Black Spot on Roses

black spot on roses

black spot on roses

With all the wet weather Sydney has been experiencing lately, it has provided perfect humid conditions for the development of black spot on roses. I recently got this question from a reader and thought I would answer it here.

Q: have found black spot on my roses and have cut all the bad leaves off, now some one told me that soapy water will help this and affes can you please tell me pretty new at the game but love my roses.

A: The soapy water will help with aphid control but I have never heard of it helping with black spot.

You’re doing the right thing by removing the badly diseased leaves. Also be sure to pick up any fallen diseased leaves around the base of the plant. Unfortunately you usually need to use a fungicide to manage black spot. If you don’t want to use a fungicide then you could try this mix which a lot of organic gardeners use with some success, but you need to apply it weekly.

In a six litre sprayer put 4 level tspns bicarb soda, and 3 tspns of fish emulsion, fill it with water to the six litre mark. Agitate the sprayer as much as you can to dissolve the bicard soda and spray the underside of the leaves as well as the top of them.

I usually use this mix one week, then a fungicide the next week, but that’s for sixty roses all planted in the one area. If you’ve only got a few roses you might be able to get away with just using the organic mix weekly, and you might also want to adjust the measurements accordingly and use a small spray bottle if it’s just a few plants. Don’t spray this on a really hot day. This mix. along with good garden hygiene should help you manage black spot on roses.

16 Comments so far

  1. Ingrid Lee on November 26th, 2010

    My roses have just started blooming, and I’ve noticed with the wet weather, then hot weather and back again (Melbourne weather :) )that I’m getting blackspot. I have removed all the leaves, I’m using a fungicide, but it keeps raining on and off. How frequently should I still try spraying?

  2. admin on November 26th, 2010

    Hi Ingrid

    black spot thrives in this rainy then hot weather we’re having at the moment, and unfortunately all we can do is try to manage this nuisance rose disease. It makes it hard too when you’ve just sprayed and then it rains. I would follow whatever recommendations are on the back of your fungicide spray – different fungicides require different spray frequencies, so let whatever is on the pack be your guide.

    As far as how often you should spray when it keeps raining on and off? Manufacturers of fungicides say you shouldn’t spray if rain is expected within 24 hours.

    Personally if it looks like it is going to rain or rain has been forecast, I don’t bother spraying, it’s just a waste of your time and the cost of the fungicide that is now useless. So if it rains every day for 3 weeks, it’s pointless spraying because the fungicide won’t have time to work effectively.

    If you do spray and it rains within say 6 hours I would probably spray again the next day and then leave it till the recommended time on the label, regardless of whether it rained again after that 2nd spray the next day.

    It’s a real challenge trying to manage black spot in rainy hot weather; spray the fungicide as above and also try the bi carb recipe mentioned in the article above between fungicide sprays (eg one week fungicide one week bi carb mix). The bi carb changes the pH of the leaf surface (but doesn’t harm the leaves at all and black spot doesn’t thrive at that pH level), and the fish emulsion feeds the leaves and helps the mix stick.

    Sometimes I’ll also use liquid seaweed (mixed at half strength) as a foliar tonic to the leaves – it helps keep them stronger and less prone to getting blackspot. So I might go fungicide one week, bi carb the next, fungicide the next, then seaweed spray the next, then repeat.

    Good luck with managing this pesky disease Ingrid

  3. Kristi on March 24th, 2011

    I am a newbie so I am finding much help from this site. Could you please elaborate on the seaweed spray? Thanks.

  4. admin on March 24th, 2011

    Hi Kristi
    re the seaweed spray, I just mix some concentrated liquid seaweed with water in a sprayer (according to the manufacturers dilution recomendations) and spray this over the top and underside of the rose leaves. Your question inspired me to write an article about seaweed and roses which you can read here.

  5. Annie on March 31st, 2011

    My roses are just blooming, we had had some strong winds, the tops look like they are dead, should I trim them back?

  6. admin on March 31st, 2011

    Hi Annie
    if the tops look dead, they’re not going to flower so trim them back and cut off all the dead looking bits. You’ll lose all your budding blooms, but they won’t flower if they’re dead-looking either. After deadheading them, give them some liquid seaweed at the recommended rates on the bottle; this is a great tonic for the roses. Also if you haven’t fertilized them as yet, give them some rose food to get them going (follow directions on packet – don’t overfeed them). If you have already fertilized them, don’t feed them again now, just give them another feed 6 weeks from the date you had first fed them.

  7. rita on May 30th, 2011

    Hi,
    I am going to plant roses in an area that remains wet. Any planting suggestions to make sure that the area drains well and only requires water remains. What can I use to ensure better drainage and still ensure proper watering.
    Thanks.

  8. admin on May 30th, 2011

    Hi Rita
    I wouldn’t plant roses in an area that remains wet. Roses hate wet feet and will die because they need air in the soil as well as moisture and if the soil is constantly wet, then no air can penetrate between the soil particles. If you must plant there, either build raised beds on top of the area; build them at least 18 inches in height. Or put in some drainage so the area drains very well before planting any roses there.

  9. Mary on June 23rd, 2011

    In your recipe for bicarb and fish emulsion, you said “fill it to the six litre mark”. Is that fill it with water? I want to make sure I get it right. Thanks

  10. admin on June 24th, 2011

    Hi Mary
    yes, fill to the 6 litre mark with water.

  11. patrick o sullivan on July 11th, 2011

    Where can I get Fish Emulsion?

  12. admin on July 11th, 2011

    Hi Patrick
    you should be able to purchase fish emulsion from garden centres or hardware stores

  13. shirley hayes on July 25th, 2011

    I have a Henry Hudson white rose. Every year the leaves on some of the branches turn brown around the edge and fall off. The stems don’t seem to die. There are other roses in the same bed but this is the only one that has this problem. Some of the buds turn yellow and drop off also. I have tried soapy water but have had no luck. Thank you Shirley

  14. admin on July 26th, 2011

    Hi Shirley
    There are a number of things can cause this condition; a spate of really hot weather can cause some of the leaves to go brown at the outer edges, giving a scorched appearance; if that is the case be sure to keep the water up to them.

    Hot winds can also cause this condition. Some roses are more susceptible to moisture stress due to hot weather/windy conditions than others and this could be the situation here.

    Other causes of brown leaf edges can be from over-fertilizing or the use of chemical fertilizers on certain rose species. The Henry Hudson is a Rugosa hybrid and from research I’ve done, Rugosa roses don’t like liquid chemical fertilizers, whereas other rose varieties in your garden bed may be fine with them, so be aware of the type of fertilizer you are using on this particular rose. A slow release organic fertilizer (one of the pelleted ones) or compost placed around the base of the plant might be a better option for this particular rose.

  15. Dan on September 16th, 2011

    I have 80 roses in pots for sale at a fete on 19 Nov 2011 … most of the roses are 18 months old and some are 30 months old … all were potted in June … I would like to have them flowering on 19 November, can I achieve this by pruning them 50 days before that date or would you recommend otherwise?
    Thank you in anticipation.
    Dan

  16. admin on October 5th, 2011

    Hi Dan
    your potted roses should have been pruned mid winter (unless you’re in a cool climate in Australia) so should be budding and starting to flower now, so all you need to do is deadhead the spent flower blooms as they appear on your potted roses which will allow new buds to form and bloom on an ongoing basis through October and November. If you prefer you could cut off all the newly forming buds 6-7 weeks before the day of the fete so that the potted roses will flower all at once around that time. Give them a liquid feed after doing this (stick to recommended dosage rates) and then another feed a month later. Hope you raise plenty of money for the fete with your roses.

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