How to treat black spot on roses
Have you noticed dark spots on your roses lately? If left unattended, this can be a serious problem. don’t worry! Let’s talk about how to get rid of this disease.
Black spot is one of the most common rose diseases and, if left untreated, can damage the entire plant and lead to premature death. The fungus Diplocarpon rosae is the main cause of this condition, and in this article we will discuss how to identify and prevent it.
About black spot disease and “Diplocarpon rosae”, the fungus
【Symptom】
On roses, black spots with fringed edges appear on any leaf surface, but mainly on the upper surface of the leaf. Infected leaves will turn yellow, have black spots, and fall off the plant. Similar symptoms appear on petioles and fruits. The petals develop red spots and some distortion. Shoots may become infected during their first year of development. The lesions are purple-red, then black, and slightly raised. Black spots can cause plant malformation and stunted growth, making the plant susceptible to other infectious and non-infectious problems.
【Life cycle】
This fungus (Diplocarpon rosae) overwinters on rose branches and fallen leaves. Primary infection occurs when spores splash onto new leaves in the spring. Many secondary cycles follow, peaking in late summer. Environmental conditions that promote infection are moist leaf surfaces, high humidity, and warm temperatures.
【Manage】
Various rose varieties are resistant to this disease. Ranging from highly sensitive to highly resistant. In large rose plantings where susceptible varieties must be grown, planting a mix of susceptible and resistant varieties can help increase yields. Measures to increase air flow reduce disease severity by promoting rapid drying of leaves. Because the fungus survives in fallen leaves and infected cane, it must be removed in the fall or the following spring before bud break. Fungicides can be used to control this disease, but multiple preventive applications are required, starting with the emergence of new leaves and continuing through fall on highly susceptible varieties. During dry weather, extend the intervals between spraying or eliminate the spraying method entirely.
What are the black spots on the rose?
Over time, this disease, Diplocarpon rosae, or black spot, can affect roses, causing them to become weak and resulting in fewer blooms. It also makes the plant susceptible to winter or heat damage. You can spot it easily by the dark spots on the leaves. The outer edges of these circles are rough or feathered and surrounded by a yellowish ring. They appear on the upper and lower sides of leaves.
The impact of black spot disease on roses
It can also affect new shoots, causing black or dark brown blisters:
•Affected plants produce fewer flower buds and leaves begin to fall off.
•Soon, it moves to every part of the plant, causing stunted growth and failure to bloom.
•If left untreated, plants will drop leaves, wilt and die.
Rose types susceptible to black spots
All rose varieties are somewhat susceptible to black spot, but some are more susceptible than others. According to the University of Nebraska-Lincoln, hybrid tea roses, miniature roses and large-flowered roses are most susceptible to black spot disease. So, if you grow a lot of roses, it’s best to look for resistant varieties to avoid this problem.
Causes of dark spots on roses
The primary reason behind this fungal problem is due to the chronic presence of moisture on the leaves and lack of air circulation.
Excessive watering and damp leaves
This fungus likes to thrive in moist conditions, and spray watering is the main reason. Do not water the plant unnecessarily to wet the leaves as this makes the rose very susceptible to this disease. According to Texas AgriLife Extension: “For the fungus to infect a rose, the spores on the leaves must remain moist for at least 7 hours.”
This means that if the weather is humid or you are growing your roses in a low-light, low-air circulation area, be careful about watering.
Insufficient air circulation
Proper airflow around the plant ensures that the leaves and stems are always dry, leaving no room for fungus to grow. Leave at least 30 to 60 centimeters of space between your rose branches for optimal air circulation.
Spring
Rose bivalve fungi grow best in a temperature range of 18 to 24 degrees Celsius, which is the most common temperature range in spring and summer. However, high temperatures above 30 degrees Celsius will limit its growth. Therefore, when the temperature is in the range of 18-24 degrees, you must be extra careful to keep the leaves dry and the plant well-ventilated.
Purchase of infected plants
Pathogens can also spread from the nursery to your garden. If you are buying a rose shrub, look carefully at the tops and bottoms of the leaves for infected leaves.
Note: Young plants are most susceptible to this fungal problem because they have not developed the proper defense systems to protect themselves from the fungus.
How to prevent dark spots on roses
Prevention of disease-resistant varieties
The easiest way to solve this problem is to plant disease-resistant varieties. Ask a nursery specialist or search online. Among contemporary rose varieties, there are many varieties with excellent disease resistance. We have a large amount of basic introduction to variety information, which is also convenient for flower lovers to check before purchasing.
Make sure they have adequate sunlight and airflow
If you want to ensure that your plants are fungus-free, you should provide them with adequate light. The more sunlight your roses get, the better for their health and flowers. In addition, you must space them at least 30-60 cm from other plants so that they can get good air circulation.
Water your plants the right way
If possible, avoid spraying to avoid wetting the leaves. When the topsoil feels a little dry to the touch, irrigate with adequate water. Additionally, it’s a good idea to get into the habit of watering in the morning, so the plants have plenty of time to dry before the end of the day.
Prune in time
Prune old, tangled stems and leaves as they may be sites of hidden moisture. It also ensures that you remove any diseased parts, stopping it from spreading to other parts of the plant.
Discard diseased leaves and branches; do not put them in the compost pile or leave them in the garden as their fragments can re-spread the infection.
Avoid wet weather
If your rose bushes are already suffering from this disease, it’s a good idea to provide rain protection to prevent the leaves from getting wet. If you are growing them in pots, it is best to move them to a dry location.
How to treat dark spots on roses?
Insecticidal Soap
Mix insecticide soap and water in a ratio of 1:3 before use. It will take care of the fungus. If you want to make your own insecticidal soap, the relevant information is not covered further here.
Soda water
Take about 1 liter of water and add 1 teaspoon of baking soda and mild liquid soap. Fill a spray bottle with the solution and spray the affected areas.
Neem Oil
Neem oil will penetrate into the plant, so you won’t need to reapply after a rain. It can burn foliage if used in large quantities in hot weather.
Milk
Mix milk and water in a 1:1 ratio and apply to the affected area with a soft cotton ball. You can also use it as a foliar spray. It promotes the growth of a certain type of fungus that feeds on black spots. It has been scientifically proven to be an effective method!
Vinegar and hydrogen peroxide
Add a teaspoon of each to a liter of water, stir well, and pour the solution into a spray bottle. Use it as a foliar spray on affected areas.
Use fungicides
If these things don’t work, strong fungicides containing copper or sulfur can be used to quickly control the disease. Refer to the drug label for dosage and directions.
Summary
In addition to all these measures, it is important to take care to remove fallen leaves and twigs affected by this disease, carefully discarding everything. After pruning a diseased plant, be sure to disinfect the pruners you used.
Original article author：Fragrant Road Full，If reprinted, please indicate the source.：https://www.theroadfull.com/article/3069.html
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