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Water sprinklers and black spot

Posted by dewyd S. Fla. (My Page) on
Tue, Feb 4, 14 at 14:58

I moved to a apartment complex and they have an issue with tenants planting plants. I have various potted roses, hybrid teas, floribundas, and a few climbers. There are many spots to plant the roses, but they have rejected any spots close to any of the few available water spigots.

The only other available spots are watered by sprinklers. My concern here is that the sprinklers go off at various times during the night and cause black spot.

Do you think the water sprinklers would cause black spot and eventually kill or stunt the growth of the rose plants?

Any replies appreciated, thanks.

This post was edited by dewyd on Tue, Feb 4, 14 at 19:37

Follow-Up Postings:

RE: Water sprinklers and black spot

If the roses are wet for, let's say, 7 hours at night, that might very well promote BS problems, and if your rose has chronic BS problems, that could affect its long-term health.

On the other hand, isn't Florida a BS-plagued area anyway? Do you normally spray a fungicide? I would think you have to.

Under the circumstances you describe, I would just keep the roses in their pots and place them in more optimal conditions.

Hope that helps.


RE: Water sprinklers and black spot

Thanks. Don't spray with anything. I don't have to many options here in a apartment complex. I would rather hand water them, but there are no water spigots in the areas that the property manager wants to place them. So pretty much have my hands tied trying to say anything here.

Some of the roses need to be re-potted into bigger pots I don't have, or put in the ground.

Probably the best bet is to find another property to put them on, or maybe sell them.

Thanks, Bill.

RE: Water sprinklers and black spot

  • Posted by seil z6b MI (My Page) on
    Thu, Feb 6, 14 at 9:51

I know night time and overhead watering are considered verboten but Mother Nature does it all the time and our roses survive. If that's all you have to work with, I'd rather deal with it than not have roses!

While I don't water at night I do overhead water all the time because the one bed I have that's my only option. In comparison with the soaker bed the overhead bed gets LESS black spot! I don't know if that's because of the difference in location or varieties of roses but it's true.

Contact a local rose society and find out what roses they'd recommend for a no spray garden in your area.

RE: Water sprinklers and black spot

Seil, the British rosarian, Peter Beales, pointed out in his book, Classic Roses, that overhead watering decreased the incidence of blackspot in his commercial rose fields. He saw a clear increase of blackspot in roses which were beyond the limits of his sprinklers. He attributed this to washing off the blackspot spores before they could germinate.

RE: Water sprinklers and black spot

  • Posted by seil z6b MI (My Page) on
    Thu, Feb 6, 14 at 11:48

Mike, that is great news! I have heard that some people will wash their roses off with a hard spray of water and they feel they get less black spot. I guess it's the same principle. I know that overhead is less efficient/more wasteful but there are just some areas where it's the only option available to me. Glad to know there is a silver lining, lol!

RE: Water sprinklers and black spot

I've come to believe that a certain amount of aerial watering is a good thing because it washes the roses and here in SoCal it seems to wash off some powdery mildew spores. (Here BS is not a problem.) However, a surface drip system is also necessary in order to get the maximum amount of water to the roots. So I'm now doing both.

RE: Water sprinklers and black spot

  • Posted by saldut 9-10 st pete, fl (My Page) on
    Thu, Feb 6, 14 at 15:54

I use overhead sprinklers and no problem, however, I don't see B S on most of my roses anyway, most of mine are now Antiques, mainly China...I weeded out the Modern roses when I stopped spraying 3 years ago... my China roses get no BS, in fact, not much of anything bothers them, even Chili-Thrips......sally

RE: Water sprinklers and black spot

I have a few Hybrid Teas, which I understand are more prone to black spot.

A few Floribundas, which right now have black spot,

Two climbers, Purple Splash [PS] and Fourth of July. With some black spot on the PS.

A few David Austins, less than a year old, and still in one quart containers.

I understand Teas, which I presume means China Teas, gets less black spot?

Maybe I shouldn't be that concerned with water sprinklers?

Mike_Rivers, I presume that the commercial rose grower you spoke of and others that use water sprinklers, do so during the day, so the sun can at least dry the leaves off. Whereas if the roses where water sprayed at night, they would be more prone to black spot, think?


This post was edited by dewyd on Thu, Feb 6, 14 at 19:03

RE: Water sprinklers and black spot

Overhead irrigation does not, in itself, cause blackspot. It may go some way to create the conditions necessary for infection but, although I don't know the exact infection cycle of diplocarpon rosae(Blackspot), I do know that precise conditions need to be met for successful sporulation and infection of most fungal pathogens. Late blight (phytopthera infestans) in potatoes require a very precise set of temperature, humidity conditions, over a prescribed time for the fungal spores to germinate and penetrate the plants cellular system. These conditions are known as 'Smith Periods' and can be predicted since the cycle takes place over 2 consecutive days with minimum temperature of 10 °C and 10 hours of relative humidity higher than 90% on the first day and 11 hours of relative humidity higher than 90% on the second day.
Presumably, blackspot fungus also requires particular conditions which are not likely to be met with a sprinkler system operating in normal daylight hours or for periods of time less than several hours. I would not let this situation be a reason for failing to enjoy growing roses....although there are roses with a higher resistance than others....and this can be both fun and exasperating, in discovering which roses do well for you.

RE: Water sprinklers and black spot

The one main difference between my experience growing roses in CT where BS is a fact of life and here in SoCal where there is no BS, is humidity. Water on the foliage dries but humidity persists. Also, from experience, you don't need rain to get BS in CT. It will arrive right on schedule in the spring if you don't spray. It may even be that rain makes no difference at all or perhaps it is beneficial because it washes off the spores. I think if constant humidity is there at whatever level is necessary, there will be BS. I don't think watering practices have anything to do with it.

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