Last updated on April 5th, 2022
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Roses can succumb to infection and diseases, the same as any other plant. The three most common diseases that impact roses include powdery mildew, black spot, and rust. Most diseases can be prevented by growing your rose bush in a suitable environment and spraying them with a fungicide, just as the buds start to open in the spring because this will help prevent any diseases. You need to make sure that your roses get as much sun as possible, are planted at least a metre apart so that they have good air circulation, and you should avoid feeding them with any high nitrogen fertiliser.
In order to help your roses thrive also use a fungicide (such as Rose Clear) to act as a preventative measure and eradicate diseases. Most fungicides for roses are preventative and this means they can be applied to your rose bush before it becomes infected and will work well to prevent fungal infection.
Powdery Mildew
Powdery mildew is the most common fungal disease, followed closely by 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. It can even spread to the stems and flower buds. Even if you rub it off with your fingers it will soon reappear.
Prevention
The best way to treat this problem is with a fungicide mixture. You can also use year-round fungicides to protect your plants before any symptoms of the disease start to manifest by spraying the rose just as the buds begin to open or as they come into leaf.
Try to avoid getting water on the leaves when watering. This can be achieved by watering around the base of the plant and watering in the morning so that the foliage has a chance to dry before the evening. It also helps to avoid burning the leaves if you water in the morning instead of the afternoon when temperatures might be at their highest. You can also help air circulation by spacing roses around a metre apart and removing several stems from overcrowded roses to help the air circulate through the rose bush.
Learn more about preventing and treating plants with mildew in this guide by clicking here
Rose Black Spot
Black spot is a problem that manifests itself 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 leaves from top to bottom but it is spread from splashing water which moves the spores from one leaf to another.
It isn’t as much of a problem when the weather is warm and dry but it becomes particularly noticeable when things get wet.
Prevention
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 that would 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.
Learn more about treating black spot in this guide by clicking here
Rust
If you have rust on your rose bushes it will appear in the form of tiny spots along the top and bottom 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 surface until eventually 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.
Prevention
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 (one that states it treats rust) to make sure the problem is fully eradicated. Regularly spraying things like garden fungicides not only eradicates the issue but can prevent it from actually occurring in the future.
Stem Cankers
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.
Unfortunately, there is no cure, which means the only treatment is to cut the cane at least 10-15cm below the canker and dispose of them immediately. Do not compost any stem canker bits that you have removed from your plant.
Viruses
You might get viruses on your roses but only if your bushes are typically 10 years old or older. Most of the time viruses will appear on the new foliage of a stressed rose bush, 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 season 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 you are much more likely to get mildew, rust or black spot, all of which are treatable.
