TastyLandscape Growing fruit trees at home in Southern California
Grape Powdery Mildew (Uncinula necator)
AKA (Erisiphe necator)
If you grow grapes in coastal California, (or almost anywhere in the world for that matter), you are probably going to see a white powdery substance on the leaves. This is grape powdery mildew. While this is common, it is a disease that will damage your grape plants and your crop if left untreated.
Grape powdery mildew (white)
What is powdery mildew?
Powdery mildew is a fungal disease that affects a wide range of plants. The specific fungus that causes powdery mildew on grapes is Uncinula necator.
Grape powdery Mildew
How do you get grape powdery mildew?
- The fungus that causes grape powdery mildew is all around us and it is therefore close to impossible to avoid. It is spread by the wind.
- The fungus is thought to have originated in North America. Therefore, North American grapes that co-evolved with it are more resistant than European grapes.
- A small amount of the fungus stays dormant on grapes in the winter, and when conditions are right it spreads rapidly over the plant.
- Like any fungus, it does best in cool moist environments. This is why the disease is particularly problematic in coastal areas. A wet growing season and/or excessive marine layer will exacerbate the disease.
- Ideal temperatures for the growth of grape powdery mildew is between 70° and 85°F. Welcome to California.
- High temperatures and sunlight are inhibitory to powdery mildew.
Grape powdery Mildew dehydrating and curling grape leaf
Where can you see powdery mildew first?
- Because the disease is a fungus, you will first find the disease on the undersides of leaves. This is because the undersides of leaves are protected from the sun. The fungus is also more common in the deeper parts of the plant where there is poor air circulation.
What will powdery mildew do?
- Grape powdery mildew will suck the life out of your plant, damage leaves and spoil your grapes.
- The disease can and will cover the entire plant if not controlled.
- It can cause leaf curling, withering, red blotchy areas and distortion of leaves.
How do you treat powdery mildew?
- Because the disease lives on the surface of the plant, topical spray treatments are very effective.
- I recommend that you get (and label) a separate garden sprayer for each of your different garden needs. That way you don’t have to worry about spraying residue of something like an herbicide on a plant that you would actually like to keep around. It is also nice to have one with an angled spray nozzle so you can easily get the bottoms of the leaves.
- The first few treatments of the season are the most important, and should be applied at bud break and during early growth.
- There are many different anti-fungal sprays that can be used to fight powdery mildew.
- A few of the organically acceptable methods include sulfur, Serenade, Sonata, and Stylet oil. There are many other good options out there, I happen to use a copper based spray.
- Many professional wine growers rotate through different types of fungal sprays to prevent the fungus from developing a resistance to one specific treatment.
- Most spray treatments for grape powdery mildew are on a near weekly basis depending on your micro-climate. Complete spray coverage is important to get the hard to reach parts of the plant that are also the most susceptible to fungal disease.
- A Powdery Mildew Index (PMI) was created to determine how frequently you need to spray grapes for powdery mildew. The University of California, Davis has the one most widely available models, which requires data entry for leaf wetness and temperature. However, for the home grower, it is a lot easier to just spray on a regular interval as suggested on the fungicide label.
My method:
- I found that the most important element for success is to spray the buds in the dormant season with a mix of horticultural oil and anti-fungal spray. This is process is kind of like treating for peach leaf curl. For example, if you wait till the leaves are already out and infected then it is an uphill battle all season long.
- That being said, you can also spray all season long for powdery mildew and it will help while in the case of peach leaf curl, spraying after bud break doesn’t reverse the damage.
- Specifically: I am using a mix of “Bonide All Seasons oil” and Bonide Copper Fungicide. I just use the recommended concentrations of both in the same spray bottle.
More on horticultural oil:
- Overall, horticultural oil is an awesome alternative to systemic pesticides and it kills all kinds of sap sucking pests.
Wine Industry Experience:
- My good friend Stasi Seay has extensive experience in the wine growing business as a viticulturalist. She has recently contributed some farming perspective to the issue of grape powdery mildew. Please read her 6/18/13 insight in the comment section below.
Prevention of powdery mildew?
- While you can’t change the weather, there are some other things that you can do to battle this disease.
- Planting grape rows in a North to South orientation will result in a more even sun exposure on the plant. This will reduce the areas where fungus will thrive.
- Pruning out overlapping and clumping branches will help with aeration and sun exposure.
- Use drip irrigation and keep your plants clear of sprinkler irrigation.
- Plant grapes away from humid micro-climates such as close to a pool or hot tub.
There is a very easy way to prevent powdery mildew from every happening and, if you get it, to treat grapes, squash and cuke plants. Just mix 1 part whole milk with 9 parts water and spray, weekly. It is a proven treatment for vegetables and actually got it’s biggest field test with grapes. Wrote about it here
http://growsoeasyorganic.com/2013/01/19/grow-so-easy-organic-bugs-that-bug-summer-squash/
and there is a link in my post to the information on Bettiol’s research! Cheap, easy and organic. Love those solutions.
Thanks Pat!
Very interesting.
Do you know how the whole milk works against powdery mildew (the mechanism of action)?
Thanks, Tom
I don’t! But I would love to know. It seems so simple just to spray milk and water on your vining plants. Can you share?
Dear all Greetings! I have working on Grape Vine in Ethiopian Institute of Agricultural Research. I have faced powdery mildew in grape research. Can you suggest any fungicide chemical which control powdery mildew? Please send any suggestion with my E-mail: mulukend04@gmail.com
I am a viticulturalist in California. I haven’t heard of the milk treatment (interesting!) but know that the key to controlling powdery mildew on grape vines is disruption of the spore cycle, followed by use of elemental sulfur. To do this, you need to spray with high volumes of water and a light detergent. The high volumes of water, coupled with a bit of soap, breaks up the spore cells.
For home use, you can put a few drops of dish soap in a spray bottle of water. For several plants, consider using a 2-3 gallon sprayer and add 2 ounces of laundry soap. Cover each plant thoroughly.
For high infection, as soon as the leaves dry from the soap treatment, use dusting sulfur, which is an organic product. You can buy it at your local home and garden store or farm center. Give the leaves a light dusting and always follow the label directions.
Cheers! Stasi
http://www.unlockwine.com
Thanks Stasi!
Great advice. Ill add your reference to the the post!
thanks for that i,ll give it a go AD gilberdyke
Stasi, when applying the sulfur after the dish soap application, can the sulfur be ‘wettable’? I have 80 vines and don’t know how to apply dry, but can easily apply through a wet sprayer.
Thanks … John
Your website won’t let me leave the page.
My browser stopped it from opening 6 pop-ups.
this is what is called unprincipled use of the web.
Annoying, unnecessary and it has just lost you me as
a potential reader.
Hi Gerry
Sorry and thank you:
Sorry to hear about your experience.
It does sound annoying and this would never be my intention.
But thank you very much for sharing this important information.
Overall:
I am very surprised and a bit alarmed to hear about your popup issue.
I have never added any advertisements to this site, so I dont know how popups could be associated with this site.
Testing:
After your note, I have tested this site on multiple different computers and devices and there were no popups or other issues leaving the page.
Favor:
If you could be so kind and provide me additional information so I can further troubleshoot, that would be great.
* Did you get a specific type of popup or specific adds?
* Did you experience this with a particular browser (Internet Explorer, Firefox, Chrome, etc)?
* Have you had similar experiences with other websites?
Thank you very much,
Tom
How long into the growing season can I apply sulfur?
I have 3 grape plants out of many that have this powdery mold on it real bad this summer. Now in Oct, I have cut all the branches off the plant to try and rid it of the infection. I just have the main mother stalk now. Would now, in the fall, be a good time to spray with soap or sulfur? What should I do with the old branches and fruit? Will it spread on other things if I try to use the debris for a hugo culture or something?
Hi Diana
Great questions.
Winter treatment:
There are a lot of potential anti fungal treatments you can use. I happen to like copper-based sprays but others work great too. Some people only spray when they see the powdery mildew on the leaves. But in my opinion, once you see it your really behind on things. Spraying before the buds open seems to make a big difference much like spraying for peach leaf curl. For reference, see article on peach leaf curl treatment
What to do with cuttings:
The disease is spread by tiny spores and the spores are probably everywhere.
However, the spores are in the highest concentration where you see the “powdery mildew” which is basically a dense concentration of fungal parts and spores. Therefore, anything that you can actually see powdery stuff on has a huge volume of infectious material on it. Thats trouble. In addition, the more you move these infected leaves and branches, the more you spread the disease. So, if I was you… I would carefully move all the infected plant parts to a trash bin. Collect all the dead grape leaves and throw them away too. Once you have cleaned up everything and trimmed everything then do the fungal spray. Spraying again in late winter/early spring before buds break is also a good idea.
Good luck,
Tom
Dr. Osborne,
Thank you for your insight on powdery mildew. We have a home vineyard, 80 vines in hot sunny Southern California.
Last season we had a terrible time with powdery mildew, so bad that it left rust brown spots on the canes. We treated every 10 days, alternating with Neem oil and Stylet.
We have taken your advice and sprayed the vines with Bonide Copper Fungicide and Bonide All Seasons Oil before bud break.
Going forward, I’m not sure how to treat. Stasi’s advice is intriguing but I’m just not sure how to proceed since our buds are on the verge of breaking.
I would appreciate your advice.
Thank you for your time and expertise,
Tammy P.
hi Tammy
The key for me has been to spray with copper/oil mix in the dormant season and just before bud break. Spraying after leaves get infected has much less effectiveness but may help some.
Carefully cleaning up and trashing all the dead leaves on the off season is also very important because they are typically full of spores.
Best of luck.
I have few questions;
1. When to apply spray?
2. Shall we apply it on winter or when grape bloom in to 3 to 4 inches?
3. Bud break?
4. How is lime sulfure?
Hey Shafiq
There are differing opinions regarding the best time to apply treatment for powdery mildew.
In my experience, it is important to spray before bud break (much like you would treat for peach leaf curl).
Some people will spray several times in the dormant season. However, if you are going to spray once, I would time it for about a week or two before bud break. For me that is usually late winter, early spring.
I have not tried lime sulfate. I would apply any antifungal with the same timing protocol.
Happy holidays!
We have many gardens of grapes in Afghanistan/Kandahar.
The grapes got powdry mildew now we don’t knw the exact time to spray…
How if the 1 to 2 inch bloom, we spray…?
Hi Shafiq
The best time to spray (in my opinion) is before buds break.
Of course you can spray later but that will be less effective.
It will also be more expensive because you will need to cover more surface area (spraying all the leaves vs just branches).
Spraying sooner is better than waiting till later.
Best,
Tom
Do u mean that now we should start spray…?
If u could please tell us the month or date of it…?
Thank you
Hey Shafiq
The best time to spray is before bud break.
If you miss that, then the best time to spray is sooner than later (as soon as possible).
The longer you wait, the worse the infection gets.
The problem is that it is really hard to deal with the infection after untreated leaves open up. When this happens the leaves are inoculated with the fungus. You will then need to spray more during the growing season and the spraying will have less of an effect.
Prevention is a really important part of the equation (as detailed in the article).
Hope this clarifies things for you.
Best of luck,
Tom
Thank you Dear Tom!
But I have one presentation of University of Kentucky about fungicide they gave details about to spray early season… 1 to 3 inch growth through 3 to 4 weeks after bloom…
I want to share it with you give me ur email address.
Hey Shafiq
Thanks for the info.
Feel free to send the link if you like so everyone can benefit.
My suggestions come from personal research and personal experience.
I have found it is best to do the first spray before bud break and then again after that as needed (per fungicide brand-label recommendations).
If you feel more comfortable with the University of Kentucky’s suggestions then that’s great too.
Best,
Tom
Interesting discussion of use of oils. I had mites on my lemon and tried a gentle finger-rub of coconut oil on the infected leaves and it worked like a charm. I also gave it a few weeks of semi-shade to prevent sun burn. That solution worked because the tree is small and the infestation was limited. I will try same on my grape fungus.
Hi Ann
Great idea with the coconut oil.
Looking forward to hear how it works on your grape fungus.
Thanks,
Tom
Great Post. Thanks for sharing this informative post with readers. This was very helpful and I enjoyed it reading.
Hi my name is Easter, I have one vine in Los Angeles ,Ca. My grapes are red globe. I got the plant as a baby from Home Depot about 8 years ago. Around 4years ago my neighbors gardener butchered my vines and keeps blowing them with his leaf blower. Since then I have fought scale and mildew. Last year I tossed a whole 30 gallon bag of grapes. This year my vine is only half the size and full of green pea size grapes that are beginning to get patches of powder but the leaves aren’t blotchy. Soap doesn’t work and the fungus sprays available don’t work. I will try the milk. Does anyone have any other suggestions?
Hi Easter, thanks for your note.
So sorry to hear about your sad grape situation. One of the keys (at least in my experience) is to do off-season prevention work. For example, after the leaves fall, destroy/throw them all away (dont leave leaves lying around because the fungal spores on those previously infected leaves are just waiting launch their damage in the spring).
After you trim back all the dead branches and prune for the winter… also spray with anti-fungal. I also spray antifungal again in the spring before the buds break. This is key because once the infection gets those young buds, it is super difficult to do anything about it.
Best of luck,
Tom
I’m in southern California and well into the growing season. I have a vineyard in my property and have just noticed, now that the grapes are on the vines that some of the grapes have powdery mildew! I did not have a problem last year so decided best not to spray in the early spring. What a bad idea! Can I being to spray the vines and grapes with Rally going forward?
hi Monica
Yea, grape fungus is a big problem and not forgiving. Spraying on the off season is so important. I have not had success spraying grapes late in the season. At best it seems to temporize or slow the infection.
Best,
Tom
Hi Monica,
We also have a home vineyard and have had the same issue here in SoCal. We find that dormant spray in the off season is critical to managing the demon “powdery mildew”. We’ve tried many different solutions but seem to have found what works. We begin with the dormant spray, twice, in the off season to kill spores hiding under the vines bark. I’ve also used copper sulfide to kill the spores but be cautious with it and be sure to spray before bud break and use only once a season. Then, about two weeks after bud break or when the shoots are 4-6 inches long we begin a weekly routine of spraying Natria neem oil (Amazon). Neem oil does not kill the pest but it prevents it from spreading. If we see an affected leaf, we pluck it and throw it away, don’t leave it lying on the ground. We have 5 varieties and I’ve noticed that some are more susceptible to the disease and the more mature the vines, the less affected they are.
We mix 1oz per gallon. You can mix it stronger, but be careful not to burn your leaves. Early morning spraying is critical especially during our hot days. Be sure you discontinue spraying approximately 2 weeks prior to harvest so as not to get the neem flavor in your wine.
As for your already affected fruit, the only thing you can do is pick out the fruit that has the mildew, toss it and try to salvage what good fruit you can for your wine making. I empathize with you, last year we suffered the same blight.
Good luck to you, I hope this helps you.
Tammy P.
We have a garden of grapes. We have a issue of powdery mildew. And want to control with effective fungicide. Means to find out the most effective fungicide for the control of powdery mildew of grapes. I have fore 4 Systematic fungicides have a trade names of some companies. And also keep the control in experiment.I want experiment in field or in garden of grapes. How is the method of experiments
Hi Moinuddin
Great idea, I am a big fan of controlled experiments.
First off, I have found that spraying plants early in the season (early spring) before the leaves pop out is critical regardless of they fungicide you use.
You can do experiments in many different ways, One thought for this one would be to evaluate and quantify the mildew before the experiment. Ideally, it is the same for all your plants so it is a fair experiment… This is important bc some species of plants are more/less susceptible to fungus and the location (shade/not shade) also makes a difference. Ideally they are all the same species growing in identical environments. More plants in the experiment the better.
mark off and label 4 groups of your plants for the different methods you are utilizing. Treat them based on the directions and don’t cross contaminate the treatment methods. Watch/observe/quantify.
Looking forward to hearing how it goes.
Good luck,
Tom