For the last three weeks, or more, entomologists have talked about the record-setting capture of black cutworm moths in pheromone traps. Those traps are designed to catch moths to get a handle on how many are migrating from their winter home in the south to lay eggs in fields in Indiana. John Obermeyer and Christian Krupke, both Purdue University entomologists, believe the next week or two will tell the story on black cutworm infestation this season.
Their advice is to scout, and be ready to apply an insecticide if necessary. Once the larvae which do the cutting to young corn plants grow relatively large, they are hard to control, the pair notes. It's important to find them as soon as possible. This pest often doesn't infest a whole field, so it's important to check various areas of the field for possible damage.
Many of the moths arrived on strong storm fronts during mid- to late-March. Based on heat unit accumulation, the entomologists say the black cutworms are already out in southern Indiana, and should reach larva stage soon farther up in the state. It takes 300 heat units to accumulate for larvae to develop, on average. Many parts of extreme southern Indiana have already passed that mark. Other areas within the state will be reaching it soon. Even with average highs and lows for this time of year, heat units will now begin to accumulate, and are useful in tracking insect development.
One problem is that if you planted corn coated with a seed insecticide or if you're using Bt corn, you may think that you don't need to scout because those tools will control them for you. They do in many cases, but not in all. When infestations are heavy, these modern tools can be overpowered, and black cutworms can still thin corn stands unless the field is scouted properly and insecticides are applied in time, they note.
Tracking growing degree days, or heat units, can be valuable in a number of ways and you can do that using your smart phone. The Farm Progress Growing Degree Day application works on iPhone, Blackberry and Android phones. Go to the download page.