COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

Winter-growing weeds, including those that are herbicide resistant or difficult to control chemically, tend to germinate in winter in winter-rainfall areas such as the Coastal region. Cover crops can play an important role in suppressing the germination and growth of these weeds. Summer-growing weeds tolerate a wide range of conditions and can

increase rapidly if not controlled. Cover crops that produce sufficient biomass to create an effective mulch can help suppress the germination of summer-growing weeds, thereby supplementing chemical control measures. If weeds can be totally suppressed, or reduced to insignificant numbers in November, no further chemical control is needed during the remainder of the grapevine-growing season. The weed population will differ in species composition and abundance at different sites. Weed populations are affected by factors such as climate, soil type, soil cultivation, competition, and chemical control. The continuous use of a control method will change the weed species

IF WEEDS CAN BE TOTALLY SUPPRESSED, OR REDUCED TO INSIGNIFICANT

NUMBERS IN NOVEMBER, NO FURTHER

CHEMICAL CONTROL IS NEEDED DURING THE REMAINDER OF THE GRAPEVINE- GROWING SEASON.

composition by exerting selection pressure. For this reason, ongoing reassessment and adaptation of weed-control measures is key to effective management. In the trials discussed below, winter-growing grasses in combination with herbicide application just before bud-break achieved significant and sustainable weed suppression over periods of five years or longer in the Coastal region and Breede River valley. Legumes were not as effective as grasses, but still reduced the stands of winter-growing weeds by at least 50% in the Breede River valley. The number of years that a cover crop must be sown before it suppresses summer-growing weeds varies by region and cover crop.The application of a herbicide just before bud-break generally resulted in the best control of summer-growing weeds, and reduced the amount of irrigation required. It is not advisable to postpone the application of herbicides to the end of November, as weeds may proliferate over time.

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