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An eye on the bugs

Jeff Caldwell 05/31/2011 @ 3:09pm Multimedia Editor for Agriculture.com and Successful Farming magazine.

Though there are still a lot of corn and soybean acres left to plant in parts of the country, the seed that's in the ground is starting to take off. Now, before you know it, your attention will have to turn to pest protection and insect scouting in your fields.

But, 2011 is a whole new ballgame -- each bushel of corn and beans is worth about twice what it was just a couple of years ago. That could change your approach to pest protection.

"Remember that, with high-priced corn, the damage threshold for treatment is lower," says Iowa State University (ISU) Extension field agronomist Jim Fawcett.

Here are a few pests common to the Corn Belt in the first stages of the growing season and what their economic treatment thresholds are today and how they have changed because of higher grain prices.

Already discovered at near record levels in Indiana earlier this month, the most dangerous corn pest in Fawcett's area of eastern Iowa right now is Black Cutworms. The economic threshold for this bug is when the average larvae in the field is around 3/4 inch long. If you have 2% or 3% damage (in the form of wilting or cutting), you have a strong case to spray an insecticide, says ISU Extension Entomologist Jon Tollefson.

"If cutworms are longer, treatment should be applied if 5 percent of the plants are cut. If the field has a poor plant population, (20,000 or less) these thresholds should be lowered," he says. "With the black cutworm, the infestations are sporadic and uncertain. Don’t forget to check the rest of the fields if you find infestations in the 'sentinel' fields."

Corn Earworm

A pest that can hit both corn and soybeans, Corn Earworm can start showing up as early as June in the Midwest after migrating northward from the South. In Wisconsin, for example, there are typically 2 generations each year, according to a report from University of Wiscosin-Madison Extension and Research. The largae are typically white in color with a black head. And, they're cannibalistic, meaning only one is found per ear.

"Pheromone trap catches of 5 to 10 moths per night for three consecutive nights indicate that moths are likely laying enough eggs to warrant treatment of fields, if corn is in the vulnerable stage between the brush stage and silk browning," according to a university report. "Blacklight traps can also be used to monitor populations, though they collect fewer corn earworms. Consider treatment when blacklight traps catch 3 to 5 moths per night for three consecutive nights if nearby fields are in the vulnerable stage."

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