December 2, 2020

Rooting Out Corn Rootworm: Top Tips to Protect Your Crop

20140723_maxyield_424 (1024x681)If it seems like corn rootworm (CRW) has become more of a challenge in your fields, you’re not alone.

“CRW has become a bigger issue in MaxYield’s east area in the past four or five years,” said Greg Sweeney, MaxYield Cooperative’s seed team leader. “We’ve also seen a lot more CRW pressure in the central area in the last year.”

The situation reflects not just resistance issues, but increasing CRW pressure from western corn rootworm and northern corn rootworm, Sweeney added. “When the CRW trait first came out 10 years ago, we saw a whole set of roots chewed off in our Answer Plot at Whittemore. Was there resistance then? No. Was there a lot of CRW pressure? Yes.”

The corn rootworm complex is one of the most widespread, problematic corn insect pests, causing at least $1 billion in lost annual revenue for growers across the Corn Belt, according to
the Genuity® website. Root feeding and pruning by CRW larvae can reduce yield by limiting uptake of water and nutrients, which can prevent corn plants from reaching their full genetic potential. In addition, severe feeding can increase lodging, which makes the corn harvest more difficult.

Yield losses from CRW can range from 20 to 100 bushels per acre, said Sweeney, who has seen consistent losses of 50 bushels per acre in areas of strong CRW pressure. “If you don’t manage this pest this year, you’ll have a significantly higher risk of crop failure next year,” he added.

Understanding the enemy
To control CRW, it helps to understand the life cycle of the pest. Western and northern corn rootworms have only one generation per year. Eggs of both species are deposited in the soil by female beetles from mid-summer until autumn. The eggs overwinter and begin hatching from late May to early June in most areas of the Midwest, although this is changing.

“We’re seeing larger hatches, and we’re still finding CRW larvae through August and even into September,” Sweeney said. “In the last two years, some beetle populations in our trade territory have been increasing around the time of the Clay County Fair.”

Why? The pest has adapted to the region’s cropping systems. Also, soil-applied insecticide fizzles out about the same time in mid-season that the CRW trait gets diluted and delivers lower
doses to pests feeding later in the season, Sweeney said. “For nearly 60 years, we’ve essentially been selecting for late-hatching larvae,” he added.

It’s not time to push the panic button, however. CRW can be managed through crop scouting and varying modes of action to lower the risk of insecticide resistance, Sweeney noted.

MaxYield Seed Team Leader Greg Sweeney says, "We're seeing larger hatches...and CRW larve through August and Septebmer.

MaxYield Seed Team Leader Greg Sweeney says, “We’re seeing larger hatches…and CRW larve through August and Septebmer.

Taking control
The first and easiest step to manage CRW is to rotate to a non-host crop like soybeans. With careful management, however, CRW can also be curbed in corn-on-corn acres. “I’ve seen fields with 20 or more years of corn-on-corn production that successfully control CRW,” Sweeney said.

It’s also important to select the right traits to control CRW. Sweeney recommends Genuity® SmartStax®, which offers two different modes of action to manage rootworms. You may also need to use a soil-applied insecticide at planting, Sweeney added.

Not only is it important to address CRW challenges to limit damage to the corn crop, but it’s vital to reduce the number of egg-laying females and suppress the number of larvae that could emerge in the next growing season, Sweeney said.

“The main thing growers aren’t doing is spraying for beetles. While the beetles normally come out around silking time, they are emerging later as they’ve evolved through the years.”

Crop scouting from the early tassel stage through early September is also useful to monitor adult CRW beetle counts and assess whether insecticide applications are warranted. “Once we start seeing beetles, we wait a week before we line up the aerial applicator,” said Sweeney, who noted that MaxYield has sprayed for beetles after corn tasseling. “Why? Because male beetles hatch approximately one week earlier than the females.”

Aerial application can be a good investment that will benefit you in the future, Sweeney noted. “You’re spending those dollars to protect next year’s crop.”

Take these factors into consideration as you plan for your 2015 crop, added Sweeney, who encourages you to contact your local MaxYield agronomist to develop a CRW management strategy for your acres. “The good news is that CRW is extremely manageable, if you follow the right steps.”

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