Advice on Mildew: You May Not Realize You Have It

The message below popped into the GBN mailbox this afternoon from Charles Schmebre, Program Manager at the UNR’s Desert Farming Initiative. Here’s Schembre’s advice for identifying mildew and preventing it.

Since I have taken the job here, I have heard from many that they do not get mildew or now they do get it. I also have reason to believe that some of you may not realize you getting mildew if it is a small scale. The fact is, most vineyards will get mildew at some time in its life if you are not spraying to prevent it. Mildew is not specific to moist regions. In fact mildew enjoys warm temperature to thrive, and sporulation begins and is most rapid around bud break. Once mildew has inoculated vines, it is hard to remove, but achievable.

I have attached a couple pictures for your viewing to see intermediate signs of mildew. What I mean by intermediate, is it is not too late to kick this in the butt. Mildew can be identified much earlier on the rachis of the cluster, before it spreads to the berry. This requires a hand lens. In the pictures (below) you are looking at Pinot Noir Clusters, which are a variety that is more susceptible to mildew. Chardonnay is also a variety that is very susceptible.  Advice from Charles Schembre continues after the photo…

Signs of mildew on the grapes. Photo courtesy of Desert Farming Initiative at UNR

In the picture above, the clusters are heading into “bunch close”. It is imperative to nip this in the butt with fungicides before the cluster closes up, or the mildew is almost impossible to stop. All spray nozzles from the sprayer should be directed at the clusters and the cluster should be dripping after the spray. At this stage it is best to use a systemic fungicide like Elvate (if you are not organic), and a knock down, such as Kali-Green or Patassium Bicarbonate (combined). Advice from Charles Schembre continues after the photo..

Photo courtesy of Desert Farming Initiative at UNR

If you are oganic, you will want to use Serande and Kali-Green. Best to also mix with a surfactant to guarntee good coverage and proper spray droplet sizes for penetrating the cluster. I do not recommend using Sulfur at this time of the year, it is well known that sulfur interferrs with grape quality and skin texture at this point of the cluster development, and can lead to skin burn. But most imporantly, your fruit zone should be leaf thinned in the inside of the canopy and under the clusters, but be sure not to expose the clusters to too much sun, and only leaf on the morning sun side. Leave the afternoon sun side “un-leafed” to prevent sunburn. You can actually prevent mildew to some degree with proper canopy management of early leafing, shoot positioning, and get away with little spraying. Most vineyards spray as a preventative every 14-21 days until verasion.

Preventing mildew starts at budbreak, and sulfur or mineral oil should be applied every 10-14 days for 3 spray intervals. This generally can prevent mildew 90-100%. We have mildew because this vineyard had a bad case last year, and our spray timing has been off a bit. But overall our vineyard looks pretty clean, and it is mainly the Pinot and Chardonnay that have mildew (not a surprise).

I just wanted to give a quick understanding and some quick tips since a few growers have asked me questions. I have managed pesticide programs in organic and conventional vineyard for the last 10 years. If you have any questoins please feel free to ask.

I hope this helps and feel free to pass along to other grape growers you know. I am hoping to put together blogs like this in the future. Stay tuned and let me know if these types of growing tips are helpful!

You can contact the Desert Farming Initiative here.