Abstract
Field and laboratory studies were conducted to determine the persistence of imazapic at two Texas locations. Field studies were conducted at Yoakum and Stephenville, Texas. Imazapic was applied to peanuts in 1998 at 0, 70, 140, and 210 g/ha. These rates represent 0, 1, 2, and 3X the labeled use rate in peanuts, respectively. In 1999, IR corn, conventional corn, cotton, grain sorghum and soybean were planted into the treated plots and were evaluated for carryover injury. Data collected to determine injury included stand counts, plant heights, and plant dry weights. To accurately assess carryover injury to the rotational crops, imazapic rates ranging from 2 to 35 g/ha were applied preemergence to the five rotational crops during 1999 to form standard curves. Soil samples were taken from the carryover plots throughout the year and were used in a controlled-condition bioassay to determine the amount of plant available herbicide remaining in the soil over time. A laboratory incubation study was performed on three Texas peanut-growing soils at two moisture contents. Soils were incubated for 0, 30, 60, 150, and 300 d at 30 C and then imazapic was chemically extracted and quantified using solid-phase extraction (SPE) high performance liquid chromotography (HPLC) equipped with a photodiode array detector. All field data from both locations showed no significant carryover injury to any rotational crop from any of the imazapic rates. Controlled-condition bioassay data indicated no significant reduction of fresh weight of grain sorghum or cotton from soil collected three months after treatment. These data support field data and the conclusion that up to a 3X rate of imazapic did not cause carryover injury to five rotation crops planted the following year. Results from the incubation study showed similar rates of dissipation for the three soils. However, dissipation rate increased with increasing soil moisture indicating that soil moisture is a critical factor contributing to herbicide persistence.
Matocha, Mark Andrew (2000). The persistence of imazapic in peanut (Arachis hypogaea L.) crop rotations. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -M385.