Away from the Pacific Coast, PM is rarely a severe or chronic problem. IMO, if you are going to be spraying, there is no need to remove diseased tissue.

Since the fungal body is on the outside of leaves and stems, it can be killed even by non-toxic sprays such as oil, sulfur, or bicarbonate.

Can your plant afford to lose the canes and foliage in question? As long as it is green, it is feeding the plant. The more foliage you remove, the less available food to maintain the plant.

If your rose mildewed, it means the spores were already there to germinate when and where conditions supported them. Will is "spread"? Yes, and no. That infected tissue is generating more spores to add to those already in the air, so in that respect, possibly, yes.

But, there are ALREADY mildew spores in the air in your garden. If none of the other roses have contracted the infection, it means either the conditions the other roses grow in do not support germination, or those roses are more resistant to mildew.

Of all the fungal issues, mildew is the easiest to deal with here. Most often, here, it goes away as soon as the weather conditions which support it go away. Cool, damp, restricted air flow, as well as extreme water stress, even in hot and dry, can encourage mildew. Some roses are highly resistant to powdery mildew. Dr. Walter Lammerts proclaimed Buck's Maytime as "immune to powdery mildew", which is one reason I use it for breeding. Those which are highly susceptible to mildew have been shovel pruned from my garden.

Increasing the water to stressed plants; improving air flow around them and waiting for the cool, damp conditions to become warm and dry are my main "treatments". As Michael advised, many chemical treatments work well, too. You can find suggestions from baking soda, through milk all the way to oils and harsh chemical treatments. Changing the pH of the leaf surface appears to work fairly well. Milk and other oils can smother the fungus (and most insects) but can cause burn in hot sun and higher heat, so those may or may not be appropriate for you to try.

But, I wouldn't cut off the leaves and canes which are mildewed. They will always show the "scarring" the mildew infections cause, but the fungus CAN be "cured" from them. How valuable are they to the performance and protection of the plant? Kim

PM is a pretty common problem in the Great Lakes area because of the high humidities we always have. Almost as common as black spot. And the closer you live to the big lakes the more so.

We have had pretty much all of the conditions Kim talks about, cool, damp, cloudy, etc. then, boom, a week or so of unseasonably hot and dry (back to cold and cloudy now). So it's not surprising that you have it. Or that it may have already had it when you brought it home from the nursery either. Depending on where you bought it the conditions may have been such that it picked it up there and you simply brought it home to your garden. We tend to think of nurseries as having perfect growing conditions, and some do in some respects, because they receive good care usually. But they're also usually pretty crowded for space and the plants may not get the room they need for that important air flow and watering may have been uneven or sporadic and the plant was stressed. I've seen many a garden center with rows of black spotted roses for sale. And don't get me started on the big box stores where they're crammed together like sardines!

I agree that if you are spraying you don't necessarily need to remove the cane but if you would feel safer and the plant can lose it without problem than go ahead and take it off and dispose of it because it can spread it from one plant to the next under the right conditions.

I shopped a local wholesale nursery yesterday. They are in a "dip" where the fog and cool collect. They had several thousand Iceberg roses in all three colors, canned, sitting on black plastic weed cloth which absorbs the heat, reflects and radiates it. All were water stressed and all looked like powdered donuts. The ones planted along the public street where they receive a LOT of reflected, radiated heat from the asphalt and concrete, but whose roots are IN the soil where they remain cooler and damper, had clean foliage with just the flowering stems showing mildew. They weren't a hundred feet away from the canned plants, but their conditions were vastly different. They hadn't suffered the greater water stress and they benefited (at least before the HIGH heat arrives) from the increased artificially supplied heat. Kim

ok...possibly a crazy question, but when you mentioned spraying with oil, Michael, are you referring to buying a can of Pam (or something similar) and spraying it on roses? I prefer not to use chemicals because I love the bees & butterflies, plus I have pets and don't want them around harsh chemicals when they are in the yard.

Same thing confuses me with the alfalfa pellets; do people mean to go buy actual rabbit food at the pet store? I already buy llama food at the co-op for my alpacas, which is cheaper than rabbit pellets...so that would be an option too...

Tammy

This post was edited by TNY78 on Sat, May 11, 13 at 15:54

Just because something is natural doesn't mean that it is safe to use around pets.

I like to look at the material safety data sheet when evaluating products to use.

Here is a MSDS for Green Cure, a fungicide based on potassium bicarbonate.

We can get powdery mildew when there is a large difference between the day and night temperatures.

Here is a link that might be useful: MSDS for Green Cure

Here is a list of MSDSs for Bonide Products

Here is a link that might be useful: MSDS for Bonide Products

Great example, Kim!

No, Tammy, not PAM, lol! Neem oil is usually what's used for plants. The oils is a suffocant (sp?) for insects and diseases. I personally don't use oils ever. Did that once and literally fried the leaves, and no, it wasn't that hot outside.

Alfalfa pellets are best used in a "tea" but can also be dug into the soil. They probably just take longer to feed the roses that way. I have no idea what llama food is made of so I don't know if it would work or not. You can find them at feed stores where they're probably cheaper than pet stores and in larger quantities.

Oh so true, Zack! Even so called "organic" sprays can still be toxic. They are still chemical compounds of one kind or another.

You can find Neem, Jojoba, Ultra Fine and Sun Oil (both usually highly refined, water soluble paraffinic oils), even mixtures with Canola Oil (probably its best use) for use as insecticides and fungicides. Unless right on the coast (or where those conditions prevail) where humidity is very high, sunlight is quite diffused and reduced and temperatures remain VERY mild in comparison to inland conditions, all oils are best restricted to the winter months. Inland here, even in December and January, any of them can fry a plant in a matter of a few hours with even the weakest concentrations. Our transpiration rates are simply too high and heat and light extremes too severe for us to safely use oils. Jiminshermanoaks, eight miles east of me, can use Jojoba and Neem right now because of his marine, coastal conditions from being in the Sepulveda Pass where those patterns push into the inland San Fernando Valley. Where I am is significantly hotter, drier and more brilliantly sunny. Right now, Wunderground reports his conditions to be 85.8 F with 46% humidity. Mine right now are 96.5 F with 24%. Quite a difference for being the same distance from the ocean, at roughly the same altitude in the same mountains and only 8 miles distance. Kim

I can safely use Neem (or other oils) when the fog is thick, and temps don't get above the low 60's.

Once we get into the HIGH 60's, I wouldn't even consider it. Been there, done that, burned all my foliage.

I'm sure it's OK SOMEWHERE, but that somewhere ain't in MY garden.

My take on mildew -- observe the plant. If it is a chronic mildewer in your conditions, you can probably live without that rose.

Just MHO.

Jeri

Ok! thanks for clearing that up! I can just imagine my neighbors laughing their heads off as I walk around the yard spraying my roses with Pam! I knew it couldn't be that easy :)

As for the alfalya, I'll have to look for it next time I'm at co-op. As for now, I still have MORE than enough alpaca droppings to use as fertilizer anyway! Any takers for the extra? LOL

Tammy

I am up the coast from Jeri, but moms garden faces the pass and will be fog free when other places are socked in. I am paranoid about using oils because I know as thick as the fog is NOW, it can be gone along with the leaves on the place in no time at all.

Oil is one of those traditional spray materials (also sulfur and soap) that can burn if foliage is stressed for water. Irrigate before spraying and spray in the morning when it is cool. Agitate thoroughly and frequently so it is evenly distributed. I have used all these materials with temperatures rising into the 80s later in the day and haven't had much trouble if I followed the above rules.

Okay, I'm a newbie-my first rose. I used sodium carbonate (1/2 tea-scant) and a drop of dish soap : 32 oz water as a spray. I can't recall where I got the recipe, but is the soap needed? Has anyone tried it? Then, like an idiot I went nuts with the shears. The deformed, shriveled, powdery leaves and shoots-bu-bye. I finally realized that I'd wind up chopping all the leaves off and a shoot has come in with the first leaves looking discolored and shrively, but newer leaves look better. Then, our SF summer time winter has set in, slowing growth. I've got leaves towards the bottom, stems mostly empty, and leaves at the top. Some of the stems never developed shoots, but some got cut because they were white with fungus while others just fell off. We will get summer again next month, but a lot of my sun will then be blocked by the building across the street. Is there any hope here? This was my first rose plant and I got it for my birthday...I have one idea-it's 4 plants that I couldn't separate when I repotted. What if I were able to get rid of the least healthy ones? I hesitate to cut the stems because some of the top leaves are relatively healthy and doing their job. Finally, my husband tells me he's going to put bicarbonate in the water he waters with-his got ingected though I was so careful-rather than spraying the leaves-very few apparently infected-his has very glossy leaves-but that makes no sense to me at all! Help! Whenever I look at that plant I want to cry. Thanks for reading this.

Hi there, I just treated a rose (Zephirine Drouhin) for powdery mildew. I searched this forum and I think someone had said something about washing/rubbing the mildew off the affected leaves. I went ahead and tried that one morning, using a strong water spray and rubbing the affected leaves gently between my fingers. I did this in the morning so that the leaves would have a chance to dry out with the day's heat. The next evening (so as not to fry the leaves in the sun), I sprayed neem oil on the affected parts which were already looking much better because most of the whitish bits had been washed off. Now, a week later, the rose looks pretty good!

I didn't end up cutting anything and was really surprised at how effective this simple treatment was. Zephirine Drouhin is supposed to be a PM magnet where I am (SF bay) so we'll see what happens. Oh, I also took this forum's advice to make sure the rose was well watered every day (it's a new planting) so that it wouldn't be stressed and that seems to have helped as well.

Hope this helps and good luck!

I get PM around the first of September when it starts cooling down. I get it on my minifloras only. I used Green Cure last year and I stayed clean. The whole thing is knowing when to treat , not treat after you have it. PM is a cooler season disease. You don't see it when it's 80-90 degrees. Spores germinate at 71 degrees with high humidity Warm days and cool night does it for me!. A lot of mildew we get on the minis and the minifloras comes from the greenhouse growers. PM becomes resistant to all sprays like blackspot does.
Good air circulation helps.
Just watch the long range weather reports and take action

You can also force roses (and many other plants) to mildew even when the condtions are completely wrong for the disease by water stressing them sufficiently. I didn't believe it when I read it in LeGrice, until I DID it. If you think the conditions aren't right for mildew and you experience it, check the water. I also discovered you can force many roses to rust by keeping them too dry. R. Arkansana rusted terribly in early summer here. Even the new foliage was badly affected. I knew rust was how Nature signaled the plant to shut down at the end of summer, but late spring and early summer? I increased the water and the new foliage opened with no rust. To check my theory, I stressed it for water again. All foliage began rusting.

Makes sense. Too little water, just like too few nurtrients, and you suppress the immune system. Before you reach for a fungicide, check to make sure the plant is not only receiving enough water, but it's hanging around long enough for the plant to absorb. Kim

ghetto g: Please do not try to apply bicarbonate through the irrigation water. It will cause a buildup of salts in the soil that is very harmful to plants. Also, don't cut off the mildewed foliage. The white stuff is superficial (on the surface) and can be killed or removed. The distorted foliage will then still function normally to help build the plant's energy.

The best course is to discard the mildew-prone roses and plant resistant varieties. If you are willing to spray regularly during mildew season, there are better things than baking soda. One is potassium bicarbonate, sold as KaliGreen, Green Cure, and Remedy. These are inexpensive products.

This post was edited by michaelg on Mon, Jul 29, 13 at 13:40

I have to disagree that powdery mildew is only a problem on the Pacific coast. We are completely opposite geographically. and PM is a notable problem here. Not just on roses, either.

Around here, if you haven't been treating a rose bush for fungus prevention, you can be almost certain that PM will show up on it by late summer. We don't spray our Knock Out roses and many of our other shrub roses for black spot, and by late summer, we generally have to take some action because of the PM.

All of our OGRs get PM also, but on the ones that aren't repeaters, we don't do anything about it. They may look awful but otherwise, they seem to work through it with no lasting effects. They aren't going to bloom at this time of the year anyway, so it really doesn't matter how they look. .

A few roses, like Home Run, seem to be immune to PM, but those are the exceptions. Otherwise, we've found that we can clean up PM very effectively with Green Cure (potassium bicarbonate plus spreader sticker)

This post was edited by nickl on Mon, Jul 29, 13 at 10:51

Dr. Walter Lammerts, who created Bewitched, Charlotte Armstrong, China Doll, Chrysler Imperial, Golden Showers, Queen Elizabeth, Sunny June and dozens more commercial roses; and who is responsible for the creation and introduction of the Descanso Hybrid Lilacs which most of us have seen and/or grown (Lavender Lady, Angel White, Descanso Pink among others) which will flower in milder climates, proclaimed the Griffith Buck rose, "Maytime", "Immune to powdery mildew."

Maytime can spot a bit, but in all the years I've grown it, there has never been one instance of either mildew or rust, the two most frustrating diseases in my climate and conditions. Perhaps not everyone's cup of tea, but very much in the mold of a Pink Knock Out. If mildew is a large issue for you, consider Maytime. It does NOT mildew in any conditions I have ever seen it in, nor under which I have ever tortured it. Kim

Here is a link that might be useful: Maytime