This week cattlemen and extension agents reported finding damaging populations of fall armyworm in hayfields in 4 counties: Pike, Calhoun, Etowah, and Marshall. It is best to control fall armyworm caterpillars before they have molted into the last and largest size. The caterpillar consumes about 80% of the food it will eat during the few days it is in this last feeding stage. Then it burrows into the ground, and transforms itself into a moth and the life cycle starts all over again. It takes about 30 summer days for a female fall armyworm to develop from an egg to the point where she is ready to lay an egg of her own. That is why early on, it seems that the reports of fall armyworm damage come in in batches about a month apart, corresponding to a new generation of caterpillars molting into that last feeding stage. Later in the season, the generations overlap, moths are laying eggs almost every day, and all sizes of fall armyworm caterpillars can be found in a given field.
A sweep net is a good way to find fall armyworms when they are small. Sweep nets cost about $30-40 and you may eventually decide to buy one. If you want to try one first, most county offices of the Alabama Cooperative Extension System have a sweep net that you can borrow to look for fall armyworm caterpillars. Animal Science and Forages Regional Extension agents also have sweep nets you can borrow. A few cattlemen in almost every county have sweep nets, too. This video shows how to use a sweep net. If you find armyworms with a sweep net, follow up by checking to see how many caterpillars are present per square foot. If you find more than 2 caterpillars per square foot it is probably time to apply an insecticide, cut the hay, or graze the affected forage.
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