Photo: ©Debra L. Ferguson
To manage resistant weeds, these Midwest and Midsouth crop consultants attack on multiple fronts with communication, cultural practices, crop rotation and residual herbicides.
Plus, they blend in big doses of proactivity.
Here’s a baker’s dozen of their tips to consider:
#1. Coffee with your consultant.
Sitting down and discussing the upcoming season can reveal misunderstandings and knowledge gaps that can be plugged, say David Hydrick who, with his son Tyler, operates Hydrick’s Crop Consulting in Jonesboro, Arkansas.
“For the last couple of months, we’ve been meeting with all our growers and discussing plans, whether it be seed selection or what you want to put down at planting. Invariably, you’ll uncover all kinds of issues,” says David Hydrick. It’s better to straighten out misconceptions – especially about weed management strategies – ahead of equipment moving into the field.
#2. Smart crop rotation.
In the Midsouth, rotations with rice or corn expand the arsenal of herbicides that can be used on resistant weeds versus a cotton/soybean rotation, where herbicide options are more limited, according to the Hydricks.
Also, be sure you match herbicide technology with the weeds in your field.
“If you have glyphosate-resistant Palmer amaranth, plant an Xtend cotton, or Enlist cotton or LibertyLink cotton, or a combination thereof,” Hydrick stresses.
#3. Use full rates – and tank mix when necessary.
Premixes don’t always contain full rates of their respective herbicides, says Dorian Gatchell, an independent agronomist who owns Minnesota Agricultural Services, in southwest Minnesota.
“We’re getting away from premixes and going to full, standard rates of soil-residual herbicides,” he explains. “Our attitude is that if we let a weed come out of the ground, no matter how big or small it is, we’re already in rescue mode. And that’s not where these premixes have been taking us.”
#4. Reduce tillage.
“When you till a field, you’re killing the weeds that are growing, but you’re planting 10 times as many and making a good seedbed for them,” Gatchell contends. “If you can reduce tillage passes, you eliminate some weed germination.”
When reducing tillage, producers find that emerging weeds are often more uniform in size, Gatchell points out. “So, when they apply a herbicide, they’re attacking one weed size versus multiple sizes, which makes herbicide efficacy that much better.”
#5. Travel back in time – well, sort of.
It would be nice to go back to the 1990s and right all the wrongs of resistance management. The next best thing is to use preemergence herbicides early and often.
“Back in the days of glyphosate-resistant crops, we were told we didn’t need to use preemergence herbicides,” Hydrick says. “We just used glyphosate. That’s how we got into this situation.”
#6. Overlap residuals on a tight schedule.
The Hydricks recommend a bi-weekly schedule for residual applications, or every 14 to 17 days.
“If you wait until 21 days, you’ve waited too long,” David Hydrick says.
Why the urgency?
“With Palmer pigweed resistant to glyphosate, PPOs and ALS herbicides in soybeans, it’s difficult to kill pigweed with anything postemergence,” he says.
Gatchell’s producers put residuals down preemergence, then continue to apply them to keep weeds from emerging until canopy.
“Our goal is to use residuals to in such a way to never have to make a postemergence application on weeds,” Gatchell specifies.
Unfavorable weather and disease can stymie this approach, according to Gatchell. “With iron deficiency chlorosis, which is prevalent in this area, soybeans will turn yellow and may actually die, so we have open canopy in areas. When you have an open canopy – plus rain and a little sunshine — weeds emerge late.
“Our biggest challenge is to come up with some sort of soil-residual herbicide program that will allow a quick-enough canopy that we can rely on cultural practices (such as narrow rows) for our postemergence weed control. Part of the problem is that there is nothing new on the market in terms of herbicides.”
#7. Keep weeds guessing.
“Using at least two effective modes of action is paramount,” Gatchell says. “But we have to use full rates. Then we have to switch those products. I do not like using the same chemistry on corn and soybeans.”
“If you can get four modes of action in during the season, you’ll be a lot better off,” David Hydrick adds.
#8. Narrow-rows and cover crops.
Narrow-rows will help soybeans get to canopy quicker and throw shade on weed growth. Gatchell says producers who engage in cultural weed control practices like narrow rows, strip-till and cover crops are having more success with weed control than producers with conventionally-managed practices. “I can’t say enough on how important cultural practices are for weed control,” he adds.
In northeast Arkansas, the Hydricks’ growers plant cover crops, partly to prevent resistant weed development.
“Those cover crops include wheat, oats and turnips,” David Hydrick says. “We even drill our turnrows.”
#9. Wide rows and a hooded sprayer work, too.
A preemergence application on drilled 7.5-inch soybeans that have canopied may never hit the ground, Hydrick points out. “When soybeans are 1 to 1.5 feet tall, pigweeds start sticking up through the canopy.”
The Hydrick’s prefer wider rows “because we can run a hooded sprayer with Gramoxone and take out the pigweeds,” he says. “You can do the same thing in cotton. There may be some crop injury, but it’s a lot cheaper than chopping out drilled soybeans.”
#10. Turnrow management — defending against the outside world.
“We’re trying to push our farmers to do a good job of weed control on turnrows, ditch banks and roadsides, too,” Tyler Hydrick says.
Southern crop advisors sometimes talk about how resistant Italian ryegrass became established in their farmers’ fields after building on turnrows. The grass probably didn’t gain resistance on the turnrows. Instead, resistance was selected in ditches along county roads where crews periodically sprayed and put resistance into play.
#11. Extremism — zero tolerance, take no prisoners.
“If there is a pigweed out there in the field, or a coffeebean, red rice or whatever, we’re going to get it,” David Hydrick stresses. “We have a lot of guys who try to be that good.”
Pigweed populations have been reduced significantly where farmers commit to barring plants from going to seed, according to “zero tolerance” studies by the University of Arkansas. This is a holistic approach that includes equipment sanitation practices and taking a “no prisoners” attitude toward escapes.
Here’s a hard number from one such study – the time required to hand chop escapes in one 50-acre cotton field was reduced from 110 hours to 5 hours after one year of zero tolerance.
#12. Good coverage — don’t scrimp on carrier.
Good coverage is much easier when weeds are small, Tyler Hydrick says. That includes increasing per-acre gallonage, and busy farmers don’t like the prospects of more refilling.
“It’s something that growers don’t always like to do because it doesn’t match up with the tank capacity,” he admits. “If they have a 1,000-gallon tank, at 10 gallons per acre they can go across 100 acres. If they go up to 15 gallons per acre, they can only spray 75 acres.”
#13. Remember next year — control pigweeds post-harvest.
“In corn, we’ll have pigweed coming up after harvest,” David Hydrick says. “We’ll use a non-selective herbicide and add metribuzin, Valor or Boundary depending on what weeds we’re going after.”