Comparative Responses of Three Apple Rootstocks to Soil-Incorporated Simazine1

EM VII, EM IX AND MM 106 apple rootstocks were grown under greenhouse conditions in cans containing soil-incorporated simazine at concentrations of 0–6 ppm. In general, except for severity of foliar injury, the rootstocks responded similarly to simazine. Least foliar injury occurred on MM 106 rootstocks and the most injury on EM VII. Fresh weight increases indicated, however, that this difference may be of no practical significance. Simazine levels of 1 and 2 ppm improved above-ground growth and increased total leaf nitrogen (N) but suppressed root growth. At concentrations of 3 ppm and higher, simazine suppressed both above-ground growth and root growth but markedly increased leaf N.