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Mark Sosnowski, Adrian Loschiavo, Trevor Wicks and Eileen Scott

Contents 

Pruning wound protection
Cultural practices
Sanitation
Remedial surgery
Acknowledgements
References

Summary

• Control of eutypa dieback can be achieved by protecting wounds from infection by the fungus, Eutypa lata or by physically removing infected wood.
• Wounds can be protected with fungicides, paints, pastes and biological control agents. It is also important to time pruning in order to avoid rainfall events and to maintain good sanitation.
• Controlling established infections is achieved by removing infected wood and retraining of watershoots from below infection.

Pruning wound protection

Fungicides

Carbendazim (Bavistin^®) was the most effective of the fungicides tested for ability to prevent pruning wound infection by E. lata. Pyrimethanil (Scala^®) and fluazinam (Shirlan^®) reduced infection by E. lata, but at rates higher than those recommended for other grape diseases. Pyraclostrobin (Cabrio^®) and Cyprodonyl + fludioxonil (Switch^®) provided some control of E. lata but were less effective than the other fungicides.  Figure 1 shows results of selected trials in Australia and more details can be found in Sosnowski et al. (2008). Research in the USA, South Africa and France showed that flusilazole (Nustar^®) is effective at rates higher than those recommended for other grape diseases. Boric acid reduced infection by E. lata in trials at University of California (UC) Davis and similar results were obtained in South Australia. All of the above fungicides were applied by hand to fresh pruning wounds. Trials to screen more fungicides as potential wound protectants are continuing.

It is important to note that fungicides alone are not registered for control of eutypa dieback on grapevines in Australia.

In preliminary trials, carbendazim applied by commercial spray equipment controlled eutypa dieback (Figure 2). Research is currently underway to optimize application with spray equipment to provide a practical and efficient method of controlling eutypa dieback in vineyards.

Paints and pastes

Wound protectants, such as Garrison^® paste and Greenseal™ paint, which are formulated with fungicides (cyproconazole + iodocarb and tebuconazole, respectively), and acrylic paint (with and without fungicides) all prevented infection by E. lata (Figure 1). Greenseal™ paint was registered in 2008 for control of eutypa dieback in Australia. These treatments, applied by hand, are strongly recommended for larger wounds, such as those made during reworking or remedial surgery. The application of fungicide immediately after wounding and before application of a paint or paste minimises the risk of sealing a wound on which spores may already have landed and germinated, and of infection via cracks in the surface of the paint as it dries over time.

Figure 1. Efficacy of pruning wound treatments applied 1 day before inoculation with E. lata.

Figure 2. Efficacy of carbendazim applied with either a paint brush or commercial sprayers in the protection of pruning wounds inoculated with E. lata.

Biological control

Biological control agents, such as the fungi Trichoderma spp. and Fusarium lateritium and bacterium Bacillus subtilis, have controlled infection by E. lata in trials worldwide. However, results have been variable and the products were usually less effective than fungicides, paints and pastes. John et al. (2005) reported the control of eutypa dieback by Trichoderma spp. and a commercial formulation of these species (Vinevax™) was registered in 2004 as a wound protectant in Australia. Although biological control offers long-term protection, the 1-2 weeks required for biological agents to colonise the wound provide a window of susceptibility to infection by E. lata.

Alternative non-chemical control

The use of non-chemical alternatives to fungicides has not been critically evaluated for the control of E. lata. Research is currently underway to assess garlic extracts and lactoferrin as wound protectants in field trials. Both were effective at reducing spore germination and mycelial growth in laboratory trials.

Cultural practices

The risk of infection by E. lata is reduced when:

• pruning is avoided in wet weather when spores are released from fruiting bodies
• vines are pruned at least 36 h after rain begins, by which time spores are depleted
• pruning is conducted late in the season, when wound healing is fastest and the sap is flowing
• the number and size of cuts to wood two or more years old is kept to a minimum
• pruning cuts are made at an angle to encourage water to drain from the wound surface

Spores are released within 2 h of the onset of rain (>2 mm) and spore production persists for at least 36 h, after which fruiting bodies become exhausted (Carter 1991). After 12 days fruiting bodies are recharged and produce a further generation of spores.

The risk of infection is determined, to a great extent, by wound susceptibility (Carter 1991). A number of factors influence the duration of wound susceptibility, including the time of year when cuts are made, the rate of wound healing, sap flow and temperature. Wounds made in early winter are susceptible to infection by E. lata for 4-5 weeks whereas those made in late winter to early spring may remain susceptible for only 10-14 days.  Wounds heal faster when made in late rather than early winter due to the vine’s natural healing mechanisms. Wounds also tend to dry faster in the warmer weather, which aids healing. The warmer weather in late winter also encourages the growth of other microorganisms on wound surfaces, promoting competition for nutrients and antagonism and thereby reducing the ability of E. lata to infect. Furthermore, wounds made in late winter exude sap which may “flush” spores out of xylem vessels, further reducing the likelihood of infection.

Wound size also affects susceptibility (Carter 1991). Large cuts are more prone to infection because of the increased chance that a spore may land on the larger surface area. Large cuts also take longer to heal. Studies have shown that there is no difference in the susceptibility of fresh wounds on either one, two and three-year old wood to infection by E. lata. However, cuts made on one-year-old wood tend to be considerably smaller than those made on older wood, reducing the likelihood that spores will land on the wounds. Also infections in one-year-old wood are more likely to be removed in subsequent years through normal pruning practices than are infections in older wood.

Double pruning, a method developed by researchers at UC Davis, is the practice of mechanically pre-pruning to leave long spurs in early winter followed by hand-pruning to short spurs in late winter. US trials showed this practice significantly reduced infection by E. lata (Weber et al. 2007).

Sanitation

Removal of dead wood from the vineyard may reduce inoculum levels, however this alone is not sufficient for managing eutypa dieback. Spores can be blown up to 50 km in the wind and there are many alternative hosts, such as stone fruit and pome fruit as well as numerous ornamentals such as poplar, ash and pepper trees, which may also act as inoculum sources (Carter 1991).

Contamination of pruning tools is unlikely to be a major means of spreading the disease. Furthermore, the use of fungicides on wounds should kill any fungal material spread by pruning tools. However, cleaning of pruning tools is advisable when moving from an infected block to a young healthy block, in accordance with good hygiene practices.

Remedial surgery

There is no reliable means of eradicating the fungus once it becomes established within a vine. Foliar nutrients and trunk-injected fungicides failed to control eutypa dieback. Consequently, many growers “renew” infected vines by removing diseased wood and reworking. Due to delayed symptom expression in the foliage it is imperative to be vigilant in detecting early symptoms of eutypa dieback, so that less wood needs to be removed. When infection is restricted to part of one or both cordons, wood is removed until the cross-sectional wedge of discoloured wood is no longer visible and then a further 10 cm cut out to ensure that all infected wood is removed. A cane is then trained to replace the section of cordon removed. Where cordons are infected and the fungus has progressed into the trunk, two methods may be used to restore vines (Sosnowski et al. 2004).

1. The cut and train method involves cutting off the trunk 30-40 cm above the ground, inducing and training up a watershoot to replace the lost canopy (Figure 3). Stumps can also be grafted. This method maintains the existing rootstock, but the roots may suffer from a loss of photosynthates as a result of the canopy removal. Commercial yield is delayed for several years until the new canopy is established.
   
2. The train and cut method, where a healthy shoot selected from the base of the trunk is trained up to form a new canopy (Figure 4). The infected trunk is not removed until the new shoot begins cropping, thus leaving some canopy growth to support the root system. Some grapes may still be harvested from unaffected parts of the vine supported by the infected trunk.
    

 
The cut and train method reduces the likelihood of the pathogen remaining in the trunk, however, watershoot production may also be reduced (Figure 5). When trunks fail to produce watershoots, vines can either be replanted or layered. Layering is the use of a healthy cane from a neighbouring vine which is buried in the soil to induce root growth and hence create a new vine in the position of the old dead stump. The new vine is severed from the mother vine once the root system is sufficient to maintain the young vine.

The train and cut method increases the likelihood of watershoot production (Figure 5), however, the shoot selected may originate from infected wood, leading to recurrence of symptoms on the new shoot (Figure 6).

  
Remedial surgery is an effective method of controlling eutypa dieback and maintaining the longevity of premium vines. However, there is no guarantee that the disease is eradicated. It is important to rework vines from shoots below infected wood, to minimise the recurrence of symptoms, as shown in Figure 7.

Figure 7. A grapevine trunk with a symptomatic cordon (left) originating from the crown of the trunk and a healthy cordon (right) originating from the base of the trunk.
 

Acknowledgements

This research was conducted by SARDI and the University of Adelaide with funding from the Grape and Wine Research and Development Corporation and the Cooperative Research Centre for Viticulture.

References

Carter, M.V. 1991. The status of Eutypa lata as a pathogen. Monograph – Phytopathological Paper No. 32. International Mycological Institute, Surrey, UK.

John, S., Wicks, T.J., Hunt, J.S., Lorimer, M., Oakey, H. and Scott, E.S. (2005) Protection of grapevine pruning wounds from infection by Eutypa lata using Trichoderma harzianum and Fusarium lateritium. Australasian Plant Pathology 34, 569–575.

Sosnowski, M.R., Creaser, M.L. and Wicks, T.J. (2004). Managing eutypa dieback of grapevines by remedial surgery. The Australian and New Zealand Grapegrower and Winemaker 488, 35-39.

Sosnowski, M.R., Creaser, M.L., Wicks, T.J., Lardner, R. and Scott, E.S. (2008) Protecting grapevine wounds from infection by Eutypa lata. Australian Journal of Grape and Wine Research 14, 134-142.

Weber, E.A., Trouillas, F.P., Gubler, W.D. (2007) Double pruning of grapevines: A cultural practice to reduce infections by Eutypa lata. American Journal of Enology and Viticulture 58, 61-66.

For more information, contact Mark Sosnowski