Without rain we wouldn’t have a vineyard, but this stuff also causes us a bit of grief.
As a rule rain received in Orange prior to Christmas is beneficial and after that… not necessarily.
Early in the season the vine canopy is fairly small and airflow through it is reasonably good. After Christmas the canopy starts closing in, airflow is restricted, the air is warmer, and humidity increases within the canopy. This increased humidity favours the growth of fungal diseases such as Downy Mildew and Botrytis and like us, they like it when it’s a bit warmer.
Heaps of rain exacerbates problems, as it makes vines grow rank making it very humid within the canopy.
We do things like shoot thinning, leaf plucking and trimming to maximise the airflow which reduces humidity… this helps but it is not enough to control an outbreak of fungi in wet years, so we hold an intervention.
There are several preventative measures available that limit the entry of these fungal spores into the vines. And thanks to consumer demand for organic products the chemical companies have propagated some friendly bacteria and fungi we can apply that compete with the fungi for attachment sites helping prevent the entry of these spores into the vines.
We keep an eye on the forecast and when rain is predicted we get really busy with preventative measures in the vineyard. It is necessary to be pre-emptive because it is difficult to control disease once it is visible on the vines.
There is good research available on timing for control with early season intervention playing a very important roll. The spores for these fungi are present in the vineyard from overwintering on dead plant material and sometimes in the buds themselves. These fungi multiply when conditions are favourable and become a problem when their numbers reach a critical mass… It’s our job to keep the fungi numbers low. Fungi spores aren’t a problem in the early part of the season, but once they get a roll on they are really hard to rein in and can explode into an uncontrollable problem late in the season.
So, it isn’t really the rain that stuffs up a good vintage but it’s the fungal conditions that develop as a result of the rain that is the main problem except for the ripening period… When the grapes are very sweet they suck up water from rain which expands the grapes so much that the skins split. This causes obvious problems by itself and is complicated by the fact that Botrytis loves sugar and becomes very hard to control once the grapes split.
In dry seasons these fungi are much less of a threat. In fact, Downy Mildew and Botrytis are almost non-existent in the hot Mediterranean climate of the Central Valley of California where I grew up as it simply doesn’t rain during the summer months.
Enjoy the Season and when it rains, snuggle up to a glass of red.