Outwitting Pests

Early Insect Control Helps Protect Corn Yields

PARAGOULD, ARK.
   Insect control in corn and grain sorghum was addressed recently by Dr. Glenn Studebaker, extension entomologist with the University of Arkansas Cooperative Extension Service.
   “There are several things farmers can do early on to help manage their insect pests in corn,” he said. “Corn doesn’t have a lot of insect pests but some can be quite damaging some years. In corn and really with any crop we tell the growers the best thing they can do is to get the crop in the ground early because planting early does tend to help avoid some of the insect problems later on in the season.”
   Insects are cold blooded, so they generally are at their lowest populations in the spring, and farmers want to get that crop finished out before those populations build up, which is usually by the end of the summer. That really helps a lot with managing insects. The same is true in grain sorghum.
   “One thing we do need to watch for in corn is soil insects,” Studebaker said. “There are a lot of things already in the soil that may affect the seed or the roots of the seedling as it grows. All growers use a seed treatment which helps to manage a lot of those pests and that really has helped the whole industry.  I don’t get near as many calls as I used to about seedling pests or root pests in corn since seed treatments have been around. That helps with our seed corn maggots, corn rootworm, wireworms; those are probably the main pests in the soil on corn. Depending on the situation, some growers also have white grubs, and the seed treatments help with those as well.
   “One question I do get is whether to use some of the higher seed treatment rates,” he continued. “Corn is a little unusual in that the seed treatment rate on insecticides is a pretty big range. The base treatment is usually a 250 rate which is the low end but it can go all the way up to 1,250 which is five times that low rate. For the most part, the 250 rate does a great job for most pests in Arkansas.”
   The 1,250 rate may help if you have a field that might be more apt to be hit with some seedling pests, above ground pests like cutworms or stinkbugs. Those are other pest that come in some years and can attack seedlings and cause some problems.









   Dr. Glenn Studebaker, extension entomologist
   with the University of Arkansas Cooperative Extension
   Service explained there are things farmers can do early
   on to help manage insects in corn.
   Photo by John LaRose, Jr.







   “If a grower already has a history of stinkbugs in the area,  I recommend they think about that higher rate on their seed treatment. If they don’t, the low end rate really works well,” he said.
   The one pest that sometimes brings more trouble if planting early is the seed corn maggot. That is a cool season pest and if that seed stays in the ground for awhile it does make it more susceptible to it; but even here, the 250 rate does a great job in controlling those.
   “Really with corn, once that seedling is about 18 inches tall we’re about out of the ballpark from having any problems from insects until we get that full grown plant and it starts to sprout ears,” Studebaker noted. “Then, our major pest in Arkansas in corn is the southwestern corn borer which can attack the seedling; however, usually populations are so low we don’t have a problem with it. Then that second generation period generally comes out around the first part of July and we do see problems in non Bt corn.  One thing with the southwestern corn borer is it’s controlled pretty much 100 percent in Bt corn hybrids, and most of our growers do utilize those.”
   With Bt corn, farmers are required to plant a refuge of non Bt corn of either 20 percent of the crop or 50 percent depending what Bt hybrid they use.  If it’s the single Bt genes, the Yield Guard Herculex requires a 50 percent refuge. So they’ll have to manage for southwestern corn borer in their non-Bt  corn. If they planted the multiple Bt hybrids like SmartStak, Viptera, that refuge drops to 20 percent.
   “That is something farmers need to keep in mind because they need to plant a refuge,” he said. “However, in that non Bt corn we do use pheromone traps to catch those moths as they come out, and we can predict when those populations are going to be in the field. When that second generation appears, we do recommend that growers, number one trap; find out if someone is trapping in the area; see what the populations are like, and if the populations are high you will need to scout your field and maybe make an application of an insecticide.
   “Corn borers are hard to control because the moths lay their eggs on the leaves but then they hatch and they bore into the stem and then we can’t control them with a foliar insecticide,” Studebaker said. “But there is about a week when they are on the outside of the plant and can be controlled. We do have some pretty good long residual insecticides available to the grower, such as Intrepid, Belt and Prevathon. These are the main three and they give us about two, three and maybe even up to four weeks of control. “So if they make that application a little bit early before the corn borers can even hatch, it’s still there and it can control those corn borers.”
   If they use something with a short residual like pyrethroid, they’re really going to have to time that application close to egg hatch or they’ll miss it. So for the most part a lot of growers would go with these long residual insecticides.
   Once farmers get past these pests like southwestern corn borers, they’re rather safe from a lot of insects. There can be some pressure from corn earworm which is always in field corn, even in Bt field corn and sometimes growers are tempted to spray for this pest. However, research  the past few years has shown that corn earworm feeds in the tip of the ear and does not cause a yield loss in field corn. So there’s no reason to spray for it, and there’s not much benefit as yield goes in using some of the other hybrids that do control it because there’s really no yield loss.
   “So basically, we like to tell growers to plant early to avoid those insect pests; use some kind of soil insecticide or seed treatment to control those insect pests, and then scout that field, especially during the seedling stage for seedling pests such as cutworms, stinkbugs, chinch bugs,” Studebaker said. “Then watch closely for southwestern and European corn borers later on when ear formation is underway. That really will help a grower maximize his profits and his yields in Arkansas.” ∆
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower