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Black Cutworms Showing Up In Iowa

Black Cutworms Showing Up In Iowa

For the past 5 days or so, ISU Extension entomologist Erin Hodgson has been getting calls and emails about significant black cutworm damage to young corn seedlings in central and southern Iowa. It's very important to begin scouting fields as corn emerges and spray insecticide if needed.

Black cutoworms are here! For the past several days, Iowa State University Extension entomologist Erin Hodgson has received lots of calls and emails about significant black cutworm damage on young corn seedlings in southern and central Iowa. "The predicted cutting dates for black cutworm larvae are pretty close to our degree-day map published on May 5th," she says. "

Mark Carlton, ISU Extension field agronomist based at Albia in southern Iowa, had a client with fields approaching 7% infestation. That density is clearly above the economic treatment threshold and was sprayed with an insecticide to protect the corn yield. Mark Licht, ISU Extension agronomist in central Iowa, has also verified black cutworm damage in young corn plants in some fields.

"It is important to keep scouting corn fields regularly, looking for cutworm larvae and signs of cutworm damage to small corn plants through the V5 stage of growth, especially after weeds or nearby grasses have been killed," says Hodgson. "Remember, if cutworm larvae are found in the field and they are smaller than ¾-inch long, then a threshold of 2% to 3% wilted or cut plants indicates an insecticide application is warranted."

Yellow corn plants are emerging in some fields, is that a problem?

A lot of the corn that emerged last week in Iowa is yellow, not coming up as green and as good looking as farmers would like to see. Some of it is a little bit stunted, not growing vigorously. "That makes sense, because we've had cold weather. We've had wet soils and not a lot of sun, especially over last weekend and late last week," says ISU Extension agronomist Roger Elmore. "But that yellow corn will grow out of it. In fact, as the sun started shining the week of May 16 to 20, that yellow color began to disappear and the plants have for the most part recovered to show their green color very quickly."

Now, at emergence and thereafter, is an excellent time to check your fields and your corn stands. Do some stand counts, and look for plant-to-plant variability. Plants of different sizes indicates they came up at different times, says Elmore. Dig up some plants, look at the roots, check seedling health and figure out what happened if you have a non-uniform stand or poor emergence. Was your seeding depth too shallow? Or, did you plant too deep? Do you have sidewall compaction in the seed furrow, restricting root growth? Sidewall compaction is caused by planting corn when soils weren't ready yet; too wet and sticky.

"Counting your stands now to get an idea on population per acre you've ended up with, and looking at stands for plant-to-plant uniformity, won't necesarilly help you this year, unless you are replanting a poor stand," notes Elmore. "But doing a stand count and evaluating uniformity of the plants will give you a better idea of what you should do in 2012. Now is the time to walk your fields."

You can tune-in to ISU Extension's weekly "Crop Minute" on ISU's ICM newsletter at This week Roger Elmore, ISU Extension corn specialist, discusses yellow corn emergence and the benefits to farmers who walk their fields gathering information to prepare for next year. Look for the weekly Crop Minute on the right side of the ICM News homepage, under More Resources. Or go directly to the May 16, 2011 interviews (mp3).

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