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Corn+Soybean Digest

2006 Insect Guide

Even without a crystal ball, entomologists know that pests will be around every year. Weather, migration and other factors, like the loss of beneficial insects to treatments, all factor in to what you'll see on your farm.

While the types of problem insects vary from year to year, these entomologists review what growers dealt with last year and predict which will be the biggest pests in their areas in 2006.


The primary insect of concern in corn will be corn rootworm, according to Kevin Steffey, an entomologist with the University of Illinois. “We'll continue to monitor for western bean cutworms,” he says. “We'll also continue to be watchful for European corn borers.”

Steffey says that although the numbers of overwintering soybean aphids are low, he'll keep an eye on them throughout summer, and be watchful for bean leaf beetles.

These predictions are similar to insect problems last year. “Corn rootworms and two-spotted spider mites in soybeans were two primary insect problems in Illinois in 2005,” he says. “We also experienced localized ‘hot spot’ outbreaks of the soybean aphid in northern Illinois. We observed a slight increase in the overwintering population densities of European corn borers, too.”


“In corn, the principal problem continues to be western corn rootworm and, more specifically, the rotation-resistant variant of this insect. In soybeans, the soybean aphid was a significant problem in the northern portion of Indiana (in 2005),” says Christian Krupke, Purdue University.

Growers should be ready for similar pest problems this year, in both corn and soybeans. “We expect these two pests to be the key pests again in 2006. The soybean aphid has shown the propensity to be a sporadic pest and growers are hopeful that 2006 will be an off year,” he says. “We'll be monitoring for the aphid since it has the largest damage potential of any pest in soybeans.”


Iowa State University entomologist Marlin Rice says northern and western corn rootworms were the biggest problem for corn growers in 2005.

“Millions of dollars are spent each year on chemical insecticides to control these insects. Now farmers have the option to plant corn rootworm hybrids that will provide even better protection against these two pest species,” he says.

In central and northern Iowa soybean aphids were a major problem last year. “Estimates suggest that 2 million acres of soybeans were sprayed during 2005,” he says.

Rice expects northern and western corn rootworm will again be a problem in corn this year, as well as soybean aphids.


“Right now we're hoping that the cold, dry weather in early December may have been enough to reduce the winter survival of the southwestern corn borer, otherwise it might be a pest to watch for in corn in 2006. For soybeans, the soybean stem borer and soybean aphid are probably the pests of greatest concern,” says Phil Sloderbeck of Kansas State University.

The increased use of crop rotation has decreased the impact of the western corn rootworm, although it continues to be the biggest pest on corn in Kansas, he says. Last year in soybeans, “the warm summer seemed to restrict the soybean aphid populations, but there were some serious outbreaks of green cloverworm that caused heavy defoliation, especially on late-planted soybeans.”


The soybean aphid was the biggest problem growers dealt with in Michigan last year, according to Chris DiFonzo, Michigan State University.

DiFonzo doesn't predict any particular outbreaks for 2006 yet, “because many of the overwintering insect populations are impacted by winter conditions and we aren't through with winter yet, and other important pests such as potato leaf hopper and armyworm arrive each year from the south.”


In 2005, northern corn rootworm was a major problem for farmers in the southern half of Minnesota, and the soybean aphid was a problem statewide, according to Bruce Potter, University of Minnesota.

This year, growers should be on the lookout for similar problems. “Of the insects that overwinter in Minnesota, soybean aphid and northern corn rootworm have the greatest potential to cause problems,” Potter says. “Bean leaf beetles seem to be on the increase in the southwestern portion of the state as well.”


Last year dingy cutworm and white grub caused significant early season damage in corn, according to Wayne Bailey, University of Missouri. Later season problems in 2005 included two-spotted spider mites, corn earworm, green cloverworm and fall armyworm.

“Possible economic pest problems in Missouri for 2006 would include black cutworm, soybean aphid, Japanese beetle and white grub,” says Bailey. “Soybean aphid numbers in more northern states may result in heavy aphid infestations during June and July if several days of north winds bring migrant aphids to the state.”

Bailey also warns corn producers to be aware of corn rootworm damage in first-year corn. “Although this problem is just emerging in Missouri, I'm receiving reports from Northwest Missouri and along the Missouri-Illinois line concerning damage to first-year corn,” he says. “Time will tell whether corn rootworm are causing it.”


In Nebraska the corn rootworm complex is usually the most important corn insect pest, says Bob Wright of the University of Nebraska. “Unless the winter gets a lot colder than what we've seen, it will likely be the biggest insect pest in 2006.” Wright says western and northern corn rootworm caused economic loss on the greatest number of acres in the state in 2005.

For soybeans, growers should be on the lookout for soybean aphids. “The soybean aphid has been causing damage in some fields the last two years, especially in northeastern Nebraska,” Wright says.

“We're encouraging growers not to routinely mix an insecticide with the last glyphosate application to ‘clean up’ any insects present,” he says. “This kills off many beneficial insects that occur in soybeans, and may lead to higher pest populations later in the season.”


In 2005, infestations of European corn borer increased with an average of 25-50% of the stalks infested in North Dakota, according to Janet Knodel, North Dakota State University. “Significant corn rootworm infestations were isolated and only common in irrigated corn where continuous corn is grown,” she says.

For 2006, Knodel says soybean aphids continue to be a serious threat to soybean growers as high populations of eggs have been observed on hawthorn in overwintering areas. And populations of a major predator of the soybean aphid, the Asian lady beetle, were lower than normal.

“With high populations of soybean aphids and low populations of predators, fields will need to be monitored closely this upcoming crop season,” she says.


While there were localized outbreaks of Mexican bean beetle and bean leaf beetle in 2005, the soybean aphid was the major problem in parts of northern Ohio. Ron Hammond of The Ohio State University says 2005 was a typical year for corn with no major problems aside from “the usual suspects.”

Hammond says growers should watch for normal local problems in 2006. “If the aphid continues on a two year cycle, which we predict in Ohio, we won't have a major problem with aphids,” he says. For corn, “there's nothing major on the horizon. Sampling in soybeans for western corn rootworm variant suggest their numbers continue to be low, so we're not recommending widespread treatment for them unless sampling indicates larger numbers.”


The mild winter in South Dakota has Mike Cantangui of South Dakota State University worried because it often means more insects in the upcoming growing season. “We'll be watching for all insects because of the mild winter weather,” he says. “The best thing to do is scout the field.” Corn borer and soybean aphid, which are often controlled by colder temperatures, could be a problem in 2006.

Last year the soybean aphid was the biggest pest problem in the state, however Cantangui says there was not much corn insect pressure aside from corn rootworm because of continuous corn.


Last year Wisconsin soybean growers had trouble with the two-spotted spider mite in the southern, central and east central parts of the state, while corn growers dealt with a second generation armyworm outbreak in northwest and north central Wisconsin, according to Eileen Cullen, University of Wisconsin.

In 2006 she expects western corn rootworm in continuous corn to be a problem, based on a Wisconsin Department of Agriculture 2005 survey of adult beetles. “The variant western corn rootworm can also be expected to affect some first year corn fields in areas of southeast Wisconsin, where it was identified through yellow sticky trap scouting of soybean fields in 2005,” she says.

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