COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

in December. From February to April the snails aestivated as the weather warmed and became drier. The snails caused very little feeding damage, probably because they were inactive for most of the time that they were on the vines. At the second site, white dune snails moved into the vines after herbicide application to the vine rows in October, and remained active for the rest of the season. As the snail numbers were much higher at the second site, moderate to severe feeding damage occurred from véraison until harvest. It follows that, when snail bait is used, it should be put out before snails move into the grapevines. Once the snails are in the vines, bait is ineffective. The researchers concluded that snail numbers were significantly higher when weeds grew in the work row throughout the year than when triticale was grown as a cover crop during winter.This is because snails feed on weeds, but not on triticale, and weed numbers were low where a cover crop was grown. Snails also prefer to hibernate on weeds. Soil cultivation in preparation for sowing cover crops further reduces snail numbers by damaging their eggs. Note that, if cover crops are only established in every second row, snails can still proliferate in the other rows, feeding on weeds and moving into the grapevines after weeds have been controlled. Reference list Vermeulen A, Allsopp E and Fourie J. 2014. Integrated snail management in vineyards of the Western Cape (Part 2): Seasonal biology and control. Wineland Technical Yearbook , 2014, 53–56. Ants and mealy bugs Ants promote mealy-bug ( Planococcus ficus ) populations in grapevines through protecting the mealy bugs from predation. In return, the mealy bugs provide the ants with a sugary secretion called honeydew. Four species of ants are commonly associated with mealy bugs inWestern Cape vineyards: Argentine ants ( Linepithema humile ), pugnacious ants ( Anoplolepis custodiens and A. steingroeveri ), and cocktails ants ( Crematogaster peringueyi ). Addison and co-workers examined populations of pugnacious ants and mealy bugs in a vineyard in the Breede River valley for two years. They

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