Some fall-applied residuals may injure following year’s rice crop

Italian ryegrass

Populations of glyphosate-resistant Italian ryegrass, such as this photographed in Washington County in 2010, have been found in at least 31 Mississippi counties – photo courtesy Mississippi State University

Although fall-applied residual herbicides are recommended to control glyphosate-resistant Italian ryegrass, some can be detrimental to the following year’s rice crop, according to recently published research.

Involved in the project were Ben Lawrence, a Mississippi State University graduate student; Dr. Jason Bond, MSU weed scientist; Henry Edwards, MSU graduate student; and Dr. Bobby Golden, MSU Extension agronomist.

The researchers looked at the effects of labeled rates and twice the labeled rates of clomazone (Command), pyroxasulfone (Zidua), S-metolachlor (Dual Magnum) and trifluralin (Treflan) in the fall before rice seeding. Of those, only clomazone is labeled for use on rice.

They then planted rice in the spring and measured seedling density and height 14 days after emergence. All but the clomazone treatment negatively affected seedling density and height. The three others caused injury to rice 28-36 percent greater than clomazone 14 days after emergence.

The plots also were taken to yield. Applications at the 2X rates of pyroxasulfone, S-metachlor and trifluralin reduced rough rice yields compared to clomazone.

Based on their trials, the researchers say, “Of the herbicides evaluated, only clomazone should be utilized as a fall-applied residual herbicide treatment targeting GR Italian ryegrass before seeding rice.”

Their work, “Effects of Fall-Applied Residual Herbicides on Rice Growth and Yield,” appeared in the Weed Science Society of America’s “Weed Technology.”