By Richard Jauron, Greg Wallace
Raspberries are a delicious part of any garden, but they are vulnerable to intrusion from pests and other maladies. What is the best way to keep them healthy and edible?
Here are some tips from Iowa State University Extension and Outreach horticulturists on how to obtain a bountiful raspberry harvest. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.
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 through prompt harvesting of ripe fruit and the removal of damaged, diseased and over-ripe fruit from the site.
Insecticides are not very effective and difficult to use because of preharvest waiting periods. If you decide to spray, use an insecticide with a short preharvest waiting period and read and carefully follow label directions.
How do I stop yellowjackets from feeding on my raspberries?
Yellowjackets are social wasps that build paper nests in the ground, a log, building wall, attic 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 yellowjackets 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 yellowjackets to the area.
Applications of insecticides to raspberries are of limited benefit and difficult to use because of preharvest waiting intervals. Yellowjacket nests in the ground, logs or walls can be destroyed by placing an insecticide dust in and around the nest entrance during the night.
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.
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 re-infesting sound fruit.
Insecticides are a possible control option. However, most commonly available garden insecticides have preharvest waiting periods of several days, making their application to ripening fruit impractical. If you decide to use an insecticide, select one with a short preharvest waiting period (such as one day) and carefully read and follow label directions.
Parts of the berries on my red raspberries are white in color. Why?
A raspberry fruit (berry) is composed of more than 50 drupelets. The white colored drupelets are likely due to sunscald. Sunscald is a physiological disorder caused by sun exposure (solar injury) and excessive temperatures. Berries with full exposure to direct afternoon sun are most susceptible to sunscald. However, high temperatures also appear to be involved as berries shaded by the leaf canopy may also develop white drupelets.