Corn starting to tassel and silk - Time to watch for insect damage
Much of the field corn has made tremendous growth during the past few weeks, despite the dry spell. And with the rain we did have, things are looking a little better as the corn starts to tassel and silk. As we get into this period of time, both sweet corn and field corn growers need to be aware of what is happening in the ear zone of their plants. Each silk is attached to an individual kernel on the ear. When the silk catches a grain of pollen, a pollen tube will grow down the tube and fertilize the kernel. If the silks are in good shape and the growing conditions after pollination takes place are favorable, you should end up with a nice full ear in a few weeks. But if the silks are continuously being clipped by insects, pollination will not take place and no kernel will develop. A saving grace of the corn silk is that it doesn’t just grow to a set length and stay there. It normally keeps on growing until pollination takes place- up to a point. If you want to test this, use a rubber band to fasten a gallon-size plastic bag or bread wrapper over the tip of an ear just as the silk starts to emerge. With no insects to feed on it and no pollen to halt its growth the silk can grow to a length that puts Cathy Quick Curl to shame.Insects that can cause damage to the silks and prevent pollination include rootworm adults, Japanese beetles and sometimes grasshoppers. For the next three weeks, growers can go out and check about 25 plants in each field to see what is happening and determine if their yield is being threatened enough to make it worthwhile to use a rescue treatment. Two observations need to be made for each plant. The first is how severe the silk clipping is and the second is how many beetles there are per plant. If pollination has not yet taken place and there is an average of more than five rootworm beetles or two Japanese beetles per plant and 75 percent of the silks are being clipped to within a quarter inch of the ear, a spray application will need to be made to make sure the ear will fill out. It has been a rare occasion where we have actually reached this threshold, but it has happened. These rootworm adult counts can also be used to determine if you need to rotate to another crop, use a soil insecticide or plant a variety of corn with the RW trait next year in order to reduce rootworm larval feeding on next year’s crop.
In soybean fields, spider mite damage has been light- probably due to all the humid weather supporting fungi that control the spider mites. Aphids have also been light.
Other scouting updates: Cucumber and muskmelon growers need to be aware that we have found downy mildew in Wayne County on both crops and a curative type fungicide needs to be added to the protectant fungicides in your spray schedules. We are also starting to find moths from the second flight of European corn borers, so spray schedules to protect sweet corn and peppers need to be observed.