April 30, 2016

1 - Curling leaves of stone fruit plants in the spring often results from aphid insects.

Yard and Garden April 30, 2016

Q.

I have sent a picture of the new leaves on my peach tree. They are curling up and are discolored. What is the cause and is there a cure for this problem?

- Judy O'L.

Silver City

A.

This is a common spring time symptom and question in New Mexico. The problem is due to aphids that attack the new growth of peach and related plants (plum, apricot, nectarine, cherry, almond, etc.) in the spring. Dr. Carol Sutherland, the NMSU Extension Service Entomology Specialist, has provided a very detailed answer to your question. With her permission, I am providing this answer to all readers of this column.

Aphids are indeed the culprits. It is not unusual to have 'green peach aphids' (GPAs) (usually pale green) now and potentially later in the growing season---as well as some one or more species of 'leaf curl aphids' that are much darker (very dark red to black with a reddish tint).

The GPAs may be active during only the cooler ends of the growing season, although remnant populations may persist throughout the growing season and overwinter as eggs on the same trees. GPAs have the reputation of transmitting viruses to their hosts. One of those viruses results in tiny shot holes in host foliage. Expect to see little holes in foliage.

The leaf curl aphids overwinter as eggs on the rough bark of host trees, hatch, they spend some time sucking sap from tender new growth and then move on to assorted broadleaf weeds that they use for hosts during the rest of the growing season. As that growing season ends, the leaf curl aphids produced winged forms that fly back to nearby Prunus species where they mate and females lay overwintering eggs on the bark---like the GPAs do.

As for management options---I think you have probably missed the best opportunity to decrease plant damage. That would have been a dormant oil spray in late winter before any evidence of bud swelling or new growth. However, eggs of any insect are vulnerable to various egg predators and parasitoid. Plus, there are egg predators, parasitoids, and environmental factors that can take a toll on egg counts and survival.

The convergent lady beetles and their larvae are actively consuming your aphid pests. They can do a pretty good job of cleaning up the aphids...sometimes, they are all you need. As it gets hotter, the heat slows down the GPA populations, also. Insecticide applied now will likely kill your beneficial insects that are feeding on aphids and helping you. Repeated applications of insecticides may keep the beneficial insects from re-entering the 'aphid zone' and extend aphid damage. Aphids can produce lots of little aphids in a short period of time and they can mature to adulthood in a little over a week---very prolific.

These little creatures (GPAs) can be the cause of the yellowing leaves---the foliage of the tree depends on nutrients in the sap for its survival, so do the aphids. In this case, the foliage loses when the aphids "steal" the nutrients. No pesticide will fix the twisted leaves; they will be replaced by the plant later in the season.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

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