A Season-Long Approach to Corn Rootworm Management

Flattened and lodged corn plants were strewn across the Midwest in 2020 following various wind events, including a devastating derecho in Iowa. Growers who had intense management programs, including a strong corn rootworm (CRW) offense, realized more successful outcomes than those who did not.

“My plants stayed upright during last year’s wind event,” reports Kyle Van Bogaert, a third-generation corn and soybean grower in Belmont, Wisconsin. “I use crop rotation, insecticide treatments and a seed trait package to combat corn rootworm.”

That multipronged strategy could soon become the standard. Higher-than-normal adult CRW beetle activity in 2020 points to potentially increased pressure in 2021. That’s bad news for corn growers — especially those with corn-on-corn acres — who lose more than $1 billion to CRW damage every year. CRW larvae feed on roots from Colorado to New York, reducing water and nutrient uptake and causing lodging in extreme situations. Adult beetles feed on tassels and clip corn silks, further impacting yield.

But for growers like Van Bogaert who implement multipronged, proactive CRW management plans, fields can see strengthened crops and better profit opportunities. Committing to the multiyear approach needed for management strategies to work can be challenging, but the reduction of CRW root feeding represents a tantalizing reward.

Interpreting Natural Signals

Environmental signals from the previous year will allow growers to plan for potential pressure in subsequent seasons. Wet springs, for example, can kill CRW larvae in the ground, due to saturated soils. On the other hand, dry conditions in May and June create ideal environments for populations to thrive.

With most insect populations, predicting pressure is difficult. The life cycle of CRW, however, offers opportunities to plan control measures. Depending on monitored population levels, growers can begin incorporating insecticide treatments and seed trait stacks into their ongoing planning.

“Through better understanding of the CRW life cycle, growers can anticipate potential CRW populations before they become a problem,” says Meade McDonald, Syngenta product marketing lead for insecticides. “This includes scouting for larval feeding and damage as well as monitoring adult populations.”

Growers can dig corn roots in June to check for larval feeding and damage that can provide clues to coming adult beetle numbers. In July, monitoring populations of adult CRW beetles offers an indication of CRW larval pressure for the following year, according to McDonald. Scouting reports that showed high CRW beetle populations last July are driving expectations of heavy CRW pressure this year.

Working the Bugs Out

A key strategy for CRW management is crop rotation — not planting corn in the same field two years in a row. “It’s the easiest tactic growers can add to the mix of solutions for managing this pest,” says Andy Heggenstaller, head of agronomy for Syngenta Seeds, U.S. “But for some growers, crop rotation isn’t economically feasible, so they have to rely more on alternate solutions.”

The next step for growers to consider is using seed trait stacks — such as Agrisure Duracade^® trait stacks — that act against CRW larvae. However, while trait stacks provide ample protection against CRW feeding, growers should consider a multipronged approach in high-pressure fields.

“Especially in corn-on-corn fields, growers may need to deploy multiple management tactics to protect roots, stands and harvestability,” McDonald says. “Growers in these situations should consider a soil-applied insecticide application on top of their trait stack.”

Syngenta offers two Force^® brand insecticides to control CRW larvae. The first — Force 6.5G — is a higher-loading granular insecticide than the former Force 3G formulation. Packaged in a 20% lighter bag, Force 6.5G has a more concentrated formulation that allows growers to cover 175% more acres per bag.

Those features helped Van Bogaert handle a planting time crunch in spring 2020. “One bag of Force 6.5G per box covered more than 300 acres of corn at once. We could fill up once and plant all day,” he says. “We have a lot of corn-on-corn growers in our area, and Force 6.5G made a real difference in our fields during the season and at harvest. We will definitely be using it again in 2021.”

The second Force brand is Force Evo insecticide, a liquid formulation with excellent starter fertilizer compatibility. It’s an ideal choice for growers who are injecting starter fertilizer at planting. They can apply Force Evo through a proprietary closed application system developed by Syngenta, with on-farm service and support provided by Direct Contact, Inc.

Paired correctly with a trait stack, Force insecticides can add an average of 10 bushels per acre in yield in high-pressure fields, according to more than 500 Syngenta trials between 2007 and 2017.*

Growers can also use Warrior II with Zeon Technology^® foliar insecticide to control adult CRW beetles during summer months. If growers see adult beetles in July, Warrior II with Zeon Technology can minimize tassel feeding and silk clipping, which can dramatically impact yields.

Planning for 2022

When planning for next season, the first product a grower should consider to defend their fields against CRW damage is a Syngenta Bt corn seed trait stack.

Syngenta Bt corn seed trait stacks contain modes of action that target and kill CRW larvae. Agrisure Duracade is the primary Syngenta trait stack for CRW management and contains two proteins that are specifically toxic to CRW larvae when they feed on corn plant roots.

“By combining two separate traits into a plant, Agrisure Duracade delays adaptation to a single technology,” says Todd McRoberts, agronomy manager for NK Seeds. “This preserves yield potential and helps prevent problems years down the road.”

Still, a multiyear approach is necessary for effective CRW management. In heavy-pressure situations, rotating traits every few years can provide another defense.

“Especially for growers who don’t rotate crops, rotating traits may become necessary to prevent entrenched adaptation in CRW populations,” McRoberts says. “Even some growers who do rotate crops may need this tactic in high-pressure geographies.”

Agrisure^® 3122 E-Z Refuge^® is an excellent alternative trait stack for corn growers using the Syngenta genetic base. It contains a different mode of action plus the Herculex^® rootworm trait.

How long growers can use trait stacks depends on local pressure; but if trait rotation is needed, growers should stick to a schedule. Even in lower-pressure seasons, rotating traits can help preserve trait durability.

There is no catch-all treatment for CRW, and planning for this pest spans years instead of months. But by finding the right mix of agronomic practices, seed traits and insecticides, growers can fight back against even the heaviest CRW infestations.