The insect pest of the year, so far, has been the fall armyworm. When we have a big outbreak of them it doesn’t matter if you are a farmer, rancher or homeowner because these voracious little eating machines have the ability to hit everyone hard! The good news is that in many cases, the damage looks far worse than it really is.

There is a group of insect pasts known as armyworms, cutworms, etc that are around every year, and most years they aren’t a problem. The larvae (worm) of all of these may look similar, but are distinguishable. As adults these are all moths that are often nondescript and what many of us just basically call “millers”. It is important to differentiate the species though as they all have quite different life habits and as such different periods when they may become a pest.

Fall armyworm adults do not overwinter in Kansas. Both the moths and the larvae die with freezing weather. They overwinter in warmer climates like south Texas or Mexico. The adults fly, or are blown, north every summer usually first being found in the state in July. Once here, the females start laying eggs. We expect an average life cycle to take about 30 days. Normally, weather and food dependent, we will have 2 to 4 generations per year.

The female lays eggs in what looks to be a good food supply location. Fall armyworms are particularly fond of grasses but will also feed on alfalfa and many crops we have in our gardens. They are rarely found feeding on soybeans or garden beans however. The good news is that if crops are good sized, which normally happens by late summer, they aren’t much of a problem. Heavy infestations in sorghum can require treatment but normally damage to corn is superficial. Alfalfa may lose some production but those late summer cuttings are often pretty thin anyway due to heat and drought. Bromegrass can also be heavily defoliated. But with cooler weather and fall rains, most of these crops are going to be just fine without a need for treatment.

Lawns, especially irrigated lush looking lawns, can be very attractive to fall armyworms. The eggs are laid, the small larvae start feeding and as they grow they will just start clipping off grass blades and moving across the lawn leaving large areas of brown grass. While unsightly, the fall armyworms usually move on and don’t eat off the new growth coming up. If you feel the need to spray then just about any lawn and garden insecticide is going to be labeled for them. Of all the ones that are currently out there spinosad is probably my favorite as it is an organic product, highly effective against larvae that turn into moths and has much lower non-target injury. Whatever product you use look for those that attach to the garden hose. It eliminates mixing and cleanup afterwards. Attach, turn on the water, it automatically mixes the right amount, turn off the water and set the container on the shelf for when you need it again.

The one area where fall armyworms do really concern me is with new seedings in the coming weeks of either lawn grasses, wheat or alfalfa. Fall armyworms can move into these as they are emerging and since the plant is just starting to grow it does not have the root system or crown developed yet to withstand the assault and young stands can be killed. After you have any of these planted start checking the field about the time it starts to emerge and then check it daily until it freezes!. You may only have a one or two day window to save that young stand if fall armyworms move into it! If you are unsure if you have a problem, don’t hesitate to call me!

CHUCK OTTE is the agricultural and natural resources agent with the Geary County Extension Office.

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