Powdery Mildew vs. Large Potted Rosemary Brought Indoors

mrobbins(6b - Brooklyn)February 26, 2006

We had such a good time last May, friends and I, when I visited them in Ohio and we spent a day at the Mulberry Creek Herb Farm. They bought a 3' tall rosemary in a pot that's probably 16" in diameter, and left it outside for the summer, where it was very happy. However, after a few months of living indoors for the winter in front of a sunny windowsill, the rosemary developed a white bloom that I assume is powdery mildew. Is there some relatively non-toxic way of treating this plant? (I've heard Neem oil or certain solutions of baking soda in water help, but would love to hear about anything organic/natural that worked.)

Thanks in advance for your reply!

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You can try cooled chamomile tea, chamomile tea is a great antifungal! :o) I use it all the time.

    Bookmark   February 26, 2006 at 11:53PM
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Garlic spray (tea) is also a specific for powdery mildew. For goodness sake, put the poor plant outside where it will get some air circulation, lack of which is one of the main causes of the problem.

    Bookmark   February 27, 2006 at 7:27AM
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teryaki(z5B NE OHIO)

The shock of going outside now would probably kill it. If you get a day above 45 degrees, THEN you can put it outside for the day and bring it in just after sunset. Jojoba oil and neem oil are both recommended antifungal agents.

You need to trim off the worst affected areas of the rosemary and BURN them.

Is this a little Christmas tree rosemary? If so, it needs pruning anyhow on the smaller inner branches to open up airflow. Those poor things are always vulnerable because they get such poor airflow. Put a small fan on the plant as well to aid airflow.

Because powdery mildew can and will develop resistance and can move to other plants in new resistant forms, a treatment plan should include pruning for airflow and rotating applicated of several fungicides to completely eradicate the infection. I'd suggest using a neem oil product, a jojoba oil product, and a solution of 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil with one gallon of chamomile tea in spray bottle. Treat with one each day, then switch the next day. Keep going for at least 2 weeks after all symptoms dissapear. It's like taking antibiotics.

You SHOULD vigorously hose down any plant affected with powdery mildew to dislodge spores, but that could easily kill the rosemary, so I dunno.

The other option would be to set the poor little thing outside, douse it with lighter fluid, and put it out of it's misery. :(

    Bookmark   February 27, 2006 at 12:13PM
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francescod(6b/7a VA)

The dreaded scourge of powdery mildew is very common in rosemary brought indoors. Powdery mildew is a fungus that although thives in warm, dry conditions needs high humidity for the spores to germinate. Therefore hosing down a plant with water will have very little effect on the fungus. Poor air circulation also gives pm an ideal environment to grow and thrive. The sooner you treat the plant the better. Be careful, even organic/natural remedies can damage certain plants. Don't assume that because a little bit works that a little more will be better. Always try on a part of the plant before treating the whole plant (not just the affected area) to be sure there are no ill effects. Observe for at least 2 days before making a final judgement. I have seen damage occur or worsen over that length of time.

Do try the baking soda method. Detected early, powdery mildew can be effectively controlled by spraying with a solution of 1 tablespoon baking soda dissolved in 1 quart of water. A second application the following day may be necessary. If the problem still persists, you may need to use garden sulfur or all season horticultural oil. Don't use oil and follow up with sulfur as a reaction can occur that will damage your plant. Another method you can try is milk! One part milk to 9 parts water has been shown to be very effective in grape vineyards . There is an effective commercially available product new to the market from Pharm Solutions that contains several plant oils such as peppermint and others. They have one for pm for roses. I used it on rosemary with fairly advanced mildew with great results, however at the recommended dose it did burn the leaves of (ironically) peppermint, pineapple sage, and one of my tender lavender varieties L.x heterophylla. The label says to dilute if burning occurs but I have yet to try it diluted.

I really don't think that pm can develop a resistance easily or at all. Viruses mutate, I'm not sure that fungi do all that much. Although the fungus can jump from plant to plant powdery mildew is host specific ie. the same species or subspecies that affects rosemary may not be the same that affects grapes. For more information visit http://www.ext.colostate.edu/pubs/garden/02902.html

Good luck,

Francesco DeBaggio

    Bookmark   March 1, 2006 at 11:15PM
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2 gallons warm water
3 tbls murphy oil soap
1/2 cup baking soda

Used it on rosemary and crape myrtles. Wash well before consumption.

    Bookmark   March 12, 2006 at 1:00AM
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I had the same problem last winter, and 3 weekly sprays with a mixture of one-half cup fat free organic milk with 2 cups water knocked it out completely. I could see immediate results after the first application, and followed up with two more sprays to make sure it didn't come back. It's important to use the milk cure on a sunny day when you can put the plant outdoors. The fungicidal effect occurs when a protein in the milk interacts with sunlight. I promise, this really does work!

    Bookmark   May 8, 2006 at 7:34AM
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yes... I have tried non fat milk, it does work.

    Bookmark   May 8, 2006 at 10:40AM
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Before I cheked out this site I used my own home remedy and sprayed my rosemary plants with a solution of apple cider vinegar and water. Do you think I have killed them?? Any advice would be helpful. Thanks!!

    Bookmark   February 11, 2008 at 10:00AM
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ksrogers(EasternMass Z6)

Vinegar in strong amounts is used as a WEED KILLER. It burns the leaves down. About the best way to combat most any fungal problems is to use Serenade Solutions. Its a powder, mixed with water and not only stops fungal problems, but also helps the plants to be more resistant to fungal problems I used in on cukes and watermelon and both were very hardy, with absolutely no disease deaths.

    Bookmark   February 11, 2008 at 12:37PM
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I used neem oil with excellent results. Got a pre-mixed hand spray bottle at the garden center and it took care of the problem fast.

    Bookmark   February 13, 2008 at 5:29PM
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ksrogers(EasternMass Z6)

Neem is also used as an insect repellent as well as a bug killer.

    Bookmark   February 13, 2008 at 10:56PM
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Can you pinch off the rosemary leaves and eat them after using neem oil on the plant?

    Bookmark   April 1, 2010 at 10:45AM
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I've used the diluted milk spray for four days. Put the plant out in the sun each day, sprayed it in the mornings with a mixture of about 1/6 fat-free milk/water (I'm not a good measurer), and gone! No more powdery mildew. Thanks, folks. I'm now really committed to this forum. Good info.

    Bookmark   April 7, 2010 at 8:38AM
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If you use the milk spray, can the sunlight be through a window, or do you need to put the plant outdoors? It's way too cold where I am to do that, so I'm wondering if I should try the milk or something else. Thanks!

    Bookmark   February 26, 2011 at 1:19PM
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Just a follow-up: It's Dec. 2011 now. I tried the baking soda spritz last year and it seemed to work great. I just brought my plants in last weekend, and it looks like one is already developing some powdery mildew, so I'll try it again and hope for the best. I used 1 Tbs. baking soda in 1 qt. of water and spritzed the whole plant well. Also avoid over watering of course. It came back once or twice, but the solution kept it at bay 'til spring when they could be re planted outside again.

    Bookmark   December 8, 2011 at 2:44PM
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I don't know who came up with the idea to spray rosemary with milk to combat powdery mildew, but it works extremely well. I am zone 4 and move my numerous rosemary shrubs in my greenhouse for the winter. Powdery mildew has always been a problem in the past, but especially bad this year because of a warm winter (even for Minnesota). Its very hard to keep the humidity down. Washing the plants just wasn't cutting it this year. I googled the subject Sunday and came up with the milk idea. My numerous rosemarys were badly infected, but one application of 1 part low fat milk to 6 parts water along with a 1/2 tsp of baking soda per 1 qt cleared it up. It did happen that the day was sunny which was mentioned as part of the cure process. I'm not sure about that. Milk, go figure.

    Bookmark   January 31, 2012 at 8:53AM
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Just posted a cry for help with this problem, should have checked here first! Will definitely try the milk cure ASAP. Thanks, GardenWeb members all come through!

    Bookmark   June 24, 2014 at 8:29PM
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