Although the feeding season for secondary soil insects has come to a close, the aftermath of these early-season corn pests is apparent in corn fields across the country.
Pockets of heavy infestations of white grubs and wireworms were reported in southern Illinois, southern Indiana, Nebraska and Missouri, making replanting of cornfields necessary in some cases.
With limited or no rescue treatments available for secondary soil insects, having a damage-prevention strategy is a key management tool in protecting crops from these pests. Many entomologists agree now is the time to begin evaluating damage and population levels in order to formulate a risk-management strategy for 2004.
Their observations indicate utilizing seed-applied insecticides at planting can help protect crops from the damaging effects of these early-season insects and limit the need for scouting as well as potential costly insecticide treatments.
Wayne Bailey, state Extension entomologist for Missouri, reports a steady increase of wireworms and white grubs over the past five years in that state.
“While infestation levels of the two pests are not as high this year as last, we still saw a high level,” explains Bailey. “We're concerned that the population of these and other secondary insects such as seed corn beetles and flea beetles are steadily building, yet we have limited ‘rescue’ treatments available.
“Overall, we've found that seed treatments and seed-applied insecticides helped protect seed from many of these insects.
Essentially, they offer a security blanket for the seed early in the season and give producers time to get in the fields and scout for the insects,” Bailey adds.
Entomologist John Obermeyer of the Purdue University Extension Service reports damage from infestations of secondary soil insects was very low in Indiana this year, even though there were pockets of high infestation in southern Indiana. He believes the growing utilization of seed-applied insecticides by producers to prevent damage from secondary soil insects is working.
“Since producers were able to plant early this year, we were very concerned, but we saw surprisingly few problems,” Obermeyer says.
“Typically, early plantings are more susceptible to secondary soil insects because the seed sits in the soil for an extended period of time.”
He attributes low infestations to less overwintering by pests this past year, plus the use of risk management tools by producers.
“Many producers were prepared for insects to thrive under such conditions and utilized the available systemic protection of seed-applied insecticides when planting this past spring,” Obermeyer says.
Gustafson officials, manufacturers of a variety of seed-applied insecticides, saw an increase in use of the products in 2003. They say products help improve plant stands and crop performance by protecting germinating seeds from the damage and stand loss caused by wireworms, seed corn maggots and imported fire ants. The label on some seed-applied insecticides also states they reduce feeding by white grubs during emergence and seedling stages and protect seedlings from flea beetles through the first true leaf stage.
Gustafson's Gaucho insecticide has been available on Pioneer brand corn hybrids since 2001. Paula Davis, senior marketing manager for insect- and disease-resistant traits at Pioneer Hi-Bred International, Inc., says company research shows significant wireworm presence this season throughout southern Illinois, southern Indiana, Nebraska and Missouri. But she attributes the lack of any widespread heavy damage from the pest, particularly in Illinois and Indiana, to the significant increase in the use of seed-applied insecticide in these areas.
Davis also indicated Pioneer will likely offer additional seed-applied insecticide treatment options for 2004 planting.
Kevin Steffey, Extension entomologist at the University of Illinois, reports secondary soil insects were at five- and six-year lows in much, but not all, of Illinois this past spring.
“Populations of secondary soil insects such as wireworms and white grubs have been less of a threat to Illinois producers this year, but due to the unpredictable nature of these insects, the challenge is determining which fields to treat when planting in 2004.”
Evaluating the damage from pests this year and preparing for next year can help prevent a repeat of yield loss. According to the University of Missouri-Columbia, fall samplings of grubs and wireworms in crop fields generally are good, early indicators of pest numbers the next season.
Pest management guidelines established by the University of Missouri-Columbia state that treatment of wireworms is justified if the field has a chronic history of wireworm problems or if the number of wireworms collected from bait stations exceed the economic threshold (average of one or more per trap). Treatment for white grubs is justified if grub numbers average one or more larvae per square foot.
Many producers, however, routinely include a seed-applied insecticide in their pest management programs, particularly in fields with a history of mild infestations.
“For many, it's a low-cost form of insurance,” Bailey says.
Thus, the experts agree that now is the time of year to evaluate the cumulative effects of feeding wireworms, white grubs, seed corn maggots, flea beetles and other secondary soil insects. Producers should compile and evaluate this information, exploring all their pest management options, including seed-applied insecticides.