Grain sorghum producers may soon have a much needed, new option for weed control. Research in Kansas has documented the effectiveness and crop safety of Lumax herbicide on grain sorghum, said Dave Regehr, Kansas State University Research and Extension weed scientist.

"Lumax is a herbicide used in field corn since 2002, but is not yet labeled for use in grain sorghum," Regehr said. "We have 16 site- years of research testing Lumax on grain sorghum at full and double rates. The data show excellent sorghum tolerance for Lumax applied 10 to 20 days ahead of planting."

Based on these data and the need for the product, the Kansas Department of Agriculture is applying to the U.S. Environmental Protection Agency for a section 18 emergency exemption permitting the use of Lumax in grain sorghum, Regehr said. Until this emergency exemption is approved by the EPA, however, Lumax must not be applied to grain sorghum.

Lumax is a premix containing the active ingredients in Callisto and Dual Magnum, along with a low rate of atrazine. It is manufactured by Syngenta Crop Protection.

There are several potential benefits of Lumax for use on grain sorghum if the emergency exemption is approved, Regehr said.

"The primary basis for the emergency status is the need to improve control of triazine- and ALS-resistant Palmer amaranth and waterhemp, two of the most common species of pigweed in Kansas," he explained.
ALS-resistant weeds are weeds resistant to acetolactate synthase inhibitor herbicides.

Another benefit would be better preemerge control of large-seeded broadleaf weeds, especially velvetleaf, kochia, sunflower, and morningglory.

"Many grain sorghum growers now apply postemerge herbicides to control these weeds," Regehr said. "Based on K-State research and grower experience in field corn, preemerge control of these weeds with Lumax would be improved to the point that postemerge treatments would be reduced or eliminated."

This herbicide option would also help reduce the amount of atrazine applied in grain sorghum. Atrazine rates are lower in Lumax than in the preemerge herbicides presently being used. This would be especially helpful in atrazine mitigation areas, such as the Solomon River watershed, which provides water for the city of Beloit.

If the emergency exemption is approved, Regehr said, growers can expect the following directions for the use of Lumax on grain sorghum:

• Application rate: 2.5 quarts per acre.
• Application method: 7 to 14 days preplant; no mechanical incorporation.
• Crop restrictions: Concep-treated grain sorghum seed only; no forage sorghums or sudangrasses. Concep is a treatment that makes seed safe against metolachlor (Dual) and acetachlor (Lasso) herbicides. When a herbicide that contains either metolachlor or acetachlor is applied ahead of planting grain sorghum, the seed must be Concep-treated or emergence will be reduced.
• Soil restrictions: Do not use on coarse-textured soils.
• Tank mixtures with herbicides such as atrazine, glyphosate, paraquat, and 2,4-D are allowed for burndown.
• End users and/or growers will agree to accept full responsibility for failure to perform and for crop damage from use of Lumax on grain sorghum.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus in Manhattan.