I have no doubt that manure can make a good mulch, and I know nothing about the soils and bacteria you are talking about. However, there seems to be one factor relating to blackspot that you didn't mention, so I'm not sure you took it into consideration.

I don't remember the exact temperatures, but blackspot only forms when the temps are in the lower-mid 80s. This summer we have had almost no blackspot because the temps in June jumped up to 100 and stayed there until Sept.1--at which point they dropped below 80 degrees (70s in daytime and 40s at night). Hence, any BS tests would be skewed--since blackspot would have trouble growing in those temps.

I don't know what the weather patterns are in your area, but I'll bet that your region, like mine, has temps more conducive to BS some summers and less condusive other summers.

But I must agree--blackspot on Knock Outs in any weather is rather strange!

Kate

There are a couple of fungal diseases that look similar to black spot. One that typically starts at the top is downy mildew-BS typically starts at the bottom. DM requires high humidity (>85%) and a rather narrow range of temperature (around 68 F), so it isn't as common as BS.

Here's the info. from University of Florida regarding the optimal temp. for black spot:

"The infection cycle starts when spores are spread by rain or overhead irrigation from leaves or canes infected from the previous season. The conidia must be wet for several hours to infect plant tissues. Symptoms begin to appear in three to 16 days after infection. Mature conidia can be produced 10 to 18 days after infection and initiate a new cycle. Conidia are colorless and two-celled (Fig. 2b). A temperature of 64�F is optimal for black spot development, but conidia germination still occurs from 59 to 81�F."

Here's the info. from U. of Mass Extension: "Seven hours of wetness at 65 to 75 degree F is sufficient for infection to take place."

Our temp. today is 64-66, tonight it's 61 degree. Zack_lau: I checked downy mildew picture, all my tall summer phlox flowers get them. I checked pics of black spots from both University Extensions - they match the black spots on my Knock-out leaves.

I did not fertillize my Knock-outs for the past 3 years. I don't mulch Knock-outs with horse manure - I mulch with them pine bark nuggets, since I never water them. One possible explanation is that my Knock-outs don't get the potassium like my 10 Austins.

Plants deficient in potassium are more prone to black spots.

Here is a link that might be useful: U of Mass. info on black spot

Knock Out isn't immune; in our climate it gets some blackspot and some cercospora. A plant that I see every day is sort of hollowed out with loss of all the interior leaves to spot diseases, but there is plenty of newer foliage on the outer shell, so it looks fine. Blackspot spots have fringy margins; cercospora has smoother and usually more purple margins.

It takes 7-10 days after germination for spots to be noticeable, so let's see what the Austins look like at mid-Fall. Also, newer plants may take a while to pick up the operative strains of blackspot. The disease is not highly mobile.

I don't mean to pooh-pooh your observations. These are always welcome.

It turned out to be 64 degree last night, another night of rain. That's 2 nights, plus one day of rain, or 25+ hours at the optimal temp. of 64-66 degree for black spots.

I'm 1 hour west of Chicago, and 1 hour south of Wisconsin. I checked my 6 Knock-outs this morning:

1) Red Knock-out in full sun, mulched with pine bark nuggets, next to a grill and a patio. Black spots are on leaves AWAY from the grill/patio. I suspect artillery fungus, rather than lack of air circulation. Both upper and lower leaves are affected.

2) Pink Knock-out against the wall, mulched with pine bark on top of horse manure. Less black spots, but still on top leaves AWAY from the wall.

3) Four Knock-outs in a bed of ZERO mulch, but got fertilized yearly with raked in leaves. These are completely free of black spots, despite being crammed in with mildew summer phlox flowers.

4) Ten Austins are 100% black spot free on horse manure mulch. The whole-grain corn meal that I dusted on Sept. 1 are still stuck on, despite the 25+ hours rain. I'll dust them again just to be safe - since we will get 3 more days of rain coming.

If folks want to experiment with corn meal, make sure that it's the WHOLE GRAIN, and not the refined box from the grocery store. My Eglantyne came in the mail badly black-spotted, I sprinkled refined corn meal. She hated it, leaves turned brown, and the stuff stank up and attracted flies. Eglantyne's black spots cleared up when I mulched with horse manure.

Whole-grain corn meal does not stink up, does not attract flies, and the birds/rabbits like to eat that stuff. Like Laura from Illinois, I get annoyed when some pompous authority from University Extension announced that corn meal does not work on roses - WITHOUT doing any field experiments to prove so, and WITHOUT making the distinction between refined versus whole-grain corn meal.

For info. on artillery fungus and tree bark mulch see:

Here is a link that might be useful: Purdue's info. on Artillery Fungus and plants

Thanks, Michaelg, for pointing out the difference between cercospora and black spot (both are fungal diseases). I checked my Knock-outs again: it's cercospora.

Black spots are usually associated with yellowing as well. Personally I think black spots are more lethal in deleafing roses. My purpose in doing these experiments is to find an easy, organic way to grow roses without hurting the environment, esp. the bees.

I don't want the entire world to be dominated by Knock-outs, it's very boring. OGR's and Austins get the bad rap for being sprayed, making rose growers look like evil bee-killers.

There must be a way to preserve the beautiful diversity of roses and nourish the bees at the same time. That's more important than benefiting the pockets of chemical companies.

Here is a link that might be useful: Difference between cercospora and black spot

Blackspot is indeed more aggressive in de-leafing the plant. Leaves with cercospora can hang on and function partially for maybe 6-8 weeks.

Unfortunately, many of the roses most resistant to blackspot are highly susceptible to cercospora.

There's a difference between spraying for plant diseases and spraying to kill insects. Those are 2 different chemicals and using one of them doesn't achieve the other.

You CAN spray for disease and not kill bees.

When you mention "black spots", are you referring specifically to blackspot disease, or is this something totally different?

Laura: Yes, insecticides kill bees. Fungicides we don't know until later. With the Organic Chemistry and Biochemistry classes I took in college, I tend to be more cautious. With every chemical we studied, there's a long list of adverse effects.

I prefer to benefit the farmer by buying cracked corn a giant bag for $5. I prefer to benefit the horse stable by getting rid of their manure.

We are talking about black spots, same as blackspot disease. All I know is that my garden with 10 Austins have more bees than the public garden with hundred of rose bushes, but with fungicide spraying.

Here's an excellent link on pesticides and human health. This includes fungicides and insecticides.

Here is a link that might be useful: Effect of chemicals on human health

Strawberry, evidently you are not aware that there are many rose growers on these forums that do not spray or only rarely spray an occasional fungicide.

I gave you some of the ways that many of us have greatly cut down and/or eliminated fungicide spraying in our rose gardens, but evidently anyone else's opinion bores you. However, I would appreciate it if you didn't refer to us as "bee-killers." I'd guess most of us do not spray insecticides and many of us do not spray fungicides or only very limited amounts of fungicide. Your self-righteousness is offensive--besides we have heard most of your theories many times before. They are not news to us even if they are to you.

Kate

This comes up quite often here.....

I used to work at a pharmacy, and everything there had warning labels and side effects as well. However, I don't think we'd be where we are today (or as many of us as there are today) without some of them.

For every person who says that they spray sparingly and have no problems, there will be another person that finds it deplorable, and that's ok; this is a matter of personal preference. The link provided is specific to pesticides, which I won't use.

The public gardens around me also lack flora and fauna, but more often it's because they are generally in decline and haven't been deadheaded or cared for as well as some of our personal gardens. Downstate is broke & local governments have done away with most of the garden maintenance jobs and funding.

I think your horse manure vs. leaf mulch idea sounds really interesting!! I think that it is definitely worth trying. Sure can't hurt - and we all know that manure is really great for fertilizing.

I'm really glad this worked for you!!! Please keep us posted next year to see if it continues to help.

Carol

Do you all dig down through the fresh manure to get to the composted manure at the bottom of the pile? If horse manure is really that good and stables want to get rid of it, someone should recognize a soft spot in the market and bag it for us squemish types.

I think Kate misunderstood me. The public looked at me as BAD, NOT you. This happened 15 years ago when I was spraying my roses with chemicals. A neighbor walked to me and said, "why do you even bother growing roses with all these spraying?" It's even worse now, like the protest of bee keepers in France against Bayer.

My observations do not apply to anyone else, since it's different with them. If I live in a hot area, I would pile up the bark mulch. But I live in a wet area - where it's more conductive to fungi growth. My defense is with the OGR and the fragrant Austins. These get the bad rap of black-spot prone, poor disease resistance - and less people bother to grow them.

I did not want to buy Radio Times and Wise Portia because of the bad reports about their poor disease resistance. They were the only ones available, so I had no choice. Now both I and the bees enjoy these. I have never seen any bees on Knock-outs.

We tend to reject certain roses as being disease prone, rather than seeing what we can do to protect them. The fault lies in us, and not in the roses. How did these old fragrant rose flourish in the old days without chemicals? Chemicals get the bad rap. Roses get the bad rap as NEEDING chemicals. Then Knock-outs take over the land. I'm trying to find a way to break this cycle, making roses to be more environmentally friendly.

Lainey2: you don't have to dig down to get to the bottom. It's a big pile higher than a house. Actually it's easier to get the bottom, most aged stuff, since it's at your height. You would have to climb up a big mountain to get the fresh manure on top.

Strawberry, I think your fundamental premise is flawed--that Knock Outs need extra protection or they will get blackspot, causing us to spray them and kill the bees.

I have only ever heard TWO people complain that their Knock Outs get blackspot--and the second of those TWO is you.

In other words, for the overwhelming majority of gardeners, Knock Outs do NOT get blackspot and therefore it does not matter what you do or do not spread around them. I have no idea what you are doing that causes your Knock Outs to blackspot, but I promise you, the rest of us do not have that problem.

As for the bees, I never checked to see if they hang around the Knock Outs in my garden, but if they do not, it is not because I've been spraying fungicide on anything, so absence of bees doesn't prove much of anything.

You will be pleased to learn, however, that I have tons of bees hanging around all my salvia--lots of salvia, lots of bees. Of course there is an Austin rose sitting in the middle of all that salvia--no extra protection supplied and it is NOT having blackspot problems.

My point is that if you are using your garden as typical of most gardens out there, that is not necessarily true. For instance, your garden is not typical of my garden--so I guess we cancel out each other out, and nothing has ended up being proved one way or another in the end.

Kate

Wait a minute.....unless I'm a complete moron, hasn't everyone here (and on the Antique Roses forum) been touting the benefits of old garden roses as the most disease resistant type? I have one OGR and it's the only rose that never needs spray.

Yes, we DO talk a lot about certain roses being disease magnets. It's one of the biggest services we can offer each other so that we don't waste time and money if we're not willing to give a difficult rose the attention it needs to flourish. Example: Angel Face. Beautiful, lovely rose but referred to as Angel Farce by many because of her desire to be a leafless wonder in certain parts of the Midwest.

Knock outs are more disease resistant and great starter roses for people who want to set it & forget it. However, under the wrong conditions, they'll get disease just like any other rose. If you see blackspot on your Knock Outs, that may be the reason why bees don't frequent it. I also tend to shy away from an otherwise yummy treat that has fungus on it.

Strawbeery Hill, I am heartened to learn that Radio Times can be grown and maintained without disease in zone 5.

The three I had when I lived in CA were very susceptible to mildew, both kinds,but I loved them anyway. I don't use any kind of fungicide or pesticide, partly because they represent an extra expense and partly because there are always small children about my yard. Radio Times was so vigorous, that I was able to cut off the mildewed parts,without permanent damage to the plants. I do not have access to horse manure, but I am intrigued by your coments about potassium and whole grain cornmeal.

Alot of our new roses will not show disease right away. I've had some that did great for 2 or more years then they start getting fungus diseases.
So your experimenting will need to be carried out over a long period of time to really see in my opinion.

By the way-sorry to hear your KO's got blackspot.
Ko's do very well here.

Strawberryhill, could you post a photo so that we can confirm that it is blackspot or another leaf spot disease? It would be good for me to see as a reference. Some have suspected that once in the ground for a few years a blackspot (or other fungal disease) might crop up and KO isn't resistant to that particular strain.

IME, this time of year, with some cooler weather, it may be anthracnose. I don't have any KOs, but some neighbors do. I've seen them have spotty leaves, but only in September. I used to think that it was BS too, until I learned the difference between anthranose and BS.