The growing body of science for corn growers

“We are in a complex herbicide and insect-tolerant landscape now,” says Drew Thompson of PRIDE Seeds. Photo: File

When your parents got their start, farming was relatively uncomplicated. The farm season was pretty much divided into plowing, planting, cultivation and harvest. Weed management meant getting on top of quackgrass, Canada thistle and mustard, and soil organic matter was out-of-sight, out-of-mind.

And transgenics was a word no one had ever heard.

Some things make us nostalgic for the past. But who would want to give up the science and technology that every corn grower brings to the field today?

It’s breathtaking how science, agri-business and primary producers have altered the landscape. Weed management requires a blend of herbicides, while different insects and diseases pose constant challenges and new mechanical technologies fall under the heading of “precision agriculture,” with very steep learning curves.

It has many people asking, “What’s necessary in farming today?”

Since 1996, when Bt corn hybrids and Roundup Ready technology arrived in farmers’ fields, researchers and plant breeders have been on a treadmill, anticipating emerging weed and pest challenges while attempting to find the most cost-effective solutions. But that’s a lot easier said than done. The first transgenic innovations addressed broad-spectrum issues like European corn borer (ECB) and crop resistance to glyphosate, and both paved the way for more specific transgenic applications.

As researchers and breeders enhanced tools such as molecular markers and haploid technology, the door opened on advanced breeding and accelerated the development process for corn hybrids (and soybean varieties). At the same time, resistance became more of an issue. Initially, Bt technology worked well for growers with ECB: dealing with corn rootworm and western bean cutworm wasn’t as successful due to resistance development.
As beneficial as new traits are to higher yields, resistance to herbicides, pests and diseases is only a matter of time.photo: File

It’s the degree of difficulty in managing different weeds, insects and diseases that are challenging researchers, breeders, the seed trade and growers: there are no simple solutions. Tank mixing is the norm in weed management, and various insect pests and disease pathogens have developed resistance to chemical means. Although they may be occasional problems for farmers, they’re hurting crop quality as much as the quantity when they do show up.

What’s changed

According to Drew Thompson, the constant evolution of resistance complicates the process of bringing new hybrids to market, even though trait development has changed very little in the past 25 years outside of changes in the kinds of tools that breeders use. Instead, the problem comes after the hybrids are introduced.

“The challenge around rapidly developing resistance is not caused by the breeding techniques or the traits, but rather the use of the traits,” says Thomp­son, market development agronomist for PRIDE Seeds. “We as an industry still need to focus on best management practices (BMPs) when it comes to stewardship and integrated pest management (IPM). We are in a complex herbicide and insect-tolerant trait landscape now, and the market faces driving change with evolving insect, disease, weed pressure and resistance.”

Consider the rate at which new hybrids are released for commercial availability. The best hybrids might last four or five years but on average, their peak usage fades after three. Although the goal of any breeding program is to ensure the best products are available to the grower, insects, diseases and weeds are evolving, and possibly accelerating in their resistance capabilities.

That means trait providers and seed companies must work harder to provide product choices that protect against pests like western bean cutworm, northern corn leaf blight or gibberella ear rot. Despite the use of double haploid technology or winter nurseries in the southern hemisphere, resistance continues to confound growers and the grain trade. The pace of technology often can’t keep up with natural evolution.

But are there cases where the trait is introduced proactively, i.e. before the weed species or pest issue is present? Thompson is not aware of any instances where resistance or any other problem has developed from a trait used in the absence of a pest. He cites SmartStax technology that’s often grown on rotated ground, where there’s little requirement for corn rootworm protection.

“Crop rotation is key in this and the traits are there as insurance, to protect the genetics should there be an issue with a pest,” says Thompson.

The other key to trait development is how it has an impact on yield, which is still the primary measure of success in agriculture. It’s possible for one breeder to develop an experimental hybrid that can grow to 12 feet. But with poor standability affecting its yield potential, the chances of it reaching farmers is extremely low. Yield remains the primary focus, both in terms of performance in the field and the traits that are developed.

“Unfortunately, there is the belief that a new silver bullet will come along for each problem that arises,” says Thomp­son. “However, the reliance on these new technologies has put tremendous selection pressure on the pests in question and the results have been more and newer resistance cases.”

Simplify the approach

The “silver bullet” mindset continues to hinder growers in their annual drive to push yields. As soon as a grower starts using a technology trait, it’s only a matter of time before resistance develops. Growers may delay the development of resistance — through rotation of crops, technologies and chemical products — but they cannot prevent its development.

“One of our issues is that as soon as we have a trait that works well, it’s an easy solution for farmers and they overuse it,” says Peter Johnson, an agronomist with RealAgriculture, echoing Thompson’s assessment. “They rely on it because it’s the easy answer and even if the more progressive farmers don’t completely rely on that, there are too many who do.”

An example that Johnson cites is the development of glyphosate-resistant Canada fleabane, which occurred in fields near Windsor Airport. To limit birds feeding on corn or cereals, farmers grew continuous soybeans, taking full advantage of Roundup Ready technology. Growing only soybeans with glyphosate resistance trait and using only glyphosate for weed control created the perfect environment for resistance to develop. It spread from Windsor-Essex in 2010 to the Quebec border by 2015.

“We have to learn from the errors we’ve made in the past,” says Johnson, noting the use of Viptera technology in corn to combat western bean cutworm. “We’re already at the stage where entomologists are saying, ‘Yes it works, but if all you use is Vip technology, it won’t work for long.’”

Johnson remembers when glyphosate became the popular herbicide option and industry representatives stated there will never be resistance to glyphosate. But it did happen. Any overuse of technology will yield the same result, likely even with genetic editing tools such as RNAi or CRISPR.

Thompson acknowledges the undeniable potential that newer genetic editing tools can offer researchers and breeders. News of their impact has generated considerable discussion and praise but if they’re not used in conjunction with other pest management practices, resistance is inevitable.

“We need to keep in mind that when using RNAi or even CRISPR technology, we are impacting a very specific site or action within the targeted pest,” says Thompson. “If we’re limited to this narrow focus, a single mutation is all it will take to develop resistance.”

That’s the reason why Thompson and other seed company representatives, agronomists and advisors urge more attention on BMPs and IPM stewardship strategies. Nothing compares to “boots on the ground” and farmers also have a role to play in that approach. Robust monitoring means as soon as growers and industry reps see something in a field, they have to be ready to act quickly.

Weeds still the focus

Asked if weed resistance has lessened the focus on research and investment on pest management, Thompson dismisses the notion that fungicide and insecticide development is outpacing that of herbicides. Regardless of weather conditions — which affect pressure from insects and diseases — every field and every crop faces weed challenges.

“I think at the moment, there’s more focus on herbicides,” says Thompson, adding that the majority of resistance problems develop in the U.S., so there’s an opportunity here to avoid the circumstances that lead to the problem. “If the problem does arise, we have universities and the agriculture ministry to help with control strategies.”

He refers to some of the innovations currently in the research pipeline, including stacked trait products and new tolerance traits for Group 27 (HPPD inhibitors) and Group 14 (PPO inhibitors), both of which have developed resistance in the U.S. The stacked-trait herbicide addresses tolerances to Groups 1, 4, 9, 10, 14 and 27. The timing reflects the urgency presented by herbicide resistance: growers in the parts of the U.S. are dealing with common waterhemp that’s resistant to six modes of action with Group 15 joining Groups 2, 4, 9, 14, and 27.

Resistance in six groups seems like a lot to overcome, but Johnson cites rigid ryegrass, a weed species found around the globe but is a special problem to growers in Australia. In 1994, it was determined that the weed was resistant to nine groups of active ingredients: by 2004, that number jumped to 11. In spite of that range of resistant factors, the weed species has not forced growers to stop growing crops; it’s caused them to adjust and find ways around it.

“It’s the same with multiple modes of action,” says Johnson. “We need to use all of the tools in the toolbox. Even when we’ve gone to multiple modes of action, we’re relying on the herbicides and asking them to do the heavy lifting, but we have to find other ways.”