J.C. Fourie

Effect of seeding date on the performance of grasses and broadleaf species evaluated for cover crop management in two wine grape regions of South Africa.

A selection of species suitable for cover crop management in the different wine grape regions is required to enable more producers to apply this environment friendly practice in a sustainable manner as part of an integrated production strategy. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of seven grasses and sixteen N-fixing broadleaf species, as well as varieties of three of these species, was determined. The decomposition rate of the mulches was measured to determine the mulch persistence of the different species. In the cooler climate of Stellenbosch (Coastal region) the Medicago species, subterranean clovers, pink Seradella (Omithopus sativa L. v. Emena) and three Vicia species did not compete effectively with the winter weeds if the weekly precipitation from mid-March to mid-May (autumn) exceeded 18 mm. The two oats varieties, as well as rye (Secale cereale L.) and triticale (Triticale v. Usgen 18), however, produced more than the five tons of dry matter deemed necessary for effective cover crop management if the precipitation exceeded 18 mm per week. The DMP of all the above-mentioned species was consistent between years at the warmer and arid Lutzville (Olifants River Valley) and indicated that these species could be considered for cover crop management in this region as well, if full surface irrigation of 18 mm per week could be applied for the first 10 weeks after sowing, followed by a fortnightly irrigation of 18 mm. Seeding date had a significant effect on DMP in the Stellenbosch region and showed similar trends in Lutzville. The study showed a highly significant correlation (r = 0.85, P < 0.0001) between the decomposition rate of the mulches and the initial amount of dry. matter present on the soil surface.

Soil management in the Breede River Valley wine grape region, South Africa. 1. Cover crop performance and weed control.

Eight cover crop treatments were applied for 12 consecutive years on a medium-textured soil in a vineyard near Robertson (33˚50’S, 19˚54’E). A treatment with full surface straw mulch and full surface post-emergence chemical control applied from just before grapevine bud break to harvest (BB), and one with no cover crop combined with BB, were also applied. The control consisted of mechanical control in the work row and post-emergence chemical control in the vine row applied from bud break to harvest. Rotating Triticale v. Usgen 18 (triticale) and Vicia dasycarpa Ten. (vetch) did not improve the dry matter production (DMP) of either species. Average DMP decreased as follows: triticale > Secale cereale L. v. Henog (rye)/Vicia faba L. v. Fiord (faba bean) mixture > triticale/vetch biennial rotation > triticale/vetch annual rotation > vetch. Triticale (BB) resulted in total winter weed suppression from 1995 to 1996 and from 2001 to 2004. Total weed control from bud break to the pea size berry stage of the grapevines was achieved with straw mulch (BB), triticale (BB), rye/faba bean mixture (BB) and triticale/vetch rotated biennially (BB) from 2001 to 2003. For triticale combined with full surface post-emergence chemical control applied from grapevine berry set (AB), and for triticale/vetch rotated annually (BB), this was restricted to 2001 and 2003. From the pea size berry stage to harvest, straw mulch (BB), triticale (BB), vetch (BB), rye/faba bean mixture (BB) and triticale (AB) reduced the weed stand significantly in comparison to the control.

Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 3. effect of different cover crops and cover crop management practices on organic matter and macro-nutrient content of a medium-textured soil

The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium-textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), which is situated in the Coastal wine grape region of the Western Cape, South Africa. Sixteen treatments, consisting of three cereals and five legumes, managed according to two cover crop management practices, were included. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full-surface post-emergence chemical weed control was applied from before bud break to harvest (BB) (weedchem) was also included. After five seasons, the soil organic matter (SOM) content in the 0 to 300 mm soil layer increased in all the cover crop management treatments. In weedchem and in the control, SOM remained unchanged and decreased by 16% respectively. The SOM content in the 0 to 150 mm soil layer of the cover crop treatments was, with the exception of Vicia dasycarpa Ten. (grazing vetch), significantly higher than that of the mechanically-cultivated control after a period of 10 years. The SOM content in the 0 to 300 mm soil layer of Secale cereale L. v. Henog and the treatments in which the N-fixing cover crops were sown (with the exception of grazing vetch) was significantly higher than that of weedchem. The total inorganic N (TIN) concentration of the 0 to 150 mm soil layer in the BB treatments of the two Medicago species and Trifolium subterraneum L. v. Woogenellup, as measured for the 1996/97 season during full bloom of the grapevines, was significantly higher than that of the control, weedchem, and the treatments in which full-surface chemical control was applied after bud break (AB). The TIN concentration of the 0 to 600 mm soil layer in the AB treatment of a species, measured after harvest in 2002/03, tended to be higher than that of the BB treatment of that species. The applied treatments had no significant effect on the exchangeable K, Ca and Mg.

Cover crops with biofumigation properties for the suppression of plant-parasitic nematodes: a review.

Plant-parasitic nematodes are a problem in vineyards worldwide, with some species acting as vectors of grapevine soil-transmitted viruses. Global pressure on the use of soil-applied chemical nematicides has led to a search for new control options, or for alternative methods to suppress plant-parasitic nematodes as part of integrated pest management. This paper gives valuable background information on the use of cover crops with biofumigation properties for the suppression of plant-parasitic nematodes in vineyards.

Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 2. effect of different cover crops and cover crop management practices on grapevine performance

The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), situated in the Coastal Wine Grape Region of the Western Cape. Sixteen treatments, consisting of three grain species and five legumes, managed according to two cover crop management practices, were included. The one cover crop management practice consisted of cover crops being sown annually and full surface post-emergence chemical control being applied before bud break and when the berries reached pea size (BB). The other management practice consisted of cover crops being sown biennially and postemergence chemical control applied to the vine row before bud break and full surface when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence chemical control applied at the end of November was advanced to mid-October. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full surface post-emergence chemical weed control was applied from before bud break to harvest (weedchem) was also included. During the 1994/95 season, the shoot mass of the two-year-old grapevines in the BB treatments was significantly higher than that of the control and the AB treatments. In the following season, the shoot mass and grape yield of the BB treatments was, with the exception of Vicia faba L. v. Fiord (faba bean) and Avena sativa L. v. Overberg, significantly higher than that of the control and weedchem. The grape yield of the control and AB treatments was significantly less than that of weedchem. Although significant differences in shoot mass (2000/01 and 2002/03) and grape yield (2002/03) were detected between treatments, no significant differences could be detected between the BB and AB treatments, with the exception of the shoot mass of Medicago scuttelata v. Kelson (‘Kelson’ medic). The mean petiole NO3-N concentration for the period 1994/95 to 1998/99 tended to be lower in the AB treatment of a cover crop species compared to that of the BB treatment of the same species. In the case of ‘Kelson’ medic (BB) the petiole NO3-N and juice N concentrations were significantly higher than that of the control and weedchem. The juice N concentration of the control and weedchem was significantly less than that of the faba bean treatments during 2000/01 and 2001/02, the Vicia dasycarpa Ten (grazing vetch) and ‘Kelson’ medic treatments during 2000/01, as well as that of Medicago truncatula Gaertn. (BB) and Trifolium subterraneum L. v. Woogenellup (BB) during the 2001/02 season. Wine quality did not differ between treatments.

Cover crop management in a Sauvignon Blanc-Ramsey vineyard in the semi-arid olifants River Valley, South Africa. 3. Effect of different cover crops and cover crop management practices on the Organic matter and macro-nutrient contents of a sandy soil

The trial was conducted over a period of ten years (1993/94 to 2002/03) on a sandy soil in a Sauvignon blanc/Ramsey vineyard near Lutzville (31o35’S, 18o52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Fourteen treatments, consisting of three cereals and four legumes, managed according to two cover crop management practices, were included. One management practice consisted of cover crops which were sown annually. Full surface post-emergence chemical control was applied before bud break and again when the berries reached pea size (BB). The second management practice consisted of cover crops which were sown biennially. Post-emergence chemical control was applied to the vine row before bud break and full surface control was applied when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence control applied at the end of November (berries at pea size) was advanced to mid-October. Two treatments in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were sown annually, controlled mechanically in the work row and chemically in the vine row from bud break to harvest (MC), were also applied. These treatments were compared to a control, in which no cover crop was sown and MC was applied. A treatment in which no cover crop was sown and BB was applied (weedchem), was also included. After five years (1997/98), the soil organic matter (SOM) in the 0-150 mm soil layer of the BB and AB treatments of grazing vetch was significantly higher than that of the control and weedchem. During March 2003, the SOM content in the 0-600 mm soil layer of grazing vetch (AB), as well as the 0-150 mm soil layer of Ornithopus sativus L. v. Emena (pink Seradella) (AB) and Secale cereale L. v. Henog (rye) (BB), was significantly higher than that of the control and weedchem. The total inorganic N concentration (TIN) of pink Seradella (BB) was the highest in the 0-150 mm soil layer during the full bloom stage of the grapevines in 1995/96 and significantly higher than that of the other treatments in the 150-300 mm soil layer. The TIN measured in the AB treatments of grazing vetch and pink Seradella as measured after the grapevine harvest (1995/96), was significantly higher than that of the control, weedchem and cereal treatments in the 0-300 mm and 0-150 mm soil layers, respectively. The TIN in the 0-150 mm soil layer of the legumes was, with the exception of pink Seradella (BB), significantly higher than that of the control, weedchem and the BB treatments of the cereals during March 2003. The TIN in the 150-300 mm soil layers of the AB treatments of pink Seradella and the two Medicago truncatula Gaertn. varieties, namely, Parabinga and Paraggio, was significantly higher than that of the control, weedchem and the grain treatments. Potassium concentrations in the 0-150 mm soil layer of the two pink Seradella treatments, the AB treatment of rye, Medicago truncatula Gaertn. v. Paraggio and grazing vetch, as well as the 150-300 mm soil layer of grazing vetch (BB) and pink Seradella (BB), were significantly higher than that of the control, weedchem and ‘Saia’ oats (MC) during March 1997.

Cover Crop Management in Vineyards of the Lower Orange River Region, South Africa: 2. Effect on Plant Parasitic Nematodes

This study was conducted as part of a larger investigation into the effect of management practices on selected sown cover crops and the effects thereof on grapevine performance. The aim of this study was to determine the effect of these cover crops on plant parasitic nematode populations under natural field conditions. The trial site was in an own-rooted Sultanina vineyard situated in the Lower Orange River of the Northern Cape Province. Three management practices were applied selectively to ten cover crop species, with two control treatments consisting of weeds. Nematodes were monitored for a period of four years. ‘Saia’ oats were indicated as being poor hosts to both root-knot and root-lesion nematodes, while ‘Overberg’ oats showed poor host status against ring nematodes. ‘Midmar’ ryegrass and ‘Paraggio’ medic were also poor hosts for root-knot nematodes, while grazing vetch appeared to be a good host for root-knot nematodes. The most notable result from this study was the relatively high numbers of all three nematodes on the vine row, as opposed to the inter-row where cover crops were established. This indicates that vines were much better hosts for these nematodes than the cover crops. It is recommended that if more definite trends are to be observed, Brassica species, which have direct toxic/repellant effects on nematodes, should be tested.

Cover Crop Management in a Sauvignon Blanc/Ramsey Vineyard in the Semi-Arid Olifants River Valley, South Africa. 2. Effect of Different Cover Crops and Cover Crop Management Practices on Grapevine Performance

The trial was conducted over a period of ten years (1993/94 to 2002/03) on a sandy soil in a Sauvignon blanc/ Ramsey vineyard near Lutzville (31o35’S, 18o52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Fourteen treatments, consisting of three grain species and four legumes, managed according to two cover crop management practices, were included. One management practice consisted of cover crops which were sown annually and full surface, post-emergence chemical control which was applied before bud break and when the berries reached pea size (BB). The second management practice consisted of cover crops which were sown biennially. Post-emergence chemical control was applied to the vine row before bud break and full surface when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence control applied at the end of November was advanced to mid-October. Two treatments in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were sown annually, controlled mechanically in the work row and chemically in the vine row from bud break to harvest (MC), were also applied. These treatments were compared to a control, in which no cover crop was sown and MC was applied. A treatment in which no cover crop was sown and BB was applied (weedchem), was also included. During the third growing season of the vines (1994/95), the grapevine shoot mass of the BB treatments of grazing vetch and Medicago truncatula Gaertn. v. Paraggio (‘Paraggio’ medic) was significantly more than that of the AB and MC treatments, with the exception of Secale cereale L. v. Henog (AB) and grazing vetch (MC). The first harvest (1994/95) from the grapevines in the BB treatments was significantly higher than that of weedchem and the MC treatments. The grape yield of the BB treatments, grazing vetch (AB) and Ornithopus sativus L. v. Emena (pink Seradella) (AB) was significantly more than that of weedchem and the control during the 1997/98 season. The NO3-N concentration in the leaf petioles in all the cover crop treatments was, with the exception of the AB treatments of rye, M. truncatula Gaertn. v. Parabinga (‘Parabinga’ medic) and grazing vetch, significantly higher than that in weedchem and the control, as measured during the 1994/95 season. The NO3-N concentration in the leaf petioles of the BB and AB treatment of a species differed significantly. The N concentration in the juice of the cover crop treatments during the 1995/96 season was, with the exception of ‘Saia’ oats (MC) and ‘Parabinga’ medic (AB), significantly higher than that of weedchem and the control. During the 1998/99 season, the N concentration of the juice in the BB and AB treatments of grazing vetch and pink Seradella was significantly higher than that of the MC treatments, two rye treatments, weedchem and the AB treatments of the other cover crops. The concentration of Ca in the juice of the cover crop treatments was, with the exception of the pink Seradella treatments, significantly higher than that of weedchem and the control. Wine quality did not differ between treatments.

Soil management in the Breede River Valley wine grape region, South Africa. 2. Soil temperature.

Five soil management practices (treatments) were applied in a micro-sprinkler irrigated Chardonnay/99 Richter vineyard on a sandy clay loam soil near Robertson, commencing in April 1993 (one year after planting). The effect of the treatments on the soil temperature at a depth of 200 mm was measured on an hourly basis from April 1995 to March 1999. Differences in soil temperature between the un-mulched and mulched treatments, as measured in the grapevine rows, were negligible from late April to the end of August. From mid-September (grapevine bud break) to the end of March, the temperature of the mulched soil was, with the exception of the third week in October, lower than that of the un-mulched soil. Results indicated that soil temperatures during early spring had a slight effect on the onset of grapevine bud break. Mulching minimised the diurnal variation in soil temperature. The annual cover crop did not cause any delay in bud break and kept the soil temperatures below 25°C, with the exception of a three week period just before harvest.

Cover crop management in the vineyards of the Lower Orange River region, South Africa: 1. Performance of grass and broadleaf species.

This trial was conducted over a period of four years on a sandy soil in a Sultanina vineyard on own roots in Keimoes (28o40’S, 20o54’E), situated in the semi-arid Lower Orange River region. Eighteen treatments, consisting of three cover crop management practices applied selectively to ten cover crop species, as well as two treatments in which the weeds were managed in accordance with two management practices generally applied by producers in the region, were applied. The average dry matter production (DMP) of the cover crop species sown annually (SA) and controlled chemically before bud break (BB), as determined during bud break (beginning of August) was: Medicago truncatula Gaertn. v. Paraggio > Vicia dasycarpa Ten. (grazing vetch) > Secale cereale L. v. Henog (rye) > Ornithopus sativus L. v. Emena > Avena sativa L. v. Overberg > Lolium multiflorum Lam. v. Midmar (‘Midmar’ ryegrass) > Avena strigosa L. v. Saia (‘Saia’ oats) > Trifolium subterraneum L. v. Woogenellup. ‘Midmar’ ryegrass and grazing vetch re-established successfully. Winter growing weeds were effectively suppressed (weed stand less than 10% of that of the control) by rye (BB/SA) and ‘Saia’ oats (BB/SA) for the duration of the trial. Weed growth from veraison to harvest (mid-November to the end of December) was effectively reduced in all the annual cover crop treatments compared with the treatment in which the weeds were controlled mechanically from bud break during the 1997/98 season. Festuca arundinaceae L. v. Cochise, slashed regularly throughout the season, suppressed the winter and summer growing weeds effectively during the trial, but eventually got infested with common couch.