The activity of emulsifiable concentrate (EC) formulation of pendimethalin was studied using a petri dish bioassay based on root response of corn, oat, sorghum, and sugar beet grown in soil. Furthermore, the oat bioassay was used to determine the activity of EC, microencapsulated (ME), and water-dispersible granule (WDG) formulations of pendimethalin. Also, field persistence in soil of these pendimethalin formulations was studied with petri dish and pot bioassays, based on root response of oat and sugar beet. All bioassays indicated that activity of all pendimethalin formulations was increased with increasing herbicide concentration. In silty clay loam soil, oat and sugar beet exhibited the highest sensitivity to EC-pendimethalin concentrations and corn the lowest; sorghum showed intermediate herbicide sensitivity. EC of pendimethalin showed the highest activity on oat and ME pendimethalin the lowest; WDG-pendimethalin showed similar activity to that of ME pendimethalin. Field persistence was significantly increased with increasing rate of application, but it was slightly increased by the ME formulation.
Nomenclature: Pendimethalin; corn, Zea mays L. ‘Pioneer Costanza’; oat, Avena sativa L. ‘Kassandra’; sorghum, Sorghum bicolor L. ‘5515’; sugar beet, Beta vulgaris L. ‘Bianca’.
Additional index words: Microencapsulated formulation, pendimethalin.
Abbreviations: DAT, days after treatment; EC, emulsifiable concentrate; GI10, days after treatment for 10% oat root growth inhibition; GR50, herbicide concentration required to give 50% inhibition of plant indicator root growth; ME, microencapsulated; PRE, preemergence; WDG, water-dispersible granule.
