Return to the Roses Forum | Post a Follow-Up

 o
battleing blackspot

Posted by montana_rose 3 (My Page) on
Mon, Aug 15, 11 at 13:07

Hello Rosarians,

I know this topic comes up every year and for those of you who are tired of the question, I am sorry. I did the search and still did not find exactly the information I am searching.

I am once again battleing late summer blackspot. I have tried the baking soda/oil mixture and haven't been impressed. I am wondering what my next step is. (I know picking blackspot-resistant roses will be suggested, and I have some, but at this point, I just want to keep some leaves on my other less-resistant roses.)

I worked this weekend at changing my sprinkler system to a drip system, but I am wondering what SPECIFICALLY works to combat that blackspot. Those of you who spray, what specifically do you use, how often, etc. Also, we have hives in the area, so I don't want to use anything that might harm the bees, just the blackspot. Those of you that don't spray, what do you use, how often, etc.?

In my internet research, I saw people recommending potash as a potential blackspot deterrent. Does anyone do this? If so, where do you get it, how and how often do you apply?

Thanks in advance.

Katie


Follow-Up Postings:

 o
RE: battleing blackspot

Tebuconazole, available in Bayer products, is probably the best available spray for blackspot.

The best organic sprays are probably horticultural oil or elemental sulfur. The potassium-containing sprays usually suggested are potassium phosphite and potassium bicarbonate. Both have tested superior to sodium bicarbonate (baking soda) but inferior to oil or sulfur.

Overhead sprinkler systems can splash blackspot spores from the ground up onto the leaves but if you have a mulch in your rose bed the main effect will be to wash the spores down into the mulch where they can't do any harm. A sprinkler system can actually provide good control of blackspot (Peter Beales, the British Rosarian, was the first to point this out).


 o
RE: battleing blackspot

Mike R's advice is always good. If overhead watering is done at a time when the leaves will dry completely within a few hours, it reduces blackspot slightly by washing off some of the spores. But if any water drops remain on the interior leaves for 8+ hours at moderate temperatures, it causes the spores to germinate. However, in your dry air, drip systems are considerably more efficient than sprinklers.

Bayer Disease Control for Roses, Flowers, and Shrubs (not the Bayer combo products) works extremely well at two-week intervals. Products containing propiconazole are also effective. I'm pretty sure there is no harm to bees. Sulfur (considered "organic") should be adequate in your climate, but it must be sprayed thoroughly every week if any rain occurs, and it doesn't completely prevent disease.


 o
RE: battleing blackspot

I use Bayer Advanced Disease Control. I've found that starting a spray program early in the season, before symptoms arrive, is the best way to make sure I'm not battling an infestation come July.

If I wait to spray until I see a problem, I have to spray more frequently. An ounce of prevention.....


 o
RE: battleing blackspot

... what everyone above me in this thread has said. For blackspot, I use and recommend either Bayer Advanced Disease Control (contains tebuconazole) or Banner Max/Honor Guard (contains propicolazole). You can use these products every two weeks, reducing the number of times you have to spray a chemical in your garden. Time your spraying to coincide with a time when your bees are less active ... it would be okay to spray them at dusk, because the moisture remaining on the leaves overnight would be fungicide, and would not contribute to development of more blackspot.

Infrequent, scheduled, and deliberate use of a chemical in a controlled and responsible manner can be a GOOD thing.


 o
RE: battleing blackspot

flaurabunda's advice is traditionally sound, but the new fungicides are so effective that if you wait until symptoms appear, they will still stop the spread of the fungus entirely. Doing so can further reduce the amount of chemical used. Don't let the whole plant get spotty, but act when you see a few spots.

If you choose to use an organic control method, you should apply it as preventive from leafing-out through the whole season.


 o
RE: battleing blackspot

I did research on blackspot and found a British paper that confirms what Michaelg said, "water in the hottest sun, like mid-afternoon, and use horsemanure as mulch rather than tree bark (wish they would explain why). My guess is that blackspot spores don't breed as well on horsemanure mulch.

Our nights in zone 5a Illinois are getting colder, while the day remains hot (perfect for blackspot). I checked my roses: zero blackspot, although I planted them in partial shade, evening sun.

This is a pleasant surprise to the blackspot inferno that I bred 15 years ago: full sun, water at 6 pm, and tree bark mulch.


 o
RE: battleing blackspot

I've witnessed different results downstate. In my garden, the roses that are affected first & worst are the ones that do not get morning sun. Every rose that had wet leaves at 10 am from overnight condensation had problems, while the ones that were given a chance to dry out seemed to do much better.

I wonder if the horse manure provides less splashback or 'bounce' on water droplets?


 o
RE: battleing blackspot

Thank you, flaura, for reminding me that east sun is best. I planted too many blasted trees, so the only space I have left is evening sun.

This got to be our wettest season in 5a Illinois. We got many all-night rains in July. So far, zero blackspot on my roses. Eglantyne which CAME IN THE MAIL badly blackspot now is 100% clean.

My method of watering is dumping a giant bucket of used water from the kitchen, so horse manure splashes up everywhere.

The best answer I can give is: the fermentation of aged horse manure produces an acidic environment that blackspot spores can't breed. It's like trying to grow mold on sauerkraut.

Soaking a moldy shower curtain in a bucket of diluted vinegar works just as well as diluted bleach.


 o
RE: battleing blackspot

Ohhhhhhh I so envy you & your rain. It keeps missing us. We've had only a half inch since late June.

Someone planted blasted trees everywhere around us also, so our rose beds are in aesthetically awkward locations, but they're the only places where they get the right amount of sunlight.

I use the bucket method too, often, but I have wood chips. Neato tip on the horse manure; I will look into it next season!


 o
RE: Battling blackspots

Flaura, thanks for the funny remark - you made me laugh.

I banned tree bark mulch from my garden, although there's a free mountain of municipal tree bark nearby. We used those one year, and got absolutely GROSS looking fungi growing everywhere.

I have never seen a fungi growing on banana peels. There's this exotic recipe of whipping banana peels, garlic, and manure in a blender - and you just point and shoot at Mr. Evil Blackspots. To enhance the recipe, you can add a toad head, and some toe nail clippings (I made that up).

Seriously, have you ever seen a mushroom growing on a pile of horse manure - I didn't. Or have you ever seen a mushroom growing on pile of leaves? Most likely you have seen fungi growing on fallen tree trunks in the forest.

There are no tree bark in my rose bed, except for last year's leaves, and horse manure mulch. No breeding ground for fungi means no blackspots.


 o
RE: battleing blackspot

Interesting thoughts on the effectiveness of horse manure on the BS. I've heard growers in Ventura County here in California, have positively affected control of Armillaria, oak root fungus by use of horse manure as a mulch with copious water. That grows in compacted, nitrogen deficient soil. The nitrogen and bacterial action alleviate a lot of the conditions which favor it. Interesting it seems to do the same for BS. Kim


 o
RE: battleing blackspot

Always glad to hear from you, roseseek! I want to thank you for that interesting info. You are like a rose-mentor to us bumbling newbie-fools. I read all the info. you gave, in particular to those dating a few years ago regarding the fragrance in roses.

You will be missed dearly by many if you are ever gone!! So keep us posted. Thanks for instilling in all of us the passion and love for roses.


 o
RE: battleing blackspot

For Katie: thanks for your info. of potash as a blackspot deterrent. I checked on that, and banana peels around roses are effective against blackspot due to its potassium.(roses in soil low in potassium and magnesium tend to blackspot more easily).

I have never seen a mold growing on banana peels, so there are other anti-fungal agents involved besides potassium.

Other antifungal sources are: garlic, olive leaf, geranium, rosemary, oregano, and sage.

15 years ago I wasted money on chemical spray and lost my battle against blackspot. Now I realize that mulching with tree bark was the culprit. I'm better off mulching with something that fungi can't grow: horse manure and banana peels.

Spraying with baking soda doesn't work, because baking soda is alkalizing. You want to make the environment acidic, such as spraying with sulphur, so that fungi can't grow.


 o
RE: Battling blackspots

I did further research on blackspot prevention and found spraying with a wet solution is tricky for these reasons:

1) Leaves have to be sprayed BEFORE the spores land and germinate.

2) Blackspots occur when leaves are wet for more than 7 hours.

3) Rain washes the spray, so you have to respray after the rain.

No wonder I lost my battle with chemical sprays with our constant rain in the spring/fall.

Prevention works better than ineffective quick-fixes.
Oklahoma University Extension advised DUSTING the mulch in the spring with sulphur, making the ground acidic so the spores can't breed. (Fermented horsemanure mulch works the same by making the ground acidic).

Another University Extension Abstract mentioned about iron deficiency worsening blackspots in plants. Iron deficiency is a problem with potted plants, since it leaks out. The worst blackspots I have seen are the potted plants at the store.

My William Shakespeare 2000 is still in a pot (I can't decide on full-sun or partial shade for him). He has the classic iron deficiency that Michaelg alerted: young leaves turn yellow between the vein.

Besides potted plants, iron deficiency is a problem with alkaline clay soil. Iron chelates can burn, so I'll stick with the safe method recommended on gardenweb years ago: soak a steel wool in a bucket until it rusts, then put it next to the plant.

A deficiency in potassium also causes reduced disease resistance. Symptoms are: older leaves become mottled or spotted, edges dry and scorched. Weak stems. Poor root system. Mulching with banana peels will fix this.

Another problem with clay soil high in limestone and calcium like mine is: Deficiency in magnesium - lower leaves turn yellow, then brown. Leaves are thin, brittle, and cup upward. Epsom salt will fix this.

The above info. can be found at primaseeds.org/nutrients/


 o
RE: battleing blackspot

In my experience, fungicide sprays aren't started early enough in the season. Rose growers wait until they see blackspot before they start treatment. What has been effective for me is to start applying a systemic fungicide early in the season, meaning a week or two after pruning in late March, and keeping on a regular (every two weeks) schedule. I use Banner Maxx and mancozeb in combination, I know many people who have switched to Bayer Advanced Disease Control for Roses, Flowers, and Plants with success.

With synthetic systemic fungicides, as soon as they dry, they are effective, even if it rains later that day. You don't have to reapply. With surface fungicides (Daconil, mancozeb), many (like mancozeb) can also stay effective, but for a shorter period of time, and products like sprays that contain baking soda do need to be applied after it rains.

I haven't found that any particular mulch has supressed blackspot, but everyone's experience is different in that respect.

The most effective way is to plant disease resistant roses. In my garden, Blushing Knock Out, Caramel Fairy Tale, and Floral Fairy Tale are clean and full of leaves, and have not been treated all season.


 o
RE: battleing blackspot

Hi Strawberryhill, thank you! Much appreciated, but none of us are "bumbling fools"! Everyone is a virgin at everything once. Many of us remain so on many things forever. Ignorance and lack of experience are completely correctable and are nothing to be embarrassed about. Who of us was born knowing it all? Dang! As has frequently been stated recently, the more I think I know, the more I realize I don't! Thank Heavens! Knowing everything would be so bloody boring.

Thank you for that information about acidity and black spot. That can "cure" a ton of ills! And, do it completely sustainably and probably tremendously more cost effectively. It is great knowing the "why" behind observations you've made. This gave the explanation for what has shown itself to work and I thank you for it!

I agree with Diane's statement about the best way to battle disease is to plant varieties resistant to the types of problems you have in your area. Some years ago, Jeri from these forums and her husband gave a presentation at a Huntington Old Rose Symposium about ridding your garden of disease. Every person in attendance hit the edge of their seat when she stated "It is possible to eliminate disease from your garden!" Then, her husband held a shovel over his head and shook it! Absolutely, if the rose isn't happy where you grow it, shovel prune it. There are plenty of others just as beautiful and many a whole lot more agreeable to be with you!

Research done in conjunction with the Earth Kind program, IIRC, has shown four distinct types or populations of black spot in the US. They have tested a number of roses against all four types prevalent here and only ONE cultivar has shown resistance to all four, Applejack. Interesting that rose is behind Knock Out, twice. How fortuitous Dr. Buck created that rose without the black spot information!

This research not only explains why resistant roses in my area, defoliate from the problem in yours, but listed the particular varieties they've tested and to which populations each is resistant. Knowing which type of fungi you have predominantly in your area and which roses proved resistant to that type, can enable you to select roses which should be more resistant for you.

I had that information distributed at the GROTW event recognizing David Austin, but have misplaced it. I've sent a few emails to friends in hopes of finding it online. My searches haven't panned out for it, yet. You might try searching for it. It basically said there are 18 populations of the fungi world wide, with four of them occurring in the US. It gave the list of tested cultivars and to which of the four each was resistant. I'll keep trying to find it again to share it, until someone else pops up with it.

I did unearth this interesting piece from the University of Minnesota about hardy rose selection, should anyone find it helpful. Thank you! Kim

Here is a link that might be useful: Univ. of Minnesota hardy rose selection


 o
RE: battleing blackspot

Strawberryhill wrote:

"... so I'll stick with the safe method recommended on gardenweb years ago: soak a steel wool in a bucket until it rusts, then put it next to the plant".

Strawberryhill, I don't think that gardenweb advice is very good in this case. Rust is just ferric oxide and almost all soils everywhere already contain plenty of ferric oxide. Iron deficiency is not caused by a deficiency of ferric oxide but rather by a deficiency of soluble ferrous forms of iron in the soil.


 o
RE: battleing blackspot

Absolutely. Alkalinity locks the iron into insoluble compounds. Acidifying the soil will help to unlock them, making them more readily available to plants. Nitrogen is a great acidifier. Your fresher horse manure should help quite well with that. Kim


 o
RE: battleing blackspot

I agree with Diane, I try to do my first spray as soon as the roses leaf out. If I don't I can risk an outbreak if the conditions are right. Then it's every 2-3 weeks or more, depending on conditions.

This summer has been so hot and dry, I haven't had to spray. But my roses are defoliated anyway for the most part because of lack of rain. We finally got some yesterday. I think it's been a month. I'm still holding out hope for a decent fall flush.


 o
RE: battleing blackspot

Thank you, Mike and Roseseek, for saving me from foolish experiments. Luckily I haven't tried the steel wool method.

I got the "alfafa-on-top" idea from gardenweb and stunted both Shakespeare and Eglantyne. Thanks to Melissa, who sounded the alarm on "Rethinking alfafa", I realized that TOPPING with alfafa meal is a bad idea.

Roseseek, you are right about "Nitrogen is a great acidifier". The baby roses that got 2 cups of alfafa meal mixed with soil BEFORE planting are deep green, bushy, and heavy with blooms. Shakespeare and Eglantyne are both stunt and yellowish without that pre-planting addition of nitrogen.

Thank you, Diane, for informing me about systemic vs. surface spray. The last time I used chemical spray was 15 years ago, and I'm glad to be updated. You are right about "everyone's experience is different" in regard to mulch and blackspot.

Here in Chicago area we have gusty 50-60 mph wind in the spring and fall that blows mulch all over the lawn. Then we have weeks of non-stop rain, cloudy days that breed UGLY mushrooms on the mulch. We have flash floods and heavy thunderstorms that sphlash water everywhere. That's different from a sunny, calm and humid South.

The public rose park nearby with many Austins, HT, and others don't mulch either, it's just bare dirt ground.


 o
RE: battleing blackspot

HI Guys, I'm a newbie to the forum and a amateur rose lover. I'm from the NC area and have (18) climbers that I grow in oak half barrels along a split rail fence with turkey wire. I too battle blackspot every summer, this year I tried Bayer advanced disease for the first time and it seems to work well for me, also I mix 2 oz with two & half gal.of water and add to the soil about every month, am I the only nut that does this ??


 o
RE: battleing blackspot

  • Posted by jim1961 z 5/6 Central Pa (My Page) on
    Mon, Aug 22, 11 at 17:03

Annie2011,

If your using regular Bayer Advanced and spraying your foilage you should not have to use it as a soil drench.
Waste of product...


 o
RE: battleing blackspot

  • Posted by seil z6 MI (My Page) on
    Mon, Aug 22, 11 at 19:00

When I do spray for spots (and that's rarely) I will spray up and down the plant and then once around the ground under the rose. I don't know if it makes a difference but it makes me feel better.


 o
RE: battleing blackspot

Same here. I figure, get 'em, and get 'em good, and then I don't have to come back out and repeat the process in a couple of weeks. I spray the upper leaves lightly and concentrate more attention on the lower third of the shrub, as that's where my problems always seem to start.


 o
RE: battleing blackspot

I'm glad to hear from both seil and flaura about spraying the ground, since that's where the breeding ground is.

There's that British paper regarding tree bark mulch as the culprit for blackspot - and acidic, fermented manure/compost as the cure.

There's a link that tells people NOT to use tree bark mulch: http://www.gardensalive.com/article.asp?ai=802

And Oklahoma University Extension advised dusting MULCH with sulphur in the spring.

We had 10 hours non-stop rain yesterday, humid today. It has been wet since July. My roses in partial shade are still clean, including William Shakespeare in a pot (mulched with acidic manure, he's bushy and heavy with blooms).

The roses in containers AT THE STORE all show blackspots, and half-naked from rain. Fermented, acidic manure works the same as spraying the ground with sulphur.


 o
RE: battleing blackspot

  • Posted by seil z6 MI (My Page) on
    Wed, Aug 24, 11 at 18:47

Well, I've never used mulch of any kind (I hate the stuff) and I still have a ton of black spot so I'm not so sure the mulch is the culprit. Fungus spores drift on the air, are in the soil and float on the water so they're pretty much everywhere. So if acidity helps kill them, and roses do like a more acidic soil, that's a good thing.


 o
RE: battleing blackspot

Blackspot overwinters primarily as lesions on rose canes, visible as purple spots. From there, in spring, it infects leaves close to old wood, and then moves from leaf to leaf. Fallen leaves play a secondary role, and covering these with any sort of fresh mulch would probably reduce that. Because of the role played by old wood, very severe pruning of winter damaged roses will postpone the onset of disease in spring by some weeks.

Back when we had sub-zero winters and I grew mainly hybrid teas, I had to prune nearly to the ground; black spot did not appear until the beginning of the first flush in mid to late May and only on the lowest leaves. Now that I am growing hardy shrubs with high pruning, blackspot appears earlier and all over the plant. Plants can defoliate by June 1 without fungicide.

Any science-based and up-to-date web page will mention the role of cane lesions. Compendium of Rose Diseases, 2nd ed., says this:

"Raised, purplered, irregular blotches develop on the immature wood of first year canes of susceptible cultivars (Fig. 14). Spots later become blackened and blistered; they contain acervuli but lack fibrillose strands. Lesions are often small and rarely kill branches but are extremely important in the survival of the pathogen over the winter."

I stress this point because I think this thread is overemphasizing the role of the soil surface and mulch.


 o
RE: battleing blackspot

Some more evidence on the minor role of the soil surface and mulch on blackspot infection: F&N tests reported that covering rose plants with plastic quonset style huts lowered the incidence of blackspot from 36.1% infected leaves to 1.1% infected leaves, about the same degree of control shown by fungicides in the test. This suggests that most blackspot infections come from the air and not from the soil or mulch.

I don't know if there is open access to F&N Results but here's the link:

Here is a link that might be useful: F&N tests


 o
RE: battleing blackspot

Mike, Michaelg, and Seil all have valid points. There's no mulch in the CONTAINER ROSES at the store, and they are half-naked by mid-August. So hot and humid air, coupled with wet leaves will germinate blackspot, no matter what.

I agree with Seil that acidic rose leaves can withstand blackspots better. There's a British website that told people NOT to use horsemanure for vegetable garden, only for roses, because it's too acidic. More alkaline cow manure is more appropriate for veges.

I did an experiment last month: I scraped OFF all horsemanure around Lilian Austin and Mary Rose. After 10 hours of rain, one hot and humid day - Lilian Austin has 1 BS leaf, and two yellow ones on Mary Rose (I can't decide if it's BS or too much rain). Not a single blackspot on the other 8 Austins, heavily mulched with horsemanure.

Eating yogurt, high in probiotics (beneficial bacteria), helps yeast infection in the human body. There are bacteria in horsemanure, plus tons of crawling millipedes, which help to restore nature equilibrium. The rose leaves become more acidic, which discourage blackspot formation.

This year is much better than what I did 15 years ago: Mulched with tree bark, used chemical fertilizer and insecticides, plus chemical spray: My roses were infested with asphids, JB, and half-naked by October with BS.


 o
RE: battleing blackspot

I like to experiment (had too much fun with lab classes in college). One experiment I might consider doing is: Chew a young leaf of a Knock-out, and spit it out - to see how acidic it is.

Then chew another leaf of a BS-prone variety - which I have plenty: Eglantyne, Wise Portia, Radio Times, Golden Celebration, and Mary Rose.

Unfortunately I don't have any hybrid tea, nor the ones NEVER BEEN altered by acidic horse manure. The bunnies eat young rose leaf in the spring, so I guess it's OK to just to taste, then spit out.

The corn meal experiment is another one I am testing. I tested the de-germed type from the grocery on Eglantyne when she came in the mail badly blackspotted - it was a disaster, leaves turn dark at the edges in the hot sun.

I tested the WHOLE-GRAIN cornmeal from the feeed store a few days ago, leaves look fine. I'll see by October if the WHOLE-GRAIN cornmeal, horsemanure, and NO spraying works.

I should had known better NOT to use the de-germed cornmeal from the store. One time my pantry was infested with bugs. They were only in my brown rice, and none on the white flour, nor the refined noodles. If bugs don't eat that white stuff, neither should we.


 o
RE: battleing blackspot

Typo correction on my last post, it should read, "Bugs were only in my brown rice, and not on the white flour, nor the refined noodles."

Here's the result of my leaf-tasting experiment, I'll report it to spare someone else the misery of trying:

1) Black-spot resistant Knockout: I chewed on the youngest leaf. Absolutely bitter and acrid - I spit out, can't even rinse off the sticky bitter taste.

2) Lilian Austin with NO horsemanure: The young leaf was pleasant, almost like spinach - something that I can easily swallow. This one has 1 blackspot leaf after 10 hours rain.

3) BS-prone Eglantyne on horsemanure: bitter and acrid, very much like Knock-out, I had to rinse my mouth repeatedly. Eglantyne is 100% clean.

I have zero asphids in my low-nitrogen clay soil. In a different garden 15 years ago, with chemical fertilizer, I had tons of asphids. There's an article that links asphids to high-nitrogen fertilizer.

Flaura from IL is right about morning sun as best for roses. William Shakespeare in a pot was barely alive in full sun - I moved him to the east side of the house. Now he's bushy, full of buds, and zero BS. Eglantyne is stunt in full sun, and my other 8 Austins are in partial shade, 4 to 5 hours of evening sun.

The humid air has a lot to do with mold: All my aluminum sidings have mold, except on the south and east side.



 o
RE: battleing blackspot

I have moss on my North & West sides, just like the trees around my house. The shed in the backyard is just covered with it on the North side, and I think it's beautiful.


 o
RE: battleing blackspot

For Flaura: Do your hybrid-teas lose more leaves to blackpots? Are Austin shrubs better than HT's in battling blackspot? Many thanks.

Everything is region-dependent, including the tree-bark mulch or horse manure choice. I can see why the English and the public rose park in my Zone 5a don't use tree-bark mulch:

1) The constant rain can breed different types of ugly mushrooms on the mulch. Plus the splashing upwards of heavy rain.

2) As tree-bark mulch breaks down, it robs the soil of nitrogen

The horse manure is also region-dependent. If the horse stall uses hydrated lime, sprinkled on the stable floor to deodorize the smell, then application of horse manure raises the pH of the soil, making it alkaline. It's always good to test the pH of the horsemanure before using.

Cow manure is superior to horse manure since horse manure is often mixed with hay, sawdust, or bark - and as these break down, it robs the soil of nitrogen. The best show of roses was when the public park used cow manure in the spring.

In his book, "The English Rose", David Austin recommends mulching with barnyard manure. I take it that he means cow manure, since he didn't say, "stall manure".

Both the Enclyclopedia of Roses and David Austin wrote about blackspot-prone varities, such as: Wise Portia, Happy Child, Portmeirion, and Radio Times.

The above is also region-dependent, as Roseseek (Kim) informed us that there are 4 different species of blackspot. My Radio Times and Wise Portia are 100% clean, and gave me the most cut-flowers. These two might be blackspotted by a different species elsewhere.

Yesterday I did the LAST application of horsemanure mulch around my roses, including Lilian Austin and Mary Rose. I'll wait for 1 month, before I taste the youngest leaf of Lilian Austin, to see if the horsemanure will make it bitter and acrid like Knock-Out rose.


 o
RE: battleing blackspot

Dunno about HTs vs Austins; I just planted my first Austin, Jude the Obscure, this year.

It doesn't seem to matter which class a rose is; if one of them that is less disease-resistant starts showing signs, it can spread so easily to the others. This year hasn't been so bad and I think I have the heat wave and lack of rainfall to thank for it.


 o
RE: battleing blackspot

I can envision the bacteria in the manure competing with Black Spot. I recall an expert saying that the problem with biological fungicides was that spraying it onto the leaves would only provide protection for a short period of time.


 o
RE: battleing blackspot

Zack_Lau: I always value your opinion (you have 200 roses, right?) - eHow has a description of how to spray for blackspot using a compost/manure tea. Blackspot can't flourish when there are inhibiting bacteria in the manure.

Spraying with manure tea is pretty gross, I would rather dust with cornmeal.

It took less than 5 minutes to dust 10 roses with WHOLEGRAIN cornmeal after a heavy rain. Since the leaves were wet, the cornmeal stuck on pretty tight and are still there.

I used to live in Connecticut, it's not as wet as Illinois. CT is the ideal place to grow roses, and Elizabeth Rose Park is stunning.


 o
RE: battleing blackspot

Strawberry, I grow 300 roses in central Illinois...a mix of minis, Austins, Bucks, HTs, floris, shrubs, rugosas, antiques, climbers, and 3 lonely Knockouts. I use the Bayer Advanced on all but the Knockouts because they never get BS.

As far as Austins being more BS-resistant than HTs, it's my experience that each individual cultivar is different. Some of my Austins such as Lilian, Christopher Marlowe, and Winderemere are pretty much bullet-proof if they don't get sprayed on a regular basis, while Summer Song and Munstead Wood become a BS-ridden mess and defoliate sometimes even with regular spraying. The same with HTs...it just depends on the individual rose.


 o
RE: battleing blackspot

Terryjean: glad to hear from someone in my state.

My Lilian Austin doesn't look like the on-line pictures. It doesn't look like the one I saw at the rose park. It looks more like DaisyinCrete's unknown rose (Any Ideas?). It looks like a faded Pat Austin (apricot-yellow). It smells more fruity than Pat, but less intense than Golden Celebration.

Thank you for the info. on Summer Song and Munstead Wood.

I like my Austins better in partial shade: William Shakespeare in fun sun is ugly dark purple, but in partial shade it gives a glowing reddish crimson, which is prettier.


 o
RE: battleing blackspot

Stawberryhill, Age tree bark does not rob the soil of nitrogen otherwise our forest would be in pretty bad shape. Fresh wood mulch will can cause some nitrogen tie up but then again so can fresh shredded leaves or grasses clipping for that matter. Using fresh manure is never a good idea unless burnt garden plants are what you want. The manure needs to be aged (especially horse which can contain lots weed seed) so that it releases the nitrogen slowly as it breaks down.

I live in blackspot county, so mulch or no mulch I will get blackspot. I think the idea is to increase the acid content of the area. I collected used coffee grounds some months back with the intent of using it but I forgot. I guess I had better find that bag.

I wonder if using compost instead of manure, would that deter blackspot too?

And so that you know fungus will grow on almost anything including manure.


 o
RE: battleing blackspot

Moril: I appreciate your raising question about how much nitrogen tree bark robs compared to others. There's this government website http://www.fpl.fs.fed.us/documnts/fplrn/fplrn091.pdf

which makes a big issue out of tree bark and nitrogen deficiency by suggesting addition of 25 ammonia, or 80 lb. of urea, or 100 lbs. of ammonium nitrate or ammonium sulfate.

On the other hand, there's this Colorado University Extension that says tree bark doesn't rob the soil that much nitrogen, since it's a very slow decomposition.

Then there's another University Extension that recommends stable owners to add nitrogen to their horse manure mixed with hay, so that they can get rid of their manure easier to the farmers.

My take: Horse manure on hay breaks down faster that big chunk of tree bark, so nitrogen deficiency is more of an urgent issue with aged horse manure.

My main concern with tree bark is NOT the nitrogen issue (I have to supplement NO MATTER what with my poor-nitrogen alkaline clay). My concern is the fungus issue. Check out this website from Pen. State University:

http://www.personal.psu.edu/users/d/d/ddd2/

The above links is about artillery fungus on decayed wood bark that gets on white cars parked nearby. That's the same concern that the British paper wrote about tree bark mulch contributing to blackspot in roses.

I take www.greenharvest.com recommendations of using number choice 1) oat straw and 2) pine park
with a grain of salt: I used pine bark in the past with my 15 roses and had the worst blackspot, despite chemical spray. This website makes a good point about potassium deficiency as making the rose more prone to blackspot.


 o
RE: battleing blackspot

I prefer the science of this. I'm going to lean the chemistry and botany courses that I took in college and use at work. One thing you must keep in mind is where and when where those studies were done. The soil I have here in Kansas is not going to the same in Washington, Colorado or in the UK for that matter. What was the parameters (conditions) of the study? Was in done in lab or was it a field study? What type of wood mulch did they test was it pine, hardwood and what type of hardwood was it? As a person who now grow cells for a living (was an analytical chemist). I have a pretty good idea under what circumstance fungus will grow. Trust me when I say fungus will grow just about anywhere if the right conditions are met.

I also know what fresh manure will do to a garden. To much of a good thing. Its was sorry sight, I was a kid I didn't know any better. Yes manure breaks down faster then tree bark, however the key is breaking down(decompose) which means releasing elements not taking away.

So what I'm trying to say is it depends on where you are.
Blackspot has been horrible for my area due to our weather. Rain one day, 100 degrees heat the next, with clay soil and now the wood mulch doing its part to make it worst for me. However, I did goof when we had all the rain then three weeks of the heatwave I forgot treat the soil with the usual soil condition spray and it shows. So I'll be adding that to my gardening duties this holiday weekend.


 o
RE: battleing blackspot

I use Bayer Rose Disease Control and Honor Guard-generic Banner Max, for my regular sprays. When I have an outbreak of blackspot, I forget to spray sometimes, I use Manzate. This is the only product that will kill the blackspot spores.
I will use it twice a week for three weeks then switch back to my regular sprays and put a reminder to spray on my calendar!!! Actually we got infested with cicadas and I couldn't go outside at all in June. Well blackspot got started. I got it stopped and cleaned up with manzate.

About the bark issue, blackspot spores do not come from the bark, or grow in the bark. The spores come in from the wind. That is why it's so important to keep a good protective spray on your plants.


 o
RE: battleing blackspot

I think the issue with mulch is that the spores can drop to the ground around the roses and spore infected leaves also drop. Then if it rains or you water and the water can splash the spores on the ground up to the plant and infect it. The spores can also overwinter in the ground. That's why a dormant spray is important before you put down new mulch. And when I do spray my roses, I also spray the ground immediately underneath to kill any spores lingering on the ground.


 o
RE: battleing blackspot

Thank you, dan_keil for info. about Manzate. I don't spray this year, I am doing dusting with cornmeal experiment. If it doesn't work out this year, I'll spray next year.

Buford, you have an excellent point. That's why Oklahoma University Extension recommends dusting mulch with sulphur in the spring. Also people who put fresh mulch early in the year can control Artillery Fungus better (shoots up from mulch, which blackens house siding, and rots wood). Penn State University did an excellent research on this.


 o
RE: Info. about Rose-Flora and resistant roses

I want to thank Zack_lau for his insight on bacteria in the horse manure inhibits black spot fungi. He grows more than 200 roses!! I checked on that, and found this product called Rose-Flora, which consists of soil-based bacetrium, but kills a dozen variety of fungi.

The info. is in this website, which also has a long list of what type of rose is best resistant to black spot. Check this out:

http://www.better-flora.com/blackspo.htm

I read what Michaelg wrote, and as always, he has a good point. University of Illinois Extension recommends chopping the rose down to 1 to 2" as a drastic way to stop black spot.

Another UK website mentioned that black spot spores can mutate and breed new types which are immuned to the resistance in the rose. This site states that the spores are carried by wind, as well as by splash up water.


 o
RE: battleing blackspot

  • Posted by jim1961 z 5/6 central pa (My Page) on
    Fri, Sep 2, 11 at 14:42

Strawberryhill,

It's too bad organic fungal disease treatments do not stay on the leaves longer, that's one of the biggest drawbacks to why their not very effective.
They just get washed off to easily and most are just not effective at all anyhow.
Best to plant the most disease resistant roses for a certain area. Some areas need to use chemical BS fungus control because most everything grown rose wise loses all or most of it's leaves...


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Roses Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here