Problems and Solutions

Gallery of Pests

Aphids commonly appear in the early spring in large colonies. Nymphs and adults can all be found feeding on the new growth at the ends of branches. We commonly find aphids on Spirea, Viburnum, Tulip Trees, and even oaks. Some ants tend these colonies to collect the sweet honeydew that aphids secrete and to protect them from attacking insects. If ants are controlled, the number of aphids usually drops, because beneficial insects, such as lacewing and syrphid fly larvae, find and destroy them. When immediate control is necessary, we hose the plants off with water as needed.

The red gum lerp psyllid is a relatively recent pest of several species of Eucalyptus, notably red gum (Eucalyptus camaldulensis) on campus. The young psyllids hide under a sugary 'lerp' or dome as they feed on plant juices, while the adults feed openly and fly to neighboring trees as their population grows. Infested trees can become completely defoliated. Don Dahlsten at U.C.Berkeley, in conjunction with the California Department of Agriculture, is coordinating releases of a beneficial wasp that parasitizes the psyllids. Both pest and parasite are introductions from Australia, where eucalyptus is native. More information is available at the web site for University of California at Berkeley's Pest Management Program.

A number of caterpillars feed on new growth in springtime. We find many western tussock moth, fruittree leafroller and California oakworm caterpillars on native oak trees. These insects overwinter as eggs, hatch into larvae (caterpillars) in springtime, then pupate in early summer before becoming adult moths that mate and lay eggs to start the cycle anew. People usually notice the caterpillars when they drop down on strings from the canopy or crawl down the trunks to pupate on nearby structures. Many beneficial insects either parasitize the larvae (such as tachinid flies), or the pupae or eggs (such as tiny wasps). Various birds feed on both larvae and eggs. In problem areas, green lacewing larvae can be released to eat the first caterpillars that appear, and egg masses together with pupal cases can be "power-washed" from tree trunks in late summer.

There are many kinds of scale insects present in the landscape, but because of their appearance, they're easy to miss. In general, they look like round or oval scabs without legs or wings or a head. Usually several are found in colonies on branches. Like aphids, they secrete honeydew that attracts ants and sooty mold, and their numbers are often kept in check by parasitic wasps or various lady beetles. If scale is a problem, the young crawler stage can be sprayed with a horticultural oil spray.

The story of the Eucalyptus long-horned borer is an IPM success story. This pest caused serious damage in the early 1990s, but has been brought under control by natural enemies imported from Australia. Susceptible Eucalyptus species lost resin, branches and ultimately their lives, as the borer larvae fed on and girdled the trees. Many blue gums (Eucalyptus globulus) in the Arboretum died, but many remain and now appear to be out of harm's way.

Elm leaf beetles are pests of elm trees throughout the United States. Both the larvae and adults feed on the leaves in summertime. We estimate when the larvae will appear using degree-day calculations. (A degree-day is the amount of heat accumulated in one day.) We then begin monitoring for this pest to see if control measures are needed and take action only if pests occur in large numbers. (This beetle is not the pest that spreads the deadly Dutch Elm Disease. This disease is spread by the Elm Bark Beetle.)

Thrips are minute slender insects, some of which feed on the undersides of leaves. Because of their small size, these animals are not obvious, and it is their damage one notices: plant leaves look bleached or silvery, and the undersides are often spotted black with frass (droppings). Usually the older leaves are affected, and the visible damage is accompanied by a foul odor. We do a paper-shake test to see if thrips are present, and we commonly find them on plants we shear, such as myrtle and viburnum. Open pruning helps to improve air circulation and provide access for beneficial insects. Another insect whose damage is similar to that of thrips is the lacebug. The lacebugs are visible to the naked eye and look like pieces of dandruff; the same open pruning and reliance on beneficial insects is recommended.

Weird and often colorful growths are common on some oak trees, particularly Valley Oaks. They can look like tomatoes or brown balls, amongst other shapes, stuck to leaves or twigs. These galls are actually "houses" for developing cynipid wasps. The female wasp lays her eggs into branch tissue and the plant responds by growing a "tumor" around the developing eggs. The shape and location of the gall distinguishes which species of wasp is present. Trees seem to tolerate this activity – we dismiss the galls as harmless.

The photos are taken from the University of California, Davis, IPM website, which is a great resource for further information.