Plant Health Problems
Diseases caused by Fungi:
Leaf and twig blight, Blumeriella kerriae.
Leaves and stems may be infected. On the leaves infection shows as reddish spots with dark borders and, if numerous, leaves yellow and fall. Stem cankers are produced as discolored more or less extended darkened areas which may crack open to reveal the black fruiting bodies beneath. The perfect stage of the fungus is produced on fallen leaves that have wintered over on the ground.
Raking and composting of fallen leaves and pruning out any infected twigs are designed to reduce the inoculum. Control can also be achieved with the use of fungicides before symptoms are severe. Among the compounds registered for use in Connecticut are chlorothalonil and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Japanese beetle, Popillia japonica.
This beetle, in the adult stage, feeds upon a great variety of trees and plants, including kerria. The beetle is ½" long, bright, shining green, with copper colored wing covers. Two white spots on the tip of the abdomen show beyond the ends of the wing covers, and there are five white spots formed by patches of white hairs on each side of the abdomen. The beetles begin emerging in late June but their greatest abundance is usually about the middle of July. During drought periods populations of Japanese beetle are drastically reduced.
Japanese beetle traps containing floral and sex attractant lures are readily available at home and garden centers. These traps may help reduce the overall number of beetles. However, beetles often land and feed on plants close to traps, so traps should be placed well away from valued plantings. Feeding on kerria foliage can be prevented by using sprays of acephate, azadirachtin, carbaryl or malathion, which are among the products registered for use against this pest in Connecticut. Imidacloprid, applied early in the season as a soil drench, will provide season-long systemic control. Consult the labels for dosage rates and safety precautions. Larvae develop in turf, so treatment of lawn areas should reduce the numbers of beetles. See Lawns, oriental beetle.