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Sanitary control measures against trunk disease pathogens in grapevine nurseries
Paul Fourie (Department of Plant Pathology, University of Stellenbosch, E-mail: phfourie@sun.ac.za)
Introduction
Research from various sources has identified propagation material as one of the most important primary sources and distribution media of certain grapevine pathogens to existing and recently established grapevines and vineyards. South African research has proven that, apart from virus (e.g. leafroll) and bacterial (e.g. bacterial blight and crown gall) diseases, pathogens of important grapevine diseases such as Phytophthora and Pythium root rot (Von Broembsen and Marais, 1978), black foot (Halleen et al., 2003, 2006a, 2006b), Petri-disease ('black goo'), esca ('beroerte') (Mugnai et al., 1999; Fourie and Halleen, 2002, 2004a, 2004b; Mostert et al., 2006) and Phomopsis and Botryosphaeria dieback (Van Niekerk et al., 2003, 2005, 2006; Fourie and Halleen, 2004a) may be disseminated by grapevine propagation material. These pathogens may infect rootstock and grafted material systemically via infected mother plants in mother blocks. Furthermore, wounds made during the preparation and grafting processes may also be infected by fungal and bacterial pathogens (Fig. 1, 2 and 3). Grafted vines may also be infected by fungal and bacterial pathogens from nursery soils. Sanitary and protective measures to limit such infections are therefore crucial.
Potential inoculum sources of fungal infections, critical infection opportunities and control measures have been studied in several research projects of the Department of Plant Pathology (University of Stellenbosch) and Plant Protection Division of ARC Infruitec-Nietvoorbij, funded by Winetech (Fourie et al., 2001; Fourie and Halleen, 2002, 2004a, 2004b; Halleen et al., 2003, 2004, , 2006a, 2006b; Halleen and Fourie, 2006; Retief et al., 2006). In view of these research results, it is possible to recommend an integrated management strategy for grapevine nurseries (Fourie and Halleen, 2005). These aspects are summarised in this article.
Wound protection in mother blocks
Most grapevine trunk pathogens, inter alia Phaeomoniella chlamydospora and Phaeoacremonium spp. (cause Petri-disease and esca), Botryosphaeria and Phomopsis spp. (cause trunk dieback), penetrate grapevines through wounds. Wound protection, in particular pruning wound protection, is therefore extremely important to prevent such infections, especially since graft shoots may be infected from such infections in mother plants. Research is currently under way to identify wound protection substances that are effective against the entire complex of grapevine trunk pathogens. It was also ascertained that pruning wounds remain susceptible to infection by these pathogens for at least three weeks. Wound protection substances should therefore have lasting efficacy. In this regard, the biological control substances containing species of the Trichoderma fungus should be ideal, as this fungus has the ability to occupy pruning wounds and in so doing, it offers a live protective barrier against trunk pathogens (Halleen and Fourie, 2006). There are several such products on the market, but their direct and long term efficacy against the entire complex of trunk pathogens has not yet been ascertained. Certain chemical fungicides (benomyl, tebuconazole, prochloraz manganese chloride and flusilazole) are effective against the entire complex of trunk pathogens, but their long term efficacy and the concentration of application still have to be determined in actual practice.
Trunk pathogens survive on pruning cuttings and diseased or dead plant material in vineyards. This material also serves as important sources of inoculum from which the pathogen may be disseminated. Pruning and diseased/dead material must therefore be removed from vineyards and burnt or composted so as to reduce the inoculum pressure in vineyards.
Sanitary measures during gathering, preparation and storing of graft material
Fresh wounds are made during the gathering and preparation of grafting material. By implementing sanitary measures, infection of these wounds may be prevented or limited. Firstly, graft material should be prepared on sterilised tables. These surfaces must be disinfected with general sterilisers (e.g. Sporekill or Terminator) on a regular, ongoing basis. The premises must also be clean and disinfected daily. All waste material should be continuously removed and burnt or composted and dust must be restricted to the minimum.
Grafting material must be treated in Sporekill (150 mL/100 L water) or benomyl (100 g/100 L water) for at least one hour as soon as possible after preparation. Then it should be drip-dried and placed in clean, ventilated plastic bags for cool storage (1-4°C). Previously it was recommended that grafting material be treated as soon as possible with 0.25% chinosol (Marais and Van der Westhuizen, 1978). ., However, Fourie and Halleen (2006) found in semi-commercial nursery trials that benomyl and Sporekill was considerably better than chinosol at limiting trunk pathogen infections.
Sanitary measures during grafting
Hot water treatment (HWT; 30 min at 50°C) of graft shoots before grafting may be strongly recommended, research having shown that it resulted in a significant reduction in the Petri-disease pathogens in nursery plants (Fourie and Halleen, 2004b). HWT should be followed by a 1-hour cooling period in cold water with Sporekill (150 mL/100 L water), benomyl (100 g/100 L water) or Trichoflow (Trichoderma harzianum; 200 g/100 L water) (Fourie and Halleen, 2004b, 2006). If HWT is not applied, nurseries should treat all grafting material in Sporekill or benomyl before grafting. This measure will sterilise the surface of grafting material (especially Sporekill), thus ensuring that 'clean' material is handled during grafting. Benomyl or Trichoflow will, however, also protect wounds.
Grafting premises should be kept clean of waste material and be disinfected daily. Dust should also be kept to the minimum. All graft material should be handled and grafted on disinfected tables. Tables, grafting equipment and the staff's hands should be continuously washed and disinfected. Staff should also try not to touch grafting wounds, especially during hand-grafting when a bigger wound is made. The graft joints of grafted vines must be waxed as soon as possible in a fungicide-containing product.
Sanitary measures during callus
As grafted vines may be infected during the callus period (Retief et al., 2006), it is once again important to have sanitary measures in place to ensure that callus crates and callus media are not infected with these pathogens. There has not been much research in this regard recently, but basic disease management principles may be recommended: crates and medium should be sterilised effectively before use so that all pathogens are killed. In New Zealand, crates and callus medium (mostly perlite) are sterilised with steam. At the recommendation of Marais and Van der Westhuizen (1978) and Le Roux (1988b), callus medium in South Africa (mostly pine shavings) is soaked with contact fungicides such as captan and iprodione. These fungicides are, however, not effective against all trunk pathogens. Nurseries using products that contain Trichoderma are warned that the use of chemical fungicides during this treatment will also kill the beneficial Trichoderma fungi on the plant surface.
Treatment of vines during planting
So far no effective measure has been found to protect callused vines against infection from pathogens from the soil (in particular the black foot pathogens, Cylindrocarpon and Campylocarpon spp.) (Halleen et al., 2004, 2006a). In some instances, a soak treatment of callused vines with Trichoflow (200 g/100 L water) resulted in a moderate decline in infection as well as an increase in root mass (Fourie et al., 2001). Research in this regard continues. Aspects such as crop rotation, soil additions and bio-fumigation will be investigated.
Throughout the growing season, effective management of foliar diseases is crucial. Optimum irrigation and fertilisation management will result in healthier plants that are generally more tolerant to pathogens. Downy mildew management with phosphonate products is recommended, as this systemic product will also protect the roots against Phytophthora and Pythium root rot pathogens.
Dormant nursery plants should be removed with the minimum damage. Classification should take place strictly according to the guidelines of the Scheme and attention must be paid to symptoms of fungal infection. All reject plants should be burnt or composted. Excess soil should be washed from classified plants, whereafter it may be dipped in Trichoflow so as to protect any such wounds. These plants may then be preserved in sandy soil, or packed in clean containers for cold storage. Plants may also be infected from the soil during the preservation period, and to limit such infections, future research might investigate management measures such as crop rotation, solarisation and bio-fumigation.
HWT (30 min at 50°C) of dormant nursery plants was effective in dramatically reducing the infection levels of the pathogens of Petri-disease and black foot (Fourie and Halleen, 2004b; Halleen et al., 2006a). Furthermore, it was also effective against Phytophthora and Pythium root rot pathogens and certain nematodes (Von Broembsen and Marais, 1978; Barbercheck, 1986). Various other grapevine pathogens are able to survive in and on nursery plants, and their infection levels may also be reduced or eliminated by HWT. Consequently, this practice is especially recommended where nursery plants are intended for new vineyard areas or new soils. HWT is logistically intensive and producers and nurseries should make sure it is done thoroughly and treated plants should be handled with care, especially since it breaks dormancy and makes treated plants more sensitive to drying out.
Healthy grapevine establishment
The grapevine trunk disease complex is stress related. Optimally growing plants have the ability to suppress infections. Errors made during vineyard establishment result mostly in stress, which then predisposes the plants to these diseases. Producers are therefore admonished to take the utmost care with the establishment of vineyards. Growth stimulation during the first three years should be aimed mainly at root development. An imbalance between vegetative and root growth will seriously hamper plants due to the inability of an underdeveloped root system to supply the water demands of profuse foliage. Furthermore, crops should be limited during the first three years because young plants do not yet have the root and vascular tissue capacity to supply the water and nutrient requirements of heavy crop loads.
Future research priorities
This year new Winetech-funded research projects started to investigate alternative, more environmentally friendly options, as well as healthy grapevine establishment. In future, results from these projects will possibly be able to supplement the above-mentioned recommendations.
Acknowledgement
Winetech is acknowledged for funding of the relevant research projects (USPP 03/2001; WW06/15, 06/19, 06/20, 06/21, 06/25, 06/26 and 06/27), and the authors would also like to thank the collaborators, students and technicians involved.
References
Barbercheck, M., 1986. Control of Meloidogyne javanica in dormant grapevine nursery stock. Phytophylactica 18: 39-40.
Fourie, P.H., Halleen, F., 2002. Investigation on the occurrence of Phaeomoniella chlamydospora in canes of rootstock mother vines. Australasian Plant Pathology 31: 425-426.
Fourie, P.H., Halleen, F., 2004a. Occurrence of grapevine trunk disease pathogens in rootstock mother plants in South Africa. Australasian Plant Pathology 33: 313-315.
Fourie, P.H., Halleen, F., 2004b. Proactive control of Petri disease of grapevine through treatment of propagation material. Plant Disease 88 (11): 1241-1245.
Fourie, P.H., Halleen, F., 2005. Integrated strategies for pro-active management of grapevine trunk diseases in nurseries. Phytopathologia Mediterranea 44: 111.
Fourie, P.H., Halleen, F., 2006. Chemical and biological protection of grapevine propagation material from trunk disease pathogens. European Journal of Plant Pathology (In press).
Fourie, P.H., Halleen, F., van der Vyver, F., Schreuder, W., 2001. Effect of Trichoderma treatments on the occurrence of decline pathogens in the roots and rootstocks of nursery grapevines. Phytopathologia Mediterranea 40: S473-S478.
Halleen, F., Crous, P.W., Petrini, O., 2003. Fungi associated with healthy grapevine cuttings in nurseries, with special reference to pathogens involved in the decline of young vines. Australasian Plant Pathology 32: 47-52.
Halleen, F., Fourie, P.H., 2006. Biological and chemical protection of grapevine pruning wounds against Eutypa lata. European Journal of Plant Pathology (In preparation).
Halleen, F., Fourie, P.H., Crous, P.W., 2006a. Control of black foot disease in grapevine nurseries. Plant Pathology (Submitted).
Halleen, F., Fourie, P.H., Crous, P.W., 2006b. A review of black foot disease of grapevine. Phytopathologia Mediterranea 45 (Supplement): S55-S67.
Halleen, F., Schroers, H.-J., Groenewald, J.Z., Crous, P.W., 2004. Novel species of Cylindrocarpon (Neonectria) and Campylocarpon gen. nov. associated with black foot disease of grapevines (Vitis spp.). Studies in Mycology 50: 431-455.
Jaspers, M.V., 2001. Effect of fungicides, in vitro, on germination and growth of Phaeomoniella chlamydospora. Phytopathologia Mediterranea 40 (Supplement): S453-S458.
Le Roux, D., 1988a. The collection and storage of vineyard grafting material. Farming in South Africa, pamphlet VORI 209/1988.
Le Roux, D., 1988b. Bench grafting of vines. Farming in South Africa, pamphlet VORI 212/1988.
Marais, P.G., Van der Westhuizen, J.H., 1978. Hygienic measures during vine grafting. Farming in South Africa, pamphlet Oenology and Viticulture C.2/1978.
Marais, P.G., Van der Westhuizen, J.H., 1979. Disinfectants of vine grafting-material. Farming in South Africa, pamphlet Oenology and Viticulture C.3/1979.
Mostert, L., Halleen, F., Fourie, P.H., Crous, P.W., 2006. A review of Phaeoacremonium species involved in Petri disease and esca of grapevines. Phytopathologia Mediterranea 45 (Supplement): S12-S29.
Mugnai, L., Graniti, A., Surico, G. 1999. Esca (Black Measles) and brown wood-streaking: Two old and elusive diseases of grapevines. Plant Disease 83:404-418.
Retief, E., McLeod, A., Fourie, P.H., 2006. Potential inoculum sources of Phaeomoniella chlamydospora in South African grapevine nurseries. European Journal of Plant Pathology (In press).
Van Niekerk, J.M., Crous, P.W., Groenewald, J.Z., Fourie, P.H., Halleen, F., 2003. DNA phylogeny and morphological characterization of Botryosphaeria species occurring on grapevines. Mycologia 96: 781-798.
Van Niekerk, J.M., Fourie, P.H., Halleen, F., Crous, P.W., 2006. Botryosphaeria spp. as grapevine trunk disease pathogens. Phytopathologia Mediterranea 45 (Supplement): S43-S54.
Van Niekerk, J.M., Groenewald, J.Z., Farr, D.F., Fourie, P.H., Halleen, F., Crous, P.W., 2005. Reassessment of Phomopsis species on grapevines. Australasian Plant Pathology 34: 27-39.
Von Broembsen, S., Marais, P.G., 1978. Eradication of Phytophthora cinnamomi from grapevine by hot water treatment. Phytophylactica 10: 25-27.
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