Using pruning to keep vineyards disease-free
By Brandy Rawnsley
Pruning is essential for obtaining desired yield and fruit quality but when done right can make an equally positive impact on managing pests and disease for the coming season.
Grapevine trunk diseases such as Eutypa dieback and Botryosphaeria are key diseases that can be managed by pruning strategies. These trunk diseases are caused by fungal pathogens that infect wood which slowly kills the cordon and eventually the trunk.
At pruning, remove infected wood. Where cordons are affected, remove dead wood as well as 10 cm of healthy wood to ensure you remove all infection. This will encourage shoots from lower uninfected parts of the vine.
Spores from Eutypa are released from infected dead wood in wet conditions. When released, they land on new pruning wounds and the infection process starts all over again.
For this reason, pruning hygiene is critical to minimise the spread of disease when airborne spores are most prevalent.
Firstly, make sure pruning tools are clean. It may seem obvious, but can help stop the spread of disease, just like handwashing to reduce the spread of influenza and other viruses.
Secondly, avoid pruning during rainfall. This can be hard to achieve in winter but reduces the ability of the spores to infect. For Eutypa, spores can be released up to 36 hours after rainfall. Botryosphaeria is a little more forgiving and spores are released up to 2 hours after rainfall.
Next, apply a fungicide or a paint directly to large cuts. This creates a physical barrier to mitigate the risk of infection, especially for Eutypa. There is also the option of treating wounds with a biological control agent such as Trichoderma spp.
Other diseases like Phomopsis overwinter on infected vines and pruning is an ideal time to reduce the inoculum source in the vineyard. Often infected spurs have a white, bleached appearance so prune these spurs if Phomopsis is suspected.
Powdery mildew survives in green tissue so a ‘prune and remove’ strategy doesn’t assist disease control. However, if powdery mildew was a problem, there is likely a high level of infected buds. Keep this in mind with pruning strategies to reduce canopy density.
While pruning, also be on the lookout for insect pests like scale, earwigs and weevils that can be found on the underside of canes and spurs, and under the bark. Scale can infect immediately after budburst, so pruning is a useful monitoring time for impending problems.
Even if pests and disease do not appear to be a problem in your vineyard, a targeted approach to pruning assists canopy management and vine health for the coming season.
Dr Belinda (Brandy) Rawnsley is a Syngenta Technical Services Lead for Viticulture and Horticulture