Yard and Garden: Insect Pests of Raspberry Fruit

August 23, 2018, 9:00 am | Richard Jauron, Willy Klein

Raspberry bush by vaitekune/stock.adobe.com.AMES, Iowa – Raspberry plants are relatively easy to grow, and are hardy and productive in most of Iowa. If given proper care, a 100-foot-long row of red raspberries can produce 100 to 150 pints of fruit. However, several insects also like raspberries. Iowa State University Extension and Outreach horticulturists share tips on controlling these uninvited guests. 

There are small, black beetles feeding on my raspberries. What can I do?  

The small, black beetles are likely sap beetles. They also are known as picnic beetles or picnic bugs. Sap beetles commonly feed on over-ripe or damaged fruits and vegetables in the garden.  

Sanitation is the best management strategy for sap beetles in home gardens. Keep the raspberry planting as clean as possible by promptly harvesting ripe fruit and removing damaged, diseased and over-ripe fruit from the site.  

Insecticides are not very effective and difficult to use because of preharvest intervals (the wait time between a pesticide application and when a crop can be harvested). If you decide to use an insecticide, select a product with a short preharvest interval and read and carefully follow label directions.

There are small, white worms in my raspberries. What are they and how can they be controlled?  

The small, white worms are likely the larvae of the spotted wing drosophila. Spotted wing drosophila adults are small, yellowish brown flies. Males have distinctive dark spots on their wings, hence the name spotted wing drosophila. Female adults have serrated, saw-like ovipositors and lay eggs in soft, ripening fruit. Spotted wing drosophila larvae are white, 1/8-inch-long maggots.  

Spotted wing drosophila feed on soft, thin-skinned fruit. Their preferred food choices are raspberries (especially fall cultivars), blackberries and blueberries. However, they also feed on grapes, strawberries, cherries and aronia berries.  

Control of spotted wing drosophila is difficult. In the home garden, sanitation is the most practical control measure. Promptly harvest ripe fruit. Remove and dispose of over-ripe, damaged or rotting fruit. Dispose of berries in a manner that prevents flies from emerging and infesting additional fruit. Insecticides are a possible control option. However, most commonly available garden insecticides have preharvest intervals of several days, making their application to ripening fruit impractical. If you decide to use an insecticide, select one with a short preharvest interval (such as one day) and carefully read and follow label directions.  

How do I stop yellow jackets from feeding on my raspberries?  

Yellow jackets are social wasps that build paper nests in the ground, logs, building walls, attics or other sites. The workers from the colony travel up to a few hundred yards from the nest while looking for food. In early summer, the wasps forage for caterpillars and other “meat” items and are beneficial predators. However, in late summer they prefer sweets, such as soda pop, candy and the juices of fruits and vegetables.  

Discourage yellow jackets from feeding on raspberries by harvesting the fruit as soon as they ripen. Remove any over-ripe or damaged fruit from the garden area. Do not leave beverages, candy, or other food items in the vicinity of the raspberries, as they may attract yellow jackets to the area.  

Applications of insecticides to raspberries are of very limited benefit and difficult to use because of preharvest intervals. Yellow jacket nests in the ground, logs or walls can be destroyed by placing an insecticide dust in and around the nest entrance during the night.  

Photo credit:  vaitekune/stock.adobe.com

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