PREEMERGENCE HERBICIDE OPTIONS IN GRAIN SORGHUM. J. Robinson and B. Bean: Texas AgriLife Research, Bushland, Texas

ABSTRACT

Studies were initiated in 2009, 2010, and 2011 at the Texas AgriLife Research Station near Amarillo, TX to investigate weed efficacy and crop tolerance with preemergence (PRE) herbicide treatments in grain sorghum.  Both old and recently labeled products were compared.  These were: Atrazine (4 lbs/gal), Bicep II Magnum (atrazine @ 3.1 lbs/gal + metolachlor @2.4 lbs/gal), Sharpen (saflufenacil @ 2.85 lbs/gal),Verdict (saflufenacil @ .57 lbs/gal + dimethenamid-P @ 5.0 lbs/gal),  MiloPro (propazine @ 4 lb/gal), Lumax (metolachlor @2.68 lb/gal+ atrazine @ 1.0 lb/gal+ mesotrione @ 0.268 lb/gal), and Warrant (acetochlor @ 3 lb/gal). Atrazine and MiloPro were applied at .75, 1.0, and 1.25 lb ai/A. Sharpen was applied at .356, .71, .89, 1.34, and 1.78 oz ai/A. Verdict rates were 17.4 and 34.8 oz ai/A. Bicep II Magnum applications were made with 2.2 and 2.9 lb ai/A. Lumax was applied at 2.47 lb ai/A. Warrant was applied at 1.13 lb ai/A. This is a multiyear study, with some treatments having data for only one year. Treatments were applied before sorghum emergence. All applications were made using a tractor mounted CO2 sprayer using 30 inch nozzles spacing with 10 gal/A spray rate. Sorghum was planted on 30 inch raised beds, with irrigation being applied in-furrow as needed. Data was collected for yield, crop injury, and weed control. Weed control and crop injury were visually rated up to 8 weeks after application. Weeds rated were Pigweed (Amaranthus palmeri) and Velvetleaf (Abutilon theophrasti).

In 2009 injury was observed 12 days after application (DAA) with Lumax (80%), the high rate of Bicep II Magnum (30%), and the three highest rates of Sharpen (20%, 30%, and 53%). By 54 DAA injury had decreased to 35% for Lumax, and 2% and 7% for the two highest rates of Sharpen. Pigweed control at 54 DAA was 100% for both rates of Bicep II Magnum, Lumax, and the highest rate of Sharpen. Sharpen @ .89 and 1.34 oz ai/A had >90% control. Lumax and the three highest rates of Sharpen had 100% control of velvetleaf at 54 DAA, with both rates of Bicep II Magnum having 95% or better control. All rates of Atrazine and MiloPro had control rates <70% for pigweed and velvetleaf. All yields did not significantly differ, with the exception of Atrazine @ .75 and 1.0 lb ai/A which was significantly lower because of weed competition.

In 2010 injury was only observed with the high rate of Verdict (30% 34 DAA, and 3% 49 DAA). Atrazine and MiloPro @ 1.0 and 1.25 lb ai/A, Verdict @ .356 and .71 oz ai/A, and both rates of Bicep II Magnum had 90% or greater control of pigweed 49 DAA. Sharpen @ .356 oz ai/A, both rates of Verdict, and Bicep II Magnum @ 2.9 lb ai/A were the only treatments to achieve greater than 90% control of velvetleaf. While Sharpen @ .56 and .71 oz ai/A performed well on velvetleaf (88% and 93% 49 DAA), control of pigweed was less than satisfactory (17% and 58% 49 DAA). Sharpen @ .356 and .71 oz ai/A yielded significantly lower than all other treatments.

In 2011 no injury was observed in any treatment. Bicep II Magnum at both rates were the only treatments to achieve 100% control of pigweed 43 DAA. Lumax, Atrazine @1.0 and 1.25 lb ai/A, and MiloPro @ 1.25 lb ai/A had 95% or better control of pigweed 43 DAA. Sharpen @ .356 and .71 oz ai/A has provided inadequate control (<25%) of pigweed at 43 DAA. Verdict @ 17.4 oz ai/A had 72% control while the lower rate of 10.4 oz ai/A controlled only 40% of pigweed. Warrant has also struggled managing just 63% control at 43 DAA. Velvetleaf pressure has been insufficient to rate. Yield will be taken at maturity.