COVER CROPS in South African Vineyards

CHAPTER 5 WEED CONTROL

Over the entire duration of the trial, triticale consistently suppressed winter- growing weeds to less than 80% of the control.Total suppression was achieved in six out of twelve years, which reduced the need for chemical weed control during the grapevine-growing season, from November onwards. Triticale also effectively suppressed weeds in the years in which it was sown as part of a rotation with grazing vetch. Grazing vetch was effective when grown in rotation with triticale, but when grown as a continuous monoculture, it did not result in a statistically significant reduction of the weed stand. The mixture of rye and faba bean suppressed winter-growing weeds effectively in some years, and not at all in others. However, the mixture did reduce the average weed stand compared to a control with no cover crop. In addition to the annual cover crops, perennial dwarf fescue was also evaluated. It was sown every five years, and slashed regularly. Full-surface chemical weed control was not applied to the fescue. Fescue reduced the weed stand by 68% compared to the control. However, as previously discussed, perennial cover crops tend to be gradually infiltrated and replaced by weeds, and therefore did not offer long-term sustainable None of the cover crops produced sufficient dry matter to act as a mulch and suppress summer-growing weeds in the absence of chemical weed control. For most of the cover-crop treatments, full-surface chemical weed control was started just before bud-break, at the end of August, and continued until just before harvest, at the end of January. In addition, full-surface chemical weed control starting at the end of November, when the grapevine berries reached pea size, was tested for triticale and grazing-vetch continuous monocultures. The dry-matter production of summer-growing weeds in the triticale and grazing-vetch continuous monocultures compared to the control is illus- trated in Figure 5.23. Triticale was associated with effective suppression of summer-growing weeds in nearly all years, regardless of when in the season chemical weed control was started. weed control in this trial. Summer-growing weeds

100