Powdery Mildew, Sulphur and Compost Teas
Sadly Powdery Mildew has arrived at the vineyard, at the moment primarily infecting some of the Pinot Noir on Block A.Powdery Mildew survives the winter either within infected buds, which subsequently germinate to form mildewed “flag shoots”, or as tiny fruiting bodies that lodge in the bark on the vine which release new spores to infect young tissues in the spring. Leaves are highly susceptible to infection while they are expanding but become resistant soon after they’re fully expanded. Berries are highly susceptible from flowering until shortly after fruit set, but become much more resistant afterwards. Interestingly, research has shown that significant berry infection at harvest can almost always be traced back infection soon after flowering.
So far our strategy to deter fungal infections has been to use compost teas, the theory being that by populating the foliage with the good guys there will be no room for the mildews to infect the plant. Unfortunately recent weather conditions have been ideal for powdery mildew which thrives in temperatures between 15C and 25C with a high relative humidity and as a result the compost tea hasn't been fully effective.
The standard organic treatment for Powdery Mildew is Sulphur and Potassium Bicarbonate (baking powder), both of which are sprayed onto the foliage of the plant. Garlic sprays are also be used as garlic naturally contains high levels of sulphur. Rain and free moisture on the surface are also unfavourable for colonisation, sporulation and dispersal, so the sulphur and baking powder are often sprayed with high quantities of water in the morning so that the foliage takes most of the day to dry.
The problem with sulphur is that it also prevents the good bacteria and fungal content from the compost tea from doing their job; so unfortunately it's one or the other. We have decided that for the time being we cannot risk the further spread of the disease so we will be spraying the plants on Block A with sulphur and baking powder.
We will have to review our spray programme for next year; as sulphur is a preventative measure and not curative, we should really be using it from the beginning of the year if it is to be fully effective.