How to Identify, Prevent, and Treat Black Spot Damage on Roses
Are you seeing spots on the leaves of your roses? Black Spot is a common rose disease, and is especially prevalent in rainy, humid climates. In this article, gardening expert and rose enthusiast Danielle Sherwood explains everything you need to know about black spot, including how to identify, prevent, and treat it.
Perhaps you’re putting your “nose to the rose” and enjoying the perfume of your favorites, when you notice some ugly discoloration and yellowing on otherwise healthy shrubs. The first thing to realize is that black spot is nearly everywhere, and there is no cause for panic.
Black spot is the most common fungal disease for rose gardeners around the world. While it looks terrible, it’s not a death sentence for your rose. There’s no cure for black spot, but you can take steps to mitigate the damage and prevent future problems.
Let’s dive into everything you need to know about black spot and how to prevent this fungus from taking over your rose garden!
What is Black Spot?
Black spot is a widespread rose disease caused by the fungus Diplocarpon Rosae. Its spores spread via wind and water. The fungus commonly appears in moist, rainy conditions, but even rose gardeners in dry climates encounter it at one point or another.
This rose disease earned its name from the feathery, irregular brown and black spots that usually appear on the older leaves and young canes of a rose. It will first appear on the bottom leaves, and gradually work its way up the shrub.
This disease spreads during the growing season, but also grows when affected leaves and canes are left to overwinter, reinfecting foliage in spring. This eyesore is primarily a cosmetic issue, but when left untreated, it can weaken your rose and cause it to lose its leaves.
While it may seem alarming, it’s best to assess the overall health of your rose and take a common sense approach to treatment. Let’s dig into the key symptomst and what to do if you see this pesky fungus appear on your roses.
This fungal disease is easy to recognize. It first appears as splotches of black, brown, and sometimes purple on the bottom leaves of the plant, gradually moving up.
Often, yellow areas will develop around the spots before the leaves fall from the plant. Sometimes, you will also see brownish or rust colored splotches on fresh canes.
- Irregular brown, black, or purplish splotches on leaves.
- Yellowing of spotted leaves.
- Leaf loss.
- Canes with brown or rust colored scabs.
Quick Tip: The rust colored scabs can look similar to Rose Canker, another common fungal infection of roses. This disease usually looks like surface-level discoloration, while canker results from pruning wounds and looks like a lesion on the cane.
The most common causes are lack of proper air circulation, wet, humid conditions, and lack of sanitation. However, remember that most gardeners, even experts, sometimes see this fungal disease pop up in their gardens.
If it shows up on your favorite varieties, it’s not necessarily due to anything you did wrong. A bit of black spot is just a rose garden reality. Let’s gain understanding of the main causes. The primary and secondary causes may include:
Roses can be thirsty plants, but they do not like wet foliage. Black spot requires 6 + hours of direct moisture to infest your rose. If conditions are humid, rainy, or you’re overhead watering with sprinklers, it is likely to appear. Roses planted in very shady areas or watered in the evening might not get the chance to dry out, allowing fungus to thrive.
Lack of Air Circulation
If your roses are overcrowded (ideal spacing is 3+ feet), they might lack proper airflow between them, creating a breeding ground for disease. Under-pruned roses can cause lack of airflow by creating too much crowding of foliage within the plant itself.
Lack of Sanitation
You can inadvertently spread blackspot and other diseases in your garden if you don’t properly sanitize your pruners with alcohol between each rose. Additionally, don’t neglect cleanup of infected plant debris. If left on the ground, the fungus will spread via wind and water and reinfect your plants.
There is no way to completely eliminate this fungal disease. Remember that it is primarily cosmetic, and keep calm. There are, however, some key ways you can reduce the likelihood of it becoming a major issue in your garden.
Grow Disease Resistant Varieties
When selecting roses to grow in your garden, choosing disease resistant varieties is the most important step in reducing the likelihood of future fights against fungus.
Most websites highlight their healthiest varieties. In general, landscape roses, Old Garden roses, David Austin roses, and knockout roses are good bets. There are thousands of cultivars, so you won’t lack for choice.
If you’re in love with a certain type of rose, like a hybrid tea, which is more susceptible to black spot, pick the rose with the highest health rating you can find.
Yellow roses in general are more highly susceptible. If yellow is your preferred color, avoid hybrid teas and opt for a tougher rose variety to give sunny colored roses the best chance of success in your garden.
Water your roses at the base of each plant to prevent wet foliage. If you can, water your roses in the morning so that they have plenty of time to dry out during the day.
A drip-irrigation system is ideal, but you can also leave your hose at the base of the shrub, giving it a good soak (2-4 gallons) once a week. Increase the amount to twice a week or more if you have particularly hot conditions or a newly planted rose.
Provide Proper Air Circulation
Make sure your roses are adequately spaced, leaving 3-4 feet between each plant. When pruning in early spring, maintain a vase shape with open airflow in the center of the rose and strong, sturdy canes around the outside. This will reduce the likelihood of wet, overcrowded foliage.
If your infected roses are in the shade, consider moving them to a sunnier site where drier conditions will reduce germination of fungal spores. Some varieties can tolerate partial shade, but most roses do their best in 6 to 8 hours of direct sun per day.
Keep Your Rose Garden Clean
Clean up any diseased foliage after removal and remove it completely from your garden. Always sanitize your shears with a quick dip or a spray of rubbing alcohol between each plant so disease doesn’t travel throughout your garden.
If black spot has already shown up in your garden, don’t panic. Remember that nearly all rose gardeners are visited by this disease from time to time!
Overreacting, over-pruning, and spraying your roses with synthetic chemicals can cause unnecessary harm. There is no cure, only methods for prevention and inhibiting spread. Here are some steps you can take to mitigate the problem before it gets worse.
Remove Infected Foliage
First, put down the pruners! Use your hands to gently tug down and back to remove the discolored leaves. They should come off easily. Bag them up and get them out of your yard.
If you see spots on your canes, assess the overall health of your rose before removing them. For younger roses just starting out, you might want to see if the rose can tolerate a bit of black spot rather than remove all of its new growth.
If you have a vigorous, older rose with lots of healthy canes, go ahead and snip off the infected canes with your shears along with the diseased leaves.
Often, removing the infected foliage, providing adequate airflow, and keeping water off the foliage is enough to manage black spot. But what if you live in a particularly rainy, humid climate?
You might want to try some tried-and-true organic solutions used by expert gardeners. Caution: Even organic solutions impact pollinators in the garden. Please use them sparingly and only in the evening to avoid killing beneficial insects.
Baking Soda Mixture
This is often recommended as a preventative measure as well as a treatment. Mix 2 teaspoons baking soda and 2 teaspoons vegetable oil in 1 gallon water. Use a sprayer of your choice to thoroughly coat your plant. This fungal disease prefers acidic conditions, so adding alkaline baking soda will inhibit its growth.
After removing infected leaves, make a mixture of 1 part milk to 2 parts water. Spray your plants thoroughly once a week until new healthy growth appears. This method, developed and tested by horticultural professor and author Jeff Gilman, is low impact and has yielded excellent results for gardeners across the US. Many also report it as a deer deterrent!
Neem oil is a natural pesticide from the fruits and nuts of the Neem tree. Many gardeners use it to combat common rose bush pests as well as black spot and powdery mildew. Mix 2-5 tablespoons Neem oil with one gallon of water, and spray affected roses in the evening. Never spray roses with Neem in the morning of a sunny day, as Neem-coated leaves can burn in the sun. Because Neem will kill bees and other beneficial bugs, it is best used sparingly.
If you have tried everything listed and black spot is still prevalent in your garden, weigh your options. A small amount of this disease can be tolerated. However, if your roses are losing all their leaves to the disease and the plants are weakening, you might want to consider more drastic measures. Before introducing harmful chemicals to your garden, think about:
Hard Pruning: Remove any remaining leaves, and cut back until you see green, healthy cane. Clean up well, and your roses should produce healthy new growth next season.
Pickomg a New Variety: If you’ve planted particularly susceptible varieties, consider if they’re worth keeping. It might be worth replacing them with a reliably resistant bloomer that you can enjoy without constant intervention.
If you want to use synthetic chemical solutions to combat black spot, wear gloves, eye protection, and a mask to protect yourself. Apply in the evening to avoid contact with pollinators as much as possible. Be careful to follow instructions for keeping children and pets away from your garden until the solution is dry.
The most popular options are Daconil, a multipurpose fungicide, and BioAdvanced Disease Control, a systemic treatment for roses and other shrubs.
If black spot shows up in your garden, there’s no need for alarm. Roses are tough plants that have been around for thousands of years! It may look unsightly, but a small amount of this fungal disease is just part of gardening with roses. Take a deep breath, remove affected leaves, and assess if your roses are staying too wet due to improper watering, lack of airflow, or too much shade.
Remove all diseased foliage regularly, sanitize your pruners between plants, and try to take a light-handed approach to the problem. If the disease persists, try organic solutions before bringing out the synthetics in order to keep your garden full of beneficial wildlife.
If all else fails, consider replacing weak, susceptible varieties with healthy, new disease-resistant roses. After all, your garden is meant to be a haven, not a battlefield.