Submitted to: Pennsylvania Fruit News
Publication Type: Proceedings
Publication Acceptance Date: March 30, 2001
Publication Date: N/A
Technical Abstract: Weeds reduce pollination and fruit set, harbor pests, and compete with fruit trees for nutrients and water. In apples, combinations of these weed- mediated effects in fruit-bearing orchards can reduce yield by as much as 50%. In tree rows, weeds are often managed with herbicides and in this experiment one herbicide or a mixture of herbicides was applied repeatedly for several years (i.e. an extreme case scenario) to determine long term effects on herbicide residues, the weed community and soil microflora, and growth of newly-planted apple and peach trees. Diuron, simazine, and terbacil were applied each spring to a sandy loam soil in Kearneysville, WV for 15 consecutive years, beginning in 1981, either alone or in combinations at rates of 0, 2, and 4 lb/acre. One key finding of this study was that the herbicides did not build up in soil over the 15 years of application. Another key finding was that terbacil applications of 2 and 4 lb/acre provided weed control throughout most years, but few weeds almost certainly reduced soil organic matter that may have reduced soil microflora and growth of newly-planted peach trees. Growth of apple trees was not reduced by terbacil, possibly because apple trees grow slower (nearly 35% less) than peach. A third finding was that repeated applications of simazine and diuron for 15 years did not reduce growth of apple or peach trees that were planted one year after the final herbicide application. In summary, the results indicate that diuron, simazine, and terbacil do persist as long as one year after application but they do not build up in the soil after repeated application under our environmental conditions. Good weed control was obtained, but peach tree growth was reduced on soils treated for 15 consecutive years with terbacil.