What is Black Spot on Roses?:
Black spot is a fungal disease that afflicts a great many roses and it is one of the more prevalent rose diseases. Black spot is actually caused by a fungus known as Diplocarpon Rosae and the most obvious signs of the disease are the telltale small black spots that form on the leaves of the roses, followed up by a yellowing around the spot and the leaf until eventually the leaf dies and falls off the plant.
In its early stages, you may find black spot on roses to be somewhat unnoticeable until it progresses much further along and the leaves start yellowing. Unfortunately, this is one of those rose diseases that is best treated early before it can spread too far, so due diligence is required.
Should you detect black spot on your roses at any time, you should begin to take immediate steps towards treating it before it takes over your entire plant. The longer you leave it go, the harder it ultimately is to get rid of and you risk damaging the plant so much that it may not survive the winter months.
What Causes Black Spot on Roses?:
As we said in the opening paragraph, Black spot is the result of the fungus Diplocarpon Rosae, which can be blown around as spores from garden to garden, so you could have really gotten it from anywhere. Understanding how the fungus germinates and spreads however can be the difference between healthy roses and dead ones.
The spores that lead to black spot on roses thrive in damp, warm environments like most fungi do. Not to mention the warmer the weather is, the faster the disease will spread. Once the spores land on your roses, they can literally germinate within a few hours if the temperature is between 65 degrees and 75 degrees outside.
The fungus is also capable of surviving through most winters simply by clinging to dead leaves around the base of your roses. You will see in virtually all of our articles on the various types of roses, we always suggest cleaning up the dead leaves and debris around the base of your roses…this is one of the reasons!
Black spot is a preventable and treatable disease, you just need to arm yourself with a few helpful tips so that you know what to do in the likely event your roses contract this disease.
Preventing Black Spot on Roses:
The best way to combat a disease is to never get it in the first place and while this is unlikely if you are going to grow roses, there are things you can do that are not very difficult, but will greatly improve your chances of avoiding black spot on roses.
The first step comes in either the late fall or early spring, whenever you typically prune and clean up around your roses. Get rid of any dead wood, as well as any canes that look like they might be diseased. Also you should take a few extra minutes to rake up all the dead leaves and debris around the base of your roses, just to be safe. This loose debris can harbor fungi and pests all winter long and they are just waiting to re-infect your roses again in spring so don't give them the chance.
Remember, black spot requires damp conditions to infect the leaves of your roses. Many growers make their plants vulnerable simply by watering them with the garden hose on shower setting and getting the leaves soaking wet.
Do yourself a favor and try to water only the base of the plant where the roots are.
If you must water from the top down, try to do so in the morning so that your roses have all day long to dry out in the sun.
You should also try to plant your roses in a spot where they get ample morning sun light as this will help evaporate the morning dew from the leaves. What may seem like a simple thing could actually prevent black spot on roses.
There are varieties of roses out there that have been bred specifically because of their high resistance to black spot and other diseases. Many growers simply buy roses for their color anyway so why not consider varieties that are disease resistant naturally?
Treating Black Spot on Roses:
Inevitably, most growers are going to get hit by Black spot at some point in the life of their roses and they should learn how to treat and deal with it when that time comes. You need to act immediately when you see signs of Black spot anywhere on your roses.
Start by removing the infected parts of the rose right away and throw them away in the trash. Never put diseased cuttings into your compost pile or elsewhere in the yard. It's best to just get rid of them entirely, lest they risk infecting your roses again.
Once you are sure that you have gotten it all, you will need to protect the plant from further infection. One of the best remedies for black spot is anti-fungal soap and wettable sulphur, both of which are widely available at most nurseries and garden centers.
The anti-fungal soap is pretty self explanatory and that should help you out tremendously in the event you didn't quite cut away all of the existing infection of black spot on roses. The sulphur, when applied lastly to the leaves, will form a barrier between the leaves and the spores of black spot that may land on the leaves. Unfortunately, the sulphur will wash away with the first rain or top down watering, so this is something you will need to reapply as needed.
If you haven't already done so, you should also lay down several inches of mulch around the base of your roses in the spring time. In addition to its other many benefits, mulch will provide a barrier between the leaves of your roses, and the surface of the soil where any leftover spores or other nasties may have survived the winter months and are waiting to be splashed up onto the leaves of your roses.
Home Remedies for Black Spot on Roses:
There are a couple of home remedies that you can try for combating black spot on roses as well. The first is a baking soda solution mixed with liquid soap to help it stick to the leaves of the plant. Stir in 1 teaspoon of baking soda into 1 quart of water, along with several drops of a mild liquid soap. Use this mixture to spray the leaves of your roses heavily and you may find a certain degree of success against not only black spot, but rust and mildew as well.
Another option, if you have composted manure available, is to make a tea out of it by soaking it in a bucket for several days with the bucket in a warm location. Strain out the solids (which can also be used as fertilizer) and spray the liquid all over your affected roses as well. I have personally never tried this method but it is said to work well in combating black spot.
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