Weeds emerging on prevented planting (PPL) acres should be managed just as rigorously as weeds on planted acres. If not, a messy and expensive reckoning waits ahead in the following season.
Weed scientists offer that outlook after seeing the aftermath of PPL neglect over the last couple of years.
Producers across the Midsouth and Midwest also became keenly aware of this in 2020 after the spring of 2019 brought heavy rainfall, historic flooding and record PPL claims.
In 2019, agricultural producers reported they were unable to plant crops on nearly 20 million acres, according to USDA figures. It was the highest PPL total in a single year since USDA began tracking prevented planting in 2007. And the 2019 total ran 17.5 million acres higher than what growers reported in the previous year.
Of those acres, more than 73% were in 12 Midwestern states. Significant PPL acres also turned up in Louisiana, Mississippi, Tennessee and Arkansas.
Here are reports from three states that took big hits.
Ohio: More Fall Applications In The Future
Mark Loux, Ohio State University weed specialist, says problem weeds emerging this season on 2019 PPL acres include dandelion and Canada thistle.
“We had a good portion of that in northwest Ohio. Those weeds are normally controlled by a combination of herbicides and crop canopy,” Loux points out. “But if you let them go, they develop a bigger root system, and they’re tougher to control.”
Many producers in the area also shifted away from making fall herbicide applications “due to the effectiveness of Xtend, Liberty and Enlist technologies,” Loux adds. “Now, we have to get back to making those applications.”
Loux suggests farmers adopt two goals for unplanted acres:
First, prevent annual weeds from going to seed and entering the soil seedbank. Anything that goes to seed will have to be dealt with in the future.
Second, treat any perennial weeds in the appropriate growth stage to reduce their population.
“The problem with the dandelions and the thistle (on PPL acres) is that they require a more specific type of approach,” Loux adds. “If you’re going to wait until early July to make that first PPL herbicide application, the thistle has already gone to seed in certain situations. You have to spray earlier.”
But as Loux points out, few residual herbicides carry labels for PPL applications.
“The only possibilities we could find that have labels for true non-crop areas are Pendimethalin, Valor and Surflan,” Loux specifies.
Arkansas: Rice Pays A Price
In Arkansas, 1.3 million acres went idle due to rains and/or flooding in 2019, according to USDA. For northeast Arkansas crop consultant Eddy Cates, the most problematic in 2020 were PPL acres that went into rice.
Cates, of Cates Agritech, Inc., in Marion, says that in many cases farmers simply didn’t have time to manage the idled rice acres in 2019.
“Wet weather continued during the summer, so farmers weren’t able to disk or work up a lot of those fields, and in many cases it was late August before they could come in with a herbicide on PPL acres,” Cates says. “By then, barnyardgrass and pigweed had headed out, and pressure was very heavy.”
Eventually, farmers disked under many of those fields, which buried viable weed seed. In the following rice crop in 2020, those weed seeds germinated and emerged.
“The weed pressure was terrible, and it was very costly,” Cates adds.
Breaking The Seal
Weeds popped through wherever the protective seal was broken, Cates explains. That included where preemergence herbicides wore off and when deep cracks appeared in clay soils and weeds shot up through the openings.
“It was ongoing,” Cates adds. “The seed bank was so dense, it would generate incredible pressure. This has taught us that managing prevent-plant acres is just as important as managing a crop.”
The problem has been worse in row rice fields following PPL acres, according to Cates. About 70% of the rice Cates scouts this year is row rice, a technique that northeast Arkansas farmers are still learning about. With the system, farmers regularly furrow-irrigate rice but don’t establish the classic paddy flood. In part, the flood suppresses new weed emergence in conventinal rice production.
“With row rice, not having a continuous flood across the field is a problem for weed management,” Cates explains. “Where you have exposure, it’s a haven for weeds to emerge.”
In other instances in 2020, weeds emerged after farmers pulled furrows on rice fields. Pulling those furrows, in turn, breaks the seal.
“This season, we’re having plenty of problems getting enough herbicide back on that furrow to keep it clean,” says Cates. “If it’s a clean field to begin with, it’s not a problem. But if the field has heavy grass pressure, then you definitely have a problem.”
Cates advises farmers to work up PPL ground as soon as possible, and then use some combination of Valor and either Dual, Warrant or Prowl to help maintain low weed pressure and minimize weed seeds going into the seed bank. “Then go back with a Roundup application.”
Italian ryegrass was a problem in PPL fields, too, Cates notes, and it has gained a good deal of herbicide resistance.
“When the ryegrass comes up in October or November, apply Roundup plus SelectMax or Zidua. In the following spring, you should be able to make a burndown application. Taking care of all the drainage problems in the field is important, too.”
Indiana: Adding Non-Chemical Tools
In Indiana, about 1 million acres funneled into PPL in 2019 – approximately 9% of the state’s 11 million acres of corn and soybeans, notes Bill Johnson, Purdue University weed scientist.
“But in parts of the state in 2019, PPL ran as high as 20%. In those areas, it did not quit raining until the end of June,” Johnson says. “Farmers were able to do some weed control work on at least some PPL acres but were unable to do anything on the bulk of that land. Ragweed, marestail and waterhemp went to seed in many of those fields, and this year those farmers have a battle on their hands.”
Objectives for PPL Acres
The primary objective for a PPL acre is the same as for a planted acre, according to Johnson.
“Decrease the weed seed bank, so you can take pressure off the front end of the next season,” Johnson emphasizes. “Always use full rates of residual herbicides, not the ‘planned-failure’ rates.
“Also, think outside the box. Don’t rely solely on chemicals. That’s not going to be a sustainable, long-term solution.”
Cover crops, tillage and mowing can help. Johnson says producers will likely have to till more than once on PPL acres since flushes of weeds will emerge after a rain. Also, it’s important to uproot the large weeds.
Mow fields infested with large weeds, especially tough-to-control pests like horseweed (marestail), giant ragweed and the pigweeds, Johnson says. Spray the regrowth with broadleaf herbicides like 2,4-D and dicamba to finish them off. Make sure the weeds are actively growing before spraying herbicides.
With cover crops, benefits extend beyond weed suppression, according to Eileen Kladivko, professor of agronomy at Purdue University. “When you have something growing in the field, the roots help pull soil particles together and improve pore space and water penetration.
“They also add organic matter which helps glue soil particles together. A cover crop gets the soil in better shape for the next time you plant a cash crop.”