A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME Resistance of ryegrass (Lolium spp.) against glyphosate and paraquat/diquat in orchards and vineyards by F.H. Eksteen1, A.L.P. Cairns2, and P.J. Pieterse2 (1) Syngenta South Africa Pty. Ltd (2) Department of Agronomy of Stellenbosch, Private Bag X1, Matieland 7606 In orchards and vineyards, glyphosate, paraquat and paraquat/diquat mixtures form the backbone of the weed control programme. Glyphosate has been used continuously for the past 20 years in vines and orchards. In many instances the herbicide was sprayed more than once during the growing season. Prior to the introduction of glyphosate in 1974, paraquat and paraquat/diquat mixtures had been used almost exclusively as a non-selective herbicide in orchards and vines from the mid 1950's. The almost exclusive use of these products, first paraquat/diquat and subsequently glyphosate, undoubtedly favoured selection pressure for resistant individuals. One of the most important weeds in orchards and vines in the Western Cape is ryegrass (Lolium spp). The biological features of ryegrass (e.g. high genetic variability, obligate outcrossing and short-lived seed bank) apparently contribute to the rate at which resistance develops. Ryegrass has developed resistance to more groups of herbicides than any other weed (Heap 2003). Resistance of ryegrass to ACCase and ALS inhibitors in cereals in the Western Cape is widespread (Pieterse & Kellerman 2001). It was thus not totally unexpected when reports of poor control of ryegrass by glyphosate in orchards and vines started to appear 3 to 4 years ago. These reports were investigated and initial studies not only confirmed the presence of several populations of glyphosate-resistant ryegrass, but also revealed that resistance of ryegrass to paraquat/diquat was widespread. This study was therefore initiated to document the extent and nature of these resistant ryegrass populations, and to seek alternative herbicides with different modes of action for their cost-effective control. Materials and Methods Two Western Cape sites were selected from which reports of poor control of ryegrass (Lolium spp.) by non-selective herbicides had been received. One site is near Tulbagh in a peach orchard and the other in a vineyard near Klapmuts. Trials were conducted during the 2003 season to investigate the problem and to seek workable alternative solutions. In these trials the non-selective herbicides Roundup CTİ(glyphosate 240g L-1) and Preegloneİ(paraquat 120g L-1 + diquat 80g L-1) were used to evaluate the extent of the problem at the two sites. Mixtures were also made of the two non-selective herbicides and two selective herbicides, Gallantİ(haloxyfop-R methyl ester 108g L-1), and Kerbİ (propizamide 490g kg-1) in order to find a solution to the poor control obtained with the non-selective herbicides. The selective herbicides Gallantİ and Fusilade Superİ(fluazifop-P-butyl 125g L-1) were also sprayed on their own. Dosage rates were as indicated in Table 1. The herbicides were applied with a knapsack sprayer calibrated to deliver 230 L ha-1 of water. Each treatment was replicated 3 times on 5m x 3m plots. Evaluation of the trial was done 28 days after application and efficacy was scored as percentage control. Results Figure 1 (A left, B right): Control of ryegrass with Preegloneİ (A) and Roundup CTİ (B) near Klapmuts In the orchard near Tulbagh, Preegloneİ sprayed on its own gave poor control of the ryegrass while Roundupİ gave better control but still not to an acceptable level (Table 1). In the case of the vineyard near Klapmuts the scenario is reversed, with Preegloneİ giving the superior (but still not acceptable) control and Roundupİ the inferior control (Figure 1, A and B and Figure 2, A and B). Figure 2 (A left, B right): Control of ryegrass with Preegloneİ (A) and Roundup CT İ (B) near Tulbagh. Control plots are in the foreground. In the treatments where Kerbİ was added to the Preegloneİ the control at both sites were very good as seen in Table 1. Both applications were followed by light rain that was ideal for the activation of the soil-acting Kerbİ. Preegloneİ gave control of the broadleaf weeds, present in these trial plots (Figure 3). Figure 3 (A left, B right): Control of ryegrass with Preeglone 5 L.ha-1 + Kerb 1,5 Kg.ha-1 at Tulbagh (A) and Klapmuts (B). The ACCase inhibitors Gallantİ and Fusilade Superİ both gave excellent control of the ryegrass that were resistant to the non-selective herbicides Roundup CTİ and Preegloneİ. The problem is that these herbicides selectively control grass weeds. This resulted in a proliferation of the broadleaf weeds in these treatments as indicated by the arrows in Figure 4. Figure 4 (A left, B right): Trial plots sprayed with Gallantİ 1 L.ha-1 at Tulbagh (A) and Klapmuts (B). In the plots where the Roundup CTİ was added to the Gallantİ, excellent control was obtained of both ryegrass and broadleaf weeds, in this case Plantago lanceolata (Figure 5). Figure 5 (A left, B right): Trial plots sprayed with Roundup CTİ 4 L ha-1 + Gallantİ 1 L ha-1 at Tulbagh (A) and Klapmuts (B). Discussion Ryegrass showed resistance to Roundup CTİ and Preegloneİ at both trial sites. However, the additional use of Kerbİ, Gallantİ and Fusilade Superİ gives producers alternative solutions for the control of glyphosate and paraquat/diquat-resistant ryegrass. Gallantİ and Fusilade Superİ have no residual activity in the soil, which means that follow-up sprays might be necessary to control post application emergence of grasses. On the other hand, Kerbİ, due to its residual activity in the soil, gives season-long control of grass weeds. In a ryegrass resistance situation, as described above, the use of Roundupİ and Preegloneİ to control broad-leaved weeds is not ideal. Due to the high and continuous selection pressure caused by the use of these products, the resistance problem can only become worse. Options for the control of broadleaf weeds are very limited in orchards and vineyards, especially in stone fruit. In vines and pome fruit farmers can revert to the residual herbicides such as terbuthylazine and simazine. Ryegrass resistance against the ACCase inhibitors such as Gallantİ and Fusilade Superİ is well documented (Gill 1995, Heap 2003). Care should be taken that overuse of these herbicides does not result in the elimination of yet another important herbicide group for use in orchards and vineyards via build-up of resistance. More recent work (results not shown) has indeed proven that resistance of ryegrass to ACCase inhibitors in vineyards and orchards is already a problem in isolated situations in the Western Cape. To date, no case of resistance against Kerbİ has ever been reported. However, enhanced degradation of Kerbİ has been reported after continuous applications in the Netherlands (Eelen et al. 2003.). This resulted in poor control of the grass weeds due to a lack of residual activity. When using Kerbİ in a weed control programme in perennial crops, it is important to keep the time of application in mind. Kerbİ is registered as a pre-emergence or early post-emergence application. Kerbİ should therefore be sprayed early in the season, after the first winter rain (May - June) when the ryegrass starts emerging, and not later in the season (July - August), when the ryegrass is in the 6-leaf stage, as is the current practice for weed control in perennial crops. The fruit and wine industry will be facing severe problems if ryegrass resistance to the two most important non-selective herbicides continues to spread. It is therefore essential that steps be taken now to make use of integrated weed control programmes where herbicide groups are rotated every year. This action will ensure that the valuable chemistry is protected against overuse, and the evolvement of resistance to the herbicides currently used, prevented or delayed. There are no half measures in the control of herbicide-resistant weeds - you either eliminate them or they eliminate you. The choice is yours. References Eelen, H., R. Bulke and J. Bouchaud. 2003. Enhanced degradation of propyzamide after repeated application in orchards. Thirteenth Australian Weeds Conference. September 2003, Perth, Australia Gill, G.S. 1995. Development of herbicide resistance in annual ryegrass populations (Lolium rigidum Gaud.) in the cropping belt of Western Australia. Australian Journal of Experimental Agriculture 35, 67-72. Heap, I. 2003. International survey of herbicide resistant weeds. Online, Internet. Available www.weedscience.com. Pieterse, P.J. & J.L. Kellerman. 2002. Quantifying the incidence of herbicide resistance in South Africa. Resistant Pest Management Newsletter 12, 39-41.

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