Submitted to: Annual Cumberland Shenandoah Fruit Workers Conference
Publication Type: Proceedings
Publication Acceptance Date: November 26, 1999
Publication Date: N/A
Technical Abstract: In mature fruit orchards weeds are controlled to reduce competition, improve access to trees, and eliminate habitat of crop-damaging insects. Several experiments have demonstrated that herbicides applied to soil can adversely affect peach and apple tree growth. Herbicide toxicity can vary with soil conditions such as soil texture and percent organic matter, envir ronmental conditions such as precipitation, and past management practices such as herbicide incorporation. Diuron, simazine, and terbacil have been available for nearly thirty years and have been applied repeatedly for weed control in fruit orchards in widely different environments. These herbicides can persist in soil for more than one year in quantities sufficient to cause damage to plants. The objective of this experiment was to determine the effect of past long-term use of different herbicides, applied at different rates and combinations on survival and growth of young apple and peach trees. Combinations of diuron, simazine, and terbacil were applied every year over 15 and 16 years to the same plots. Apple and peach trees then were planted one and two years following the last herbicide application. In general, apple tree growth was not affected but peach tree growth was reduced by some herbicide treatments. The greatest reduction in peach tree growth occurred in plots previously treated with 4 kg ha**1 diuron plus 2 kg ha**1 terbacil. This herbicide combination also reduced weed growth the most over 15 years and, consequently, soil organic matter was lowest on these plots. Time of last herbicide treatment had no effect on apple or peach tree growth. The results indicate that reduced fruit tree growth was a consequence of re- duced organic matter rather than residual toxic effects of the herbicides.