Roses are the most popular ornamental shrubs available to the home gardener. Most bloom throughout the season, providing beauty both outdoors in your garden and inside the home in a vase or container. If you have no experience growing roses, you may be a little fearful about the whole process.
We have all heard the stories about how difficult it is to grow roses, prune roses and care for your roses. Truthfully, growing roses is like any other plant. There are a lot of variables like the location you choose, the amount of sun, watering and feeding.
If you plant your roses in an optimal location and care for them appropriately, there is no reason to think your roses will not look like the ones you admired in the rose catalog or botanical garden. Here are some variables that will help make you successful at growing roses, including:
So, your roses are beautiful, and you are thrilled with your success and proud of the additional value the roses bring to your landscape. Then, you notice a spot on a leaf that should not be there. When you look closer, you see several spots. What is happening to your roses? What is the problem and how can you fix it?
The first step is to determine what disease you are dealing with. There are several rose diseases that show up as spots on the leaves. Many will look remarkably similar, so take the time to figure out which one your roses have.
This is when it is helpful to know another rose grower in your area. They will know which diseases are most common in your area. Ask them if they have had any problem with disease and how they solved it. Find out if they use preventative measures like dormant sprays. Very few gardeners will not share their success with fellow rosarians.
Plant Perennials to Help Your Roses Stay HealthyDisease in roses can be caused by fungi, bacteria or plant viruses. Note that with climate change, diseases are spreading to new areas that never had them before. The most common diseases are caused by fungi. Here are some of the diseases that impact roses, including:
Black spot on roses usually starts near the bottom of the bush. The spots are brown or black and have feathery margins. The leaves often turn yellow before they fall. If left untreated, the black spot will quickly move up the plant until all parts of the plant are affected.
The plant will drop all its leaves and each leaf that is infected will potentially spread the disease. The plant will try to re-foliate, but those leaves will also be infected and the cycle will start over again.
The fungi, Diplocarpon rosae, will winter over in the debris under the rose plant ready to infect the plant again when new spring growth appears. If left untreated, the plant will die.
Black spot needs six hours of moisture on the leaf for spores to develop. Warm, wet weather with high humidity is what this fungus likes. If you keep your rose foliage dry when watering, you can help minimize the conditions black spot likes.
Black spot can grow spores on the fallen leaves also so meticulous cleaning is important.
Prevention is the best treatment. Prune properly for good air circulation, clean all debris especially in the late winter/early spring and spray your roses with a fungicide to prevent black spot.
Powdery mildew is also caused by a fungus. Powdery mildew causes the leaves and flowers of the rose to be covered in a film of white mildew. The leaves of the rose will also blister and twist. The infected foliage may turn to a red or burgundy color.
This fungus thrives in warm, humid weather. It does not need rain and, in fact, the free water on the foliage will inhibit spore formation. This fungus is spread on air currents and it will survive the winter on infected canes and in the leaf litter underneath the plant.
Much like black spot, prevention is easier than treating after the disease hits. Clean all plant debris, remove diseased canes, treat with a dormant oil in the winter and use a fungicide.
CLS is often confused with black spot or anthracnose. All three are caused by fungus and all three exhibit spots on the foliage. As mentioned earlier, black spot has brown or black spots with feathered margins.
CLS has purple, maroon, brown or black spots but the margins are even. Anthracnose and CLS can be differentiated by season. Anthracnose is a cool season disease of spring. CLS is a hot season disease of summer.
CLS was considered a rose disease of the deep south but now, with climate change and increased temperatures, CLS is moving north. Some varieties of roses that are resistant to black spot are not resistant to CLS. CLS will appear during hot weather with prolonged rainy spells. So far, CLS is effectively controlled with the same fungicide that is used for black spot. With the expansion of the disease, rose breeders are working to develop a resistant rose.
This fungus is found in the northern half of the country and in the deep south where the roses retain their foliage during the winter. Anthracnose appears as black spots with red, maroon or purple margins in the spring.
This is followed by leaf drop and the fungus can quickly move to the cane where it forms a bright yellow canker. The fungus is spread by splashing water from rain or overhead watering.
Control of anthracnose can be accomplished by keeping the foliage dry through drip irrigation, removal of all plant debris and by giving the plants enough space for air circulation that will promote air drying the foliage. Fungicides that are effective against black spot or CLS are also effective against anthracnose.
Rust is also caused by a fungus. Rust is most often seen in the western U.S. and sometimes on the East Coast. It does not survive in the central U.S. due to the heat of summer and the extreme cold of winter.
Rust shows up with yellow spots on the upper surface of the leaves, while pustules can form on the underside of the leaves and defoliation will occur. Rust occurs in cool, damp weather. Treatment includes removal of all infected plant material and the use of fungicide.
This disease is usually found in roses that are kept in a greenhouse or unheated polyhouse. The foliage will exhibit purple, red or brown spots. This disease likes cool temperatures and very high humidity. These are the conditions when the sun sets and the air quickly cools in the spring garden center.
While downy mildew looks and acts much like the other diseases that are caused by a fungus, downy mildew is not a fungus. It is more like a diatom or brown algae.
Fungicides will not be effective against downy mildew. It is very difficult to treat although there is a spray specific to downy mildew. Check your plants very carefully before you purchase them and never purchase a plant that has any sign of disease, regardless of how minor.
This disease is caused by a virus infection of the rose. These roses will produce fewer blossoms and have shorter canes. Symptoms include a mosaic pattern on the leaves or there may be ring spots or line patterns.
This disease is spread when infected plants are used to propagate new rose plants. The roses will not infect other plants in the garden. Again, inspect your plants carefully before you purchase them.
This is a disease caused by a virus. The telltale sign is the formation of witches’ broom overgrowth of canes and an extreme number of thorns. This disease is fatal for the rose. It is carried and spread by a microscopic mite that can travel on the wind.
The mites live on the plant above the ground, so the root is not infested with them. The mites can live up to five days without a host plant. There is no point in removing the affected canes as the mites will remain and the plant will eventually die, usually between one to three years after being infected.
During that time, the mites will spread to other plants. Once you determine that your rose has RRD, you must remove the plant. Place a bag over the plant and tie it off at ground level. This will prevent the spread of the mites.
Cut the rose off at ground level and dispose of the plant. Dig out the root from your garden. The root will not contain the mites as they cannot survive underground. Dispose of the root. You will be able to replant with a new rose in one week.
Since the mite can survive up to five days without a host plant, by waiting a week, any mites that remain will be dead. If you have more roses in your garden, keep a close eye on them for any sign of RRD. Remove any rose with symptoms immediately to minimize the population of mites.
This disease has resulted in the loss of many roses in the eastern U.S., but it is manageable if gardeners remove the affected roses immediately.
Shop Healthy, Disease-Resistant Roses TodayThese are some of the more common diseases in different parts of the U.S. You will greatly minimize the chances of your roses being infected by using the preventative measures suggested.
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