Nikki Hendrickson, our resident entomologist, is here to share some important information about armyworms. Read on to learn how to identify them and control them.
Why are armyworms a problem?
If you remember the summer and fall of 2021, armyworms were everywhere.
Armyworms feed on and damage turf blades, which can make lawns appear unsightly.
The armyworm is a migratory species that overwinters in Florida and Texas and is brought northward on winds. The stronger the wind current, the more armyworms arrive.
A female armyworm can lay anywhere between 1,000 and 2,000 eggs, so it’s a good idea to keep those populations in check.
Will the turf recover?
If you have turf that has been affected by armyworms, it should recover even if you don’t treat it. You might lose more and more of it, but the turf will recover. The exception would be that if the turf is already stressed (due to drought, for instance), you may lose some.
Armyworms feed strictly on the foliage. They’re not damaging the crown, nor are they feeding on the roots. So, when you strip those leaves, 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, course, or field, and they have caterpillars crawling all over the place. Sometimes, you can see the caterpillars crawling across cement and concrete areas.
On turf, you’ll notice browning and 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 a kind of windowpaning effect. 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 scalped patches of lawn.
Armyworms are unique in that they do a sort of ‘mass feeding.’ You might have thousands of them just marching, crawling, and feeding in one area. Often, you can 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. This is the best way to uncover young armyworms, since adult armyworms will already be highly visible. You can mix one to two ounces (which is two to four tablespoons) of a lemon-scented soap in a gallon of water.
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 a mottled to light reddish brown moth with little patches of gray. There is one white spot in the center of its four wings. The hind wings are mostly clear; there’s a little darker white around the outside. The caterpillars are striped; 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 the larvae mature. The big defining characteristic, if you can look at its head capsule, is 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, and Kentucky. It’s really going to be based on the weather. Stronger storm systems may move them up earlier, and then when the night temperatures dip into the low fifties, they’ll start migrating back down south. So, depending on how our summer wraps up, 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, just depending on what you’re using.
There are other products like Durentis, Balata, and Tetrino that you might also be using for grub control that can help take care of that armyworm population. One warning, though, is that if you do those applications early (if you’re doing them for, say, 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?
For curative control of armyworm, you’ve got several options. Most any synthetic pyrethroid will work. Something like carbaryl would work. You can also use Conserve and other spinosad-based products.
Our customer base is primarily using something like bifenthrin. I recommend going with a high rate of 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 young, if you happen to be out scouting for them, you can maybe use that half-ounce rate. 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 armyworm, and clothianidin-based products are labeled for curative control.
Some Final Takeaways
In 2021, I fielded a lot of calls about fall armyworm. I mentioned that they were everywhere that year, and while they aren’t posing a major issue this year, it’s always good to be prepared.
It’s also worth noting that there are other armyworm species that can occasionally affect turf, such as the common armyworm and yellow striped armyworm.
When it comes to getting rid of armyworms, your ATS rep is the best point of contact. Reach out today for advice!
