Most people who grow roses, at one time or another will face the dreaded “black spot.”
The first steps to reduce the possibility of your roses having black spot is cultural.
The 6 areas culturally are:
- Growing conditions
- Air flow
- Proper watering
- Plant resistant cultivars
Where Does Black Spot On Roses Come From?
Black spots on roses are caused by a fungal disease called Diplocarpon rosae. Roses are especially susceptible to this malady when the weather is hot and humid and the nights are damp and cool.
You must be especially vigilant during extended rainy periods in the summer time.
Black Spot disease is not just unsightly it can also seriously compromise the health of your roses. In fact, it can even kill them.
Black spot fungal disease manifests as black patches on the leaves which lead to yellowing of the entire leaf. Eventually, the leaves fall off, leaving bare stalks, which wither and die.
Prevention is the best treatment for Diplocarpon rosae, and it is also important to watch for the symptoms carefully.
- Early detection increases chances of recovery. Act quickly if you see any of these symptoms:
- Round black spots appearing on the tops of leaves and sometimes on the bottoms.
- The outer edges of the spots will be raggedy or feathery and may be surrounded by a yellow ring.
- You will first begin to notice the spots on the leaves of the lower branches of your bushes.
- New leaves may already be spotted when they unfurl.
- Leaves may begin dropping.
- Young canes and stems may be affected as demonstrated by black or deep purple blistering.
- Blossoms may also be affected.
- Severely affected plants become stressed and cease setting buds.
It is important to note that once a fungal infection gets established, it is extremely hard to overcome. That’s why prevention is so important.
If your roses are strong and healthy and your garden conditions are not conducive to fungal growth, it will be easier for you to deal with any small outbreaks that may occur.
How To Get Rid Of Black Spot on Roses Begins By Establishing Ideal Growing Conditions
Be sure your rose garden is as uninviting as possible for black spot disease. It is far easier to prevent the development of this fungus than it is to cure it.
Remember, for all types of fungal conditions, the fact is fungus spores are always present. Fungi simply stay in a dormant state when conditions are less than ideal.
This is why it’s very important to create an environment that is conducive to good rose growth and hostile to the growth of fungus.
1. Be Sure Your Rose Bushes Are Healthy
Give your plants the right balance of nutrients, sunshine, proper drainage and water to keep them healthy and strong. Select Knock Out Roses and disease resistant varieties that have a strong immune system will deflect fungus.
2. Provide Proper Air Circulation and Airflow
Be sure rose bushes are not planted too close together or too close to other plants. Close plantings restrict air flow around plants which encourages fungal growth.
Be sure to prune your roses including Knockout roses regularly so that there is enough space between the canes for good air circulation. If your roses become too dense, they will be susceptible to black spot disease.
3. Water The Right Amount… The Right Way
Be sure not to over-water and careful not to get the leaves and flowers wet. It is best to give your roses a good, deep soaking about once a week rather than a light spraying more frequently.
When you use this method of watering, you avoid splashing fungal spores up from the ground. By keeping the leaves and flowers dry, you avoid creating a habitat for fungus.
4. Spread A Thick Layer Of Mulch Below Your Bushes
When you cover the soil with mulch, it will further prevent fungus spores being splashed up onto your bushes when you water. Additionally, it will hold the water in the soil so that you can wait longer between watering.
5. Purchase Labeled Disease Resistant Varieties Of Rosebushes
When you purchase your rose bushes, you will notice that they are labeled by resistance level.
When you start out with plants that are bred to be highly resistant to black spot disease, you will naturally have better results. It’s also smart to look for bushes that are resistant to powdery mildew and to rust.
6. Prune Affected Limbs and Leaves Promptly
The moment that you notice any signs of black spot disease on your roses, prune away the affected limbs. Do so very quickly because the disease can spread rapidly as the spores are windborne from one limb to another.
7. Be Sure To Prune Rose Bushes Correctly
Aggressive pruning (6-8 inches below signs of infection) will ensure that you have removed the disease.
Only prune when the weather is dry and…
Dip your pruning shears into a solution of 10 percent bleach or alcohol between each cut. This will help prevent spreading the spores as you work.
8. Keep Your Rose Garden Clean!
Prune your roses properly and dispose of the pruned limbs promptly. When you leave them lying around, any spores that may be on the leaves will reproduce rapidly and can be blown about easily.
How To Prevent & Treat Black Spot on Roses
Even if you have not seen black spot disease on your own roses, it’s a good idea to check around and see if other rose gardeners in your area have had a problem with it.
It’s smart to stay on top of it and take some preventative actions if this is the case. You may need to spray your plants with preventative treatments once a week beginning early in the spring and throughout the growing season.
Here are a few simple treatments for you to try:
Using A Baking Soda Solution To Treat Black Spot Naturally
Make a baking soda solution by dissolving a teaspoon of natural baking soda in a quart of warm water. You can also add a teaspoon of dish soap. Spray your plants and leaves thoroughly to prevent black fungal disease and also powdery mildew.
Use a hydrated lime and copper sulfate fungicide called Bordeaux Mix (decades old solution).
You can use this as a dry powder or you can mix it with water and spray it as you would the baking soda mixture.
It is also effective in eliminating and repelling some insect pests.
However, you must be aware that it will also kill and eliminate some beneficial insects.
Additionally, be advised… this product can burn the leaves of roses. If you are going to use it, do so early in the spring before the leaves appear.
Sulfur is a good natural product for both the prevention and elimination of fungal disease. It is also quite effective in controlling a number of insect pests.
You must use with caution, though. It does have a mild toxic effect for both people and pets. Whenever you use sulfur, be sure to wear protective clothing.
Wettable sulfur can be mixed with water and applied as a spray. Be advised that it can corrode metal equipment, so you should apply it using a plastic sprayer.
Don’t apply sulfur spray in hot weather because it can burn plant leaves.
An insecticidal soap/fungicidal combination may also be effective. This type of product is an organic fungicide that often contains sulfur.
The benefit of this type of product is that it adheres smoothly and evenly to plant leaves for complete protection.
Neem oil an organic fungicide/insecticide that is quite effective. This simple product comes from the seeds of the neem tree. It works systemically by entering the plants system.
For this reason, it does not wash off when it rains. You must be careful, though. If you apply it when the sun is very hot, it can burn the leaves.
Additionally, you should not use it in combination with sulfur or within two weeks of using a sulfur-containing product.
In this video, Dave from Growing Wisdom discusses black spot disease and prevention and offers his tips on its control both organic and chemical.
A Fungus Free Rose Garden Is A Healthy Rose Garden
Whenever fungus is able to get a foothold, it is a sign that something is wrong with the general health of your rose garden.
When you diligently follow good gardening practices by pruning regularly, watering carefully and taking preventative measures as needed, you are sure to have success in preventing and treating black spot disease.
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