COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

bud-break, at the end of August, was compared to full-surface chemical weed control starting at the end of November, when the grapevine berries reached pea size. Dry-matter production of summer-growing weeds was measured at the end of November. The dry-matter production of summer-growing weeds in the grass cover- crop treatments is shown in Figure 5.27. It can be seen that, where grasses were combined with chemical weed control starting at grapevine bud-break, weed growth was largely or entirely suppressed. In some years, no or few summer weeds emerged in the cover-crop treatments, and therefore post- emergence weed control during the grapevine-growing season was not necessary. Where full-surface chemical weed control was delayed until November, weed control was less consistent. Rye did not suppress weeds effectively, and was invaded by ryegrasses. Ryegrasses are problem weeds that readily develop resistance to the post-emergence herbicides used in vineyards. m August. m November. l from August. l from November. l from August. l from November

5,00

No cover crop

4,50

Henog rye. Weed control from August. Henog rye. Weed control from November. Overberg oats. Weed control from August. Overberg oats. Weed control from November. Saia black oats. Weed control from August. Saia black oats. Weed control from November

4,00 3,50 3,00 2,50 2,00 1,50 1,00 0,50 0,00

2001

1993

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1998

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Year

Dry-matter production of weeds in tonnes per hectare FIGURE 5.27. Dry-matter production of summer-growing weeds in grass cover-crop treat - ments with two different weed-control strategies compared to a control without a cover crop in the Coastal region. Adapted from Fourie et al (2006).

Legumes were less successful at controlling summer-growing weeds than grasses.The dry-matter production of weeds in the various legume treatments is shown in Figure 5.28. Full-surface chemical weed control was applied at grapevine bud-break, at the end of August, for all these treatments.Although

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