EFFECTS OF ANNUAL REPEAT APPLICATIONS OF SIMAZINE, DIURON, TERBACIL, AND DICHLOBENIL IN A MATURE APPLE ORCHARD

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Abstract
Annual tree growth and yields of mature Bancroft apple trees was higher when simazine (2-chloro-4,6 bis(ethylamino)-s-triazine), terbacil (3-tert-butyl-5-chloro-6-methyluracil) and dichlobenil (2-6-dichlorobenzonitrile) were applied annually for 6 yr to control weeds compared to trees that were regularly mowed. Fruit maturity was slightly delayed with herbicide treatment. While acceptable weed control was afforded by all herbicide treatments, repeat applications of terbacil annually gave the highest level of weed control. There was an indication after a number of years of simazine use that common vetch (Vicia cracca L.) would become a major problem. In these trials all herbicides accumulated in the 0- to 15-cm surface layer of the soil profile. Continued use of specific herbicides would have some effect on both potassium and magnesium in foliage collected in mid-July. Nitrogen levels in the leaves were not increased significantly during the study.