Grain growers updated on herbicides at conference

PAINTER, Va. — Corn growers on Virginia’s Eastern Shore are facing severe shortages of glyphosate (Roundup) and glufosinate (Liberty) and significant price increases.
That and other production challenges were discussed by Extension specialists during Corn Specialist Day at the Eastern Shore Agricultural Research and Extension Center on March 31.
Dr. Vijay Singh, Extension specialist and assistant professor of weed science at Virginia Tech, assured the group that “we have excellent pre- and post-burndown herbicide options for corn. Soybeans are more challenging.”
Supply chain issues for paraquat, 2,4-D, dicamba, Prowl and atrazine have occurred because growers are accumulating them.
He said growers have only 50 to 75 percent of the herbicide they need for the season; the rest is on order or not available.
He said this year corn growers should apply herbicides in early spring burndown, residue plus possible additional burndown at planting and post-planting.”
Dr. Singh mentioned the three major weed species in the area: Palmer amaranth, horseweed (“mare’s tail”) and common ragweed. Horseweed can be controlled without herbicide, he said, with a cover crop or with just one-half inch of soil over the seed in tilled systems.
Weeds need to be treated when they are small, Singh stressed.
“If you miss [the three- to four-inch stage] you won’t be able to control after three, four days after that stage. Big weeds can grow four to five inches every day. He recommended atrazine at preplant.
“Higher rates may be required depending on the product you use, especially if you are using mixes that have glyphosate in them,” he said, also noting that muddy or hard water reduces glyphosate effectiveness because the product binds with the soil in the water.
He reminded growers that the adjuvant AMS must be added to glyphosate mixtures to assure herbicide effectiveness, even at a lower application rate.
He recommended 10 to 15 gallons per acre for small weeds and 15 to 20 gallons for larger weeds. He also advised applying herbicides at midday on sunny days and at least 30 to 40 minutes before any rainfall because, if the plants are stressed, the herbicide will not be translocated effectively within the plant.
“Only apply when the plant is healthy so the translocation system is effective,” he said.
When purchasing alternative burndown herbicides, Singh encouraged growers to check the labels for “GT” in the product name which indicates they contain glyphosate.
Singh urged growers who mix herbicides to adhere to rates on the label and assure the mixture contains products that will control both broadleaf weeds and grasses. Glufosinate excels at controlling broadleaf weeds but is only 80 to 90 percent effective against grasses, he said. Certain chemicals have planting time restrictions, some as long as one to two months, so care must be taken in selecting herbicides, he stressed.
“This year you will see a lot of benefits of cover crops because of the shortage of herbicides,” he said. “Many cover crops, especially cereal rye, leave residue on your field that does not decompose early.”
He said a good residue may mean that only one or two post-emergence applications would be adequate to control weeds.
“The longer the residue stays, the more suppression of the weeds,” Singh added. “Cereal rye helps control common chickweed, common ragweed, Palmer amaranth and horseweed.”
Many growers spray the cereal rye cover crop then use a roller-crimper to lay it down for a mulching effect.
But Singh and his colleagues found that using the roller-crimper before spraying results in 20-25 percent better weed control because laying down the crop first helps assure the herbicide is more evenly distributed along the length of the plant.
He advised farmers who are growing both corn and soybeans to use whatever glyphosate they have for the soybeans because there are more options for corn.