Visit www.hort.cornell.edu/diagnostic for assistance in diagnosing problems with currants and gooseberries. Currant aphids, leaf spot, and powdery mildew are the most common problems that plague currant and gooseberry plantings. All disfigure or damage the leaves and can cause defoliation.
Currant aphids. These tiny, soft-bodied insects feed under young leaves toward the shoot tips, causing affected leaves to curl downward, blister, and become reddish. In severe cases, the leaves become excessively distorted and fall off, and the fruit does not ripen properly. Insecticidal soap and certain horticultural oils (check labels) can help control aphids.
Powdery mildew. This fungal disease is a problem particularly on European gooseberries. In early summer a whitish, powdery growth appears on the
surface of leaves, shoots, and branch tips. If left unchecked, the fungus can progress to the berries themselves. Later in the summer, the growth may turn from white to brown. Warm, humid conditions and poor air circulation favor powdery mildew. Prune and dispose of infected branch and shoot tips in early spring. Some home gardeners are experimenting with trellising gooseberries because it makes disease management and harvesting easier (see Figure 25). Certain horticultural oils (check labels) applied at the first sign of powdery mildew can prevent its spread.
Anthracnose and leaf spot. Both these diseases can become serious problems, especially in wet, humid years. Symptoms range from brown spots and yellowing on leaves, young shoots, and stems to early defoliation. Destroy affected leaves, and apply mulch after leaf drop.
San Jose scale. These insects occasionally infest currant and gooseberry plants. They feed by sucking valuable plant juices, and in severe cases they affect the fruit as well. Scale insects are easily seen on the dormant wood. Prune out and destroy infested canes before new growth begins in the spring. Certain horticultural oils (check labels) can help reduce infestations.
Currant borers. These moth larvae burrow in the pith of currant and gooseberry canes. Infested canes do not die in the fall, but they put out sickly growth in the spring. The adult, a clear-winged moth, appears in June and lays eggs in leaf axils. To prevent the next generation of moths from emerging, remove and destroy infested canes before June 1. Proper pruning to remove old canes is the best control.
Currant stem girdler. This immature sawfly eats around, or girdles, the tips of new shoots, which eventually die and fall off. Cut off affected tips in May or June about 3 to 4 inches below the girdle, or if left until later in the season, about 8 inches below the girdle.
Imported currantworm and other sawflies. As soon as leaves expand in the spring, adults deposit eggs on the undersides ofleaves along the major veins. A week to 10 days later, tiny larvae emerge and begin eating holes in the leaves. If numerous, they can strip a bush of its foliage in a few days. Remove leaves harboring eggs by hand.
Gooseberry fruitworm. This greenish caterpillar feeds in the fruit, causing it to color prematurely and fall off. The adult moth lays eggs on the fruit, and the larvae enter the developing berries and feed on the pulp, moving from one fruit to another. Several berries may be tied together by a silken webbing. Handpick infested berries before larvae move to adjacent ones.
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