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Midwest Gardening

what to do with flowers covered in powdery mildew!!

14 years ago

Never had I this problem... late summer phlox and zinnias would get powdery mildew on bottom leaves... no big deal. BUT... I have talculm like powder over all my roses, some on hostas and other usually ok plants. What would YOU do?

It is unsightly. Hasn't spread to everything but some may be resistant... I hope/ Please share your knowledge. Probably with me, the cure is worse than the disease because I panicked and tried many things. HELP! Thanks.

Ellie

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Comments (5)

nejackson
14 years ago
I have a few suggestions:
1. Mildew is sometimes a problem on some varieties of a flowering tree in the Deep South called crape myrtle. If it's a serious problem, some people spray the leaves with Lysol.
2. If you're having an unusually cool/cloudy/rainy summer it might be a problem for this year only.
3. Some plants don't like wet leaves and preferred to be watered under their leaves. The wet leaves can mildew.
4. I don't know much about roses; you might try posting your question on a rose forum.
5. Take some of the leaves and examine them with a magnifying glass. You might find it's not mildew at all.
zen_man
14 years ago
NE,

"3. Some plants don't like wet leaves and preferred to be watered under their leaves. The wet leaves can mildew."

A common misconception about Powdery Mildew is that PM is promoted by wet leaves. That misconception is so widespread that it is now almost an urban myth. Many supposedly authoritative books say that wet foliage promotes Powdery Mildew. Wet foliage does promote many foliage diseases, but not Powdery Mildew. Apparently most garden writers refer to the works of other garden writers and this has become a glaring example of the hazards of "Group Think".

The truth is that Powdery Mildew spores cannot germinate in water and that water prevents it. Powdery Mildew grows on dry leaves. Refer to the National Gardening Association's Q&A on Powdery Mildew on Zinnias in which they say,

"Powdery mildew is unique among common plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather, which is why you see it appearing in August. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with frequent sprays of water."

Considering all the books and other publications that are wrong on this subject, and how widespread this urban myth actually is, its going to take a lot of effort to correct this deeply rooted misconception about Powdery Mildew. I am giving it a shot here, but it's a shot in the dark.

ZM
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Powdery Mildew is mostly opposite of downy mildew in that it thrives in dry weather, not humidity. Powdery Mildew does not require free water to propogate. The hyphae only burrow into the epidermis layer of the upper side of the leaf. Some home spray remedies work because any spraying (water too) during the day will remove the fungal structures off the leaf surface (it is delicate). However, increasing daytime free moisture will reduce powdery mildew and quite possibly increase the likely infestation of moisture-loving downy mildew. Downy mildew is much more destructive and attacks through the leaf structure itself. If you have that fuzzy mildew on the underside of the leaf, then you are quite sure to have downy mildew setting up shop there. Sulfur dust has been the #1 remedy for powdery mildew, however you will want to sample this on a leaf and be careful with this and any fungicide material.
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Hi - In spring spray your gardens with 1 part skim milk to 9 parts water. Tests some years ago showed that this stops powdery mildew from forming - this has worked for me for years. This spring I didn't get around to spraying the gardens down and sure enough my monarda, asters, phlox, dahlias, lilacs and anything in the mint family got great coverings of powdery mildew! This also works wonders for keeping PM off grape vines. You can use only skim milk - it makes no difference using the higher fat content milk - except that it reeks! Here is the link to the original research in 1999. http://www.pioneerthinking.com/tv-mildew.html You can do a google search on this and find out more whenever you want. Cheers from Michigan Here is a link that might be useful: Powdery Mildew & Milk
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You're welcome. I'm not a flower seller, just a flower lover. I was answering the part about the plant growing deformed flowers. I've not done any research or investigation to see if my cut zinnias last longer if the plant does not have PM. Sorry if that was not clear from what I said. Since moving to AL, I haven't seen much PM, and so far none on zinnias. But if memory serves from when I used to live in OH, flowers cut from plants with PM weren't noticeably shorter-lived. That's as scientific as I can get on that. Good luck!
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Comments (5)
Ken....PM starts out on the surface of the plant tissue but very soon into the infection will send structures (haustoria) into the cells. That's how PM can result in the death of tissues. It's not merely a disease of the surface. Highlander, I have not tried the baking soda or milk treatments so can't speak to their effectiveness from personal experience. I can share my very positive experiences with horticultural oils, including neem, applied to the foliage. The oils do two things: kills the spores on the surface upon contact AND prevents the successful spore germination in the first place. Avoid spraying anything directly on the flowers. Read and follow the directions on the labels. I assume that you know the importance of practicing good garden hygiene in terms of your maintenance practices regarding PM. The spores overwinter in plant debris, old mulch, and even on the soil. I opt to avoid disease prone ornamental varieties in favor of resistant cultivars. That's my choice for all kinds of problem prone plants. But the vegetable garden is different. That's where I have to resort to neem oil or frequent syringes of water. I don't have and can't recommend any particular commercial fungicide though I know that there are many which are labled for PM control. But without all of the cultural controls in place, no amount of chemicals will be of much good. Hopefully, Zenman the zinnia sensei of the forum, will see this and share his expertise.
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tsugajunkie z5 SE WI ♱
14 years ago
I agree with zenman. I have even read (and naturally I can't find them now) that wet leaves helps to inhibit powdery mildew. Never had it on hostas, though. The strain of mildew that affects zinnias and phlox can be minimized with a milk/water solution (I have had success with it, anyway) but once mildew sets in, its tough to get rid of.

tj
frozen_north
14 years ago
Funginex
Captan
Daconil
Maneb

Pick one
zen_man
14 years ago
A safer choice is GreenCureÂ®. It was developed at Cornell University as a superior alternative to homemade sodium bicarbonate formulas and it is effective against several plant diseases, including Powdery Mildew. I give my zinnias a frequent bath in GreenCure.

ZM

P.S. I am in no way associated with the GreenCure product or any of its vendors. I just use the stuff because it is safe.

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