Pest-wise, it’s shaping up to be a strange, and problematic, year. “We’re seeing some odd things — things we’ve never seen before,” said Gus Lorenz, Arkansas Extension entomologist. “Honestly, I’m a little worried about what this means for later in the season. We’re going to have to be on our toes.”
In mid-May Lorenz was called to Elaine, Ark., to check some puny soybean fields. Just beneath the soil Lorenz found white grubs feeding on the young soybean plants.
“It’s a mess there. These grubs — from the May or June beetle genus — being in soybean fields is weird. For some reason, over the last couple of years, the beetles laid eggs in the soybean fields. The devastation they’ve caused is serious.”
The large fields hosting the grubs are along both sides of an old railroad track. Soybean acreage nearest the track suffered the most serious damage. When Lorenz arrived, the producer, already hit by the grubs once, had replanted and there was a new flush of plants emerging.
“I told him, ‘This beetle is on a two-year life cycle. The good news is you probably won’t have a problem next year. But these things won’t go through pupation and become adults until late summer. They’re going to be out here feeding for the rest of the summer.’”
There are no control measures for the grubs. Only time will tell how much damage they cause.
“They aren’t even close to finishing their life cycle. I guess there are other fields in the area that have these grubs, too. Producers should check fields bordering wooded areas. I’d look there because typically the adult beetles feed on deciduous trees. For some reason, the females laid eggs in soybean fields.”
Lorenz is sure the beetles were in the fields last season but were so small they didn’t cause enough damage to be noticed.
“The beetle overwinters several feet deep in the soil. When spring came, they moved up to the root profile, maybe 2 inches deep. They fed on the emerging soybean plants.”
Lorenz and colleagues are also seeing higher-than-normal numbers of bean leaf beetles in many fields across the state. The pest is causing defoliation and “more concern by the day. Until now, it hasn’t been a big deal for most farms. But the early-planted fields are very vulnerable.”
Producers usually have to contend with three generations of bean leaf beetle annually. With the high numbers already, “I’m worried that by season’s end we’ll see a ton of these beetles. They’re defoliators mostly, but when numbers get high enough, they feed on pods. It also worries me that this beetle vectors a bean pod virus. We could see some virus impact.”
Thrips and aphids
Thrips have also been marching through soybeans and cotton in high numbers. Lorenz said soybean producers don’t usually treat for thrips because research hasn’t shown spraying makes a big difference in yield. That may change this year.
“With the hot, dry conditions we’re facing in many areas, the thrips situation is getting much worse. The beans are stressed and thrips aren’t helping. We’re seeing a lot of thrips damage in both soybeans and cotton. If they’re causing severe injury, in some situations action may be needed. But with thrips in beans, it’s case-by-case. I doubt there will ever be a standard recommendation.”
Pests in cotton are “all over the board. One of the biggest problems we’ve got in southeast Arkansas is a terrible, and growing, aphid situation.”
Aphid numbers have “blown up,” primarily due to foliar applications for thrips.
“Often when we go after thrips we kill beneficial, predacious insects. That releases the aphids. So now, we’re seeing spotted aphids all across the state, but particularly in the southeast.”
Mites and Loopers
While it’s very early to be seeing so many aphids, spider mites have made an early mark as well. Mites are particularly bad in northeast Arkansas.
“I talked to a source in Mississippi and was told they’ve got a similar situation there,” said Lorenz. “Such big numbers of mites this early on seedling cotton don’t inspire confidence. These mites flare for the same reason aphids are. Some fields need spraying. I encourage every cotton producer to check fields for spider mites.”
Extreme southeast Arkansas has also experienced a flush of loopers.
“The new Bollgard label — allowing pest treatments on refuge cotton — is out and we’re seeing problems on the refuges. The Bt technology gives us great control, but loopers are building up, defoliating the conventional refuges and taking the tops off seedling cotton. There’s been a lot of spraying for loopers already.”
Producers are also seeing more cutworms than normal. “Growers have had to go back over-the-top of their cotton to control them.”
Rock and hard place
The product of choice for cutworms is a pyrethroid. Using those, unfortunately, likely will allow aphid and spider mite populations to rise even more.
“By spraying broad-spectrum insecticides over-the-top of small plants, we’re killing beneficial insects. What we’re doing is building a bigger and bigger problem. We’re exacerbating the situation by releasing what are usually secondary pests.
“But what choice is there? We have to control the pests we’ve got now — not two months from now. Unfortunately, that’s making the situation worse.”
As it gets hotter and drier, Lorenz fears for the state’s row crops.
“Look, as ditches begin to dry up, it’s going to push even more insects into our crops. We’re going to continue to have problems. Honestly, it’s not shaping up to be a very good year pest-wise. Hot, dry weather is ideal for many pests like aphids and lep pests like bollworm and armyworms.”
Is there any good news? “Well, we’ve noticed that due to our early, wet spring, broadleaf host numbers are down compared to last year. That’s where plant bugs overwinter and stage on the edge of cotton fields. Maybe we won’t have as bad a plant bug year as we did last year. That’s strictly speculation, but I’m certainly hoping.”