infection is heavy, leaves shrivel and die.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. This disease can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut is mancozeb. Consult the label for dosage rates and safety precautions.
Symptoms first appear as small chlorotic flecks or spots on the leaves and stems. These eventually develop into whitish pustules that break open to reveal the powdery spores of the fungus. Once the pustules rupture, the leaves dry, turn brown, and shrivel.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop.
Checkerspot butterfly Euphydryas chalcedona.
The larva of this butterfly eats veronica, chrysanthemum and penstemon foliage. Control is usually not needed, but if numerous, Bacillus thuringiensis var. kurstaki (Bt) is among the compounds registered for control of this pest in Connecticut. To be effective, Bt must be directed against young caterpillars. Consult the label for dosage rates and safety precautions.
Twobanded Japanese weevil Callirhopalus bifasciatus.
The weevils vary in size, up to 1/4" long, and vary from light to dark brown. The adults especially favor feeding on tender shoots. Among the compounds registered for control of this pest in Connecticut are carbaryl or fluvalinate, which can be applied in late July and mid-August to control the adults. Larvae, which feed on roots in the ground, may be controlled with insect pathogenic nematodes. Consult the label for dosage rates and safety precautions.