New Nasty Nibblers: Invasive Species Add to Soybean Production Challenges
Farmers face an increasing number of challenges in production of high yielding soybeans. The arrival and establishment of new invasive pests makes production more challenging. The fact that the presence of these pests is unpredictable and little is known about them presents challenges as well.
“We are taking a forward looking approach to learning more about these invasive species – their biology, life cycles and damage potential – long before they get to Iowa soybean fields,” says David Wright, Iowa Soybean Association director of contract research.
The trend of invasive insects becoming economic problems was emphasized with the discovery of soybean aphid in 2000. It is now the No. 1 soybean insect pest in the North Central region.
Another invasive species, Japanese beetle, has been found in the United States for decades, but first became prominent in Iowa about five years ago. The pest has now been confirmed in 56 Iowa counties.
Japanese beetle is easy to identify with its metallic green and copper coloring. This pest is about 3/4 inch long and likes to chew on soybean leaves, mostly after flowering, from mid-June through August. Heavily infested areas can be severely defoliated by the beetles, and remaining leaves appear skeletonized, with only the veins of the leaves remaining.
A few specimens of brown marmorated stink bug (BMSB) were confirmed in 2010, but none were found alive this summer. BMSB is not yet a widespread problem, but it’s definitely on the radar screen for those in the soybean research world.
“BMSB could be a significant challenge. Like Asian lady beetle it invades homes, and produces a horrendous odor when threatened,” says Wright. “Not only is it a nemesis in homes and outbuildings, but it also feeds on soybean pods, resulting in poor seed quality.”
BMSB typically feeds on soybean seeds through the pod. During seed formation, BMSB can puncture tissue and cause deformations. The seed coat can be damaged, causing smaller, shriveled seeds. It has caused significant yield loss along the east coast for several years. Growers are struggling with multiple insecticide applications to manage this new pest.
Wright notes that there are several stink bugs in Iowa, including a predatory species, so farmers should make sure they identify them correctly. If they have questions, they can send in samples to the Iowa State University Plant and Insect Diagnostic Clinic. For details, visit: http://www.ent.iastate.edu/pidc/
If Japanese beetles, stink bugs and aphids weren’t enough, another pest on the horizon is the kudzu bug. Kudzu bug is a stink bug relative that is known to feed on kudzu vines, but also attacks soybeans. This pest is already threatening agricultural production in the eastern and southern United States, and is spreading north and west. This pest hasn’t found its way to Iowa yet, but Wright says it’s a matter of time.
“The kudzu bug has similarities to the brown marmorated stink bug, in that it’s originally from Asia, reproduces rapidly and invades structures to overwinter. “This pest causes tremendous damage to soybean in areas where it has populated,” says Wright.
According to Wayne Gardner, a professor of entomology at the University of Georgia, a small soybean seedling can have 40 kudzu bugs feeding on it. Gardner and others are looking for ways to control the new arrival’s population.
With the arrival of each of these new invasive pests, farmers will need to be more aware of what’s going on in their fields and be able to react quickly. Ongoing checkoff-funded research will determine how widespread BMSB and Japanese beetle are in Iowa, and will establish economic thresholds for battling these pests.
“Right now the unpredictability of these pests is a real challenge. This could result in additional insecticide sprays and management costs to protect yield,” says Wright.
Accurate Identification is Essential
Scouting will reveal the presence of many species of stink bugs. While most stink bugs are herbivores, one is beneficial – the spined soldier bug, commonly found in Iowa soybean fields. Both the immature and adult stink bugs of this species are predatory, and will kill many soybean pests.
Because there are several persistent soybean pests and a few emerging species, growers should be vigilant about scouting, according to Iowa State University Extension Entomologist Erin Hodgson. Sampling during the reproductive stages of soybean is the most important time to look for insects, but estimating pests at least every two weeks will provide helpful treatment information. Making timely insecticide applications when insects exceed a treatment threshold will protect yield. For new pests without an established economic threshold, consult ISU extension personnel to help guide your treatment decisions.
Hodson says invasive insects can thrive in new habitats and sometimes surge to pest levels very quickly. Soybean aphid is a good example of how a pest can become a dominant threat in just a few years. Without their native control, like predators and parasites, exotic insects can out-compete native insects and surge to damaging levels.