The Proverbial Black Spot.....

We all as rose growers come across the proverbial b/spot.

In the west here , we don't suffer as much as some parts of Australia and one person in our rose society doesn't get it at all.

Just in the last week or so , it has deceided to rear its ugly head in my garden. Now i did spray with lime sulphur after prune and then six weeks later, including the ground.

Now I have gone round to each and every bush and pulled off any leaves that has the BS on it and any leave that looks to have yellow on it. Picked up all the leaves off the ground then sprayed with triforine.

Within two days I almost had double the leaves that were infected with BS.

Why is this bug so damn hardy and why is it able to destroy perfect deep green healthy leaves in less than 48hrs after spraying. When I spray a bush the leaves are sprayed top and bottom, the canes and the ground.

Isn't there a clever scientist out there who wants to become a millionaire many times over if he finds a cure for this bug

Cure... no... breed better roses that are unaffected by it... yes.

Firstly, have you read this: [You must be registered and logged in to see this link.]

The title is about pruning myths but it also discusses black spot myths and how traditional cultural methods actually promote the incidence of blackspot infection. It's an eye-opener.

Secondly, I believe that we are actually favouring the evolution of the black spot fungi by spraying it as we do. It kills of the susceptible individuals leaving behind the resistant ones to breed and spread.

You can add things to the ground around the roses to improve their resistance. Sulphate of Ammonia @ 150g/rose encourages the rose to develop much thicker cell walls. The fungi gains access into the leaf via small openings in the bottom of the leaf called stomates and from there it extends a structure called a hyphae into the leaf and into the cells. There is only a certain amount of energy in the spore to allow it to get inside the cells after which it can drawn energy from the leaf itself. If the cell walls are thickened then the fungi will find it more difficult to gain access to the cellular contents, ultimately dying of starvation, and the plant will remain cleaner.

If you are part of a rose society I assume you know the benefits of mulching. For any newer members, mulching can reduce the amount of blackspot. If you can't mulch then underplant... it's a green mulch and has an identical effect (and looks better too). The theory is that when it rains, or when you water, water splashes down onto the ground, on unmulched soil, throwing soil and other debris upwards onto the underside of the leaf. Ever wondered why it is always the very bottom leaves that show it first? From there it can spread to the higher reaches of the plant because as the fungi matures it breaks through the top of the leaf through which a fruiting body containing spores protrudes and if 'fired' upwards to infect higher leaves. Spores in the soil infect the leaf and then can spread. When you lay mulch down it reduces the impact of the water on the soil so fewer spores are splashed up onto the undersides of the leaves. This is why a lot of climbers climb cleanly when they reach a certain height above the ground. Once they put some distance between themselves and the ground the incidence of infection drops considerably because the spores do not reach them. Wind is not a major form of transmission.

Plants do have something that resembles an immune system and the healthier they are the more able they are to fight infections such as blackspot.

The best option is to grow resistant varieties and what is resistant for me may not be resistant for you. Breeders need to breed better roses and then people need to embrace them to weed out the poor ones.

I hadn't read that article myself. Very informative.

I have noticed the method of pruning (or lack of) and reasons, are the method/preference of many used hear on RT, as I have read on previous threads.

What I found most interesting was his suggestion to not pick up leaves off the ground as a means of detering BS. I have in the past been indoctrinated to pick those leave up and dispose of them corrently. Even last week on a DVD about roses I was watching, the presenter took great lenghts in demonstrating the need to pick up those leaves and greather lenghts in how to dispose of them. I suppose it does make good sence, if the study/report is correct, and the spores die with the leaves. When I think back to my school days learning about the decaying rainforest floor full of leaves returning nutrience back to the soil to be re-used etc etc...

If the study is correct, it would also negate the reason for not added the leaves to a compost bin or the like..????? It does contradict advise from many other proffessionals....

I have alot of roses already on my property, but only a small number of varieties, as I like to mass plant to create a look/feature. But even though my plants are young, I am already noticing a pattern of varities that are BS resistant and varities that are suseptible. They are still a bit young for me to post some hard factual information yet...I would like to observe a bit longer yet for that, but the pattern is definately there already.....

Maybe Shamous you could keep a log book or a diary and log when the roses are clean and when they starting to get the BS and how long for . You could even experiment since you say you mass plant . Split your same roses into groups and experiment...ie: spray/don't spray...leave leaves/ pick up leaves etc....even take photos to check from one year to the next.......

Or Shamos you could look to varieties that are not affected by BS.

Living in Queensland near the coast with the humidity you would think our roses would be covered with it. The only ones that suffer from it to any extent are teh DAs and a couple of the Alister Clarke Hydrid teas.

The teas, chinas and noisettes do not suffer from it.

There are other varieties that have been breed with resistance to BS etc in mind.

Shamous, roses are one of those things that are as plagued by myths and legends as they are black spot and mildew. It is wise, with roses (and with everything in life IMO) to follow a simple rule: 'Challenge Your Assumptions'. Roselore is so entrenched that many of the things that we all, even the professionals, take for granted as being correct when they are in fact not. Many things are based on old/ancient and untested thinking and it is challenging for many people to question that which they take for granted as being correct. You only have to look at the resistance people show towards embracing new types of roses or how they kick and scream when they have faced with the idea of not having to spray a rose... because you have to spray EVERY rose don't you... Um no you don't! In my view, there are not many questions that come to mind when looking at whether or not the study is true, except that things may be different in different areas. I think it is wise that broad sweeping conclusions are avoided without first considering the effect of variations in climate on the way thngs behave, but the logic universally supports it IMO. This is especially true when viewed in conjunction with regular applications of mulch, which buries the fallen foliage thus preventing it from reaching the leaves so even if it does remain viable for even a short time once it causes the leaf to fall it can't physically get reach the leaf as is transmitted through the air and not thorugh the ground, despite anything anyone anywhere will tell you.

What Gary means to say when he says that Teas, China and Noisettes are not affected by black spot is that in his climate they are not affected. Down here in Tasmania, Teas, Chinas and Noisettes (oh my) most definately are affected by black spot, some to similar levels as those awful hybrid teas people insist on growing As always, it's horses for courses when it comes to roses

Yeah sorry I did mean to say that they perform that way up here and I know that they suffer in other areas. The point being you have to experiment (or get advice from others) as to what grows best in your area.

Interesting that certain parts of our garden are affected by mildew most years but others (with the same rose variety) are not. This year we have had none and I am assuming that it is because of all the rain that we have had. I am assuming that the spores are washed off before they mangae to germinate.

Rain will do it... mildew hates being wet

Yeah - I've noticed that on my property as well. I have a row of 7 "Charles de Gaul" running along a south facing wall with only a path between (with no BS) and a row of 7 "Charles de Gaul" about 7m further south running parrallel to the first in a more open position (all with BS). Not sure why, as I would have thought the more southern row had better air circulation being further from the wall, and receives more sunlight, so contradics my reasoning........a few assumptions to challenge there for me.....a few unseen variables perhaps.....new hypothesis formulating.....

I friend of my who has some sort of horticultural experience in America told me today that he uses and I quote.....

"I have had good results controlling Black Spot by spraying with either 1 teaspoon of baking soda mixed in 1 quart of water or a 50/50 mixture of fat free milk and water, and getting the soil the roses are growing in worked into a good, healthy soil."

Has anyone tried these methods out?

Have read the Baking soda method in some old books of mine (about chemical free gardening). I believe Simon responded to a similar question from HeartofFlush regarding the milk recently. I personally haven't tried either. Could be something else to experiment with, but my long term plan is to give the plant every change to grow, build resistance and be healthly, with as much encouragement and help I can give, and if that fails, it will quickly get replaced with a different variety.

Right now in Mt Barker its quite warm and quite wet for the last day or two. Feels like QLD weather. So will be interesting to see how my HTs' deal with it.....

As you can see the BS has stripped the bottom half of these two bushes. Will the bushes recover and get new growth on the bottom half or do other things come into play here


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Neptune I have found in W.A that what will do the most damage to my bushes over summer is sunburn.
I'm not talking about leaves scorching but rather the sun burning the bark on the trunk and branches on the bush. This can be a problem that can occur after a BS attack defoliates the plant and it make take only one stinker of a day to do it . If the base of the bush around where it's budded gets sunburnt , especially if it's a youngish one , kiss it good bye.

Where abouts in W.A are you ? My bushes have been the best this spring that they have been for years , I don't spray or very rarely [too lazy /don't have the time ] and although I get a bit of BS it's not something that I would normally worry about .
Having said that, the funny weather we have had the past 10 days or so has produced the worst outbreak I have seen up here so now I'm tossing up whether to spray or not . The reason for this is not that the aesthetics of BS worries me but rather I want my bushes going into summer with maximum leaf coverage to protect the stems from sunburn .
To this end I have ramped up the feeding and watering to help the bushes heal themselves before I get out the sprayer .

It's a bit hard to say whether your bushes will leaf up lower down ; you could try giving them weekly waterings with something like Thrive or Aquasol . The higher nitrogen content may help promote more leaf growth ; that's my aim over summer , flowers are a bonus.

cheers. Rosalie

Thanks for the reply . I'm in the Rockingham area and yes the sun did do its number on my roses last wednesday , which was the day before I had to bench at the rose society meeting.

I was thinkink about shade cloth over the roses to protect from the midday sun, but that would look silly at the front od my place where they are...

OzRose - would this apply to Standards...? Having no foliage for 1m+ on the base..??

With standards, one trick that was once commonly done was to get piles of tea-tree sticks, like that used to make the fences, and make a sleeve around the stem, tied on with raffia or something similar, to prevent sunburn.

So how do you stop sunburn or lessen it , if you don't put shade cloth over the top?

Underplant with something like a low growing daisy or lavender.

won't that take away the nutrients intended for the rose bush. As you can see , the bed is not that wide

Roses have extensive root systems and are effective competitotrs. They have much deeper root systems than most people are aware of. I grow things under all my full sized roses.

Does this help with your theory, that the BS spores don't rebound back onto the rose bush and re-infect them......and do these flowers object if any triforine falls on them?....

Yep. I swear by it. Bruce uses grass... I use grouncovers. I don't use bulbs because they spread and crowd out the roses but the other things are great. This one is my favourite at the moment: A creamy form of Anthemis tinctoria (a type of Chamomile Daisy also called Dyer's Daisy).


It's about 30cm high and spreads into a thick weed suppressing mat of silvery foliage and creamy yellow flowers. It attracts lots of butterflies and hoverflies to the garden and the hoverflies lay their eggs on the roses and their larvae hatch and become voracious aphid predators.

As you can see , I only have mondo grass, which I use as a border plant.....do you take these daiseys out when you do your winter prune so as let the soil build up again?

This year, I did something different for mulch....last couple of years , I used lupin mulch...looks like straw and the other day I dress with a mushroom mulch compost......will this make a difference with under growth...

Hmmm, I know this is supposed to be a BS thread, but I think I need to look at my standards (20 x Ingrid Bergmans - I love my Ingrid Bergmans), and give them some protection, now that the sun is more overhead, there going to be pretty vulnerable. I do remember someone telling me of a trick when I bought them, about rapping old stockings around the stem and stake to protect them against sunburn, but I dismissed the suggestion as I wanted old stockings flapping about my gardens about as much as I want old flanalet Knickers hanging all over my bathroom. But seriously this is a factor I used to take into account, but have forgotten about this year now that I had started over again. It's a pretty important one to.

Old hesian bags can be used as well to protect the stems of standards or again you can underplant them with something a bit taller... I have one section where I am growing a multiflora up to make into a standard and have miniature roses growing around it. Lavender would look good as would things like penstemon.