Picnic beetles are small black insects with yellowish spots on their wing covers. This nuisance insect feeds on over-ripe and decaying fruits and vegetables. Its common name comes from its annoying habit of showing up in your potato salad at outdoor events. While it can damage fruits and vegetables, picnic beetles take advantage of over-ripe produce, often eating their way through and enlarging the amount of damage. Their saliva and fecal material introduce an abundance of bacteria and fungi into wounds, hastening the decay process.
The picnic beetle’s other common name is the sap beetle, referring to its propensity for feeding on sap oozing from fresh pruning cuts on trees. This insect is the vector for oak wilt, carrying the causal fungal pathogen in its gut. Oak wilt is spread primarily from the beetle’s habit of regurgitating before feeding on sap. This pre-digestive step helps to dissolve their food and further complicates things by inoculating oaks with the oak wilt pathogen. To interfere with the spread of oak wilt, oaks should never be pruned March through October, when the picnic/sap beetle is still flying.
There is no simple answer to managing picnic beetles on produce. Insecticides aren’t necessarily good choices because produce is close to harvest. Any insecticide sprayed on fruits and vegetables requires a period of time to elapse before harvest takes place. Called a pre-harvest interval (PHI), a PHI allows for the degradation of insecticides from wind, rain and sunlight. When choosing to use an insecticide, be sure to harvest first and then use an insecticide with a short PHI, such as Sevin, Neem oil or insecticidal soap.
Further complicating things, the picnic beetle is often inside the fruit or vegetable, making it tough to reach them with an insecticide. The best option for picnic beetle management is to harvest regularly and keep the garden clear of over-ripe and rotting produce. This insect lays eggs in rotting materials, so make sure your compost pile is situated a good distance from your orchard and vegetable garden. More information about the picnic/sap beetle is found here: https://hortnews.extension.iastate.edu/sap-beetles .
Interested in finding out more about the Nebraska Extension Master Gardener program’s 2019 classes? Plan to attend one of two informational meetings in November:
November 15, 5:30 pm, Nebraska Extension in Dodge County, 1206 West 23rd Street in Fremont
November 16, 1:30 pm, Nebraska Extension in Washington County, 597 Grant Street in Blair.