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Different rose diseases and how to treat them
Last Updated on January 21, 2020 by John
Roses can succumb to infection and disease the same as any other plant. The three most common diseases that impact roses include powdery mildew, black spot, and Rust. Most rose diseases can be prevented by growing your rose bush in a suitable environment and spraying with a fungicide just as the buds start to open in the spring to help prevent diseases. You need to make sure that the roses get as much sun as possible, are spread at least a meter apart so that they have good air circulation, and you should avoid any high nitrogen fertilizer.
In order to help your roses thrive also use a fungicide such as Rose Clear to act as a preventative and eradicate for diseases. Most fungicides for roses are preventative which means they can be applied to your rose bush before it becomes infected and will work well to prevent fungal infection.
Powdery mildew is the most common fungal diseases along with Black spot to impact roses. Mildew starts as a white or grey powder coating along the leaf surface and in severe cases spreads not only across the upper leaf surface but the lower Leaf surface and can even spread to the stems and flower buds. Even if you rub it off with your fingers it will soon reappear.
The best way to treat this is with a fungicide mixture. You can also use year-round fungicides to cover your plant before any symptoms of the disease start to manifest by spraying the rose just as the buds start to open as they come into leaf.
Try to avoid getting water on the leaves when watering by watering are the base of the plant and water in the morning so that the foliage has a chance to dry before the evening. It also helps avoid burning the leaves if you water in the morning instead of the afternoon when it might be at it hottest. You can also help air circulation by spacing roses around a meter apart and removing several stems from overcrowded roses to help air circulate through the rose bush.
Rose Black Spot
Black spot is a problem that manifests in the form of small, circular black spots on the top of your leaves. The spotted skin eventually coalesces until they form a much larger spot. This disease does not penetrate the lease from top to bottom but it spreads by splashing water moving the spores from one leads to another.
It isn’t as much of a problem when the weather is warm and dry but it becomes particularly bad when things get wet.
If you notice the issue, you should remove any moderately and badly affected leaves immediately and discard them. Do not add them to your compost pile. As part of your preventative measures, you should avoid any overhead watering and always water directly at the base of your plant to prevent the issue from spreading. It might do you some good if you have a particularly crowded rose bush to prune in such a way as to encourage better air circulation as well.
We recommend spraying with a fungicide such as Rose Clear as soon as the leaf buds start to open in spring as a preventative measure.
If you have rust on your rose bushes it will appear in the form of tiny black spots along the bottom and top of your leaves. Eventually, the spots get bigger and they take on a rust colour which is when you usually notice it. The rust will penetrate the upper and lower leaf surfaces until such time as your entire leaf turns yellow and falls off. This is a mid-season disease and if you don’t take care of it immediately it will defoliate your entire rose bush.
The best treatment is to use a Fungicide and to pick off and immediately discard any severely affected leaves. As new leaves start to appear, reapply your garden fungicides which state they treat rust to make sure the problem is fully eradicated. By regularly spraying things like garden fungicide you can not only eradicate the issue but prevent it in future.
If you examine the rose canes and you see indentations running parallel to the stem they are stem cankers. They are caused by a fungus and they will eventually kill your rose stem.
There is no cure which means the only treatment is to cut the cane at least 10 to 15cm below the canker and dispose of it immediately. Do not compost any stem canker bits that you removed from your plant.
You might get viruses on your roses but only if your bushes are typically 10 years old or older. Most of the time the viruses will appear on new foliage, on a stressed rosebush, or at the end of your growing season.
You can identify which of the two main types of viruses you have by examining the leaves. The first type of virus produces zig-zag lines that look very similar to a lightning bolt. The other leaves yellow circles on your otherwise green leaves. These symptoms can temporarily disappear during the growing phases and both viruses will slightly stunt the growth of your plant but won’t do much harm beyond that. They typically spread by way of grafting. If they become systemic in your plant and are allowed to be there for the duration of your plant life, the unfortunate truth is that there is no remedy or cure. The good news is that viruses are not that common and your much more likely to get mildew, rust or black spot that are all treatable.