Insect Updates-July 7, 2017

Bryan Jensen, UW Extension and IPM Program

Potato Leafhoppers in alfalfa. This insect’s density has been variable this summer. Although the anticipated warm/dry weather could change that quickly. Within a limited geographical area this season, I have seen populations range from below threshold to 5X the established economic threshold. This really speaks to the need for scouting. Pay very close attention and be sure to identify (and count) potato leafhopper nymphs in the net. Nymphs are commonly found on the collar of the sweep net and are easily missed because of their size. First instars are about the size of a “period” in newsprint but have a very bright fluorescent yellowish/green coloration. The attached video might help to confirm identification. Furthermore, the need for regular field scouting is important because I have seen potato leafhopper populations crash in mid-July but may persist well past Labor day. For more information on potato leafhopper threshold and labeled insecticides please consult A3646, Pest Management in Wisconsin Field Crops.

Japanese Beetles. Not unexpectedly, Japanese Beetle adult emergence has started and likely will continue for a while. Adults cause defoliation in soybeans and clip green corn silks. Typically, damage will be clumped and isolated along field edges. The economic threshold for defoliation of reproductive soybean is 20%. People tend to overestimate defoliation. Remember % defoliation is based on the whole plant not just the affected leaves. In corn, Japanese beetle adults can clip green corn silk resulting in poor pollination. This usually is not considered economic unless an average of 3 adults are present/plant and green silks are being clipped.

Adult Japanese beetle are about ½ inch long with metallic copper-colored wing covers and a metallic green thorax and head. Six white tufts of hair are present on each side of the abdomen. Adults remain active until early September.

Japanese beetle adults: ½ inch in length, metallic green thorax and bronze elytra (wing covers), and 6 white tufts of hair on each side of the abdomen below the elytra.

True Armyworms. The first generation of true armyworms seems to have wrapped up in most areas of the state. Although there have been some very intense populations in very predictable areas (corn planted after a grass cover crop, no-tilled into alfalfa and possibly corn with early grassy weeds) this next generation is not as predictable in terms of “if” and “where”. High populations of the first generation doesn’t automatically predict a significant second generation. Further complicating the issue is that it is very difficult to predict which corn fields may have second generation damage. Continue to monitor wheat and other small grains until harvest.

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