The Q&A Archives: Small black beetles munching on my sweet corn

Question: This year I noticed small black beetles munching on my sweet corn kernels. My Extension agent said they were sap beetles and recommended that I spray with carbaryl insecticide. Are there any organic controls for sap beetles? Daniel Olson Vienna, VA

Answer: Sap beetles can be controlled by spraying rotenone or sabadilla on sweet corn ears at tassel time, says John Trew, commercial sales horticulturist at Necessary Trading Company, a supplier of organic fertilizers and sprays in New Castle, Virginia. Theadult sap beetles emerge from the soil when the weather warms in early spring and feed on sap from tree wounds, he explains. When sweet corn begins to tassel, adults fly to the plants and lay their eggs on pollen clumps or corn earworm frass on the corn ear, he says. The larvae emerge in three days and follow earworm tunnels to feed on corn kernels. Spraying when the tassels emerge to control the sap beetles helps control corn earworm, too, says Trew. Tilling in fall will help kill the over wintering adults on corn stubble. Varieties with long, tight husks such as Country Gentlemen and Stowell's Evergreen are also more resistant to the insect.

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