Rose Diseases
Rose Diseases Can Do Irreparable Harm to Your Plants
There are many different rose diseases that can make your plants look unsightly and/or lead to their death. The worst of these are fungi. In order to keep your roses healthy you will have to take some preventative measures, and if your plants should become diseased, you are going to have to act quickly to contain the damage.
One of the most prevalent rose diseases is black spot. It is a fungus that causes the leaves to turn black or have black spots. It usually happens on new growth and is aided by wet, humid conditions. There is also yellow discoloration or circles on the leaves of the rose plant. One way to prevent black spot is to spray early in the spring with fungicidal soap and sulfur powder or liquid. The black spot spores cannot germinate in sulfur. Also, remember to keep the plant’s leaves dry after watering. If your roses do get black spot, you must remove all diseased parts of the plant and continually spray using the fungicidal soap and sulfur.
Another of the rose diseases to be on the lookout for is powdery mildew. The first sign of the disease is when young leaves start to crinkle. Next, you will see patches of mold which develop everywhere--on the stems, foliage, buds, and flowers. It looks like someone has covered your plants with white powder. Powdery mildew is a fungus and it draws nutrients from the plant leaves, which is why the young ones dry out first. In no time at all an entire rose garden can be covered with powdery mildew.
Hot, dry weather is the time powdery mildew is most likely to form, and cool, moist nights cause the spores to germinate. Plants that are too wet, overcrowded, or that are shaded too much of the time are the first to be attacked. Pruning to provide good circulation of air inside the plant is a preventative measure, as is making sure your plants are at least three to four feet apart when planting. Treatment is the same as for black spot, spraying with fungicidal soap and sulfur. Make sure that all removed diseased parts of the plant are bagged and carted away or burned, because this is one of the rose diseases that spreads easily. You might also want to ask your local extension agent about organic rose pesticides.
Another fungal disease that is primarily experienced on the West Coast of the U.S. is rust. Rust appears as little orange-red spots that look a lot like warts. If left to grow on the plant, they will steadily increase in size and group together until the entire plant is diseased. Rust likes moist weather with the temperatures in the 60s. It is also prolific, producing spores every fourteen days that are carried to other plants by wind and rain. If the disease is present, rose plants should be sprayed with fungicidal soap and sulfur.
Brown canker is the name of a disease that is less serious than the other fungal diseases, but it is still a problem. It is marked by the appearance of little purplish white spots that eventually develop in large brown areas on the plant foliage. All diseased parts of the plant must be removed.
The best way to limit rose diseases is to buy disease-resistant plants. Many of the older species and bush roses are much more disease resistant than the newer hybrid tea roses. If you want roses that are more maintenance-free and less apt to acquire diseases, stick with older varieties.