Heads Up! Pest Alerts

As the summer months roll on, corn growers in the western part of the state are reporting large numbers of Japanese beetles attacking corn just as is it beginning to silk. Over the past decade, we have seen these excessive Japanese beetle infestations move across the state from east to west. During the first 4 or 5 years that Japanese beetle invades into an area, extreme numbers of adults can attack various preferred hosts. We are finding high populations in corn in western Kentucky, particularly west of a line extending from Hopkinsville to Henderson.

While Japanese beetles attack over three hundred species of plants, in agricultural areas, they will attack corn and soybeans in large numbers. In corn, the preferred site of attack is the ear silk. When numbers are high, twenty or more beetles may be found on the tip of a single ear. The beetles clip the silks back into the tip of the ear. If the beetles clip the silks before the corn has a chance to pollinate, then the beetles can prevent pollination to some or all of the ears. This can results in a barren cob.

The key to managing Japanese beetles feeding on corn silks is determining if pollination has yet occurred. If the plant has already shed pollen and the ear has pollinated, then the beetles only cause little damage to the corn. Generally, pollen shed occurs one or two days before the ears become receptive to the pollen. If the silks have been clipped prior to pollination, they will continue to grow. So if pollination has not occurred, and two or more beetles are attacking each ear and keeping the silks at 1/2 inch or less, then the beetles may need to be controlled.

As growers visit fields to evaluate Japanese beetle infestations, they need to keep in mind that the outside 10 to 20 rows usually have much higher numbers than the interior of the field. This is because most of the beetles colonize from outside of the field. Our experience has shown us that growers can often get by with treating just the outside rows rather than the entire field. While infestations will last several weeks, it is only during the critical time for pollination that growers need to manage these beetles in corn.

There are several insecticides that effectively control Japanese beetles in corn, but due to the nature of corn silk growth, only limited residual activity can be expected.

(first published in Kentucky Pest News, Number 1027 June 28, 2004)

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	Original document: 1 July 2004 Last updated: 1 July 2004