REDWOOD Falls, Minn. – Weed escapes may start showing up, so now is a good time to scout your fields.
“Waterhemp is probably the major one that is on everybody’s mind. There’s such a wide timeline for when it is going to be germinating, emerging from the soil,” said Steven Regan, DEKALB/Asgrow technical agronomist from Redwood Falls, Minn. “We maybe didn’t get full control of kochia, giant ragweed, or some of our other troublesome, prolific seed producers.”
Safely mowing along field edges can keep giant ragweed and common ragweed from setting seed. Scouting for waterhemp, lambsquarter and kochia – and then using a corn hook or gloves to remove weeds in soybeans is an old, but effective means of reducing the weed seed bank.
Palmer amaranth was detected in 2019 in Lincoln County (southwest Minnesota) and Houston County (southeast Minnesota). The invasive weed is considered present in those two counties after being introduced, but now absent in Dodge, Hennepin, Jackson, Cottonwood, Redwood, Lyon, Yellow Medicine, Todd, Douglas, Red Lake, Pennington, Marshall and Roseau counties.
Following Minnesota’s many prevented planting acres in 2019, growers may be seeing some troublesome weeds they haven’t seen for a while.
Regan encourages growers to take the time needed to evaluate seed traits, as well as efficacy of their herbicide program in 2020. Depending on rainfall and environmental conditions, residual chemicals may or may not be working. If some 30-inch row spacings didn’t entirely close, that could result in some weed germination and emergence.
Growers also need to determine if weed control was adequate with the number of herbicide applications that were made, the modes of action used, and effectiveness of adjuvants or surfactants. Did time run out or wind make it impossible to make a herbicide pass?
Staying alert to weed growth can becoming fatiguing in August and September, but growers can’t give up. Especially in soybeans, are there weeds escapes? Are there good herbicide options for pre-emerge control in corn in 2021?
“When we’re running into these late-season issues, it’s important to look at what our crop rotation is going to be – whether it’s corn or wheat or sugarbeets that are coming up and making that plan on how we’re going to mitigate it in the next season,” Regan said.
“Also if we do suspect that we have a resistant population, we want to get that identified and documented so that we know what modes of action are still effective against the weeds we are targeting – whether that is Giant ragweed or any other species,” he continued.
Some weeds are destroyed through tillage, but not every grower uses tillage, so perennials can be an issue to deal with primarily in the spring but sometimes in the fall, he added. Canada thistle, bindweed, yellow nutsedge, quack grass and dandelions have tap roots or rhizomes that put out roots at intervals. These troublesome weeds survive year-to-year because of their vegetative structure and ability to store energy. A September/October systemic herbicide could work well if the weed is pulling energy back into its roots.
If growers harvest soybeans early this year, there could be a window open for that fall herbicide pass this year – if a frost isn’t expected for at least two weeks. That timeframe, Regan said, would give the plant enough time to take up and metabolize the herbicide.
“Maybe hitting a perennial weed twice a year is where we are slowly going to gain back control,” he added. “It’s a bigger issue in a no-till environment.”
Whatever the grower does to observe, document, plan for control and carry out that plan helps increase yield potential, as well as farmland quality in the future.
“We don’t want to make another deposit into the weed seed bank,” Regan said. “We want to continue to control and eliminate weeds.”