Recently we have been receiving calls about armyworms attacking cover crops. Armyworms can be a devastating problem, as they march into our crops after having completely devoured all the grass in the pastures from which they originate. We have had reports of cover crops being similarly wiped out by armyworms. People have been asking me what to do about the armyworms. Obviously, like so many other problems, once the armyworms are on the march, it is too late to take preventative measures and we can only recommend reactive methods. But with the right system in place, it is quite feasible to prevent armyworm outbreaks. The ultimate key to preventing armyworm outbreaks is to target the pastures from which they originate. There is also a right way and a wrong way to go about killing armyworms once they have reached a critical level requiring treatment; most people choose the wrong way. Let me explain both concepts.
I gave a talk on pasture management a few years ago in western Arkansas. I was talking about all the expensive inputs used in the production of bermudagrass monocultures, and one of the audience members raised his hand and said “You forgot the biggest one” I asked him what that was.
“You forgot the four sprays a year for armyworms!” I first thought he was joking or exaggerating, but I could see all the audience members nodding in agreement. “You all seriously spray four times a year for armyworms?” I asked them, and the consensus was yes. Spraying an insecticide on a pasture is just beyond my realm of thought. I stumbled and bumbled around a bit after that because my brain was trying to wrap itself around the thought of four annual insecticide sprays on pasture. Why were these folks being overrun with armyworms? Will frogs, locusts, and burning hail come next? I really failed to give them a good solution to their armyworm dilemma that evening. But, just as I do after every argument I have ever had, the next day I thought of exactly what I should have said to them:
Quit spraying insecticide, quit spraying herbicide on pastures, and diversify both your pastures and cover crops.
I am already bracing for the anticipated response, followed by the crew carrying buckets of tar and sacks of feathers. “Whoa, there, college boy! Insecticides kill armyworms! If we don’t spray insecticides those critters will wipe us out! Herbicides kill weeds! If we don’t spray herbicides the weeds will choke out all our grass! You need to get out here in the real world!”
OK, before the guys with white coats and big butterfly nets come and get me and put me in my padded room, let me explain. On the way home, I was still trying to grasp the concept of spraying pastures four times a year when an observation struck me. I shared with my co-worker, Brett Peshek, who had also presented at the meeting.
“Brett, have you seen any birds today? Or yesterday?”
“No, now that you mention it, the only bird I have seen is that vulture we saw eating roadkill a while back. Why do you ask?” We had been in Arkansas, the “Natural State” for two days and had not seen a single quail, or meadowlark, or any other bird.
“What do you suppose four annual applications of insecticide do to the food supply of insect-eating birds? And what do you suppose that lack of food supply does to the population of those birds?”
“It can’t do the birds much good!” he replied.
I am sure it doesn’t. It probably doesn’t do any insect predators any good.
When my brother first started cover cropping, he used monoculture plantings of cereal rye. That first year, the armyworms about wiped him out. Then in subsequent years, a curious thing happened: the armyworms just seemed to go away. We thought maybe it was a cyclical thing, and they had run their course. But one year he was planting into a thick stand of multi-species cover crops and his planter plugged up just before dark. He crawled underneath with his headlamp and started to pull all the loose residue out of the planter unit when he had the feeling something was watching him. He looked around, and he was completely surrounded by glowing red eyes. Hundreds of them. Wolf spiders! None of them were quite brave enough to jump him by themselves, but there is bravery in numbers and it appeared they were getting more numerous by the minute, so he quickly finished and got back in the spider-free tractor cab, a little creeped out but also excited. The diversity of insects in the cover crop were enough to feed a large, healthy population of insect-eating spiders that now populate his farm. Armyworms are now just another menu item on his farm, and seldom make it to the marching stage alive in any numbers.
Back to the trip home. I asked Brett another wildlife-related question. “What do wildlife biologists say are the two worst types of grass for upland game birds?”
Brett is an astute wildlife guy, he will hunt anything that flies, runs, or slithers, and he studies wildlife management constantly. He knows his stuff. “Fescue and bermudagrass, especially in monocultures” he replied. Bermudagrass and fescue monocultures offer neither food nor cover to insect-eating wildlife, except during those brief periods when armyworms are rampant, when there is a feast to be had. But birds, spiders, and the like must eat every day, and the brief periods during which armyworms are present are too far apart to keep the insect predators alive in between. In a well-managed pasture ecosystem, there is a diversity of plants that attract a diversity of insects, that all live at different times of the year. This diversity provides a continual supply of insects so that insect eaters can eat every day and thrive.
A dense population of insect predators could go a long way towards eliminating our armyworm problems, but how do we get the insect predators back into our pastures? First of all, ditch the insecticide. I know this seems completely contrary to common sense. But as long as you keep spraying insecticide you will never have insects (the vast majority of which are harmless) so you will never have insect eaters. The armyworms will find a way to keep coming back. If spraying four times a year was the solution, wouldn’t those folks in Arkansas have gotten rid of their problems by now? Of course, it takes a while for populations of insect eaters to build up to levels necessary for good control, so it is quite likely (almost guaranteed) that you will have armyworm outbreaks in the initial years after you quit spraying insecticides. So do you have to just let them eat your pasture and then all your neighboring crops while you sit on your hands? No, there are alternatives that are much less harmful to beneficial insects and insect predators. I would suggest looking into using formulations of Bacillus thuringiensis (Bt) like Dipel or Xentari. Dipel and Xentari contain the toxin produced by a bacterium that is only toxic to caterpillars, so it leaves non-caterpillar insects and insect predators unscathed. It is a slow kill, but soon after ingesting the Bt they stop eating and die within a few days. If they get eaten by a bird, spider, or bug in
the meantime no harm comes to the critter that eats them. Another armyworm control method that has few off-target effects is the use of nematode species that specifically attack armyworm species; there is a product called Nemattack SC that targets armyworms species and can kill them in just a few days. It is important to avoid broad-spectrum insecticides that also kill insect predators.
Second, ditch the broadcast herbicides. Herbicides kill broadleaf plants that attract a wide array of insects. A wide array of insects then attracts a wide array of insect eaters: ladybugs, lacewings, praying mantids, wolf spiders, crab spiders, quail, meadowlarks, larks, and the like. But if you don’t spray, won’t the weeds take over? Okay, here is where you have to trust me: if you do daily rotational grazing, animals eat weeds. Honestly. It really works. I can’t explain it. I have heard all kinds of explanations, but none of them really make sense to me. I just know that it happens. I remember people telling me this and I thought they were full of organic fertilizer originating from a male bovine. Then I tried it on my place and all of a sudden my cows started eating weeds: ragweed, velvetleaf, sumac, and basically everything else. Trust me. If the few remaining weeds sticking up bother you (honestly, they bother me, too, so it is ok to admit it, we are all in a safe zone here) you can rotary mow or use a weed wiper after the animals leave a paddock to knock the weeds back at minimal cost without killing the palatable broadleaf plants.
Third, diversify your pastures (as well as your cover crop fields) beyond grass monocultures. The best pastures for insect-eating wildlife are composed of legumes, forbs, and native bunchgrasses like big bluestem, eastern gamagrass, and Indiangrass. If your current pastures are grass monocultures, interseed legumes, and forbs. High protein legumes and forbs attract a wide variety of insects, far more than grasses alone. Most of these insects are quite benign, and many are beneficial. All of them also attract things that like to eat insects, whether that be birds, spiders, or other insects like praying mantids. Another obvious benefit of legumes is that they fix nitrogen. If managed correctly, they may completely eliminate the need for nitrogen fertilizer (that is a topic for a future article). Be sure to add a few seed-producing plants in the mix, like some millets, cowpeas or buckwheat. This helps feed insect-eating birds in the winter when there are no insects available.
I have given similar advice for years, especially in eastern Texas where I have some business contacts. I gave talks for years down there and got laughed out of a lot of rooms when I talked about using legumes instead of nitrogen fertilizer, daily rotational grazing instead of herbicides, and plant diversity instead of insecticides. “Har! Har! That won’t work around here!” they would tell me, and basically ignore everything I told them. But they apparently felt I was good entertainment because they kept asking me back, and since the barbecue was always really good and the folks were always fun to hang out with, I kept going back. But it was sure frustrating to be considered a crackpot and to be ignored. But a year or so back, I was asked to give another talk in eastern Texas. I gave my same song and dance during the morning “inside” presentation, but this time there were no guffaws or ridicule (and the audience was still awake). Something was different. The people were actually receptive to these ideas. The afternoon part of the day featured a trip to an area ranch that was actually doing everything I had spent years promoting. It was a magical day for me. We were shown beautiful pastures, mostly bermudagrass but also full of the pink, aromatic flowers of Persian clover, the gorgeous blood-red blossoms of crimson clover, the big white egg-shaped flowers of arrowleaf clover, and the tiny yellow flowers of medic. There were weeds, I won’t tell you otherwise. But we walked to the line where the polywire divided the “just grazed” pasture from the “next to be grazed” pasture, and while there were plenty of “weeds” in the “next to be grazed” pasture, there were none left uneaten in the “just grazed” pasture. The cows ate them just fine. There were plenty of insects in this pasture, such as bees and butterflies, but not a visible armyworm anywhere, in fact, I saw no visible signs of insect herbivory at all. Despite receiving no nitrogen fertilizer, the bermudagrass in this pasture was visibly more productive than the monoculture bermudagrass just across the fenceline. This “quit spraying stuff” actually does work in the real world! That afternoon provided vindication for all those talks I gave for years that fell on disbelieving ears.
Armyworms can be devastating, but if your only response is to apply broad-spectrum insecticides, know that you are setting yourself up for future insect outbreaks of all kinds, not just armyworms because you will eliminate natural predators of your insect pests. It is far better to implement a system in which we encourage insect predators. This is done by a simple three-step process:
1. Avoiding all broad-spectrum insecticide applications,
2. Eliminating herbicide applications on pastures,
3. Diversify grass pastures and cover crops by adding legumes and forbs.
These three steps will help ensure a healthy population of insect predators that will keep not only armyworms but a broad spectrum of pest insects in check.
To summarize, if you are suffering from armyworms, the solution is not to spray more. The solution is to spray less. Trust me.
Dale is an agronomist for Green Cover Seed and works at the GCS location in Iola KS, which is located a few miles from his family farm operated by his brother. He is the author of the books The Drought Resilient Farm and Managing Pasture as well as the upcoming The Complete Guide to Restoring Your Soil, available in November 2021. He can be reached at 785-614-2031 or firstname.lastname@example.org