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Insects to Watch in 2012

As we continue our Agronomy Series, our goal is to help you Be Ready for the upcoming growing season and beyond. This week we hear from Robert Streit, owner of Central Iowa Agronomics in Boone, Iowa. Bob grew up in northern Iowa and was interested in crop production, even as a 4-H member. He graduated from Iowa State University in Ag Sciences with an emphasis in pest management, plant pathology and agronomy. He was a technical services agronomist for 20 years before starting his own business in 2002. Bob has a “full-service” business, including soil testing to maintain optimum soil conditions. We asked him to share his thoughts about anticipated insect issues in 2012 and his comments follow.

All farmers are trying to improve and strive for higher net returns. During the summer, we’re busy scouting and making comments on weeds, insects and when it’s time to apply a foliar product.

Typically, I like to get into every field at least four times in the summer. However, if my customers have a problem with corn borer or other insects, I’m in there more often. I’m familiar with the history of my customers’ fields, so I don’t need to scout for every insect every time. Insects follow a cycle and over time, you recognize the two to four week time period in which they’re most likely to appear.

We’re seeing more growers go back to hybrids with fewer traits or maybe no traits. A lot of the pests we’re fighting, such as corn borer, typically are a problem two years out of five because they follow a natural cycle based on the populations of two normal, biological entities that naturally control corn borer populations. These cycles vary by state, location and year.  The more GDUs received and the lower the rainfall, the greater the corn borer threat. For example, in Iowa, corn borers run on a five-year cycle. They were bad in 1992 and 1997. 2002 and 2007 should have been bad. This year could be an up-year for corn borers. If a farmer has planted a conventional hybrid and saved money by not buying seed with a corn borer trait, he can’t forget about corn borer. He or his agronomist will be the one who will need to scout in July and perhaps put out a light trap. A light trap is an ultra violet light that attracts most flying insects. You might spend $200 on a light trap but it pinpoints which insects are flying during a particular timeframe in the spring or summer and then you know exactly when you should be looking for the moths or the eggs.

Corn borers usually have two generations per summer in Iowa. In our area, the first one will peak around June 12-15 and the second generation typically peaks around July 20-25. If you didn’t plant corn with the Bt trait, the best option is to apply a Pyrethroid insecticide aerially or with a high clearance sprayer when the moths are beginning to lay eggs and when the economic threshold is met.

You have to determine the dollar value of the corn and what it costs to treat a field. The treatment threshold dictates spraying for second generation borers when you detect feeding or find an egg mass on about 20% of the plants. If corn is worth $7 per bushel, maybe that threshold drops down to 8 to 10% of the plants, so it’s an economic evaluation of when you need to pull the trigger. The decision is based on the cost of the treatment versus the value of the crop and the level of success you can expect with a given treatment.

In regard to other insects, rootworms are gaining lots of attention right now because they’ve become resistant to some of the traits designed to control them and they are not being controlled the way they used to be. Insects are very adaptable, so multi-year control programs are likely the best answer.

Since 2003 in the Midwest, we have been dealing with soybean aphids annually or biannually. With last year’s dry weather, there were also many concerns with aphids affecting corn plants. There are very few published studies on corn aphids and the problem varies by genotype and environmental conditions – but we believe you’ll be hearing more about them in the future. Our website is currently under construction, so if you have additional questions or want to talk to me about your agronomy issues, please call 515-709-0143 or email me at: bstreit@signatureblue.com.

Editor’s Note: What insects do you deal with on your farm? What cycles of corn borer are you seeing in your area? Let us know.

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