After the late, wet spring delayed planting in many areas, soybean stands are finally established and approaching critical reproductive stages. Now is also the time when insect pressure is likely to build. Soybean yield potential hangs in the balance.
“The reproductive period — from beginning bloom to seed set — is the time to intensify scouting efforts,” says Erin Hodgson, Ph.D., extension entomologist with Iowa State University. “You don’t want any clipping of the pods, or abortion of the flowers or the seeds. Now is when scouting is most critical to protect yield from damaging insects.”
Since its introduction the United States in 2000, the soybean aphid has become one of the most threatening pests for many soybean growers. Although the cool, wetspring may delay aphid onset this year, Hodgson cautions growers not to rule out pressure from this devastating pest. “Soybean aphid populations can explode almost overnight. If left untreated, soybean yields can take a significant hit, reducing output per acre by 15 to 40 percent.”
Hodgson reports that aphid populations in Iowahave been highly variable the past few years. “In 2011, it’s likely that not every field will need to be treated, but some might to protect yield. That’s why scouting and integrated pest management tactics will pay off financially.”
Growers who scout regularly and track insect numbers will be well positioned to make timely treatments when insect populations exceed the economic threshold.
Paul Compton, who produces 1,000 acres of soybeans near Homer, Ill., in the northeastern part of the state, says soybean aphids are joined by Japanese beetles, bean leaf beetles and stink bugs as key pests on his scouting listthis year. “Piercing and sucking insects are a serious threat to soybean acres in our area. Sometimes, you don’t realize the damage they are causing until you take steps to control them. Compared to untreated fields, my neighbors and I have seen yield increases of at least 3 to 5 bushels per acre in our treated fields. Spread across 2,000 acres, the ROI is significant, especially with favorable soybean prices these days.”
When to Scout
Dan Sherrod, Ph.D., product development manager, DuPont Crop Protection, recommends that scouting efforts be in full swing by mid to late June, and intensify when weather conditions are dry and between 78 and 84 degrees Fahrenheit, the optimum environment for soybean aphid populations to flourish. Scouting should continue through the reproductive growth stages as soybean plants fill their pods.
Scouting is particularly important in late-developing fields, says Sherrod. Under normal conditions, soybean plants have already filled their pods and are starting to dry down when insect pressure increases in July and August, “The trouble with late planting,” he says, “is you’ll have green growing plants that are attractive to pests later in the season.”
How to Scout
For accurate scouting, Sherrod recommends examining 20 to 30 plants at multiplepoints throughout the field and recording pest counts and foliar damage. Aspest populations are identified, scouting efforts should intensify, particularly with soybean aphids. “Once aphids are detected in the field, check the crop every two to three days, as populations can double in that brief time,” he says.
Soybean aphids are just one of many pests growers should watch for as they walk their fields. “When you’re out there making aphid counts, look for worms, bean leaf beetles, Japanese beetles and other pests common to your area,” advises Sherrod, adding that foliage damage is the best way to spot a worm infestation.
Familiarize yourself with the established treatment thresholds for local insects. For soybean aphids, says Sherrod, the typical threshold is an average of 250 aphids per plant over 80 percent of the plants in the field. “When populations reach this critical number, particularly during the flowering to early pod stages, it’s time to take action, before yield potential is compromised.”
Sherrod says spotting the sap-like secretion called honeydew that soybean aphids leave behind, which encourages mold growth, is an indication that the infestation is out of control. “If the field is sticky and you see black, sooty mold, its critical to make aphid counts and move quickly with a rescue treatment if thresholds are exceeded,” he warns.
Sherrod recommends a broad-spectrum insecticide treatment with good residual activity, such as DuPont™ Asana® XL. It will effectively control aphids and clean up other incidental pests present in the field, such as bean leaf beetles, grasshoppers, green clover worm, Japanese beetles (adults) and green and southern green stink bugs; and guard against secondary pest outbreaks. For severe and rapidly expanding populations, an insecticide with fast knockdown, such as DuPont™ Lannate® LV can halt the most aggressive outbreaks, and can be tank mixed with Asana® XL or another pyrethroid for long-lasting control.
Sherrod points to recent university studies on soybean aphids in high-infestation areas that revealed that on average, applications of Asana® XL helped prevent yield losses by more than 11 bushels per acre compared to the untreated check.
The bottom line, says Sherrod, is be attentive to the progress of your crop, intensify scouting prior to the critical reproductive growth stages and familiarize yourself with treatment thresholds and insecticide options. “When insect pressure mounts,” he says, “growers who take steps ahead of time won’t be caught off guard. And that’s the key to a profitable harvest.”
Even when factoring in the input costs associated with making an insecticide application, Compton says the returns make it one of the most profitable investments he can make in his fields. “Some growers enhance their insecticide applications with nitrogen or a fungicide, and those could add value, but I believe it’s the insecticide treatment that offers the greatest return on your investment,” he says. “Insects are what really rob you of yield — especially piercing, sucking insects, which also can introduce diseases. Left untreated, your crop just will not yield to its full potential.”
Asana(R) XL and Lannate(R) LV are restricted use pesticides. Always read and follow all label directions and precautions for use.