Hefty Brothers target three big agronomic issues in 2024

Speaking to a crowd at the 2024 Commodity Classic, Darren and Brian Hefty of AgPhD shared their strategies for tackling three big agronomic issues in 2024: weed resistance, rootworms, and tar spot.

Managing weeds in corn, soybeans, and wheat

"Palmer amaranth, waterhemp, kochia, marestail, and ragweed… the best way to eliminate resistant weeds is using a herbicide program that employs multiple modes of action," explained Brian Hefty. 

Corn

Paying attention to herbicide application timing is important. Most corn preemergence (PRE) herbicides require rain for activation. In some areas, moisture may be limited. “In our area [South Dakota], we don’t get a lot of rainfall so we like to apply preemergence herbicides earlier or preplant incorporate (PPI). We’ve found PPI gives us better performance than an early PRE or post-plant PRE.” 

Atrazine is a herbicide that farmers have relied on for years. For those planning to use atrazine in a weed management program, the Hefty Brothers recommend a postemergence (POST) application of 0.5 pound atrazine to corn less than 12 inches tall and not rotating to any other crop than corn, soybeans, or sorghum. “Atrazine has a lot of strengths. It’s cheap, it has contact and residual activity, and works well with many POST herbicides — but we have to worry about carryover and leaching,” says Brian.

Group 15 herbicides such as acetochlor, s-metolachlor, pyrazole, and others are seedling shoot growth inhibitors that are also common corn chemistries. These are soil-applied herbicides and control weeds that have not emerged from the soil surface. “These products generally work in the top inch of the soil, so we need to keep them shallow and concentrated. They can be used in no-till and they have virtually equal grass control,” explains Darren Hefty. “There are some slight differences in broadleaf control, so selecting for weed species is important.”

Darren does have a word of caution around Group 15 use. “I’m concerned that Group 15 is getting overused. We’re using them in both corn and soybeans. If used both pre and post in corn and soybeans, sometimes twice a season. That’s up to 4 applications in two years of the same chemistry. I don’t want  weeds to become resistant to Group 15.” 

Soybeans

In soybeans, Brian urges farmers that regardless of your chosen soybean trait platform, it’s important to use PRE herbicides that are effective against the weeds you are trying to control. The Hefty Brothers recommend a PRE mix including a PPO (Group 14) like Authority or Valor, a “yellow” (Group 3) like Sonalan, Prowl, or Trifluralin, and a triazine (Group 5) like metribuzin. “I know it costs money,” says Brian. “It’s only a bushel or two of beans and you will absolutely have better control.” 

When struggling with troublesome weeds like waterhemp, Palmer amaranth, and kochia, row spacing and plant population can also impact the  ability for soybeans to compete. “If you’ve got a major weed issue, go to narrower rows and higher populations,” says Brian. “A more dense crop canopy will choke the weeds out and you won’t have to spray as many times.”

Wheat

Like soybeans, PRE herbicides are important in wheat. “If you’re going to spend two bushels of wheat to get great weed control, how much more money will that make you? It’s going to make you a lot,” says Darren.

Darren offered several suggestions for herbicides in wheat. He says Sharpen is a great burndown option for wheat fields with kochia, especially at the 2 ounce rate. Anthem Flex is safe up to 4 tiller wheat and offers the addition of the Group 15 mode of action to manage small seeded broadleaves and grasses. “It’s a herbicide family that we haven’t had access to in wheat previously,” says Darren. 

HuskieFX and WideARmatch offer broadleaf control options with multiple modes of action. “In each case, it only costs a little more to add another mode of action. We're trying to prevent resistant weeds from continuing to grow,” says Brian. “A dead weed can never become a resistant weed.” 

Corn rootworm

The biology of corn rootworm makes it look like an easy pest to manage, according to the Hefty Brothers. “Corn rootworm larvae only have a few hours after they hatch to find a corn root before they die. And they can only move about nine to 18 inches in one direction before they find the first corn root,” explains Brian. “Except, each female can lay about 500 eggs. So it doesn't take very many of those to survive and we’ve got a real problem.”

There are no rescue treatments for corn rootworm larvae so it’s important to be proactive. Depending on the type of rootworms in your fields, management may include genetic traits like SmartStax PRO with RNAi technology, in-furrow insecticides, or a combination of both in specific cases. “If you are worried about resistance, there are a lot of soil insecticide choices available,” shares Brian. “BASF has a brand new mode of action, Nurizma, so that’s exciting.” 

Tar spot

Tar spot has been making an impact and spreading across the Midwest since initially discovered in 2015. “Tar spot thrives in warm and humid weather, especially when there's prolonged wetness on the leaves,” explains Darren. “Yield losses of 30 to 50 bushels are common.”

“Tar spot survives in corn residue, so if you have had tar spot in your fields, anything you can do to break that residue down faster is going to help reduce disease the following year,” says Brian. “In-season, we recommend you spray twice with a fungicide — right before tassel and then about three weeks later.”