Sap Beetle Injury in Sweet Corn Becoming More Prevalent in PA

Throughout the years, this roadside stand operator has purchased sweet corn from only the most reputable growers at the produce auction. By limiting his purchases to this small subset of sweet corn growers, the roadside stand operator knew he would be rewarded with high-quality, worm-free sweet corn for sale at his stand.

Two years ago, this roadside stand operator began receiving numerous consumer complaints about white "maggots" or larvae detected in sweet corn ears during husking. After receiving his fifth complaint, he decided to haul the bulk bin off the floor so he could go through the remaining corn in the bulk bin to see if he could find any of the white "maggots" or larvae that his customers had complained about.

As the stand operator husked the remaining sweet corn, he found two to three "maggots" or larvae per corn ear. While he had farmed very little in his career, he knew that the local Penn State Extension office would be able to identify the pests he found. He took the small minute maggot-like pests and placed them in a vial of alcohol to preserve them before transporting them to the local Extension office for identification. The Extension educator took the vial from the stand operator and transferred one of the maggot-like pests to an index card, which he placed under the stereo microscope for examination.

After a few gazes through the microscope, the Extension educator told the stand operator that he was dealing with sap beetle larvae. Sap beetles, he explained, are usually controlled in sweet corn fields when growers spray the sweet corn crop with synthetic pyrethroid insecticides. Over the past several years, entomologists have noticed increased resistance to the pyrethroid class of insecticides in corn earworm and fall armyworm populations. To combat these resistance issues, entomologists encouraged sweet corn growers to apply insecticides with a different mode of action than the pyrethroid class of insecticides. As growers heeded this recommendation, some growers began to observe sap beetle outbreaks on their farms because some of these replacement chemistries had very little efficacy on sap beetles. In parting, the Extension educator encouraged the stand operator to reach out to the produce auction and the growers about the sap beetle issue so they could tank-mix and spray an insecticide with good efficacy against sap beetles on their sweet corn crop.

When the stand operator contacted the produce auction, the manager refunded his money and told him that several other buyers had encountered the same issue with sap beetle larvae in the sweet corn ears. The auction manager assured the stand operator that the growers were taking this issue seriously and targeting sap beetles on their farms for the rest of the growing season.

Pennsylvania growers with a history of sap beetles on their farm should make an insecticide application 5–6 days after the first onset of silking to protect the sweet corn ear. Synthetic pyrethroid insecticides, when used alone, will provide reasonable control of sap beetles but may not adequately control some sweet corn worm pests when used late in the season. Insecticides like Lannate LV and Assail 30SG have efficacy against sap beetles. They may be used as a stand-alone application or as a tank mix with other labeled insecticides if your current sweet corn pest management program does not control this pest.