COVER CROPS in South African Vineyards

CHAPTER 5 WEED CONTROL

dry-matter production of the most significant winter-growing weeds in the Pallinup-oats treatments is shown in Figure 5.31, and of the most significant summer-growing weeds in Figure 5.32. It can be seen from Figure 5.31 that wild radish was the dominant winter- growing weed at the start of the trial, and that it tended to increase with mechanical control. Musk herons bill increased with both chemical and mechanical control, but the increase was much greater with mechanical control, and musk herons bill eventually became the dominant winter- growing weed in the Pallinup-oats plus mechanical-control treatment. Pallinup oats was able to suppress ryegrass in both the chemical and mechanical treatments, whereas other cover crops were only able to reduce the ryegrass stand when chemical control was applied. After Pallinup oats, the second-best ryegrass suppressor was Nemat combined with full-surface chemical control at grapevine bud-break.

30,00 Dry-matter production of weeds in g per 0.5 metre 2 25,00 20,00 15,00 10,00 5,00 0,00 Chemical Mechanical Chemical Mechanical 2010 2009

Wild radish Musk herons bill Ryegrass

Chemical Mechanical Chemical Mechanical

2011

2012

FIGURE 5.31. Species composition of the dry matter produced by winter-growing weeds in treatments with Pallinup oats at Blaauwklippen. Adapted from Fourie (2017a).

The dry-matter production of summer-growing weeds was measured at the end of April.As illustrated in Figure 5.32, summer-growing weeds were not suppressed in the Pallinup-oats treatment, especially when chemical control was not applied at grapevine bud-break. Common dubbeltjie eventually came to be the dominant summer-growing weed in both the chemical- and

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