How can I control black spot on my roses?
A fungus causes black spot on roses. Here are some tips for controlling it:
- Ensuring your plants are in a location with good air circulation, and avoiding wetting the leaves when watering
- Clean up and destroy any infected leaves, especially in the fall to minimize reinfection from year to year
- Apply a clean layer of organic mulch (such as shredded bark or chopped leaves) before the plants leaf out again in spring to help prevent reinfection. The mulch helps keep fungal spores from splashing up onto the plant and the new foliage.
- Neem oil may also be helpful. Neem controls aphids and mites on your roses, and also will control powdery mildew and black spot. Be sure to read and follow the label instructions. There are also other commercial fungicides available.
How do I avoid my rose blooms turning brown before they fully open?
There are a few causes of this:
- Drought stress can cause the flowers to die before they reach full bloom
- Roses need a rich soil and regular watering to keep them evenly moist but not soggy, so it is possible that there is a soil problem.
- Container plants are a challenge when it comes to watering, sometimes needing it twice a day on very hot, dry, and windy days or if the pots are too small for the plants
- You might see if the texture of your potting mix has deteriorated over time; or if it has been allowed to dry out, it may require some care in rehydrating it thoroughly.
- A top-dressing of compost is helpful for all roses, and you might also consider fertilizing (either a timed-release granular or water-soluble type specifically for roses) according to package instructions.
- Insects also can cause buds to be deformed and fail to open
- Inspect the blooms very carefully for signs of aphids or other insects. Japanese beetles may be burrowing inside the blooms, as might thrips, which are so small they are nearly invisible.
- A sharp spray of water from the hose will knock away aphids; handpicking or using a neem-based spray will take care of the beetles, and insecticidal soap used according to the label instructions may work on the thrips. The soap also is effective in case of a serious infestation of aphids.
The new shoots on my rose bush are limp and wilting. The rest of the shrub looks healthy, and it has had plenty of water. What can I do to fix it?
There's a disease (Phytophthora megasperma) that causes wilt when roses are planted in poorly drained areas. The stems near the soil surface become water-soaked, dark green, and finally dark brown. New shoots wilt and die. Check the drainage of the soil -- if water puddles or takes a long time to perc down to the roots of your rose bush, you may want to dig up the plant this fall and move it to a spot with better drainage.
My roses’ buds have brown tips. As the flowers open, all the petals have the same brown tips. The leaves are fine. What can I do?
It sounds like Botrytis blight, a fungal disease. When it becomes fully established, some buds will not open at all. The best course of action is to remove all affected buds and regularly remove spent flowers. (Old blooms can harbor the disease.) Fungicide applications will protect the canes and newly developing buds from Botrytis. Be sure to apply according to label directions.
Why did my otherwise healthy rose bush suddenly start to produce hundreds of extra thorns?
The first possible cause of suddenly excessive thorn production that comes to mind is rose rosette disease, which is caused by a virus. Unfortunately, there is no cure and the plants will die within a year or two. Infected plants should be destroyed, so you might wish to verify the diagnosis with your County Extension. They might also be interested in tracking the appearance of the disease in your area, if that is what it is.
The leaves on my roses turn yellow and or rust colored. What can I do to eliminate this problem?
Rust is common on roses and unfortunately there is no way to completely eradicate this disease. At the first sign of rust, pick off and destroy the infected leaves and spray with a fungicide (either organic or synthetic).
Carefully follow application instructions specific to your plant; generally this is every 7-14 days as long as conditions are favorable for infection (moist, foggy, 55-75 degrees F). Practice good garden sanitation: rake up and destroy all infected leaves, prune off and destroy infected twigs.
Be sure that your roses receive all day sunshine and are pruned to keep the center of the plant open, to encourage good air circulation.
My miniature rose has a fine dusting of powder on its leaves. What is it and how can I get rid of it?
Sounds as though your rose has powdery mildew, a fungal disease. It is quite common on all types of roses. Try using a homemade baking soda/oil spray: mix 1 tsp. baking soda and 2.5 tsp. summer oil lightweight horticultural oil) in 1 gallon of water. Spray this once per week, covering both upper and lower leaf surfaces. Also, keep your roses healthy through proper care, since they'll be more resistant to disease. A sunny location, good air circulation all around the plant, and ample moisture are essential. You can remove the leaves affected with powdery mildew so it won't spread to healthy leaves.
