Raspberry insect pests of the home garden
Published in Yard & Garden Brief, April 1999
Insects infrequently damage raspberries. However, when an insect pest is present, accurate identification is necessary so the proper controls can be used.
Good cultural practices can reduce pest problems. Careful, timely inspection and pruning of raspberries and removal of wild brambles in the area will eliminate many insect pests and reduce the need for insecticide applications. You may also be interested in this raspberry diseases article.
Raspberry cane borer
The raspberry cane borer is a ½ inch long black longhorned beetle (family Cerambycidae). It has yellow stripes on its elytra (wing covers), a yellow thorax (the section behind the head) with two black dots on it and antennae the length of the body.
In spring, adult females deposit eggs between a double row of punctures made around stem tips. The eggs hatch in early summer and the whitish, brown-headed larvae bore several inches down the canes, overwinter at ground level, and emerge as adults in June.
Damage: Look for a double row of punctures around the stem tip where the adult female laid her eggs. Cane wilting above the egg punctures is common with the cane dying the following season.
Control: Remove wilted cane tips six inches below the damaged area and destroy the prunings. If chemical control is necessary, spray the cane tips with permethrin or carbaryl (e.g., Sevin) just before the first blossoms open.
Red-necked cane borer
The red-necked cane borer is a blue-black, metallic wood-boring beetle (family Buprestidae) about ¼ inch long with a dull coppery color on the prothorax (the area just behind the head). Adult females first appear on canes in late May or early June, laying eggs in the cane bark. The ½ inch long, whitish larvae burrow under the bark and later bore into the pith. They overwinter in the canes.
Damage: The boring causes the cane to swell ½ inch or more in diameter, several inches along the cane. The cane may die or break off at the swollen point.
Control: Cut out and destroy all canes with unusual swellings during fall and winter. This insect is seldom of much importance as a pest. However, if the problem persists, apply permethrin or carbaryl (e.g., Sevin) just before the first blossoms open.
Raspberry cane maggot
The adult raspberry cane maggot (family Anthomyiidae) is a small, gray fly about two-thirds as large as a house fly. Adult females appear shortly after spring growth begins and lay eggs in new buds or on the tips of new shoots. The 1/3 inch long, apparently headless, legless maggot girdles the cane and tunnels down the pith, overwintering just below the entry point.
Damage: The new growing tips wilt or break off in late spring or early summer. The wilted cane often turns purple at the entry point and the broken-off ends appear to have been cut with a knife. The injury is similar to that of the raspberry cane borer.
Control: Prune and destroy wilted cane tips six inches below the entry point. Check canes again in fall or winter, removing damaged canes. Raspberry cane maggots rarely damage more than a few plants. If there is enough damage to justify chemical control, permethrin or carbaryl (e.g., Sevin) are moderately effective.
Raspberry crown borer
This insect is also known as the raspberry root borer. The adult clear- winged moth (family Sesiidae) resembles a wasp. In late summer, the adult female lays eggs on the underside of leaves. Eggs hatch in early fall and the larvae move to the soil, where they overwinter under the bark just below ground level. In spring and summer, the one inch long larvae feed in the roots and bottom of the canes (crown). They spend their second winter in the crown. The larvae pupate (make cocoons) and emerge as adults late the next summer.
Damage: The leaves turn red prematurely and canes wilt in late summer. Affected canes die the following year. If only cane tips wilt, raspberry crown borer is not the problem.
Control: Cut off wilting canes at the crown. If holes are found in the crown, the larvae can sometimes be killed with a sharp wire. Otherwise, dig and remove affected plants. If raspberry crown borers continue to be a problem, spray the crowns in early April or late fall (before November) with permethrin. Repeat the treatment for two years.
The adult beetle (family Byturidae) is light brown, hairy and about 1/8 inch long. In late May, adult females lay eggs in the developing raspberry buds and fruits. The eggs hatch into small yellowish worms which feed within the fruit for five to six weeks. When fully grown the ½ inch long larvae drop to the ground and pupate (make cocoons) in the soil. They overwinter as adults, emerging the following year in early May.
Damage: Adult beetles consume some foliage but rarely enough to cause damage. The larvae are a problem from late May to early July, eating the immature berries. If the fruits drop or decay before harvest, examine the buds and fruits for the whitish, ¼ inch long larvae.
Control: Cultivate the soil in late summer or early fall to expose the pupae to predators and the elements. Handpicking the adult beetles usually keeps the damage to an acceptable level. If raspberry fruitworms are too numerous to handpick, apply permethrin just before the blossoms open and, if necessary, again after all the blossoms have fallen.
Picnic or sap beetles
The most common picnic beetle (family Nitidulidae) is a small (¼ inch long), black insect with four yellowish-orange spots on the back. Adult beetles are attracted to all types of overripe and decaying fruit. Although not attracted to ripe, undamaged raspberries, these can be damaged once picnic beetles are in the garden.
Damage: Look for the distinctively patterned adults on partially consumed, overripe raspberry fruits.
Control: Unlike most insect pests of raspberries, picnic beetles often reproduce outside of the raspberry patch and only fly into gardens when the berries become overripe. Proper sanitation is the best control of these beetles. Make sure ripe or damaged fruits are promptly picked to avoid attracting them.
Insecticides seldom control picnic beetles. Raspberries cannot be picked immediately after applying insecticides because there is a waiting period after the raspberries are sprayed. The waiting period is the number of days required between insecticide application and harvest. During that interval adult beetles continue to fly into the patch if attractive fruit is present.
Caution: Always use insecticides strictly in accordance with label precautionary statements and directions. The label should state that the insecticide may be used on raspberries or generally on fruit.
Raspberries are sometimes referred to as 'cane berries' on insecticide labels. Carefully observe the waiting period. Protect pollinators--do not spray raspberries or other fruits when they are blossoming. If suggestions in this publication contradict label recommendations, the label is the final authority on how to use that specific product.