Thursday, August 26, 2010

Corn Earworms Building Again In Soybeans, Loopers Becoming More Apparent

From Ames Herbert, Virginia Tech Extension Entomologist

Although the corn earworm flight is still strong, we are not hearing of many fields with high numbers of worms. However, we are hearing of a lot of fields with pod-stage thresholds and many are being re-sprayed.

Several folks have reported seeing newly hatched small worms but are waiting a few days before spraying to see how things develop. Holding off a few more days may mean the difference in having to treat a third time.

There are a lot of fields that seem to be holding with no new earworms developing, especially the early planted fields. More infestations are being reported in later-planted double crop fields.

This is a typical pattern as the pods in early planted fields are getting to the point where they are no longer attractive or vulnerable. Maybe this second infestation will not be as bad as we expected, but we have another week or two before we will know.

Our advice is to keep checking fields at least every 5 days or so, until fields reach the R7 growth stage. As a side note, our pyrethroid testing of adult corn earworms is showing a gradual increase in the level of survivorship, now averaging over 40% for this past week (see chart below).

Better consider one of the non-pyrethroid options.

We are finding (and hearing about) more soybean loopers. The most we have encountered is about 15 to 20 per 15 sweeps, but even at those numbers, the level of defoliation is not bad or to the point where fields need protection. This may get worse, or may not, depending on a lot of factors.

One of the oddest situations is the extremely large numbers of green cloverworms that are being reported in some areas. Folks are finding 30-40 and more per 15 sweeps and they are definitely working on the foliage.

We always see cloverworms in soybean fields but never at these high levels. They are having to be controlled in fields with limited growth (due to slow growth during the hot dry weather).

Reports from Maryland are saying that brown marmorated stink bugs are inundating soybean fields in western and central Maryland. We have known about this pest for several years. It is a native of China, was first reported in Virginia in 2005 (one specimen) and has gradually increased in number. It has become established in Virginia and is now causing problems in vegetable a fruit crops.

Soybean is one of its many host crops in China and as we feared, it is now moving into that crop. We have found a few in Virginia soybean fields, about 1 per 15 sweeps in a couple of fields. We do not know much about damage potential or control options but a lot of research is underway.

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