Insecticide seed treatments provided a positive return in Mid-South soybeans nearly 80 percent of the time, according to a six-year study conducted by Extension entomologists Gus Lorenz of the University of Arkansas, Roger Leonard of the LSU AgCenter, Scott Stewart of the University of Tennessee and Angus Catchot of Mississippi State University.
Several changes in soybean production over the last 10 years have made insecticide seed treatments a good choice for growers, including changes in production systems which have impacted the pest spectrum for soybeans and the adoption of conservation tillage practices “which is very favorable for soil dwelling insects,” said Lorenz, speaking at a webinar conducted by Delta Farm Press and sponsored by Syngenta Crop Protection.
Lorenz also noted that growers are incurring higher costs for a bag of soybean seed “and a lot of growers are reducing their seeding rates, which can cause problems getting a good stand with some of the insect pests that we have now days.”
The shift to the earlier planting of soybeans also underscores the need for extra attention paid to early pest management, according to Lorenz. “A lot of times after growers plant and soybeans emerge, it turns cold and wet and all those pathogens and insect pests can stress seedlings. We’ve seen insect pests that we gave scant attention to in the past become more predominant, particularly thrips.”
Lorenz and other Mid-South entomologists conducted a study on insecticide seed treatments for soybeans in Tennessee, Louisiana, Mississippi and Arkansas from 2003 to 2008. The 104 trials compared the use of an insecticide seed treatment (Cruiser and Gaucho) on soybeans with an untreated check.
“There were a preponderance of trials with a positive response,” Lorenz said. “The results ranged from a low of minus 7 bushels per acre to a high of 18 bushels per acre.”
The study indicated that on average, insecticide seed treatments increased soybean yields about 3.5 bushels per acre. About 79 percent of the trials resulted in a positive net return for the grower.
If early-season soybeans are separated from the rest of the data, the net return is about 6.5 bushels per acre. “So if that’s the way you’re headed, you can rest assured that most of the time, we see a positive net return on early-planted soybeans with an insecticide seed treatment.
“What we think is that the insecticide seed treatment is helping the plant deal with early-season stress a little better,” said Mississippi Extension entomologist Angus Catchot. “And there are not a bunch of pests under the ground nibbling on the roots.”
Catchot added that there may be subtle differences in return on investment across the Mid-South, “but for the Mississippi area, we are seeing a return across all planting dates, and an even larger return across the early plantings.”
Catchot says that insecticide seed treatments on soybeans have increased significantly in Mississippi over the last couple of years. In 2007, “at most, we had an insecticide seed treatment on 2 percent to 3 percent of our soybean acres. Last year, we were probably between 50 percent and 60 percent of the acres. I expect the percentage to be higher as well this season.”
Lorenz says that an insecticide seed treatment can provide control of grape colaspis, thrips, grubs and three-cornered alfalfa hoppers. “We haven’t given credit to thrips and three-cornered alfalfa hoppers for causing yield reductions, but things have changed in the last few years.”
Other observations for the use of an insecticide seed treatment include better bean-leaf beetle control, better emergence in clay soils and taller soybeans. “It’s not all about insect control with insecticide treatments,” Lorenz said. “There is better vigor associated with the seed treatments, which equates to increased stand count.”
Lorenz says insecticide seed treatments for soybeans are especially useful “if you have had a history of field pests in a field, a lot of plant residue in the field at planting, if there are stress factors associated with the field or if you’re concerned about weather. For the last couple of years, it seemed like we had April in March and March in April. We get our fields planted, then it turns cold. That’s a situation where the insecticide seed treatments really shine.”
Other factors include field yield potential, according to Lorenz. “If you’re a dryland grower and your yield potential is low, 25 bushels to 30 bushels per acre, a 10 percent increase from a seed treatment is a lot less than one would expect from a field with a 60 bushel yield potential.
“From my perspective and most of the entomologists in the Mid-South, the insecticide seed treatments are pretty much a no-brainer. They have value to us, particularly in early-planted fields and even in the late-planted double-crop fields.
“Insecticide seed treatments are also stress busters. They can increase the vigor of the plant and get you through some of those hard times that may occur after planting.”
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