I've used wood mulch for years with no problems...
I've never seen PM on any rose here or any shrub.
SO not a true statement for our garden...

I have seen PM on a couple of my wifes potted plants
but they were NOT mulched just potted in soil....

Maybe it's true for certain areas/gardens?

Agree with Jim1961....

Also do you know that powdery mildew is species specific...meaning it can't come from other non rose plants or spread to non rose plants....

Here is a link that might be useful: Powdery Mildew

Here in SoCal powdery mildew has been a huge problem this summer but it only strongly affects about 25 percent of the roses. It comes and goes with the morning marine layer which has been bad this year but not lately. I'm getting rid of everything that is hopeless including oranges (Fragrant Cloud, Dolly Parton) and many reds and some pinks and mauves. If there is a causal factor other than genetic it may be insufficient watering. I water almost every day but it is so hot and they are so huge and need so much that you can't water enough. I think too little water possibly exacerbates both powdery mildew and rust.

Water stress absolutely exacerbates both powdery mildew and rust, Henry. I would not be at all surprised if it could also induce black spot and other fungal issues. Anything which inhibits the immune system of an organism can increase its susceptibility to disease. If lack of water can force mildew and rust, it stands to reason black spot and other fungal infections shouldn't be far behind.

At least in our arid, hot climates, the lack of mulch could easily lead to more mildew due to faster, greater water stress through higher evaporation in hotter soil. Kim

This being my first year growing roses here I know that the soil condition is still bad and the mulching insufficient and the root structures are not yet developed enough to support the huge top growth especially when it is in the 90's every day and they are blooming heavily. They are stressed and I can't do that much to help them. I almost never saw rust and powdery mildew back in CT and never worried about watering and stress but it goes to show that different places just present different problems. It should however get better as I keep adding mulch and the soil gets built up.

The proper application of mulches is a topic that is still under some controversy in the scientific community. Aside from a general consensus that SOME organic mulch is a positive practice, exactly what type, how much, and when and where it should be applied, is still under contention, even among scientists. That leads to confusion for us practical gardeners.

As for the question of mulches and disease in general, the research is very mixed and obviously depends on the specific plant species and the specific organism. I know of no research on rose mildew.

IMHO, I would say that if you follow the general guidelines of applying an organic mulch, you will reap many benefits and not be increasing the incidence of powdery mildew on your roses.

In any case, this is one of the easiest diseases to control even if you are not using chemical fungicides. Potassium bicarbonate products (Green Cure, Remedy, etc.) are a specific for it and will clean up an outbreak immediately.

If water stress exacerbates the incidents of Powdery Mildew and other such diseases, it would seem that mulch would be more of a preventative than a cause.
It is better to hear from a wide variety of practical gardeners than the mixed messages of scientists. Thanks for this thread. :)

I don't use any mulch and I still get PM all the time on certain roses. New Day has been covered in it all season even when everything else was clean.

Powdery mildew has little to do with the soil or mulch, except perhaps for the water stress issue raised by the Californians and the issue of general health and vigor. Spores of PM are airborne over long distance. Latent growth buds can be infected with PM and carry the disease over winter within the plant. Germination of spores occurs after several hours of very high humidity (but no rain) with temperatures around 60 F. I can't imagine how mulch could make PM worse.

Thanks everyone. So far you have all told me things that I have already heard/known about PM and no one has come up with any info supporting a connection factor between PM & mulch. My own belief is that mulch may help somewhat in protecting plants by covering the spores of pathogenic fungi in the soil & making it more difficult for them to reach a host plant. This is definitely the case with early blight in tomatoes because if I mulch them with 2-3" of grass clippings shortly after setting them out, they stay free of early blight.

This post was edited by wirosarian on Tue, Aug 27, 13 at 15:26

A mulch may work either way or be neutral. It could foster the growth of "friendlies". It could foster the growth of powerdy mildew. It could foster neither.

Once you know that you have mildew with a particular mulch, you may want to "play it safe: and remove that mulch and try something else.

"Again, most mulches are notorious for harboring disease spores. Wood and bark are the worst. And even though theyâÂÂre one of my favorites, shredded fall leaves should also be avoided when youâÂÂre trying to get through at least one symptom-free season to break the cycle of disease. Compost is the ideal mulch. A one to two inch layer of compost on the surface of the soil feeds your plants, prevents weeds, and provides a hostile home for spores looking to breed; high-quality compost contains living organisms that eat disease spores as soon as they land! "

The above quote is from the link below.

Here is a link that might be useful: link for quote

This post was edited by henry_kuska on Tue, Aug 27, 13 at 16:43

In June we get a heavy morning overcast with temps at 60 or below which is due to the marine layer blowing in off the Pacific. It is called the "June gloom" and it is supposed to go away in July so I didn't think I had to worry about it except that this year it never really went away. July was cool and humid for here and August got hot recently but the morning humidity has persisted. Today it is 1:30 and the sun is just coming out. You can tell by the roses how the weather has been. Right now the PM is as bad as it was in June. I ordered Green Cure on line because none of the local nurseries ever heard of it much less sell it and I can say that my regular BannerMaxx does not clear up PM even though they claim it does. Mulching is the single best thing you can do for growing anything because it improves the soil, holds in moisture which is very important here and stops weeds if you use enough of it. I can't imagine anyone advising against mulching for any reason.

PM does indeed travel by air according to Wiki, and also overwinters in plant debris, so mulch could be a culprit if the "ascospores", were extant in the mulch, but it claims to be fairly plant specific.
So, would the woodchips be carrying ascospores from wood mulch that affects Roses?

I still say that using mulch to maintain adequate moisture for the roots, is more beneficial than risky. :)

To Henry_Kuska, thank you very much, you may just have explained what happened with my roses. None of them had PM, then I brought a Lavender Lass home from a nursery, which developed PM. I couldn't cure it, so out it came. I replanted a lovely Sheila's Perfume in the same spot, which then developed PM. I've been treating the rose with Serenade, which helps, but the new growth always develops grey powder.

I think what I need to do is remove all the bark mulch from the bed and throw it away, and replace with new mulch. Thank you again for the information.

If anyone has any other good advice, I would appreciate hearing it.

Pauline, Langford, Vancouver Island Zone 8b

At the risk of repeating myself, I must a-say that "spores in the mulch" are not a significant factor for PM.

Yes, in cold climates "spores" may overwinter on the surface of the mulch. But various kinds of 'resting' forms may also overwinter on many other surfaces in the garden, including the rose plants themselves, other plant surfaces, debris such as twigs, leaves and stems, etc., etc. The dormant forms are just resting and waiting.

Although the "spores" can and do spread by hitchhiking on the surface of water droplets, they are more often wind borne (or, at least, airborne).

Most PM infections typically appear "top down" on a plant. PM can spread from an adjacent plant if conditions are very conducive, and in those cases the infection starts on the side close to the infected plant. Both indicative of airborne infection. It rarely appears "bottom up" directly from the soil surface or mulch as other fungal infections commonly do.

This post was edited by nickl on Wed, Aug 28, 13 at 12:38

"The fungus survives in the Midwest in the winter as cleistothecia, which appear as black specks embedded in the mealy or feltlike mildew growth on rose stems, thorns, and fallen leaves."

"The microscopic ascospores are carried by the wind or splashing rain to healthy rose tissue and are capable of causing infection."

"The conidia eventually break away and are carried by air currents, splashing water, or other means to new infection sites. Handling rose plants, insects, mites, and snails also helps spread conidia. As many as 3 million spores may be formed on one square inch of infected tissue over a period of several weeks."

Here is a link that might be useful: link for above

This post was edited by henry_kuska on Wed, Aug 28, 13 at 13:12

Just curious PaulineMary,

That rose (Sheila's Perfume) that has PM...
Is it crowded with other roses/plants around it OR
can decent air flow get to it?

Even though I do not feel it's a mulch problem that you have PaulineMary if it makes you feel better then change the mulch.

Because just when we think we know the facts life throws us an unexpected curve ball...

nickl, thank you very much for your response. You are absolutely right, the problem appeared and is appearing top down, infecting new growth. That would be quite a leap for bandits sheltering in the mulch. Phew! I really didn't want to bag and drag the mulch up 52 steps to the trash cans. Perhaps it's just the way the prevailing winds hit that spot, right on the edge of a small lake. Thank you.

henry_kuska, again, thank you for your valuable information. What you write about wind and splashing water builds on what other experienced gardeners are telling me. I read somewhere (perhaps on this site) that it is good practice to remove the bottom 3-4 inches of rose leaves, to help prevent spores splashing on the leaves. Do you subscribe to this? I couldn't do this to the White Meidilands, as they are practically prostrate, but could carry out this surgical procedure on Sheila's Perfume et al. What do you think? Thank you.

jim1961, thank you for your interest, very kind. Sheila's Perfume has very decent airflow, with no crowding, the little ingrate. I'm relieved that you also do not think the mulch needs to be changed, as I prefer to spend any spare time wafting about admiring the roses, rather than engaging in itchy, sweaty tasks. Thank you...and agree on the curve balls :)

Unless the mulch is many inches deep, burying the plant bases, you shouldn't have to really remove it. Just bury it under more mulch of a different type. Personally, I don't like bark of any kind. It moves around too much; requires too great a depth to actually insulate the soil, trap moisture in this climate and provides too many places for bugs to hide. Shredded material, horse manure or a good "compost" work much better here. YMMV. Kim

I have experimented with many different types of material for mulches, since I can't buy mulch in my small town in the mountains so I go out and collect my mulch materials to bring back to the garden.

Usually, I over winter the mulch collected in fall for the next spring so that it is already decomposing when I put it out and I already have it available so I can get it down before it's too hot to work.

There is no doubt that mulch does help maintain a more even moisture level in the the top inches of the rose beds. The areas where I have not replaced the mulch in a timely fashion before the summer heat hits, always show stress. Some mulch is better than none.

I find it interesting to hear speakers telling us this this-or-that is true, when it may only be true in the climates and areas they know and from their own experience.

Of course, they leave out a whole lot of variables, because to mention them all would take hours and could not be simplified in one speaking session.

We have all heard"

"Plants that are stressed or unhealthy are more disease prone."
or
"Young plants that have not developed their immune systems often outgrow mildew"

Of course, there are roses that so put up a welcome sign to any and all rose diseases, so who really knows ?

Smiles,
Lyn

Hi Kim, thank you for that. What sort of shredded material do you favour? I've been using Sea Soil as compost (under the bark mulch) after my compost ran out, and the plants seem to like it.

As we have pounding rain all winter, protecting our soil with something is necessary. I notice on Paul Zimmerman's videos that he has some kind of shredded material around his roses, and I was wondering what it was.

Thank you very much for your response.

Pauline

Hi Pauline, you're welcome! I also have to drag anything brought into, or taken out of the garden up slopes and stairs, then around (or through!) the house, so I shred any and everything suitable for use. I don't use pepper, walnut or oleander material anywhere I want something to grow, but I do shred that stuff and spread it where I want to inhibit anything from growing. Fortunately, I have a stand of golden bamboo and large Banksiae roses which over grow their spaces. There is also an enormous bougainvillea and the neighbor's forest of xylosma invades my air space, all of which (including all prunings from the roses) are fair game. I put out as little as possible in the garden waste barrel. Why drag it up there, drag the heavy barrel into the street and put it away once emptied when I can simply shred it right where I cut and want it?

In bagged products, I used to sell (where I worked) Gorilla Hair, shredded cedar. That stuff was great! It aged to a silvery gray and made a dense, stable mat of fibers which held in place against gravity, wind and water. Due to the varying sizes of fibers, it broke down a bit, but the larger shards remained useful, in place, for a very long time. Look around where you live to see what might be available for in a similar textured product. With decent rain, you can apply your organic or inorganic fertilizers on top of a fibrous material like that and they'll wash through. With little to no rain, they'll require a steady hose stream to accomplish the same results. Kim

Regarding the question: " I read somewhere (perhaps on this site) that it is good practice to remove the bottom 3-4 inches of rose leaves, to help prevent spores splashing on the leaves. Do you subscribe to this?"

H.Kuska reply. I subscribe to: " Once you know that you have mildew with a particular mulch, you may want to "play it safe: and remove that mulch and try something else." Kim's suggestion of putting a different mulch on top of the existing mulch is also a practical way of accomplishing this "removal/replacement". Please note that I did not state that the "removal/replacement" had to be in all areas of the rosebeds. The possibly "contaminated" mulch is the mulch under and within splashing distance of where the infected bush was located.

----------------------------------------

One possible point of confusion in this thread is that someone posts something due to a previous post. However, later the original post is modified. I suggest that once a post has been commented on, further replies should be done in new posts.

Earlier I cited the following:
"Compost is the ideal mulch. A one to two inch layer of compost on the surface of the soil feeds your plants, prevents weeds, and provides a hostile home for spores looking to breed; high-quality compost contains living organisms that eat disease spores as soon as they land! "

The above appears (to me) to be supported by the following published research article.

Here is a link that might be useful: link to compost tea research

Hi Lyn,

This is such a great site, people are so generous with their time and expertise.

I really enjoyed reading your post ⺠I assume you collect fallen leaves? I do that too. ItâÂÂs a 20 minute drive to the swanky part of the next city, where people thoughtfully rake and bag their leaves (actually their gardeners do that) leaving them on the side-walk for pick-up. Very handy.

Our little city is far more laid-back, with fallen leaves lying where the wind last dropped them. As you live in a small town, IâÂÂm sure you can identify. Should I be collecting anything other than fallen leaves? IâÂÂve been digging the leaves into new beds for the worms to chomp on. Sounds like we need to drive the pick-up over to the âÂÂneighborsâ a few more times this fall, and collect more of this valuable resource.

Interesting point you raise about âÂÂyoung plants that have not developed their immune systemâÂÂ. Hmmmmm! I planted my first rose 3 years ago, more last year, and more this year, so none of them are very old. That could be a big part of it. I just assumed the Lavender Lass rose was defective, great, now do I feel guilty! Perhaps I had beginners luck with the other roses. Still, going forward (in the language of conflict resolution) that rose is dead, but SheilaâÂÂs Perfume is still struggling for life. Appreciate your insights.

Again, many thanks.

Pauline

Hi PaulineMary........

I live in the midst of a forest in the mountains of northern California, so I do have favorite places to collect the mulch I am going to haul back to the garden. I check the trees first to see that they are healthy because I don't want to bring pathogens back to my garden that could cause problems.

I have found that forest duff is good for feeding the soil ...especially if you get the stuff under the top layer because it is already in the process of decomposing and it does feed the soil.

I also collect madrone leaves and white and black oak leaves from a friend's property. If the leaves are shredded, they stay put when I put them down, but if I have to use leaves that are not shredded, I go to the utility chipping pile for wood chips to lay on top of the leaves so that they don't blow all over the garden and stay where I want them. As they break down, they, too, feed the soil. Extra wood chips land in the compost pile.

I get a whole lot of wood chips when we split wood I use for heating during the winter. Most of that lands in the compost pile because I have already mulched the garden for winter.

We don't have garbage pick-up in our area and people bring their green waste to the dump station. I never use that stuff because I don't know if they have used weed killers or any other chemicals I may not want in my garden. A lot of people use Round-up to reduced the ladder fuels growing under trees because I live in a wild fire area.

Of course, I use compost, too. Why not recycle the stuff that is already here ? Like Kim, I use everything that's available. My rose prunings are shredded and placed in the beds where I am not growing roses, so I don't have to worry about rose diseases in the mulch.

I mulch twice a year for two reasons: 1) I started with lousy soil and as the mulches break down, they improve the soil; and 2) my summer heat "eats" the mulch within one season.

I don't dig the mulch in at all because I don't want to break the feeder roots of the roses. I just place it on top of the beds following nature's example.

I don't have mildew problems in this garden, but have dealt with it in my SOCAL garden. In that garden, the siting of the rose made a big difference because the air circulation varied greatly in different parts of the garden, but I have had roses outgrow the tendency to mildew as they became more mature plants. Not all of them, but some of them.

Good luck with your roses.

Smiles,
Lyn

Hi Kim,

Thank you very much for your brilliant recommendations, though you had me going with the âÂÂGorilla hairâ âº Glad to read that itâÂÂs shredded cedar, as we donâÂÂt have too many gorillas around here. We are overly blessed with raccoons, deer, rats, otters, and mink which utilize our fishpond as a sushi bar, damn their sharp little teeth.

Reflecting on your post, I may need a shredder, though possibly running over things with the lawnmower would do it. We also have bamboo, which must be native to the island as itâÂÂs all over the place though no one will admit to planting it. Always, âÂÂIt was here when I bought the house.âÂÂ

I like what you say about applying fertilizer on top of the shredded mulch, sounds convenient.

As someone quite new to gardening, IâÂÂm still surprised at how much work, and how expensive it is, to grow things. I smile when someone tells me they grow vegetables âÂÂto save moneyâÂÂ. Our garden eats money, the big-box stores would definitely be a cheaper option. Then again, it is very pleasant to need a tomato for dinner and just go pick one, or have a recipe call for basil, and go harvest a handful from the deck. Most rewarding of all is growing beauty, painting a canvas of roses and lavender and tyme, and yet more blooming roses.

Thank you once again.

Pauline

Hi Lyn,

Yet more brilliant advice! I was just reading your post to my husband, and now we are planning an expedition to the forest to collect mulch (from under healthy trees). Such a good idea, and thank you for the advice about applying it right on top and not breaking the roseâÂÂs feeder roots. We also chop wood (OK, he does) so IâÂÂll be out there picking up the chips.

I really do appreciate the gardening wisdom shared by yourself, and Kim, and Henry, jim, nickl and the others. It is so good of you to take time from what must be your very busy lives to do this. Thank you.

Pauline

You're welcome, Pauline. At first, it will seem as though gardening is expensive, but once you learn how to coax things to do what you want, where you want them to, you'll find you can often do it for not a lot of money. My biggest "expense", other than property taxes, etc., is water. Of course, if you really need to spray for diseases, that's going to be expensive. The "good old days" of a $5 quart of anything concentrate are LONG gone. You would probably enjoy a shredder, particularly when you realize everything you shred is one less thing to have to dispose of otherwise and a little bit less of anything you have to buy and schelp to the garden. Have fun! You're right, being able to just pick whatever you want to eat is lovely! I don't have vegetables due to the critters here who eat them faster than the plants can grow, and they would require MUCH more water on this arid hill than the roses, but there are herbs in pots and in one planter, so whatever is needed to flavor dinner, is usually in the yard. I like that! Kim

Henry,

Thank you very much for all the information you have kindly provided, and thank you for the links.

Good of you to go to the trouble.

Pauline

mulch has worked wonders for controlling powdery mildew on my roses here in Denver Colorado.

i've had horrible powdery mildew problems on my roses every year until this year when i mulched heavily with small pine bark fines .

in previous years my PW problem was so bad i would have to trim some roses down to the ground by August and had considered digging and throwing out my roses all together just because they looked so horrible.

this year it is late August and i have zero sign of any mildew and my roses look so healthy and are re-blooming now!

When I was starting in the 1970s, I was amazed at how people were willing to help through local rose society meetings, then longer distance rose newsletters, also exchange of ideas by postcards, and then sharing knowledge by routing a VCR tape (I think that I still have some of the postcards and one of the routed tapes)!

Henry,

I'm pretty amazed myself at being able to receive great advice from lovely people who choose to share their wisdom. And it's a gift that keeps on giving, because healthy gardens make for better neighbourhoods. 'A rose grows in Langford'...

Pauline

So Henry K quotes a guy who claims that "most mulches are notorious for harboring disease spores," and then tride says that mulch cured his powdery mildew.

If PM is active in my neighborhood, there are a million spores in the air, and spores are on all the roses, all the mulch, all the pavement, all the lawn, etc. So why aren't all my roses covered with PM?

1. Because the conditions for germination are very narrow and may occur only a few nights a year, unless I live near the Pacific or in another cool maritime situation.

2. Because many rose varieties are highly resistant to PM.

3. Because hardened stems and mature leaves of even susceptible varieties are somewhat resistant, compared to new growth.

4. Because mature rose plants become more resistant compared to young plants.

And why are there some patches of PM here and there in the garden sometimes? Because of differing microclimates and differing levels of resistance.

Mulch* = good for roses.

No mulch = bad for roses.

*Just about any organic material that is free of herbicide residue. Bark, pine straw, wood chips, whole leaves, shredded leaves, hedge trimmings, weeds (not seedy), grass clippings (thin layers at a time), compost, leaf mold.

Materials from certain exotic trees (eucalyptus, ailanthus) may retard growth, but I don't know whether they do or not.

Come visit, Michael. I will happily show you many instances where NOTHING grows under eucalyptus; old, established oleander; California and Brazillian Peppers; California Black Walnuts; even a couple of Tree of Heaven. No one removes the encroaching growth. Nothing grows within their drip zones, even when the litter isn't sufficient to physically smother weed or grass growth. Perhaps their root systems are efficient enough to compete against invaders, but soil in which their litter has remained for long periods isn't appropriate for use elsewhere for other garden uses as it won't successfully support growth of other plants. Kim

Thanks, Kim.

Around here, I see multiflora rose, japanese honeysuckle, and bittersweet vines growing in thickets of ailanthus (tree of heaven, aka tree from Hell). These, along with kudzu, are our commonest macro pest plants, and they consort happily, with ailanthus as the dominant species. I don't know whether the multiflora might grow better with a different companion, but it does tolerate ailanthus. (Interestingly, kudzu doesn't seem to grow around ailanthus much.)

AnnTN6b grows roses under a black walnut tree. So these plants that poison the soil to inhibit competitors do not affect all competitors equally.

I agree it would be taking a chance to use materials from these plants as a mulch, although I have included ailanthus leaves in compost. I suspect the toxic agent will wash out of soil or compost with enough rain. It would need to be water-soluble in order to do its dirty work.

Michael, the key words in your post are: "If PM is active in my neighborhood".

Apparently rose powdery mildew is very specific to roses (I did see one reference that it could attack one other plant.)

My sub thread is that there are mulches that are hostile to rose powdery mildew. Using such a mulch is part of what I call sanitation. In general one hears more about this with blackspot and rose rosette virus but it applies to any infection - get rid of as many of the sources of the infection as possible. This thread is about "The presenter made the claim that mulch around your roses contributed to an higher incidence rate of PM in your rose garden & he recommended not using mulch for this reason."

Notice that the presenter used the word "contributed" and the word "higher". i.e. he did not say that no mulch equaled no powdery mildew. I suggested using a mulch that contained "friendlies" rather than "not using any mulch" as he apparently did (too bad we cannot see the statement in full context). I provided scientific research documentation that compost contained "friendlies" against rose powdery mildew fungi. I also provided scientific documentation that "splashing water" is a contributer. I expect that a mulch with "friendlies" will go a long way towards removing that route of infection.

I wonder how much of it depends upon rainfall totals? Your area receives tremendously greater water than mine does. Perhaps that assists in breaking the substances down and flushing them through the soil? Here, without copious hose water, they get deposited and then remain in place. Kim

Being in the process of covering the roses with a few inches of horse manure to mulch, I am looking forward to seeing how that effects rust if at all in the spring.

We have had a lot of mildew this summer, of course we are with in a couple of miles from the Pacific ocean. But don't discount your lots micro climates.

My perfect example is 'Simplicity'. The plants that are well established and have an old garage wall to reflect some mid day heat look pretty good. The one that sits in the shade til mid day is hard to tell it is a rose for the mildew and rust

Kippy-- thanks for the great example. I didn't know 'Simplicity' got the West Coast diseases. It is terribly susceptible to blackspot here. So what diseases were those lying b*****s at J&P claiming resistance to when they promoted this variety so heavily? Back in the day, we used to get a few posts a year from newbies who had spent hundreds on a 'Simplicity' hedge and couldn't understand why it had no leaves in summer.

Kim--yes, it seems that heavy rainfall could mitigate allelopathic soil-poisoning. But part of my thought is that roses (or some roses), along with some other plants, are resistant or somewhat resistant to the toxins in ailanthus and walnut.

Here, Michael, the question is more, "What diseases WON'T Simplicity contract?" At the beach, Simplicity rusted to death. Without regular spraying, it literally rusted so heavily, it never had foliage and finally died. Not one plant, but a hedge of it. Inland, where it's much hotter, sunnier and drier, the rust was not quite as bad, but still omnipresent. Mildew was more of an issue inland, too, which is counter intuitive until you consider the water stress response. Simplicity is SO bad in these parts, I will not consider planting nor using for breeding, any rose containing its genes. Kim

It appears that the reference that I gave about the problems of wood mulches and the advantage of compost could use some backing up by more primary scientific material. The link below is to an Ohio State University Extension Fact Sheet, Plant Pathology,
2021 Coffey Road, Columbus, Ohio 43210

Title: "Control of Nuisance and Detrimental Molds (Fungi) in Mulches and Composts"

Please note the following and put in context of the full article (also note the appearance of statements such as "These bacteria compete with fungi to reduce the potential for the development of major mold problems.")

"The best way to avoid all these problems and bring about beneficial effects by mulching is to add nitrogen to woody and hardwood bark products followed by composting to lower the carbon to nitrogen ratio. Blending of grass clippings with wood wastes before composting is one way to achieve this. Addition of poultry manure or urea to supply 1.2 lbs. available nitrogen per cubic yard of material satisfies the nitrogen need also. Some landscapers add 10-15% by volume composted sewage sludge to hardwood bark or wood wastes, and this makes an ideal product that has performed very well in landscapes. These amended products should be composted at least six weeks. This process kills plant pathogens, eggs of insect pests, and produces a nitrified product that releases plant nutrients rather than ties up nitrogen. As mentioned above, the microorganisms that have colonized these products reduce the potential for growth of nuisance fungi and provide control of many plant diseases"

"What to Do Once the Problems Occur
Sometimes very little can be done to control nuisance fungi other than to spade the mulch into the surface soil layer followed by soaking with water. Another option is to remove the mulch, place it in a heap after thorough wetting to allow for self-heating to occur (110-140 degrees F). This will kill nuisance fungi. If fresh dry mulch is placed on top of mulch colonized by nuisance fungi, the problems may occur again the following year or even earlier.

The best control strategy for homeowners and landscapers is to purchase composted products low in wood content. Fresh, finely ground woody products should be avoided for many reasons unless composted first. Coarse fresh woody products are much less likely to cause problems unless applied too deep. It is important to soak all mulches immediately after they have been applied. Generally, mulches should not be applied to a depth greater than two inches. Mulches and composts applied in this manner provide many types of beneficial effects rather than nuisance problems, or worse, plant diseases. Sour mulches should be avoided altogether."

Here is a link that might be useful: link for above

Silly Mother Nature, strewing all those uncomposted leaves all over the forest floor.

I use shredded wood chips about 2.5" - 3" deep and we get a lot of rain...
Like I said I've never seen any rose or shrub that's mulched get PM here.
Blackspot & similar looking fungal diseases now that's a different story... lol

With conditions totally different from situation to situation/climate to climate how can even scientific research always be correct?
In other words if the scientific research wasn't done in my own backyard how accurate is it really?