COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

The selection and management of cover crops should take interactions with grapevine pests into account, as one does not want to create a problem while solving others.When cover crops serve as hosts for pests, control of cover crops during critical periods can lead to the movement of pests into vines, as happens with thrips when cover crops are controlled during flowering of grapevines. In this chapter, the effects of cover crops on snails; ants and the associated grapevine mealy bug; and nematodes are discussed.The results are applicable to wine, table and raisin grapes cultivated throughout South Africa. Snails A study on the effect of a cover crop on the occurrence of snails was conducted by Vermeulen and co-workers at two sites in the Breede River valley. The most common snail was the white dune snail ( Theba pisana ), followed by the brown garden snail ( Cornu aspersum ). Smaller numbers of tower snails ( Cochlicella barbara ) also occurred, but they were never seen on the grapevines.The three-banded garden slug ( Lehmannia marginata ) was recorded at the second site, but not on the grapevines.

FIGURE 9 .2. White dune snail ( Theba pisana ). (Photo: ARC Infruitec-Nietvoorbij).

FIGURE 9 .3. Brown garden snail ( Cornu as- persum ). (Photo: ARC Infruitec-Nietvoorbij).

The first site was a drip-irrigated vineyard.Triticale was sown annually, and full-surface chemical control applied in August, and in either October or November. Snail numbers were relatively low at this site. The site also had very few weeds, and those predominantly in the vine row.The only two weed species were small mallow and musk herons bill, and snails fed on both.

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