RESIDUES OF PICLORAM IN SOIL AND THEIR EFFECTS ON CROPS

Abstract

When 4.48 kg/ha (2 ppm) of picloram (4-amino-3,5,6-trichloropicolinic acid) as the potassium salt (Tordon 22K) was incorporated with soil to a depth of 15 cm; 1.86, 1.78, 1.32, 0.70, 0.28, 0.12 and 0.02 ppm were detected at 18, 63, 145, 337, 504, 690 and 843 days after application, respectively. Growth of carrots (Daucus carota L. cv. Nates), parsnips (Pastinaca sativa L. cv. Hollow crown), potatoes (Solanum tubersum L.), table beets (Beta vulgaris L. cv. Detroit dark red), and rutabagas (napobrassica, Mill. cv. Laurentian) was inhibited when these crops were planted in the greenhouse in soil containing 1.32 ppm picloram which was collected 145 days after application. The year after application when soil sampled about 1 mo before planting contained 0.70 ppm picloram, the growth of sweet corn (Zea mays L.) and oats (Avena sativa L.) was reduced by about 20%, whereas beans (Phaseolus vulgaris L.), parsnips and Swiss chard (Beta vulgaris var. cicla L.) did not grow. Picloram residue 1,055 days after application was 2.5 ppb determined by a bioassay using bean as the indicator plant.