If corn growers could have a dashboard for pest pressure, it likely would be blinking red for corn rootworm (CRW) in many parts of the Midwest in 2021, suggesting soil insecticides should be a key consideration for the coming year’s pest control program.

The good news: Growers will have plenty of choices for CRW protection to accommodate a variety of equipment and agronomic needs next year.

Signs of CRW Pressure for 2021

An extensive survey of ag retailers conducted in September by AMVAC® indicated CRW damage was greater than usual in 2020, and in fact comparable to that of 2012, after which use of soil-applied insecticides was elevated for the three seasons of 2013-2015.

“As we saw through our retailer survey and also as we talked to the marketplace throughout 2020, we believe this is due to a multitude of factors,” said Nathaniel Quinn, AMVAC Marketing Manager for Corn, Soybeans and Sugar Beets.

Factors include:

A drop in commodity prices, which led growers to seek cost savings either through a reduction in below-ground traits in their hybrids, or through decreased use of soil insecticides with use of those traits, especially in corn-on-corn situations. Growers also may have used bifenthrin and did not have the desired CRW control.

Weather conditions following planting. A very open planting window was followed by a cooler and drier 4-6 weeks, which likely resulted in an extended CRW larval hatch and a higher survival rate. Also, untimely winds in certain areas – beyond even the derecho that knocked over millions of acres of crops – led to downed corn and exposed a problem that otherwise might have been overlooked.

Increase in weed escapes, especially of waterhemp and giant ragweed, which are an attractive food source and habitat for CRW beetles during the egg-laying period.

Trait resistance. “All four commercial traits available for below-ground rootworm protection have now had field-level resistance events,” said Jim Lappin, Director of SIMPAS™ Portfolio and Alliances at AMVAC. “This doesn’t mean they fail every time in the field, but it does mean there is growing concern around the traits not performing as well as they used to.” He notes this was a factor in 2012-13 as well, leading more growers to use multi-trait pyramid hybrids.

Today, many growers are choosing either multi-trait hybrids or, to save input costs, single or no CRW traits at all. For multi-trait CRW products, major selection pressure for resistant CRW can build where a CRW-resistant population exists for one of the traits in the stack, resulting in a single effective trait providing all CRW control – a very high selection pressure situation. Not using either a CRW pyramid hybrid or a soil-applied insecticide in the 2020 season has possibly contributed to higher CRW populations.

As a result, Quinn said, “what we’ve heard so far is that growers are definitely taking a hard look at their trait packages. The question is going to be: Will those traits be available in the quantities that are desired? And those growers who are in corn-on-corn situations are really taking a hard look at not only getting the right trait package, but also making sure they get the soil insecticide that is going to give them the protection they need.”

One thing is for certain: CRW pressure can build faster than many growers realize. “I always talk about rootworm numbers,” Lappin said. This is based in large part on monitoring of CRW beetles, which are expected to reach peak activity in continuous corn in parts of several key states in 2021, according to research conducted by Wyffels Hybrids®.

Lappin noted the threshold to treat for CRW is observing an average of one female CRW beetle per plant. “Assuming 32,000 plants per acre,” he said, “even if only 4% to 5% of eggs laid by female beetles survive over winter, you’re still talking about thousands of eggs per acre that can hatch the following season.” This has the potential to weaken the crop’s root system, which in 2020 was exacerbated by high winds in many areas, flattening corn that had to be tilled under or destroyed. This in turn can create opportunities for volunteer corn in rotational crops – which establishes even more potential sites for CRW beetles to lay eggs, Lappin said.

Tools for CRW Protection in 2021

“So we have a combination of all of these factors leading to CRW pressure in 2020,” said Quinn, and with an increase in commodity prices, more growers are looking to plant corn in 2021. In anticipation of CRW pressure, many are taking another look at soil insecticides. “We’ve already seen an uptick in equipment sales, for SmartBox® systems in particular,” Quinn said. “This has given us an early indication that there is increased desire to look at these types of tools.”

AMVAC’s line of soil insecticides includes its AZTEC® brands in SmartBox, bags, and high-concentration (HC) formulation in SmartCartridge® containers for the 2021 market introduction of the SIMPAS™ Closed Application System. AMVAC’s portfolio also features SmartChoice® HC; FORCE® 10G; a liquid insecticide in INDEX®; and COUNTER® 20G, which is used as an insecticide and a nematicide. “We have quite a variety of different products, both granular and liquid,” Quinn said.

There is variety as well on the equipment side, where growers have a number of application options.

Added Lappin: “We’ve always had a basic belief at AMVAC that growers like options and choice. So in addition to our existing systems, we’re introducing the SIMPAS system – and both AZTEC HC and FORCE 10G as well as COUNTER 20G will be available in SmartCartridge containers as SIMPAS applied Solutions™ (SaS).”

What makes SIMPAS and SaS unique, Lappin said, is that the system brings prescriptive capabilities. In many cases growers currently use soil insecticides as a preventive measure because there is no reliable rescue option available for CRW. SIMPAS is a great potential solution for discrete individual zones that may concern a grower. For first-year corn, growers could target higher-yielding zones, areas where they have had weed or volunteer corn control issues, or parts of the field where they think conditions, such as heavier soil types, are more conducive for CRW. “But if a grower is in a corn-on-corn situation and has had rootworm problems in the past,” Lappin said, “our recommendation is generally to use the full rate of one of our insecticides on all those areas that have had rootworm history.”

COUNTER 20G in particular has new utility when used with SIMPAS. “COUNTER has always been viewed as a really good insecticide with the added benefit of nematicide activity,” said Lappin. “But now when you think about it from a SIMPAS perspective, it makes a lot of sense to use it predominantly as a nematicide which can be applied prescriptively.” This is important in light of studies showing the presence of nematodes in as much as 70% of Midwestern soils. “But it’s really up to growers to make decisions in terms of the level of risks they’re willing to take and what their economics and budgets will allow,” Lappin said.

Increased Application Flexibility

With SIMPAS generally, growers will have many options. “Growers are looking for convenience and good return on investment,” Lappin said. “So instead of deciding to apply just a corn soil insecticide, they would have the flexibility to say: I’m going to apply a soil insecticide to rootworm, I could apply a nematicide, or I may apply a micronutrient – we also now offer ZINC™ as part of SaS. With SIMPAS, growers can go in and essentially address two or more issues with one pass at planting, depending on their unique situation.”

In 2021 AMVAC also will launch SmartBox+™, an upgrade to the current SmartBox system. “We’ve taken learnings from SIMPAS and essentially developed what we believe is a highly accurate and more foolproof metering system for application of a single granular product,” Lappin said. And like SIMPAS, SmartBox+ is an ISO-based system, meaning it will plug-and-play with existing monitors and hardware in the tractor cab.

Quinn said: “A lot of growers are finding they want to dial in the level of control they feel they need to get the best corn crop. Having the ability to select across several soil insecticides, and across different application methods, is going to be beneficial, and AMVAC offers these options. As we think about prescriptive application, SIMPAS enables the grower to deliver the best combination of traits, insecticides, and other products to provide the desired level of control needed in the effort to reach maximum yield potential. There’s more work to do, but the technologies we’re bringing forth are enabling that kind of progress.”

As growers look ahead to 2021 and how they might plan for CRW protection, Lappin said, “our role is to say: We have multiple solutions available. Help us understand what your objectives are, and we'll work with you through your retailer to provide a management tool or set of tools that fit your operation, whether that be in a Lock’N Load®, a bag, a SmartBox or SmartBox+, or now a SIMPAS system.”