Movement of Alachlor and Metribuzin from Controlled Release Formulations in a Sandy Soil

Field and column experiments were conducted to determine the effect of controlled release formulations on weed control and leaching of alachlor and metribuzin on a Plainfield sand. Controlled release formulations including two starch encapsulations of both herbicides and a microencapsulation of alachlor were compared to emulsifiable concentrate and dry flowable formulations of alachlor and metribuzin, respectively. Herbicide movement was measured in laboratory columns and in the field throughout two growing seasons to a soil depth of 91 cm. Soybean injury and weed control were monitored. No significant differences in herbicide movement between starch-encapsulated and emulsifiable concentrate formulations were observed in either field or column experiments. Microencapsulation resulted in the greatest retention of alachlor in the soil surface in field and columns. Compared to the dry flowable formulation, starch encapsulation did not affect metribuzin distribution in the field but reduced leaching in columns. Controlled release formulations did not result in significant differences in weed control and soybean injury compared to the emulsifiable concentrate alachlor and dry flowable metribuzin formulations. Starch encapsulations had a limited effect on alachlor and metribuzin movement. Degradation appeared to be the primary mechanism for herbicide dissipation while leaching losses were minor.