182 Growth of First-year Grapevines in Desiccated Rye Residues With and Without Follow-up Weed Control

Abstract

In a previous study to determine the feasibility of using herbicide desiccated cover crops for weed suppression during vineyard establishment, we found that weed suppression is excellent for about 6 to 8 weeks after desiccation in fall-planted rye. By the end of the season, however, weed growth in rye plots was similar to weedy control plots. Vine growth was reduced in rye plots compared to weed-free bare ground plots. Because of the experimental design, no follow-up weed control was performed in the rye plots and weeds eventually became well-established. So, it was impossible to determine if reduced vine growth was due to weed competition or allelopathy from the rye residues. A second study was conducted to determine the effects of follow-up weed control (with glyphosate) in fall-planted rye plots and weedfree bare ground plots. Results indicate that vine shoot number, shoot length, leaf area, and top growth dry weight was greatest in weedfree bare ground, less, but not significantly so in rye with follow-up weed control, and significantly less in rye without follow-up weed control. Root dry weight was reduced in rye with and without follow-up weed control compared to weedfree bare ground. Root dry weight was reduced 37% in rye with follow-up weed control and 63% in rye without follow-up weed control compared to weedfree bare ground. These results suggest that weed competition is not the primary cause of vine growth reduction in herbicide desiccated rye cover crops, so there is likely allelopathic effects of the rye residues on grapevines, which would limit using rye as a desiccated cover crop during vineyard establishment. However, there may be some value in using rye in established vineyards to reduce vigor.