How to Protect Raspberries

Question:

How can I protect my raspberries from insect pests?

Answer:

Just as berry fruits approach maturity and are ready to pick, there are fruit-eating insects that can reduce the harvestable crop and contaminate the berry product. Some of the common fruit-eating insects observed in Utah include the stink bug, lygus bug, earwig, grasshopper, and several species of fruit-eating wasps. These insects suck or chew into the individual drupelets or may remove the entire fruits. Frequent inspections of ripening fruits (several times per week) by physically shaking the canes to dislodge insects onto a cloth or plastic tray can provide early-warning and help prevent fruit-eating insects from causing economic yield loss. If damaging insects are detected, the most common method of management is insecticide application. It is very important to carefully observe the pre-harvest or required time interval between application and picking fruits. Pre-harvest intervals are listed on product labels. Recommended insecticides that have low toxicity to humans include neem oil (Azatin) and spinosad (Success, Entrust). Conventional insecticides that will deter fruit-feeders include carbaryl (Sevin), malathion, permethrin, and esfenvalerate.

The consperse stink bug (Euschistus conspersus) and green stink bug (Acrosternum hilare) are large (1/2 to 5/8 inch long), brown or bright green bugs with a shield-shaped, flattened body. They feed on individual drupelets causing them to shrivel. Stink bugs release a bad odor and contaminate the berries at harvest. Lygus bug (Lygus hesperus) are small (1/4 inch long), green and brown bugs that are attracted to flowers and developing fruit. They cause misshapen fruit similar to stink bug by feeding on individual drupelets. They are usually present at low density and do not cause economic damage to raspberries.

The European earwig (Forficula auricularia) is ½ to 3/4 inches long, shiny brown, and with a pair of forceps-like claspers at the tip of the abdomen. They are nocturnal and their presence or damage may go unnoticed until harvest. Earwigs feed on fruit and foliage. Foliage feeding is of little concern. Management requires the removal of daytime harboring sites and prevention of access to fruit before it ripens. Remove weeds from around the base of canes and vines. Keep rows clear of prunings and debris under which earwigs could nest. Earwigs can be trapped by using Tanglefoot® or a similar adhesive material applied to the base of canes to prevent their crawling into plants. To monitor for earwigs, place boards or rolled-up newspapers in the fields in spring and monitor weekly for earwigs that hide under the boards or in newspapers. Treat the ground and lower canes with carbaryl at the beginning of spring activity when earwigs are found.

In areas where berry fields are situated near open rangeland or undeveloped land, grasshoppers may move onto canes near harvest to feed on fruits and leaves. Fruit-protecting insecticide treatments described above may be effective. Placement of insecticide bait (bran coated with carbaryl or Nosema locustae, a protozoan biological control) around field borders when young grasshopper nymphs are first observed may also reduce grasshopper populations. Repeat applications of bait will likely be required to cover several months of grasshopper activity and to replenish baits after rainfall or irrigation events. Insecticide baits are not effective at killing adult grasshoppers.

Two types of wasps are common berry-eaters: the yellow jacket (Vespula germanica) and European paper wasp (Polistes dominulus). They may also be a nuisance to workers by stinging them. Yellow jackets nest in the ground. If ground nests are detected, they can be treated with conventional insecticides, dug up and removed to destroy them. Also, placing commercial traps that contain heptyl butyrate bait at the perimeter of berry fields can reduce wasp numbers. The European paper wasp builds umbrella-shaped nests under the eaves of buildings and other protected sites. Paper wasps are not attracted to yellow jacket traps. Removal of nests and protection of fruit near harvest with one of the insecticides mentioned above may provide some control.

Posted on 20 Jun 2007
Diane Alston
Hort-Entomologist Specialist