The Long-Term Effect of Picloram and Its Residue on Grain Production and Weed Control

The persistence of picloram (4-amino-3,5,6-trichloropicolinic acid) was measured each spring over an 8-yr period following repeated annual applications at rates ranging from 0.020 to 0.070 kg/ha. Picloram residue levels were proportional to rate of application but averaged approximately 45% of the original levels when measured 12 months following application and declined to 10% 24 months after application ceased. Control of wild buckwheat (Polygonum convolvulusL.) was good with major population declines over the test period. Crop tolerance and yields were not affected at rates of 0.035 kg/ha or less.