Selective Action of Terbacil on Peppermint and Ivyleaf Morningglory

Abstract

The herbicide 3-tert-butyl-5-chloro-6-methyluracil (terbacil) applied in an isoparaffinic oil caused, in susceptible ivyleaf morningglory (Ipomoea hederacea(L.) Jacq.), rapid and nearly complete inhibition of photosynthesis, from which it never recovered. Photosynthesis in peppermint (Mentha peperitaL.), a tolerant species, was decreased only temporarily. Terbacil was readily absorbed by leaves of both species; however, there was little or no movement out of the treated peppermint leaves. Terbacil was translocated out of the treated leaves of ivyleaf morningglory to the untreated leaves and shoot apex. It was metabolized in both species but at a higher rate in peppermint. Therefore, it appears that foliarly-applied terbacil may be bound in peppermint leaves and this, together with the higher rate of metabolism, may contribute to the tolerance of peppermint. Terbacil was readily taken up and translocated to the foliage of both species when applied to the roots. Again, it was metabolized in both plants but at a higher rate in peppermint. However, the rate of metabolism alone did not appear to be sufficient to account for peppermint tolerance to root-applied terbacil.