Effect of irrigation and soil adjuvant on the efficacy and selectivity of pendimethalin and metazachlor in kohlrabi

Abstract

Precipitation and irrigation strongly affect herbicide management of vegetables, especial fast- growing vegetables as a kohlrabi. The objective of this study was to compare the effects of irrigation and paraffin oil-based soil adjuvant on the efficacy and selectivity of pendimethalin and metazachlor herbicides and their tank-mix combination in kohlrabi. Small plot experiments were carried out in Prague, Czech Republic during 2015 and 2016. Herbicide efficacy on Chenopodium album, Mercurialis annua, and Solanum physalifolium was significantly affected by irrigation shortly after herbicide application, but the efficacy, visual phytotoxicity, as well as both aboveground and root kohlrabi biomass were not affected by the adjuvant. Pendimethalin caused significantly greater phytotoxicity than did metazachlor. Aboveground biomass of kohlrabi plants treated with pendimethalin was about 20–50% less compared to that of plants grown on hand-weeded plots, similar as a tuber yield (tuber weight was about 30% lower). Heavy irrigation shortly after the application of pendimethalin did not affect selectivity of this herbicide treatment. On the contrary, selectivity of metazachlor was strongly affected by irrigation and natural precipitation. Weight of tubers harvested on plots treated by pendimethalin was the same or lower compared to that from plots with competition of annual weeds. The lowest yield (50% compared to hand-weeded check) was on the plots treated by herbicide mixture pendimethalin + metazachlor and irrigated shortly after the application.