As weed scientists continue to document glyphosate resistance in weeds such as horseweed (marestail) and waterhemp, some no-tillers are developing their own preventive measures.
While John Hart, a no-tiller near Cannelburg, Ind., has not noticed glyphosate resistance in his fields, he’s not taking a chance on it becoming a problem. “By going back and forth with a different corn program and with different types of chemicals, we can change things enough that resistance hopefully won’t be a problem for us,” he says.
With no-tilled soybeans, Hart uses a burndown tankmix of Gramoxone Max and Boundary herbicides. This mix allows him to guard against glyphosate resistance while tackling the prevalence of winter annuals in no-till soybean fields.
A number of no-tillers and researchers have noticed an increase in winter annuals such as horseweed, chickweed and henbit that has accompanied the growth of no-till acres and reduced use of residual herbicides, especially in Roundup Ready soybeans. While controlling these weeds with a glyphosate burndown makes no-tilling easier, weeds are developing higher tolerance and even resistance in some areas of the country.
“We’re seeing what we think might be greater tolerance to glyphosate in some weeds,” says Jim Martin, a weed scientist at the University of Kentucky. “The lack of residual herbicides can make winter annuals tougher to control.”
By using a residual herbicide, Hart prevents weed regrowth before spring planting. The herbicide mix keeps his no-till soybean ground clean in early spring, which helps the ground dry faster.