COVER CROPS in South African Vineyards

COVER CROPS IN SOUTH AFRICAN VINEYARDS

mechanical-control treatments, but there was also a significant increase in prostrate knotweed, crab finger grasses, and common couch in the mechanical-control treatment. 50,00 40,00 30,00 20,00 10,00 0,00 Chemical Mechanical Chemical Mechanical Chemical Mechanical Chemical Mechanical 2010 2011 2012 2013 Dry-matter production of weeds in g per 0.5 metre 2 FIGURE 5.32. Species composition of the dry matter produced by summer-growing weeds in treatments with Pallinup oats at Blaauwklippen. Adapted from Fourie (2017b). Caliente gave the second-best weed suppression overall. The dry-matter production of the most significant winter-growing weeds in the Caliente treatments is shown in Figure 5.33, and of the most significant summer- growing weeds in Figure 5.34. It can be seen from Figure 5.33 that ryegrass was the dominant winter- growing weed at the start of the trial.Although it increased in some seasons, this was not consistent. As was the case for Pallinup oats, musk herons bill eventually became the dominant winter-growing weed in the mechanical- control treatment. It also dominated in the chemical-control treatment. The sharp decrease in ryegrass in 2012 was due to the application of a grass-specific herbicide approximately two weeks after sowing the Caliente. This probably facilitated the increase in musk herons bill. As was found for Pallinup oats, summer-growing weeds were not suppressed in the Caliente treatments, especially when chemical control was not applied at grapevine bud-break.This can be seen from Figure 5.34. Common dubbeltjie again eventually became the dominant summer-growing weed in both the chemical- and mechanical-control treatments. 100,00 90,00 80,00 70,00 60,00 Common dubbeltjie Crab finger grasses Flax-leaf fleabane Prostrate knotweed Natal red-top Common couch

111