Every day at work I eat lunch at my desk and work through the lunch hour. I try and use that hours time to get in a morning walk and an afternoon walk instead. Most days I'm able to get in 2-3 miles around the little neighborhood at work. I'm hoping that those walks, with the gym training and our weekend hikes, will have me ready for our Grand Canyon trip next spring.
Every day I go by this set of trees. You can't really see this in this picture but I wanted to give some scale to the size of the trees
The trees are covered in Powdery Mildew. Powdery Mildew is our main pest enemy in the vineyard. It attacks the fruit and leafs of vines and trees. If left unchecked it will eventually kill the host (tree or vine) by shutting down all photosynthesis in the host. All of the green area is eventually infected and the plant can't process sunlight. Even a little on fruit can block flavor and sugar development.
It's a tough little mildew too. Once it gets started, or to an advanced stage like this, there's really nothing that can be done to stop it, or reverse the effects. Everything is in prevention. The mildew is actually fairly un-hardy. It doesn't like it too hot (over 90), or too cold (under 70), or too windy, or too damp. Those though are exactly the conditions you want in a vineyard. Between 70-90, with no wind and no summer rain or humidity. Powdery Mildew loves vineyards.
It spreads through spores that attach themselves to the green parts of the plant. That's why it doesn't really like wind. Too windy and the spores can't attach. The spores are hardy though. They can survive hot and cold spells in a dormant stage and then go active when the weather is right.
In the vineyard we use something called Integrated Pest Management to control the mildew. Basically that's putting a complete and complex system together that understands the life cycle of the pest and tries to deal with it with as few chemical applications as possible for complete control. The first step we do is to remove any infected plant material from the vineyard at pruning time. This removes a great many of the spores that would be present.
This is actually easier than it seems. If you've kept the mildew out of the vineyard during the year, there is no infected material to remove at the end of the year. When we take on a new vineyard though, there will be material to remove.
We also plan on short growing cover crops. The grasses and plants in between the rows can harbor spores so we try and select plants that grow short. Most spores spread by falling from above and attaching to a lower part of the plant. By keeping the vines the highest thing around we don't let spores fall.
Then we do all the thinning and have a pruning strategy to open up the plants to airflow. Since the spores like calm air to spread, we try and open the plant up to the wind. The idea is that a little wind will prevent the spores from attaching to the leafs as they fall.
The final part of the plan is to use sprays. All the available sprays do basically the same thing. They create a barrier on the plant surface that prevents the spores from attaching and or activating on the plant. Timing the spraying is key. You have to watch the weather closely. If it's going to be really cool, or really hot, you won't need to spray. UC Davis has a tool that will help a grower figure out when the mildew is dormant, and when it will go active. You need to spray before it goes active. You also have to watch for rain and moisture. Many of the sprays will wash off in the rain.
There are many organic sprays: sulfur, mineral oil, baking soda, that are effective. They work by creating a barrier on the leaf that 'zaps' the spores before they can get attached and going on the leaf. The in-organic sprays tend to work by getting inside the plant tissue and creating a barrier from the inside out. That means they generally won't wash off in the rain as well.
I always say "we try to be as organic as possible', and I know people usually wonder why I'm qualifying that, or what I'm hiding? Well, it's the trees. No big secret, it's just hard to explain in 10 seconds or less.
In our vineyards I prefer to use mineral oil and baking soda as treatments. I don't really like using sulfur if I can avoid it and I've found the oil to be very effective. These treatments are organic and I only use products that have been certified as organic in those cases. But in some vineyards we have had trees. Big trees, that hang over the vineyard. Big trees that were as infected with Powdery Mildew as the pictures I took today.
In those cases the organic treatments where just overwhelmed by the pressure from the trees. There was too much mildew to control with oil, sulfur and soda alone. It would have required so much spraying that I would have had to go over the maximum amounts recommended for each product. It really comes down to a simple choice; use something that can penetrate the plant and protect from the inside out or cut down the trees.
That's a very hard choice for most homeowners we've worked with. Usually they ask if the trees can be treated. They can, but it has to be done by airplane, which is not something you can do in a suburban area. So then I have to find an alternative that's as safe and low impact as I can. That's why I say "we try and be as organic as possible." As long as there are not infected trees, we'll be organic. If a tree gets mildew and overhangs the vineyard, we're probably going to spray something non organic to save the vines. That's pretty rare these days, we don't have any tree issues this year, but if it does happen we'll have to treat at least the overhang area, and that's why I qualify the organic statement.
Disclaimer for my friends at the SCC DPC - This should not be considered advice on treating Powdery Mildew, only a licensed Pesticide Advisor can give you advice on treating or preventing Powdery Mildew. This is provided as editorial comment on my practices only and should not be taken as consultation or expert opinion, which would require a license I don't have.
If some other government organization is concerned that I may be giving unlicensed hiking advice, or walking advice, or some other advice that requires a license and fee, that statement was given as personal editorial comment only as well.