Rise Of The Pests
September 9, 2008 
After an almost balmy December for much of the Midwest, a cold snap hit in February. Alas, it was not severe enough by any means to wipe out many pests, believes Christian Krupke, Purdue University. “Overwintering survival of most pest species should be quite good.”
Aphid Fever
Overwintering populations of soybean aphids in parts of the Midwest are large this winter — as indicated by 1) fall captures of winged aphids in suction traps and 2) very large numbers of eggs that entomologists have found on buckthorn, says Kevin Steffey, Extension entomologist with the University of Illinois at Urbana-Champaign.
Krupke was happy to report that Indiana’s soybean aphid numbers during the growing season were very low. “The vast majority of fields we monitored registered zero aphids throughout the season,” he says. But he agrees with Steffey that 2007 should be a different story, as “in the fall we had unprecedented high numbers of aphids going into overwintering sites, particularly in the northern half of the state,” he says. “It may be an early and active aphid year.”
Both experts suggest growers and retailers start watching for aphids in late June and July, after they fly from buckthorn to soybean and begin establishing colonies in soybean fields. “The critical time for scouting is when the soybeans are in the reproductive stages of growth,” Steffey emphasizes.
Coby Long, senior insecticide brand manager with Syngenta, says the soybean aphid has spread from its roots in the upper Midwest around the Great Lakes, and now covers New York to Iowa. “That whole dynamic has really exploded,” he notes.
Corn Feeders
With low numbers, western corn rootworm (WCR) was kind to Indiana fields, though a cold, wet spell in early May caused larger than normal losses in corn planted just before this period. Other pests such as white grubs, seedcorn maggot, and wireworms may have done the deed, says Purdue’s Krupke. “But this kind of damage is unavoidable after such weather conditions. There are no insecticides that will offer protection under extended cool, wet conditions just after planting.”
He doesn’t see enough acreage in Indiana being shifted to corn — perhaps 10% in the coming year — to impact rootworm populations in the near-term, but in areas such as southern Indiana where the soybean variant isn’t yet present, continuous corn would lead to higher pressure.
In Illinois, however, western corn rootworm and western bean cutworm are among the corn pests to watch for in 2007, says Steffey. “We anticipate that the rootworm larvae will cause injury to corn planted after soybeans anywhere in the state where the soybean variant has been established — basically any county north of the I-70 corridor. Although the focus on rootworms in recent years has been on corn planted after soybeans, corn rootworms will still threaten corn-after-corn, just as they have for decades.”
Still new to the state, western bean cutworm arrived in Illinois in 2004 — but northwestern counties in particular will want to pay close attention, as moths have been found in most traps across the northern half of the state.
Defining The Epicenter
“The epicenter of this cutworm has been eastern Nebraska and western Iowa,” says Hank King, product manager with Dow AgroSciences. “It continues to grow in its geographic scope” and has gone the distance to northeast Kansas and northern Missouri. One reason for the insect’s rise could be the move to more genetically modified crops, says Aaron Locker, product manager with FMC Corp. These modified hybrids are strong against certain pests, but have caused shifts to other problem pests including cutworms, wireworms, and armyworms, he says.
Steffey notes that Japanese beetle numbers were extremely large in southern and central Illinois and in pockets to the north. “Because they overwinter as grubs in the soil, we anticipate their return in 2007,” he says. Some soils may have gotten cold enough (about 20ºF) to kill off some, but snow cover insulated the ground in many areas. “We’ll watch for the adults to emerge from the soil in mid- to late June and keep our eyes peeled for silk clipping in corn and defoliation in soybeans,” he says.
Rust & Company Coming To Dinner?
As Daren Mueller, Extension program specialist with Iowa State, poetically puts it, “each year the table is reset” when it comes to the possibility of Asian soybean rust reaching the Midwest. “There have been some cold snaps moving deep into the South — as far as Tampa, FL, so survival of soybean rust has been lower than in previous winters. Rust did not survive in Alabama, Mississippi, and Louisiana, which is a positive for many of the Midwestern soybean growers.
“We got a glimpse of how fast soybean rust can spread during its rapid spread in October 2006, when inoculum built up in Louisiana,” he adds. At that time, weather broke in the South: Temperatures started to cool and more moisture arrived, reports Gary Fellows, technical marketing manager with BASF. “That happened in the September-October time frame, but when rust did come up, it moved very rapidly.”
“Beyond rust, there’s a continuing trend for more sudden death syndrome, frogeye leaf spot, and Cercospora leaf blight in soybean,” says Mueller. In addition, bean pod mottle virus (BPMV, vectored by the bean leaf beetle) was detected in every county in Iowa last year, reports his colleague, Alison Robertson, Extension field crops pathologist with Iowa State. “Depending on the survival of the beetle this winter, we may see a high incidence of BPMV in 2007,” she says.
In the South, both frogeye leaf spot and Cercospera are already very prevalent, and BASF’s Fellows would expect some of those diseases could be worse this year because of the warm early winter.
As more acres move from soybean to corn, many soybean pathogens “will not be happy about the extended rotations away from soybean,” which could lead to lower incidence of soybean diseases, says Mueller. Examples are the two “biggies:” soybean cyst nematode and sudden death syndrome.
Corn Diseases In Waiting
But while soybean diseases may not like a double dose of corn, corn diseases will thrive. “With more growers considering corn following corn, if we have a cool, wet spring, seedling blights — and therefore stand establishment — may be an issue,” believes Alison Robertson, Extension field crops pathologist with Iowa State University. Corn-on-corn fields, especially those with surface residue, will be more prone to seedling diseases thanks to inoculum pressure and cooler, wetter soils, she says.
Also lurking in that residue is inoculum for foliar diseases such as gray leaf spot, anthracnose leaf blight, northern leaf blight, and eyespot. Robertson says scouting will be critical in corn-on-corn fields to make sure fungicides, if being used for management of corn diseases, are applied at the right time. The goal is to protect the ear leaf and leaves above the ear from infection and extensive blight development during grain fill.
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