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Make educated, founded decisions when it comes to fungicides and insecticides

By Staff | Mar 23, 2018

Soybean aphids are starting to show some resistance to the insecticide pyrethroid. Brett McArtor, regional agronomist with the Iowa Soybean Association suggests scouting fields to ensure they need sprayed before spraying and going back later to check for resistance or to see if you have the control you were wanting.



DES MOINES – The definition of integrated pest management (IPM), according to Iowa State University, is an approach to controlling a specific pest in a specific setting that makes use of current pest information, regular monitoring and record keeping to determine if and when action against the pest is needed.

Brett McArtor, regional agronomist with the Iowa Soybean Association, recommends using IPM when it comes to making fungicide and insecticide application decisions.

“Integrated pest management is critical in aspect to think about when making any chemical application,” he said. “Think about multiple modes of strategies. Consider your seed, previous tillage operations as pest management tools. Scout your fields. Know the history of your fields; have I had a problem with this in the past? Is this something I should be looking for in the future?”

McArtor said there are several factors to consider when making those fungicide and insecticide application decisions including economic, environmental and potential resistance issues.

“The biggest thing, to me, is economics,” he said. “Will this application pay for itself?”

Producers should also consider the environment.

“There’s a lot of pests out there that are beneficial and an insecticide application would wipe out those beneficial pests,” he said.

Soybean aphids, one of the top soybean damage-causing pests, has been showing some resistance to the pyrethroid insecticide that has been used to help control the pest.

“It’s not necessarily a huge problem in Iowa yet, but this past year the Red River Valley of northern Minnesota had a very large issue with resistant aphid populations,” he said. “That doesn’t mean it can’t head south and become a problem here in Iowa also.”

To help combat the pest, McArtor said to first consider an aphid-resistant variety of soybeans.

“They won’t actually kill the insect, but it will reduce its ability to reproduce,” he said. “This isn’t a great option yet, because there’s just not a lot of varieties with those genes available.”

Scouting is also a very critical technique.

“Once you have aphids, you need to scout to know exactly the threshold that you need to have before you spray,” he said. “Evaluating your insecticide application after a couple of days will help you know if you have an insecticide resistant issue, or if you have control of the aphid population.”

As far as fungicide resistance, there has been some recent findings of Frogeye Leaf Spot having a resistance to the fungicide, strobilurin.

With this recent discovery, many experts, including McArtor, are concerned about those fungicide applications being done as preventative applications, versus spraying when a disease is discovered.

“One question I get a lot from producers is, they have already bought it. Should they just spray it?” he said. “There’s nothing saying you can’t take delivery of the product, put it in your chemical shed and spray it next year.”

There are other factors to consider before a fungicide application.

“When deciding to spray or not, first consider your seed disease package,” he said. “Your varieties can make a huge difference on how your fungicide will react and work. Look at the disease package, make sure you scout and see what’s going on.”

Another factor to consider when making the decision to apply fungicides is the weather.

“Weather patterns are huge when considering fungicide applications,” McArtor said. “They are conducive to fungicide growth. Make sure you are out there scouting. If you have had the weather problems, and you’re not seeing an issue, why bother spraying?”

If the decision has been made to spray, either a fungicide or an insecticide, McArtor suggested using multiple modes of action, as well as considering the timing of the application.

“Where I want to highlight, the timing of the products, is to get the best bang for your buck,” he said. “That’s very critical.”

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