Cover crop management is widely applied in the vineyards of South Africa.

 

Introduction
The cover crops are grown during winter and controlled chemically any time from the end of August (end of winter) in non-irrigated bush vines, to early October (spring) in irrigated trellised vines. This will avoid competition with the grapevine for water and nutrients. Therefore, a species considered for cover crop management should germinate mainly in April/May (autumn) and complete its life cycle approximately in September/early October (spring).

 

Taking these criteria into account, the following winter growing grass weeds can be considered as cover crops:

 

Oat-seed grass (Ehrharta longiflora Sm.)
Oat-seed grass is an annual grass growing mainly from winter to spring. Initially the grass has a loose tussock that becomes more dense with maturity (Figure 1a). The culms may grow as high as 90 cm. An outstanding feature of this grass is the purple band situated where the leaf-sheath merges into the leaf-blade. The purple coloured glumes are also very conspicuous (Figure 1b). The inflorescence is an open panicle.

 

Rip-gut Brome (Bromus diandrus Roth.)
Rip-gut Brome (Figure 2a and 2b) is an annual grass growing mainly from winter to spring. The culms are loosely tufted (Figure 2a) and the species can grow as high as 75 cm. The leaves at the base of the tussock dies back as the grass matures. A purple band occurs where the leaf-sheath merges into the leaf-blade (Figure 2b). The leaf-sheath and -blade are both sparsely to densely hairy, with the leaf-blade ending in an acute apex. The inflorescence is a loosely contracted open panicle. The spikelets have exceptionally long awns with a purple tinge, which makes it easier to identify the species.

 

Common wild oats (Avena fatua L.)
Common wild oats is a loosely tufted or single-stemmed annual grass (Figure 3a), growing mainly from winter to spring and can reach a height of up to 90 cm. The leaf-sheath and -blade are glabrous. The leaf-blade ends in an acute apex. The inflorescence is an open and lax panicle (Figure 3b).

 

Wild barley (Hordeum murinum L.)
Wild barley is an annual grass growing mainly from winter to spring and can reach a height of 60 cm. The culms are mostly loosely tufted (Figure 4a), but can also be single. The lower leaf-sheaths are mostly sparsely covered with hairs, but the upper ones are always glabrous. The leaf-blades are either sparsely hairy or glabrous, with the inflorescence a dense bristly spike (Figure 4b).

 

Rescue grass (Bromus unioloides HBK)
The culms of this perennial grass are densely tufted (Figure 5a) and the species can reach a height of 90 cm. The culms are glabrous, erect and striate. The leaf-sheaths are sparsely hairy. The leaf-blades are mostly glabrous and can become 24 cm long and 1 cm wide. The inflorescence is a lax open panicle (Figure 5b), which can reach a length of 45 cm.

 

The four annual grasses complete their life cycles by the end of September or early October. Although the grapevine producer has the option of no chemical weed control at this time, full surface chemical control in early October is advocated. The application of post-emergence herbicides allows the above-mentioned four annual grasses to produce seeds for re-establishment. It will simultaneously prevent the ryegrasses (Lolium species) (Figure 6a and 6b), problem weeds which quickly develop resistance to the herbicides registered for use in vineyards, to complete its life cycle and produce viable seeds as well. This aggressive winter to summer growing grass weed competes effectively with the above-mentioned grasses, as well as other cover crops, and has the ability to dominate within four seasons, if allowed to produce viable seeds (Figure 7).

The above-mentioned hidden danger of not applying chemical control during September/early October should not be underestimated. There is no quick fix once ryegrass has been allowed to dominate.

To remove the competition of winter growing broadleaf species, MCPA can be sprayed during winter after grapevine leaf fall, to promote the dry matter production of the winter growing grasses.

 


FIGURE 1. (a) The habitus and (b) the leaves and inflorescence of oat-seed grass (Ehrharta longiflora Sm.).

 


FIGURE 2. (a) The habitus and (b) the leaves and inflorescence of rip-gut Brome (Bromus diandrus Roth.).

 


FIGURE 3. (a) The habitus and (b) the leaves and inflorescence of common wild oats (Avena fatua L.).

 


FIGURE 4. (a) The habitus and (b) the leaves and inflorescence of wild barley (Hordeum murinum L.).

 


FIGURE 5. (a) The habitus and (b) the leaves and inflorescence of rescue grass (Bromus unioloides HBK.).

 


FIGURE 6. (a) The habitus and (b) the leaves and inflorescence of the ryegrass weed (a Lolium species).

 


FIGURE 7. Ryegrass dominance in the background, where full surface chemical control was postponed to the end of November for four consecutive seasons in a cover crop trial near Stellenbosch.

 

Acknowledgements
The Agricultural Research Council for funding, as well as Soil and Water Science at ARC Infruitec-Nietvoorbij for infrastructure and technical support.

 

Summary
The winter growing weeds, namely oat-seed grass (Ehrharta longiflora Sm.), rip-gut Brome (Bromus diandrus Roth.), common wild oats (Avena fatua L.), wild barley (Hordeum murinum L.) and rescue grass (Bromus unioloides HBK) can be used as cover crops in vineyards. Full surface chemical control in early October (spring) allows the above-mentioned four annual grasses to produce seeds for re-establishment, while preventing the ryegrasses (Lolium species) from completing their life cycle and producing viable seeds. To remove the competition of winter growing broadleaf species, MCPA can be sprayed during winter after grapevine leaf fall.

 

– For further information, contact Johan Fourie at FourieJ@arc.agric.za.

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