Issue No. 15, Article 3/July 2, 2004
More on Japanese Beetles
More and more reports of Japanese beetles have come in over the past week. However, reports of severe infestations have not been widespread. Rather, there are "hot spots" around the state with heavy populations of beetles and other areas where populations are very small or nonexistent.
As mentioned in last week's article ("Japanese Beetle Update"), scouting for Japanese beetles and the injury they cause is critical in corn, especially in fields nearing or at pollination. Current thresholds suggest considering an insecticide treatment when there are three or more beetles per ear, pollination is less than 50% complete, and silk clipping is occurring. We cannot stress enough the importance of scouting throughout the entire field. Questions have risen about possibly spraying the perimeter of the field. This technique is questionable. While it is true that most reports note a heavier population near the field borders, these insects are quite mobile. From 2003, in one instance the perimeter of a cornfield was sprayed because of very high numbers of Japanese beetles. However, within a couple of days, beetles were found clipping silks throughout the interior of the field. The good news is that silks continue to extend after the beetles leave for another food source. If the field has adequate moisture and silk extension is not impeded, silks that are 1/2 inch or longer can still intercept pollen.
This insect poses a great challenge when contemplating management options. We'll continue to pass information along as we receive it. --Kelly Cook