-
gardeninggoon
- Newly Registered
- Posts: 4
- Joined: Mon Sep 25, 2006 7:44 am
Black spot leaf disease
Made the horrid discovery at the weekend that my roses had black spot leaf disease. Made some enquiries online and found this https://www.videojug.com/film/how-to-deal-with-black-spot-leaf-disease which told me how to get rid. of it Had to chop loads back and I really hope they survive. Any ideas on when they will start perking up or will it be next summer until I see?
-
Cactus Joe
- Full Member
- Posts: 16
- Joined: Sat Sep 16, 2006 5:02 pm
- Location: North West Pacific
Us rose fanciers learn to live with black spot, in the knowledge that it is a rather unsightly disease, a real nuisance, but not likely to kill the roses as long as we practise good rose culture.
It is a fungal disease whose spores overwinter in the infected leaf litter left on the ground. They spread in water droplets. The spores get spashed on to the lower leaves, and from the diseased lower leaves, up to the leaves above, and so on and so forth. The spores do need warmth to develop, above 75F. They also need 5-7 hours of continuous wetness on the leaf surface to infect the plant. Resistance to this disease varies between different varieties. Susceptibility has been commonly attributed to the addition of yellow roses to the gene pool.
If you want pristine roses - for example, if you intend to participate in rose exhibitions - then, you do need a chemical spray program. Most sprays are preventative, and there are only 2 chemicals to my knowledge (I may be outdated in this information) that actually "treat" the infection. If you garden in Canada, the choice of sprays is very limited. If you use baking soda, you will need to spray every time after the leaves have been washed, either by rain or by watering.
But for most gardeners, putting up with a bit of blackspot is just part of the expectation of rose growing. However, you can minimise the scourge of the disease by taking the follwoing steps:
1. Grow roses which are known to be black spot resistant in your area. I said "in your area", because apparently there are a number of different strains of the fungus, Diplocarpon rosae, and a rose may be resistant to one strain but not to another. The strains of fungus may be specific to your locale. Look at the roses in your neighbourhood, and see which ones are not, or only minimally, affected.
2. Grow healthy roses. It is postulated that heatly thick cuticles on the leaves may reduce susceptibility to infection. There is no doubt that a young or unhealthy or stressed rose is more likely to be infected than a healthy one. Grow them in optimally ammended soil, with lots of sun, consistent watering, good fertilising and healthy pruning.
3. Be meticulously neat and tidy. Each black spot lesion produces tens of thousands of spores. Remove all of the infected leaves, as soon as they appear. Remove all leaf and fallen branches from the ground. Do this often. If your rose is badly afflicted, remove all of the leaves still left on the plant in Novmber/December. Discard all leaves and prunings and do not use them in the compost heap. After you have done the final fall/winter clean up and there is not a leaf left on the roses, mulch the soil. What you are doing is basically reducing the number of spores that is around to infect your plants. It will give your roses a head start the following year. It takes 2-3 months from the time when the leaves first unfurl in the spring to seeing the first black spots. Since we tend to have a dry July, black spots don't usually rear it's truely ugly head till August, when the rain, combined with the still warm temperature, results in ideal condition for black spot infection. By which time, I don't really care much any more.
4. Try and not wet the leaves or allow them to remain wet for too long. There isn't much you can do with rain, but avoid overhead watering if you can. If you do have to water overhead or mist or spray the plant, do it in the morning so that there is sufficient warmth for the leaves to dry quickly.
It is a fungal disease whose spores overwinter in the infected leaf litter left on the ground. They spread in water droplets. The spores get spashed on to the lower leaves, and from the diseased lower leaves, up to the leaves above, and so on and so forth. The spores do need warmth to develop, above 75F. They also need 5-7 hours of continuous wetness on the leaf surface to infect the plant. Resistance to this disease varies between different varieties. Susceptibility has been commonly attributed to the addition of yellow roses to the gene pool.
If you want pristine roses - for example, if you intend to participate in rose exhibitions - then, you do need a chemical spray program. Most sprays are preventative, and there are only 2 chemicals to my knowledge (I may be outdated in this information) that actually "treat" the infection. If you garden in Canada, the choice of sprays is very limited. If you use baking soda, you will need to spray every time after the leaves have been washed, either by rain or by watering.
But for most gardeners, putting up with a bit of blackspot is just part of the expectation of rose growing. However, you can minimise the scourge of the disease by taking the follwoing steps:
1. Grow roses which are known to be black spot resistant in your area. I said "in your area", because apparently there are a number of different strains of the fungus, Diplocarpon rosae, and a rose may be resistant to one strain but not to another. The strains of fungus may be specific to your locale. Look at the roses in your neighbourhood, and see which ones are not, or only minimally, affected.
2. Grow healthy roses. It is postulated that heatly thick cuticles on the leaves may reduce susceptibility to infection. There is no doubt that a young or unhealthy or stressed rose is more likely to be infected than a healthy one. Grow them in optimally ammended soil, with lots of sun, consistent watering, good fertilising and healthy pruning.
3. Be meticulously neat and tidy. Each black spot lesion produces tens of thousands of spores. Remove all of the infected leaves, as soon as they appear. Remove all leaf and fallen branches from the ground. Do this often. If your rose is badly afflicted, remove all of the leaves still left on the plant in Novmber/December. Discard all leaves and prunings and do not use them in the compost heap. After you have done the final fall/winter clean up and there is not a leaf left on the roses, mulch the soil. What you are doing is basically reducing the number of spores that is around to infect your plants. It will give your roses a head start the following year. It takes 2-3 months from the time when the leaves first unfurl in the spring to seeing the first black spots. Since we tend to have a dry July, black spots don't usually rear it's truely ugly head till August, when the rain, combined with the still warm temperature, results in ideal condition for black spot infection. By which time, I don't really care much any more.
4. Try and not wet the leaves or allow them to remain wet for too long. There isn't much you can do with rain, but avoid overhead watering if you can. If you do have to water overhead or mist or spray the plant, do it in the morning so that there is sufficient warmth for the leaves to dry quickly.
-
Cactus Joe
- Full Member
- Posts: 16
- Joined: Sat Sep 16, 2006 5:02 pm
- Location: North West Pacific
Cactus Joe,
It is certainly not the acidic rain and polluted air that contribute to less black spot in cities than countryside.
It is the higher tendency of catching diseases and pests problem in countryside due to higher concentration of various of vegatation. Seasonal weeds bring seasonal problems in the countryside.
However, it is not all bad in living in countryside as in the countryside we are blessed with abundant of wild herbs that are indespensible natural herbal treatments and fertilizers.
Amitié,
Pixi
It is certainly not the acidic rain and polluted air that contribute to less black spot in cities than countryside.
It is the higher tendency of catching diseases and pests problem in countryside due to higher concentration of various of vegatation. Seasonal weeds bring seasonal problems in the countryside.
However, it is not all bad in living in countryside as in the countryside we are blessed with abundant of wild herbs that are indespensible natural herbal treatments and fertilizers.
Amitié,
Pixi
Thats usefull information, as one of my roses is badly affected (whilst its neighbour is not)
Can I clarify something?
I should remove all infected leaves from my plants, should I then remove the stem if it has no leaves? how much?
Last year my roses kept their leaves all winter (UK), should I then as you suggest defoliate (non infected leaves) effected plants in December?
Cheers
gasdoc
Can I clarify something?
I should remove all infected leaves from my plants, should I then remove the stem if it has no leaves? how much?
Last year my roses kept their leaves all winter (UK), should I then as you suggest defoliate (non infected leaves) effected plants in December?
Cheers
gasdoc
-
Cactus Joe
- Full Member
- Posts: 16
- Joined: Sat Sep 16, 2006 5:02 pm
- Location: North West Pacific
When you remove infected leaves, you reduce the concentration of spores from the vicinity of your rose. The theory behind defoliating the roses for the winter uses the same reasoning - removing potentially sources of spores. It is not necessary to remove the canes - just carry on with the usual pruning practice for the specific rose you have. But do remove any weak, old or unhealthy canes. New laterals and leaves produced on these less than robust canes are likely to be more susceptible to diseases. But you need to leave a few of the strongest and healthiest canes to produce new growth.
Sure, no matter how hygienic your rose bed is kept, fungal spores will still find it's way to your garden from your neighbour's. Fortunately, most of the spread and infection occurs with water splashes, so spread is slow. And in the first 1-2 months of active growth, the temperature is too low for black spot to take hold (at least, in our garden.) It is reasonable, therefore, to expect that if you keep the spore count down, your roses should have a few months of healthy growth - enough to give you a good display.
There are some who do not believe that defoliation in the winter reduces the rate of black spot infection. I do it any way because:
1. My roses look tidier in the winter
2. I don't waste dormant oil, which I spray twice in the winter.
Sure, no matter how hygienic your rose bed is kept, fungal spores will still find it's way to your garden from your neighbour's. Fortunately, most of the spread and infection occurs with water splashes, so spread is slow. And in the first 1-2 months of active growth, the temperature is too low for black spot to take hold (at least, in our garden.) It is reasonable, therefore, to expect that if you keep the spore count down, your roses should have a few months of healthy growth - enough to give you a good display.
There are some who do not believe that defoliation in the winter reduces the rate of black spot infection. I do it any way because:
1. My roses look tidier in the winter
2. I don't waste dormant oil, which I spray twice in the winter.
-
Cactus Joe
- Full Member
- Posts: 16
- Joined: Sat Sep 16, 2006 5:02 pm
- Location: North West Pacific