COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

100%

90%

80%

70%

Hairy wild lettuce Narrow-leaf ribwort Wild lettuce Bristly oxtongue Flax-leaf fleabane Common blackjack Thorn apple Other

60%

50%

40%

matter

30%

20%

10%

Relative percentage contribution to total dry

0%

2001

2006

2001 2006 Organic production

2001 2006 Integrated production

Conventional

FIGURE 5.30. Species composition of the dry matter produced by summer-growing weeds in different treatments at Plaisir de Merle in the Coastal region. Adapted from Fourie and Raath (2008).

Based on this research, the following is recommended: • Cover-crops and herbicides should be rotated to avoid selecting for specific weeds. • Herbicide application in the grapevine-growing season should be timed to control late-germinating problem weeds such as common blackjack and flax-leaf fleabane during their early growth stages. Blaauwklippen A study at Blaauwklippen looked at the species composition of weeds in drip-irrigated vineyards over a period of five years. Chemical and mechanical control were compared in five different cover-crop treatments and a control without a cover crop. The cover crops were sown annually in May, and controlled at grapevine bud-break. Chemical control consisted of full-surface post-emergence chemical weed control, whereas mechanical control consisted of slashing and mechanical cultivation. In both cases, full-surface chemical weed control was applied at the end of November. The overall impact of the different cover crops on weeds has already been discussed. Pallinup oats gave the greatest weed suppression overall. The

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