BROOKINGS — Picnic and sap beetles are invading gardens and orchards throughout South Dakota and will be around until the first hard frost, explained Adam Varenhorst, assistant professor and SDSU Extension field crop entomologist, who witnessed them in his own garden this summer.

“I noticed some strange activity on some of my nearly ripe tomatoes. Upon closer inspection, I realized that some of the tomatoes had damage that pierced the skin, and that there were small black beetles present in the wounds,” he said.

Sap beetles are about quarter of an inch long, brown in color and do not have any spots.

Picnic beetles are slightly larger than the sap beetles and are black in color. Picnic beetles also have four yellow to orange colored spots on their abdomens.

Picnic beetle adults are attracted to ripe or decaying plant matter, which they will feed on and lay eggs within.

“These beetles are normally an indicator of previous damage to the plants, but will also assist with the breakdown of the plant material,” Varenhorst said. “In some cases, they can be a pest if they increase the size of the damaged area on fruits and vegetables such as apples, strawberries, raspberries, sweet corn and tomatoes or if they begin feeding on undamaged fruit.”

Varenhorst explained that picnic beetle feeding is usually associated with deep cavities in the fruit.

Their feeding can also introduce fungal spores that will lead to additional breakdown of the fruit.

Protecting your garden produce

To reduce picnic or sap beetle problems, Varenhorst encourages gardeners to maintain clean gardens or orchards.

“Remove any overripe, damaged or diseased fruit and vegetables regularly,” he said. “Simply throwing them into a compost pile won’t be enough as these beetles are mobile.”

The best strategy, he said, is to bury the infested fruits or destroy them using other means. “This will remove the beetles’ food sources and reduce the attractiveness of the garden or orchard,” Varenhorst said.

If picnic or sap beetles are already present, bait traps can be used to attract and remove the beetles from the area.

These bait traps can be made using a bucket baited with ripening fruit, bread dough, stale beer or vinegar.

“When using a liquid bait, add a drop or two of liquid dish soap to break the surface tension of the liquid so the beetles will sink,” Varenhorst said.

The traps should be placed outside of the area that you are trying to remove the beetles from, and the contents need to be discarded every two to three days to prevent infestations from becoming worse.

“Once the contents are discarded, the traps should be rebaited and replaced until all produce can be harvested,” Varenhorst said.

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