June is the time which Angelenos and those in Ventura County call "June Gloom." Each morning we wake to a heavy fog layer that doesn't lift until close to 11 AM. The day heats up quickly after the marine layer pulls back and then a cold wind blows it all back in starting around 5 PM. It makes it comfortable for sleeping, but increases our work grape growing.
Farming close to the coast is a mixed bag when it comes to growing grapes. The cooling influence of the Pacific Ocean allows us to keep the fruit on the vines longer than we could otherwise and contributes to the richness we are able to get in our wines. The large diurnal temperature swings preserve the natural acidity of the grape contributing to balance. Plus...it never gets too hot in the vineyard when you are working. These are all wonderful.
What isn't so wonderful is that powdery mildew also loves these conditions. Powdery mildew is a fungus that infects young growing tissues of grape vines and can destroy grape clusters and make them unusable for wine. It is native to North America, but has spread worldwide. It grows fastest in warm temperatures of 65-85F and humid environments. Every vineyard has powdery mildew to some degree and those that don't just aren't looking hard enough.
We combat powdery mildew in a couple of ways. First, we prune the vines in the dormant season so that shoots grow evenly along the cordons and we end up with an even canopy without too much overlapping growth. In spur pruning this means our vineyards have one, two-bud spur every six to ten inches. This keeps the vines relatively orderly under ideal conditions.
Since ideal conditions only exist in text books we then take the next step to trim out excess growth to keep the canopy even. If the soil has abundant water from winter rains or excess irrigation the vines will often grow excessively and we will trim the tops of the vines so the canes don't droop over and shade the fruiting zone. We try to balance the canopy growth by having the right amount of fruit on the vine, but this dance isn't always simple.
The next step is to pull basal leaves from the vines to allow air flow through the canopy to reduce humidity and allow any condensation to dry in the morning. This canopy management program works well to create a dappled sunlight in the fruiting zone and minimize mildew pressure.
Mildew pressure is limited in hot dry climates and canopy management is sometimes enough to keep the vines clean. In coastal or cooler climate areas we have to take additional steps to combat powdery mildew. We spray the vines from the moment leaves emerge until the fruit gets midway through ripening (March-July).
Vineyards that farm conventionally can spray compounds that prevent mildew for up to 4 weeks. We choose to utilize organic fungicides in our vineyards and have to spray every 10-14 days to maintain control. We begin our season using Stylet Oil to eradicate any mildew spores that overwintered and then move to using wettable sulfur every 14 days after that. The oil acts as an eradicant while the sulfur is a protectant and prevents the mildew from proliferating.
If we see some mildew starting (we generally do at some point) we switch the next round of sprays to Stylet Oil to clean up the fruit and canopy. The program works well, but is very labor intensive. The spraying is done by hand with a backpack sprayer and progresses through the vineyard at a rate of 2 miles per hour. We move up one side of a row spraying and then move back down the other side of the row. Complete coverage is important so we move slowly and take our time. It often feels like groundhog day when you spray block after block, day after day. We finish one rotation and it is almost time to start over. Sometimes we make new friends on our walks...
We had budburst on early varieties like Sangiovese and Grenache during the second week of March and did our first spray one week after that. As of 6/15 we have sprayed the vineyards a total of 7 times so far. This equals over 53 miles of walking so far this season and doesn't include the multiple passes through the vineyards leaf pulling and hedging. It is a lot of work, but we feel that the softer organic approach for mildew control is a better option for us and produces beautiful fruit with a lower impact. The walking is hell on your boots though. These didn't even make it from winter pruning to harvest.