Injury and Yield Response of Selected Crops to Imazaquin and Norflurazon Residues

Field studies were conducted in 1987, 1988, and 1989 to evaluate the effects of freshly applied residual levels (simulated residue carryover) of imazaquin and norflurazon on the growth and yield of corn, cotton, grain sorghum, rice, and wheat. Studies ware conducted on five soils, and concentrations of herbicides were determined at crop planting. Crop injury ratings were recorded 4 wk after emergence, and yields were measured at the end of each growing season. In simulated residue carryover studies, corn and grain sorghum injury occurred and yields were reduced when norflurazon concentrations were 450 ng g-1soil or greater. Rice yields were reduced at norflurazon concentrations of 710 ng g-1. Corn, cotton, and wheat heights and yields were reduced when imazaquin concentrations were 13 ng g-1, 13 ng g-1, and 45 ng g-1soil, respectively for crops. Comparisons between simulated carryover and actual carryover were made for corn and cotton grown in imazaquin treated fields as well as for corn grown in a norflurazon treated field.

Rotational Crop Response to Repeated Applications of Norflurazon

A long-term study was established to determine the effects of rate, application method, and repeated applications of norflurazon on soil persistence and plant injury for sorghum, corn, and wheat. Preplant incorporated (PPI) and preemergence (PE) applications of norflurazon at 1.1 (1X) and 2.2 kg ai/ha (2X) initially were applied in 1981. Subplots were retreated in 1982 and 1983. Rotational crops were planted each year from 1982 to 1987. Evaluations taken in 1982 (14 months after initial treatment) showed slight injury to wheat, sorghum, and corn from 1X applications and significant injury from 2X applications. Evaluations 1 to 3 yr after final application indicated that repeated applications, even at the 1X rate, increased norflurazon residues and rotational crop injury. At both 1X and 2X rates, PPI treatments increased norflurazon persistence compared to PE applications.

Determination of Norflurazon Residues in Mixed Crop Matrices

A method for determining norflurazon residues in mixed crop matrices is described. The method includes methanol Soxhlet extraction, hexane wash, addition of 10% saline, methylene chloride extraction, concentration, preparative thin layer chromatography of 10% sample aliquot, and resuspension of sample zone for gas-liquid chromatographic analysis. The lower level of electron capture detection is 0.01 ppm. Recoveries for 0.08 ppm spiked samples of cottonseed; soybean seed and foliage; peanut seed plus hulls and foliage,; orange and tangerine; lemon; apple and peach; and soil are generally greater than 80%.