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bad case of Powdery Mildew - How to treat?

8 years ago

last modified: 8 years ago

Hi, I have a Drift rose with pretty bad powdery mildew. I do have a spray program with Bannermax and Mancozeb, but I began late this year. We just finished a good stretch of rain. Stems and rose bud clusters have prominant white fuzz, and overall plant leaves are affected with leaves 'crinkled'.

What can I do? / What do I use as a more aggressive "intervention"?

It's a great shrub and I've never had this before.

thanks, growitnow

z7 Va

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Comments (5)

nikthegreek
8 years ago
last modified: 8 years ago
1. Look the other way

2. Prune and wait for new growth under more favorable weather conditions

3. Apply a fungicide containing either the active ingredient myclobutanil or the active ingredient bupirimate. There are milder 'organic' alternatives that you can use but, mostly, they will not help much curing an advanced case of PM.

4. Get rid of the rose and select a PM resistant alternative.

Pick your preferred alternative depending on your inclination and the general propensity to PM in your climate.
mad_gallica (z5 Eastern NY)
8 years ago
Mildew is caused by hot, dry weather. Unless the rose is in hot, enclosed area, in the east I'd go for choice number one. Personally, I have a mind above mildew.
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Spraying affected leaves won't get rid of any visible spots but should stop any new spots from forming and protect new leaves. What did you spray with? Old wood is the wood formed from the previous year(s). New wood or growth is the current year's growth. You can remove all the leaves if you find it unsightly. I have not done that to a mophead/lacecap (macrophylla) but I have done that to a paniculata and an oakleaf (quercifolia) with no adverse effects. The paniculata had spider mites or something else going on that looked so terrible I cut every leaf off in early summer - it completely filled out in a few weeks. The oakleaf had some kind of black spot going on but it was closer to fall so no new leaves came back which was kind of alarming but now it has all new leaves since spring is underway here.
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To Ken_adrian: Thanks for the advice, but I am not one to give up on a plant because I had a problem with it for a little while during 1 season. I have dealt with issues with dahlias as well from time to time, like slugs, spider mites and tree hoppers, but I stiIl grow them. I think some things are worth a little extra effort, and its really not that much more effort anyway to be honest. I grew the same variety of zinnias about 2 years prior to last year's powdery mildew, and at that time I had more zinnias in a more shaded area that tended to hold moisture/humidity moreso than this new area does, yet I didnt have any problem with powdery mildew at that time. I dont mind having to take 10-15 minutes 2-3 times a season mixing up some spray solution and coating the plants with a safe, relatively non-toxic spray that helps prevent fungus if it means having 5-6 foot tall flowering plants that continuously flower from June til early November. I will also try to keep them more ventilated. Maybe they were too close last year. But we also had a generally wet first half of summer.
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chris2486
8 years ago
I do not use fungicides so my advice is more in the organic way of growing. Powdery mildew does do better in dry conditions as when it rains it washes the spores off the plant. It happens usually when night time temperatures are low and day time temperatures are warm. If this happens every spring then you can use a horticultural oil (like winter oil but more diluted) but this should be done carefully and in cool temperatures because when applied in warm weather it can burn foliage. This works like a coating that the mildew spores cannot penetrate and is best done in early April before mildew is present. Right now it might be best to cut back rose and wait for better weather. Overhead watering can help, but only if it is done early in the day. The weather will change and the mildew problem will go away, but meanwhile it may really slow down the growth of the plant and it may not be attractive for the remainder of this season if it has had a severe case of mildew.
User
8 years ago
Bring on the shovel. I removed 6 roses this year because last year they were a mildew blanket all year long. I don't even want to think of growing diseased roses, so I ripped them all out. Replanted with Austin Roses. Happy now!!

Rebecca
smithdale1z8pnw
8 years ago
I like Rebecca's attitude but I'm an option1 (Nik's list) kind of person. I am great at only seeing what I want to see but in extremis I would opt for Rebecca's method.

Jane

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