Farm Horizons, June 2016

Managing crop pests

By Dave Schwartz
Certified crop advisor, Gold Country Seed

Each year, it seems we get just the right weather conditions for a pest, insect, or disease, and the population of that pest explodes.

Last year, cooler, damp weather in July triggered white mold infection in soybeans. Hot, dry summers are ideal for spider mites that feed on many types of plants.

So, what can we expect for the 2016 growing season?

It all depends on weather. We have had a nearly ideal spring for planting, with very little soil compaction, so I would expect to see less phytopthora root rot in soybeans.

It seems like we have experienced less strong southerly winds this spring, so potato leafhoppers, which blow in from southern states, are less likely to be a problem in the first cutting of alfalfa.

Some weather forecasts are predicting a warm, dry August, so this may reduce the potential for diseases, but create a more favorable environment for spider mites in soybeans.

Scouting fields on a regular basis is a good management practice. This gives crop producers time to identify and monitor pests before they exceed economic thresholds.

Over the years, I have been called out on many crop pest problems, and oftentimes, the damage had already been done, so it was too late to justify any type of rescue treatment. Economic thresholds are based on sound research, so growers know how much crop damage can occur before action needs to be taken.

A couple of diseases to watch for on continuous corn acres are Goss’s Wilt and Northern Leaf Blight. Goss’s Wilt was first identified in the state five to 10 years ago in western Minnesota in a corn field under irrigation. Since then, it has spread across the state all the way into northwest Minnesota. It does not survive well in corn/soybean rotations, so is nearly always found in continuous corn.

I’ve noticed more northern leaf blight the past two years. The fungus produces cigar-shaped lesions on lower leaves of plants. It’s a good idea to rotate out of corn when either of these diseases is identified.

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