COVER CROPS in South African Vineyards

CHAPTER 9 PESTS

The second site was a micro-irrigated vineyard with no cover crop. Chemical weed control was applied to the vine row in September and November. Weeds were not controlled in the work row, and took advantage of the micro- irrigation to grow throughout most of summer. There were eighteen weed species found at the second site. The most common were feather-top chloris, narrow-leaved ribwort, sow thistle, and wild radish.All snails preferred narrow-leaved ribwort.Wild radish was also consumed by white dune and brown garden snails, while sow thistle was favoured by only white dune snails.

6000

5000

4000

3000

No cover crop Brown garden snails No cover crop White dune snails

Snail count

Triticale Brown garden snails Triticale White dune snails

2000

1000

0

Jul-11

Jul-10

Oct-10

Oct-11

Winter Jun-10

Jan-11

Jun-11

Jan-12

Feb-11

Feb-12

Nov-10

Dec-10

Nov-11

Dec-11

May-10

May-11

Summer

Winter

Summer

FIGURE 9 .4. Numbers of white dune and brown garden snails in a vineyard with no cover crop compared to a vineyard with a triticale cover crop. Adapted from Vermeulen et al (2014).

Snail numbers are shown in Figure 9.4. At both sites, snails were most abundant on weeds in autumn and early winter, and laid eggs after the first autumn rains. Numbers declined as winter progressed. Snails hibernated on weeds and cover crops during very wet and cold winter months, and very little activity was seen until October. After the second herbicide application at the first site, brown garden and white dune snails moved rapidly onto the grapevines. Snails became more active on the grapevines from November onward, and numbers peaked

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