One of the benefits of farming in the Mid-South is the amount of cooperation between researchers across state borders. That ultimately saves area producers money.
“We work really close together across the Mid-South – Arkansas, the Missouri Bootheel, Tennessee, Mississippi and Louisiana,” said Angus Catchot, Mississippi State University entomologist, at the mid-January Cotton and Rice Conference in Tunica. “In fact, before this session began we were in here planning future projects.”
That cooperation allows a lot of data to be gathered in a short period of time. “We can get a ton of trials out compared to if we were working alone. We’re constantly evaluating thresholds, looking at new chemistries, trying to keep up with resistance. It’s a constant struggle.
“Some of the things I’ll present today are changes we’re making in the Mid-South states.”
Three-cornered alfalfa hoppers
Several years ago, there were many questions about three-cornered alfalfa hoppers (TCAH).
“We’ve gotten a lot more data since. One thing I noticed very quickly was we can chase TCAH with two and three sprays. What I saw across the state where we were making application for TCAH, we were killing them. They aren’t hard to kill. They’re very easy to control but seven days later they’ll re-infest the field.
“Before you know it, we’ll have three hopper applications between R-3 and R-5 and have flared worms leading to more problems.”
A lot of hopper research was done across the South, said Catchot.
“One graduate student was completely devoted to it. One thing he found – and I’m not discounting early-season hopper damage on small soybeans, main stem girdling – is we can’t show a yield loss from treating TCAH. It used to be that the threshold was one per sweep: 25 for 25 sweeps. So, we made a change and gone to two per 25 sweeps: 50 for 25 sweeps.”
Based on the data, most entomologists “feel you could go to three, four or five (per sweep). But currently, what we’re saying is the threshold is two, or more, per sweep.”
One of the recommendation changes for 2014 is to terminate treatments at R-6, “even if you reach that two or three hoppers per sweep. We’ve been making late-season hopper sprays and all we’re doing is flaring some of the pests that can really cause yield loss. The reason is when you begin spraying pyrethroids across the field, you’ll create a problem where one didn’t exist previously.
“Doing this will definitely save you money.”
Red-banded stink bug
Having had to deal with the pest for years, Louisiana is very familiar with the red-banded stink bug.
“In 2009, in Mississippi we sprayed 21 counties for red-banded stink bugs. Arkansas sprayed for some. They were found all the way up in Tennessee. They were really making a push and we were very concerned.”
The next winter was very cold and knocked the pest back. “They disappeared for two years. Now, after a couple of mild winters, we’re starting to see them again farther north. Last year, we actually sprayed south of Highway 82 in Mississippi quite a few fields.”
Also, in 2013, there was an increase in Southern green stink bug. “I hit some numbers in Noxubee County, on the east-central side of the state, of 100, or so, per 25 sweeps.
Question is: will Southern green stink bugs be bad in 2014 after the recent January freeze? Catchot is unsure. “I don’t know how long the sustained cold is needed to beat these back.”
Regardless, once soybeans get to R-6, “when the beans are swollen and touching in the pods, bushels-per-acre-loss is likely not going to happen due to stink bugs. There is a chance of is quality loss at the elevator.”
However, Catchot says quality losses aren’t as common as many believe. “I know producers that won’t spray for stinkbugs past R-6 no matter what the numbers are.
“What we’re telling folks now is once you hit R-6, go up from nine per 25 sweeps to 20. And terminate at seven days past R-6.”
Bean leaf beetles
Collectively, bean leaf beetles, grasshoppers, soybean loopers, green cloverworms are known as “foliage feeders.” Most of them don’t cause direct damage, says Catchot, although bean leaf beetles can feed on pods a bit.
“Yield loss is more or less from leaf-feeding. When you lose a lot of leaf surface and lose photosynthesis, you can get a yield loss.
“We had a graduate student working on foliage loss. The critical period to maintain the foliage is between R-3 and early R-5. If something happens during those stages, say you lose 80 to 100 percent of your leaves, you can see upwards of an 80 percent yield loss.”
While producers must manage these pests, Catchot cautions to be “sensible about it. You don’t need to keep every bit of foliage. The crop can tolerate a little foliage loss -- 20 percent is what most of us are working with in the Mid-South.”
Bean leaf beetles exploded in 2013.
“In Mississippi, we have pyrethroid-resistant bean leaf beetles. We had some fields that hit 300 per 25 sweeps. That led to a lot of foliage loss.
“We used to have a threshold of 50 per 25 sweeps, or a 20 percent foliage loss. We can hit the sweeps threshold easily in Mississippi. We’d make a spray and, a week later, another population would move back into the field. No chemistry would hold them more than five to seven days.
“Suddenly, you be at a two-shot spray -- sometimes three -- for bean leaf beetles. However, the field never got close to the 20 percent foliage loss. That means farmers were making a lot of unnecessary sprayings, while blowing up loopers and other lep pests because the beneficials were taken out.”
That has led to another recommendation change for 2014.
“We’ve basically gone to only a defoliation threshold for bean leaf beetles. The sweep number threshold was getting a lot of producers in trouble and causing multiple sprays.
“You can tolerate the beetle numbers, keep in mind, because the damage is only to the leaves.”
How quickly can the defoliation threshold be reached? If you’re making a once-a-week check and running five percent damage, is there a danger of coming back in a week and finding 40 percent damage?
“Five or six years ago, I was doing resistance screenings around the state. I went to a field of Group 4s and Group 5s growing together. The 4s were drying down.
“When I got to the field, which had a big unsprayed section I was working in, the beetles were running about 150 per 25 sweeps – a 3X threshold. Defoliation was about two to three percent when they were coming out of the 4s.”
While anecdotal, “it took 12 days to get from there to 20 percent defoliation. So, you have a bit of time.”
Researchers have made no changes for bollworm thresholds.
“Currently, all of us in the South are running about nine per 25 sweeps. Most people are spraying at about six.
“We’re working very hard to validate the thresholds. One thing we know for sure: bollworms are more of a problem.”
The good news is the arrival of additional materials to combat the pest. “I don’t think any of us would recommend pyrethroids for bollworm control -- particularly in soybeans or grain sorghum. We’ve seen so many failures. I believe seven out of 10 people that try to use pyrethroids on bollworms in soybeans end up in failure.
“Now, we have the diamide class of chemistry: Belt, Prevathon, Besiege. These products are incredible on caterpillar pests.”
For soybean loopers, Catchot routinely sees around 30 days residual with those products. On bollworms, “we have some really good lab data that suggest the same. However, in the field with bollworms, typically we get 14 to 21 days residual.”