Diseases Of Roses

Unlike some other flowering plants, roses are known to be rather troublesome and disease prone, requiring substantial after care. For instance, you need to coast them constantly with various different fungicides so that they are not affected by diseases. To some extent, their reputation of being troublesome plants is justified. Several varieties of roses, especially those grown in humid climatic conditions, are susceptible to mildews, rust and blackspot - the omnipresent rose diseases. On the other hand, the modern hybrid tea varieties as well as floribundas are more prone to develop fungal diseases. Generally speaking, fungi, which are among the most common as well as serious diseases affecting roses, spread faster when the climatic conditions are damp. It is true that one cannot modify the weather, but one can certainly initiate appropriate measures that will aid in putting off fungus.

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It is also important to place your roses in proper positions. In case you have planted your roses in the garden in a place where the ventilation is poor, it is very natural that the plants will take longer periods to dry after they are drenched in rain. In such situations, the roses will have a tendency to retain the moisture in the air around them. On the contrary, if the roses are planted in a place where the air movement is good, the plants will dry faster and, hence, their foliage would also be drier. This, in fact, will eventually make a great difference between the plants being heavily infested by fungal diseases or have rare occurrences. If the roses are grown in ideal locations and the plants are healthy, it is possible that they will never endure the diseases.

Apart from air movement, adequate exposure to roses is also important for preventing or inhibiting the growth of fungus. In fact, sunlight is very vital for preventing fungal growth and infestation. At the same time, pruning your roses at regular intervals will also help to augment the air circulation and sunlight received by them. While pruning the roses, ensure that they are kept to the size of small bushes.

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There is no doubt that blackspot is among the most widespread bane for roses. While majority of the roses are somewhat prone to this disease, there are a number of roses that can be stripped of all their leaves (defoliate) in case the disease is not controlled. The name of this disease itself suggests that when the plants are affected by blackspot, their leaves develop brown or black spots, especially at the beginning of summer. The leaves that were infected in the previous year are not removed or treated, they release several million spores in the atmosphere. These spores settle on the healthy leaves and start growing. Usually, blackspots are first seen on the older leaves that grow near the base of the plant. They possess the aptitude to infect the entire plant and eventually do that if not checked.

If you find any infected leaf on or below the rose bushes, collect and burn them immediately. When you do this, you actually ensure that there will be fewer spores in the ensuing season. Mulching the plants with a new layer during the fall will also help to bury the spores that fall on the ground during the winter and, thereby, check them from spreading. In addition, it is advisable that your prune the varieties that are more susceptible to blackspot to an open shape so that the plants are exposed to maximum air movement so that they not only remain drier, but also do not promote the development of the disease.

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In case you desire to grow roses that are very susceptible to blackspot, it will be essential to start an effective protective spray program during the middle of spring. Wettable powdered sulfur (sulfur powder which absorbs moisture and turns into a solution) is very effective in protecting the plants from blackspot and, at the same time, it is not toxic like other fungicides. Spray the sulfur powder each time after rain or a wet period. Using some drops of liquid soap in the sprayer will facilitate in evenly spreading the powdered sulfur on the foliage. In the absence of a proper spreader (like liquid soap), the sulfur powder is likely to turn into beads and will not remain on the leaves, but fall off on the ground, rendering them useless. Instead of wettable sulfur powder, some people employ an old technique, for instance baking soda or sodium bicarbonate in the form of a preventive spray. The best way of using sodium bicarbonate is to blend about one ounce (30 grams) of it with 40 litres (10 gallons) of water and spray the solution after rain or damp periods.

In fact, most breeders use Rosa rugosa, a very resilient rose species, to create hardy roses. In fact, Rosa rugosa is one rose species that is extremely unyielding to blackspot.


Poor sanitation (drainage) and lack of pruning are mainly responsible for the development of this plant disease. Initially, cankers appear as orange or brown spots on dead wood and subsequently pass on to the nearby live wood or plants. You can get rid of cankers partially or completely and also prevent its occurrence by removing all dead wood on the plants. It is advisable that you should always use sharp pruning shears so that you don't tear the wood in the process. Moreover, ensure that the cuts are clean and also as close as possible to the adjoining live branch. If you find any canker, burn it immediately.

Crown gall

This disease usually affects the roots of roses as well as other plants that are closely related. Crown gall is caused by a bacterium present in almost all types of soils. This bacterium enters the plant via injuries or damages caused by insects or while pruning. The galls have an irregular shape and are like bulbous growths, which turn out to be rather large over a period of time. However, there are differences of options regarding the extent of harm caused by the galls to plants infected by them. However, there seem to be no difference regarding the fact that galls have a serious effect on the vigour as well as the life span of the plants they infect. Therefore, it is not advisable to use plants affected by gall. Avoid them as far as possible. However, if you have no option, but to use plants affected by gall, you should plant it after removing the infected roots.

Currently, a biological control for crown gall is also sold in the market. Therefore, it is advisable that you dip the roots of your rose in a solution prepared by mixing a bacterium called Agrobacterium radiobacter with water. Agrobacterium radiobacter works to inhibit the crown gall bacterium's growth. Gardeners who want to use this biological control should know that this particular bacterium is very safe for using on your plants.

Powdery mildew

When your roses are affected by powdery mildew, the surface of the leaves infected by this disease will have a greyish-white coating. This condition is especially worrying at the end of summer. If you do not undertake appropriate measures to check the disease, powdery mildew can harm the susceptible rose varieties very severely.

Similar to many other plant diseases, powdery mildew usually manifests itself more on plants that are under stress compared to the healthy plants. It has been found that roses suffering from malnutrition as well as those that are fed excessive fertilizers containing high amounts of nitrogen are especially susceptible to mildew. Similarly, even roses that are not watered adequately also suffer from mildew. Therefore, it is important that you mulch your plants properly and feed them properly with compost. Ensuring this will help the plant to achieve a balanced growth, which, in turn, will be effective in preventing mildew. In addition, you need to position the varieties vulnerable to powdery mildew in places having good ventilation and where they will be exposed to maximum air movement. In case you are growing roses that have a propensity to be infected by powdery mildew, it is essential that you adopt an effective spray program, such as using wettable sulfur. Alternatively you may also use sodium bicarbonate to protect your roses from this disease.

Rose midge

Among the various insects that trouble roses, rose midge is among the most frustration. An adult rose midge is basically a minute, yellow-colored fly, which lays its eggs on the rose stem just beneath a developing bud. After the eggs are hatched, tiny larvae emerge from them and start feeding on the plant. While the larvae continue feeding on the plant, they hinder the supply of nutriments as well as water to the bud, especially on the side where they are feeding. As a result of this, the bud gradually tilts to that side. Usually, the absence of adequate food as well as water supply proves to be fatal for the forming bud and it turns black and eventually dies even before it opens.

In order to prevent these pests from invading your roses, you should carefully check the plants on a regular basis. If you notice any developing bud bending in the manner discussed above, remove it immediately. Burn the bud so that the pest does not spread to healthy areas. In addition, destroying the affected bud will also stop the development of further generations of rose midge. You need to bear in mind that diligence is the best weapon of gardeners against the rose midge.


When a plant is affected by rust, the undersides of its leaves develop orange patches. In case the disease is not controlled it can even spread to the plants' stems. This disease usually occurs when the weather is warm and humid. This disease is more extensive among plants grown in the northern regions. Rust can manifest itself in different ways in different rose varieties or it is also possible that rust cannot survive through the extreme cold temperatures during winter.

The rust's wheel of life is very akin to that of blackspot - they lie dormant on the leaves throughout the winter. If you find any symptoms of rust affecting your roses, remove and burn the infected foliage right away. At the same time, you should check if there are any infected leaves beneath the rose bush. If you find any, remove and burn them immediately with a view to avoid the plants being infected again. Moreover, adding a fresh layer of mulch will also go a long way in preventing the dropped infected leaves from spreading the spores into the atmosphere.


There are numerous different types of viruses which are present in both animals as well as plants. They are really puzzling microbes, which are often difficult to treat. When roses are infected by viruses, they display a number of symptoms, including their leaves turning yellow and having streaks. In addition, flowers of virus-infected plants are likely to be smaller as well as fewer. As of now, there is no cure for plants affected by viruses. In fact, viruses generally spread when growers in nurseries use infected stocks for propagating new plants. Therefore, if you think a particular plant and not just a rose in your garden is infected by virus or pests, suffering from nutritional deficiencies or absence of adequate water, you should simply dig out the plant and destroy it. In fact, some sucking pests like aphids may pass on viruses to vigorous plants.


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