Do you know that the black spot on the rose is a fungal disease?
Black spot is a fungal disease, Diplocarpon rosae and it tends to affect roses.
This fungus tends to develop as black spots on the leaves of the roses and eventually causes the leaves to turn yellow and drop off.
Other than looking unsightly, it can seriously weaken your rose plant.
Moreover, black spots on roses tend to thrive during cool, moist weather.
It is important to note that once this disease begins to attack your plant, it can be very difficult to control and manage.
Black spots tend to appear as irregularly shaped spots that are about 1/2 inch in diameter, especially on the upper leaf surface.
As the disease tends to worsen, the leaves will begin to yellow and eventually drop from the plant prematurely often beginning at the bottom and progressing upward.
Keep on reading.
Black Spots on Roses
Black spots on roses tend to look like somewhat circular black spots on the leaves of roses.
It often appears on the upper sides of the leaves.
However, they can also develop on the undersides of the leaves.
The outer margins of the black circles tend to be ragged or feathery, and they are usually surrounded by a ring of yellow.
Moreover, these spots often begin on the lower leaves and then move upward.
They can appear as early as when the leaves first unfurl.
Also, these spots can also enlarge and eventually merge, and affected leaves often tend to fall off the plants.
In case you leave them unchecked, the entire plant can defoliate.
The loss of leaves tends to reduce the ability of the plant to photosynthesize food, weakening the bush and causing a decline in rose production.
This fungus can also infect young canes and causes dark purple or black blisters on the canes.
And then the flowers may show some red spotting.
Infected plants will set lesser flower buds and without leaves, the plant will be stressed and susceptible to more problems.
Causes and Symptoms of Black Spot on Roses?
The fungal spores that cause these black spots to germinate in the springtime tend to disperse by splashing of water from rain and watering, as well as wind that tends to transport spores.
If you do not manage it, your roses will keep on getting black spots.
In case you experience an extremely hot summer in July and August, the high temperatures may limit the development of future spores.
The symptoms of black spots on roses are variable, depending on the rose species or cultivar and the strain of fungus.
You can, however, see the following symptoms:
Often a rapidly enlarging purplish or black patch appears on the upper leaf surface, with diffuse and radiating strands of fungus, in some cases, just visible.
Leaf tissues may turn yellow around the spots and the leaf will drop in most cases, even though other parts are as yet unaffected.
At other times, the yellow color does not appear, however, infected leaves still tend to drop.
In some cases, the spots remain relatively small and the leaf does not drop.
Small, black, scabby lesions may also appear on young stems.
It is important to note that badly affected plants can shed almost all their leaves and their vigor reduces greatly.
The symptoms tend to be so great that, anecdotally, the disease has been blamed for a decline in the popularity of roses in UK gardens in recent decades.
Life Cycle of Black Spot Disease
Though there is no cure for infected leaves of your plant, you can take steps to prevent black spots.
Existing spores tend to overwinter on infected fallen leaves and stem, waiting for favorable conditions.
Moreover, the spores tend to germinate in spring and may be continuously wet for sever hours before germination takes place.
The spores tend to develop fruiting bodies.
These are called acervuli and are in the black lesions.
Furthermore, these tend to produce spores that splash onto new tissues, spreading the disease.
Give your Plant Ideal Growing Conditions
True in order to avoid any plant disease, a healthy, vigorous plant is less susceptible to problems.
Roses tend to prefer a sunny spot with well-draining soil and regular, weekly watering.
Make sure to plant your roses in a spot where they tend to receive morning sun.
This tends to help dry moisture from the leaves.
Moreover, the full, all-day sun is best for your plants.
Good Air Flow: Make sure to provide good air circulation around and through your rose plants.
Do not plant them too close to other plants.
Make sure to prune your plants to open the spaces between the canes, and if the plant gets too dense and the air is unable to get through.
When you provide good air circulation and make sure that the canes, do not cross, black spots will have a harder time spreading.
Proper Watering: Make sure to avoid getting the leaves wet while watering your plants.
There is not much you can do about rain.
However, you can avoid overhead sprinklers and focuses water directly on the roots of the plant.
Pruning your Plants
If you have black spots on roses, you will need to cut them back.
Make sure to remove any infected leaves and always do a thorough cleanup each fall.
Moreover, remove and dispose of any remaining leaves when you do your dormant rose pruning in later winter/early spring.
Spores tend to remain on leaves and stems and can also reinfect whenever conditions tend to be favorable.
Within 10 days of the first symptoms, the disease has already started spreading.
It is important to note that spores tend to spread by water.
Prune out any canes that show signs of infection.
Furthermore, prune about 6 to 8 inches below the infection and only prune your plant in dry weather.
Then disinfect your pruners with a 10% bleach solution or alcohol between cuts.
Dispose of the infected leaves and canes and make sure to avoid composting them, as these spores can re-infect the plants.
Make sure to clean up fallen leaves as well, and dispose of them properly.
Mulch your Rose Plant
Make sure to apply a thick layer of mulch around the base of your rose plant.
This is because mulch will help to prevent soil from splashing up on the plant.
And if the spores are present in the soil, it will help stop black spots from spreading on the roses.
Make sure that the mulch does not contain rooting wood.
This is because artillery fungus can develop in a moist environment.
Tropical Sprays for Treatment and Prevention
It is important to note that there are both commercial and homemade, DIY-solutions you can use to try and prevent the spread of black spots on roses.
The treatment may seem time-consuming, it is, however, a pesky problem that you can only slow down as nothing can really kill black spots on roses.
Moreover, you can treat the plant, you will need to spray your plants weekly starting in early spring as well as after heavy rain.
This will help to keep the blackspot from reoccurring.
Also, spray the entire plant, including both the top and bottom of the leaves, as well as the stems.
Consider using a dormant sprat over winter to smother overwintering spores.
Bordeaux Mix: This is a fungicide that tends to contain copper sulfate and hydrated lime.
You can use it as a powder or mixed with water and sprayed.
Moreover, Bordeaux mix also tends to repel some insect pests, however, it can burn plant leaves.
It is often used as a preventive in the spring before your plant leaves out.
Insecticidal soaps with added fungicide: You can use an organic fungicide, which often has sulfur added to regular insecticidal.
The soap coats the leaves and helps the fungicide adhere to the plant.
Neem Oil: Neem tends to be an organic fungicide and pesticide, that is derived from the seeds of the tree.
It tends to get inside the system of the plant, so you do not need to worry about coating everything or reapplying after rain.
However, it can burn the leaves of the plant in the hot sun.
You should not apply neem oil within two weeks of using a product that contains sulfur.
Sulfur: This prevents fungus diseases and can also help control a number of insect pests.
Sulfur comes as a finely ground powder, and if you want to spray on it, look for one that is labeled as wettable so that you can mix it with water.
Home Remedies for Black Spots on Roses
It is important to note that organic remedies may work for some gardeners and not often for others, however, experimenting is encouraged as long as you keep the habit of frequently spraying your roses to keep the black spots at bay.
Some of these are:
Baking Soda Spray: You will need to dissolve 1 teaspoon of baking soda in 1 quart of warm water.
Then add up to 1 teaspoon of liquid soap.
Spray the leaves of the plant thoroughly. This mixture will work as a preventive.
Moreover, it also offers some protection from powdery mildew.
Vinegar: This vinegar-based recipe can be effective and safe for all types of rose problems, including black spots.
You will need to mix white distilled vinegar with one cup of water, 1 and 1/2 tablespoons of baking soda, a tablespoon of dish soap, and a tablespoon of vegetable oil.
Add that mixture to a gallon of water, then spray it on the rose foliage, and reapply the mixture every week to 10 days, especially after a rainstorm.
Milk: Another remedy you can try is a spray mix of one part milk to two parts water applied weekly to control black spots.
Though this cannot kill the spores, however, it may slow down the spread so you can get a handle on the problems.
Hydrogen Peroxide: There are reports that when you spray a mix of 1 tablespoon of hydrogen peroxide, i.e. 3% concentration, and 1 cup of water, it will work on a black spot.
Plant-Resistant Cultivars
Roses are often labeled for resistance, from highly resistant on down.
If you are looking into black-spot resistance, you may as well look for a rose that is also resistant to rust fungus and powdery mildew.
Moreover, rugosas, a newer shrub and ground cover rose, and many of the Canadian Explorer series like ‘John Cabot’ and ‘William Baffin’ tend to show good resistance.
Roses that are least resistant to black spots include hybrid tea roses, grandifloras, and miniature roses.
Mists-resistant rises will include hybrid floribunda, shrubs, and climbing roses.
Leave a Reply