March (No. 494)
Ben Rose , Performance Viticulture
Real Viticulture is a regular column written exclusively for Grapegrower & Winemaker by Ben Rose, principal consultant of Performance Viticulture.
I have been told by other growers that a post-harvest high-rate sulphur spray is of little value for powdery mildew and mite control. What is your opinion?
Research has shown that post-harvest sulphur sprays applied at high rates is of little benefit for reducing the over-wintering populations of powdery mildew spores and mites. This would indicate that the application is not warranted.
However, post-harvest disease control may be beneficial depending on the prevailing weather conditions and on the time of harvest. Once the grapes have been harvested many growers believe that management of the grapevines stops until they begin winter pruning, however, this is not the case. Post-harvest disease control is very important until the leaves fall. It is post-harvest that the nutrients from the leaves are taken back into the trunk and root system of the grapevine, and stored until the following season. Anything, including disease outbreaks, that reduces this recovery of nutrients may lead to poor budburst and early shoot growth the following season. Therefore continued control of disease until leaf drop is critical.
I put vine guards on my new planting last year, and the vines have grown well. I am interested in knowing when to remove the guards.
My preference is to leave the guards in place until winter pruning is undertaken, that is until after natural leaf fall. If the guards are removed while the grapevines are still growing, it may result in damage occurring to the trunk and to the leaves of the young plants. This damage may be in two forms, but both are a factor of the softness of the plant tissues.
Most guards promote high CO2 content and high moisture content and this assists the fast growth experienced by vines under guards. However, these conditions may also lead to the growth being soft, which, while the vine is protected by the guard, is of little problem (unless the prevailing weather conditions are very hot in which case the guards themselves may damage the grapevines). Once the guards are removed, however, the soft tissue is susceptible to fungal infection and to dehydration and sunburn. Therefore removal prior to natural leaf drop should only be undertaken in situations where the guards themselves may be causing problems with grapevine growth.
NOTE: The complete article can be found in the March issue of The Australian & New Zealand Grapegrower & Winemaker.