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How to Identify and Kill Armyworms

September 10, 2021 | Categories: , , ,

Nikki Hendrickson, our resident entomologist, recently sat down to answer some questions about the armyworm phenomenon we’re seeing. Watch or read on to learn why armyworms are so bad this year, how to identify them, and what you can do to control them.

Why are armyworms so bad this year? 

Over the last week, I’ve had a lot of calls about fall armyworm. I’ve had reports from Pennsylvania, up to Michigan, over through Missouri, down into Kentucky/Tennessee areas. Everybody seems to be having armyworms this year, so why is it so bad? 

Entomologists don’t have a pinpoint answer for you, but what we can say is it all has to do with weather, weather patterns. The armyworm is a migratory species that overwinters in Florida and Texas, and it is brought northward on winds. So we must have had some really good winds to get good dispersal throughout the Midwest, and they must have had some really high survivability. 

A female can lay anywhere between 1,000 and 2,000 eggs. And when you’re laying that many eggs, typically there are a lot of natural enemies, some diseases, some parasitoids that can help take those out and keep those populations in check. And there’s been some really good survivability of those eggs this year, so we’ve got a lot of moths, a lot of them laying two thousand eggs, and all of those are also living. 

Will the turf recover?

If you have turf — your yard, your golf course, whatever — that has been decimated by armyworm (and they can do a lot of damage), it should recover even if you don’t treat. You might lose more and more of it, but the turf would recover. 

Armyworms are strictly feeding on the foliage. They’re not damaging the crown, they’re not feeding on the roots. So when you strip those leaves, basically what you probably need to do is get down a little fertilizer or anything that you can do to encourage regrowth of that plant and get your grass blades back up. It should survive, though.

What are the indicators that you might have a problem with armyworms? 

For the most part, people notice armyworms when they’re getting brown spots in their yards or they’re walking out in their yard and or their turf and they just have caterpillars crawling all over the place. Sometimes you can see the caterpillars crawling across cement/concrete areas. 

But for the most part, you’ll notice that browning, that thinning, what looks like general thinning of the turf because they’re feeding on those blades. When they’re really young, they feed on partial blades, so they can create kind of a windowpaning effect. And then as they get bigger, that fall armyworm will have six instars. So as you get into those later instars, they’re going to start consuming that entire blade, so you can have kind of scalped patches of lawn. 

Armyworm’s kind of unique in that they kind of do this mass feeding, so they can kind of, you know, you might have thousands of them just marching and crawling across your lawn and feeding in one area. So lots of times you can kind of see a distinct line of where they’re feeding and where they’re not feeding.

How can you scout for armyworms?

If you want to go out and scout for armyworms or any other caterpillar/insect in the turf, one of the best things to do is go out and do a soap drench. You can mix one to two ounces (which is two to four tablespoons) of a lemon-scented soap — lemon-scented Dawn, lemon-scented Joy, something like that. 

Put it in a gallon of water and pour it around in about a square foot area, and pour it around those brown spots that you’re seeing. It might take 10 to 15 minutes, but things will definitely start coming up and bubbling up out of the ground. Then you’ll get down on your hands and knees, look in that turf, and see what you have coming up.

What do armyworms look like?

The adult armyworm is kind of a mottled brown to light reddish brown, little patches of gray, moth. There is one white spot in the center of those four wings. The hind wings are mostly kind of clear; there’s a little darker white around the outside. The caterpillars, it’s a striped caterpillar. You’ll have a stripe down the center of the body, lighter stripes down the outside edge of the body, but there is a lot of color variation. I’ve seen pictures of fairly light green to almost black caterpillars. 

There is a lot of color variation between the instars and even within an instar as that larvae and that instar stage matures. You can get different color variation on there. The big defining characteristic, if you can look at that head capsule, there’s an upside-down “Y” kind of suture that comes across the forehead and then up. If you see that, then you definitely have fall armyworm.

How many generations can occur?

So the fall armyworm, for the most part, will have one generation a year. Where Advanced Turf is located, all of our northern states tend to only have one. In our southern geographies, when you’re getting down into Tennessee and the Carolinas, places like that, you do have that chance for a second generation. 

This year it’s kind of a question mark in Central Indiana, Central Ohio, Kentucky. And it’s really going to be based on weather. When the night temperatures dip into those low fifties, they’ll start migrating back down south. So, kind of depending on how our summer weather goes, and if we still have this warm spell that we’re having, there could be a chance for a second generation.

What are the options and timing for preventative control? 

The fall armyworm, being a migratory species, tends not to hit here in Central Indiana until late July to early August. So, for the most part, your preventative applications are probably going to go down somewhat close to that timing, so if you’re doing, just depending on what you’re using. 

There are other products, things like acelepryn, Bayer’s new Tetrino, that you might also be using for grub control that can help take care of that population. One warning, though, is that if you do those applications early — if you’re doing them for, like, billbug timing and you’re putting those products down in May at the grub rate — it will not give you the control that you want for armyworm. So most of the time you’re not treating for armyworm, because it can be somewhat sporadic, until you notice a problem.

What are the options for curative control? 

Curative control on armyworm, you’ve got several options. Most any synthetic pyrethroid will work. Something like Sevin or carbaryl would work. You can use Dow’s Conserve, the spinosad-based products. 

Our customer base is primarily using something like bifenthrin. And I will say go high rate; with bifenthrin, you want to use that one ounce per thousand rate. Those bigger caterpillars can be harder to control. If you catch them when they’re really early, when they’re young, you happen to be out scouting for them and you see them, you can maybe use that half-ounce rate. But I would, that hardly ever happens, so I would go with a one-ounce rate of bifenthrin or use a high rate of any of those other curative labeled products. 

There are also two other products that I will mention. Dylox is labeled for it, and so is your clothianidin-based products are labeled for curative control.

Nikki Hendrickson
Sales Representative

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