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Red Currant Insects

Dealing with insect problems on Red Currants

By: Sandy Feather 2010
Penn State Extension


Q. We have several red currant bushes. They have done well for the past six years, but last year the leaves started curling and browning in late May or early June. A local garden center diagnosed the problem as aphids. I treated them with malathion, but not until mid-June. I managed to stop the leaf curl, but the branches look dried out. Our harvest was nothing compared to past years. Should I cut the dead-looking stems out? Should I continue spraying in April every week or two? Or are the currant bushes ruined, and I'll need to replant?

A. There are a number of insects that could cause these symptoms in red currants (Ribes rubrum), including aphids. Currant aphids overwinter as eggs on the stems of host plants. They hatch in early spring and begin feeding on the new growth with their piercing-sucking mouthparts. Their feeding causes the new growth to be stunted and distorted, and the leaves eventually curl under.

Because aphids feed on carbohydrate-rich plant sap, their excrement is very sugary and sticky. It drips down onto the lower plant parts and is often covered with a black sooty mold. Although sooty mold does not cause any harm, it certainly makes plants look terrible.


SPRAYING CURRANTS

Prolonged aphid feeding results in a reduced harvest. The aphids are small -- roughly 2 millimeters long -- and green. They are active from spring right up until harvest, so applications at two-week intervals may be necessary to keep them under control -- This is not a one-shot solution. In addition to malathion, horticultural oil and insecticidal soap are labeled to control currant aphids in Pennsylvania.

When you talk about the canes "drying out" and looking dead, I wonder if more than one insect is to blame. Two insects that damage canes through the growing season are the currant borer and currant stem girdler.

 


CURRANT BORER

Currant borer larvae damage canes by feeding and tunneling inside the pith of individual stems. They overwinter as mature larvae in the stems, pupating and hatching as adults in spring. Adults are clear-winged moths that strongly resemble wasps. Adults lay eggs on currant stems in June; the small larvae tunnel into currant stems soon after they hatch.

green aphids
Aphids on Spirea

Currant borer larvae are pale yellow and worm-like. Promptly remove infested stems at ground level, and send them out with the trash or burn them. Do not leave them on the ground in the currant patch -- the larvae are mature enough to complete their development in cut stems and would re-infest the planting.

There is no chemical control once the larvae hatch and bore into the canes. Red currants are more susceptible to this insect than other varieties.


STEM GIRDLERS

Currant stem girdlers damage canes in two ways: adult egg laying and larval feeding. The adults are sawflies that make numerous punctures in canes as they lay eggs in spring, causing the new shoots to wilt by late spring. The damage continues through summer as the larvae hatch and begin tunneling through the canes.


SUMMARY

The best recommendation is to remove and destroy infested canes as soon as you notice the damage. There is no chemical control once adults have inserted eggs into the stems.

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