Controlling Black Spot In The Home Garden Using Organic Techniques

To begin with, that black spot disease you see on your roses (Diplocarpon rosae) is a fungus disease. You know you have it by the light spot it creates on the leaf – an initial yellowing of the leaf in a spot approximately one-half inch across.

This initial yellow spot can occur on either side of the leaf and distinguishes itself from other leaf spot fungi problems by having a slightly fringed edge to the spot. After establishing itself, the fungus will turn black (see picture below)

You’ll likely need a small lens or a magnifying glass to see the fringes so most gardeners assume black spot when they see the yellowing spots on the leaves. With the lens, you’ll also be able to see the black spore-producing bodies on the spot.

Why Don’t Chemicals Always Control This Problem?

The interesting thing about this problem is that the fungus “roots” (they’re really mycellium, but what the heck) penetrate down between the layers of the leaf so they are well protected and invulnerable to anything happening on the surface of the leaf.

You can’t destroy the fungus without destroying the leaf. That is one smart fungus. (no contact sprays – chemical or organic – will work between leaf layers)

Why do the leaves fall off

The fungus is reputed to produce ethylene which causes roses to drop their leaves. Some roses hang onto the leaves for a longer time than others and on these varieties, the black spot fungus can really develop.

It produces larger yellowing circles (sometimes edged with black dying tissue) and often several different circles on a leaf will meet, causing almost the entire leaf to go yellow.

Naturally, as the fungus works away, the leaf will become paler anyway as the nutrients aren’t getting to all parts of the leaf so the leaf just gets pale and yellow. Then it drops.

Traditional Chemical Controls

Gardeners have tried to control this black spot problem over the years by drenching their roses in all manner of fungicides.

Invariably, the fungicide works for a while and then after a few years, it loses its effectiveness as the fungus become immune to that particular compound. In this way, the chemical industry has convinced rose growers to use more and more powerful compounds to protect their roses from the effects of the blackspot fungus.

Let me suggest an alternative system of control for you.

The first step to healthy roses: cleanliness

To begin with, once the fungus is well established in your garden, it is necessary to clean up the garden.

Collect and remove all diseased leaves to the dump. Do not compost them.

By collecting all the leaves, and I start with those that have symptoms on the plant, and removing them from the garden area, you are denying the fungus the ability to breed and overwinter on plant debris.

Preventing successful overwintering is the first step in a control programme and a clean garden is the first step in this direction.

Second step: Dormant Oils

The second step is to understand that many fungus spores overwinter on the canes.

In my garden, I cut down the canes to the ground and remove them from the garden each year. I can do this because I plant my bud unions at least six inches deep (I describe this in my ebook Tender Roses for Tough Climates) and the roses survive quite nicely to resprout new and clean canes the following spring.

If you garden in a more traditional manner, I suggest you spray your roses with a dormant oil and sulfur spray in the fall before hilling as well as first thing in the spring after you remove the soil covering.

The dormant oil will suffocate the overwintering fungal spores. As a side benefit, it also suffocates the eggs and overwintering adults of several pests that can bother roses.

Third step: Preventative Sprays

The third thing a gardener has to do is develop a rotation spray in the garden as a preventative measure. Remember, once the fungus is established, the mycellium are protected between the leaves so spraying will not kill them.

Establishing a preventative spray programme is easy and several things work very well.

Organic Spray for Black Spot #1

The first is household baking soda.

Mix two tablespoons of baking soda into a gallon of water and add one squirt of detergent or soap to the mix. The soap acts as a spreader-sticker to help keep the baking soda on the leaf.

The mix should be sprayed onto the rose leaves – both top and bottom – to establish an alkaline leaf surface that will prevent the fungus from establishing itself.

This will have to be repeated after a rain as the rain will clean the leaves allowing the fungus a clean leaf to colonize. This mixture will last about a week in normal practice, the dew will wash it off and wind action will abrade it.

Organic Spray for Black Spot #2

Go to your favourite garden centre to purchase lime-sulfur (see below for resources) and use this the second week. Mix as per label directions.

Spray this mix onto both leaf surfaces as it creates a very acidic leaf surface that will prevent fungus from developing as well as killing off any immature fungal bodies.

Alternate organic controls

Each week you alternate sprays – one week the alkaline baking soda and the next, the acidic lime sulfur.

The poor black spot fungus will have to work very hard to establish itself if you are diligent.
There are other sprays coming on the market based on neem products and horticultural oil that hold good promise to be included as part of the spray rotation.

Do not rely on only one spray for rose protection but continue to use several in rotation.

Step Four: Resistant Roses

The last thing to consider – or possibly the first thing – is to only purchase roses that are “resistant” to the black spot fungus. This usually means the leaf surfaces are thicker so the fungus has a harder time penetrating and propagating.

It does not mean the rose won’t get the fungus but that it resists the fungus (resist and immune are two different concepts).

Using environmental controls, your roses are still likely going to get black spot, but they will get it later in the season and not as badly as under chemical spray programmes. This means you’ll get more blooms and your plants will be healthier. You’ve done two things – you’ve eliminated noxious chemicals from your garden and you’ve got better roses. How’s that for good gardening?

My Situation is Unusual

This article on black spot was written from a traditional point of view.

In current practice, I find I rarely have to spray my roses at all for several reasons.

The reason is my unusual planting method, the bud union goes six inches under the soil so the canes die off to the ground in the fall and are cut off and removed (no overwintering sites for the fungus).
And then, given the lack of an early start, the black spot doesn’t really get going until later in the summer and it’s not usually a problem. It doesn’t have the time to really make the plants look ugly.

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Sources of Control Material For Rose Black Spot.

Dormant oil spray.
Lime Sulfur 

6 Practical Tips for Mid-Summer Rose Care You’ll Want To Read

When it comes to midsummer rose care, there are several different things to keep in mind.


If you had the foresight to plant a rose as part of a container gardenlet me remind you that these plants, including the miniatures, are greedy feeders and if you want to see a lot of blooms you will have to feed the plant every week.

Plant food provides the energy to produce those huge blossoms and the extra shoots that produce even more blossoms. I use an organic liquid fish food fertilizer on all my container plants and roses love it as well. You also do not want to let your rose get thirsty.

Remember that if you touch the soil and your finger comes away dry, it is time to water that pot. Continue applying water until water comes out the bottom of the pot to ensure the soil is soaked right to the bottom and no roots are allowed to dry out. Feed and water those containers and you’ll have fragrance this summer but without this essential bit of rose care, your containers will disappoint.

In Ground

If you have roses in the ground, whether it’s traditional rose gardening or a plant here and there, let me remind you that the above two rose care suggestions are equally valid. Feed those roses with a liquid plant food and watch the plant grow.

And remember that blossoms are over 90 percent water so if you reduce the water, you reduce the size and number of blossoms on the plant.

Rose Pruning

Rose flower pruning is one of those dull rose care chores that are necessary in order to keep the rose producing more blossoms, reduce disease in the garden and just keep things looking good. With hybrid tea roses, once the blossoms start to fade, each bloom should be pruned off.

There is some disagreement about how much of the stem to cut off along with the fading rose and while some rosarians suggest only taking a few inches, there is research that suggests cutting at least twelve inches of stem or cane off along with the rose will produce more blossoms in subsequent bloom flushes.

I have always taken the longer stem cutting in the belief that the longer the stem I cut off, the more new buds will develop to produce even more flowers. What is important is that you do remove spent flowers before they become sites for diseases to establish themselves.

Rose Deadheading

Other kinds of roses should also be deadheaded as the flowers are finished blooming and that includes all climbing roses. Suffice it to say that pruning them immediately after they finish blooming is traditional rose care.

Pruning Mistakes

And that brings me to a question I get asked regularly. What happens if I make a mistake with the pruning? The short answer is that this is a plant, it is not brain surgery. What’s the worst thing that could happen? Well, you might kill the plant, but the chances are that the plant will simply grow back and you’ll get another chance to do it correctly.

It is certainly that way with roses. Many of them will simply die over the winter anyway so why worry about a few poor pruning cuts. Do your best and let the plant live with your efforts; you might, however, try taking a book on pruning out of the library next winter.

Black Spot and Rose Care

The last thing that many rose lovers are concerned with right now is the dreaded black spot. This disease starts out as small black spots and these spots enlarge and multiply. The spots go yellowish and the leaves drop off the rose. Planting resistant varieties only delays the inevitable.

Let me suggest that a weekly spray mix consisting of: 3 tsp. baking soda, 2 1/2 tbs. summer-weight horticultural oil, mixed with 1 gallon of water will control black spot enough for the average gardener. Yes, you’ll still see it later in the summer but you’re still going to see it with the expensive, chemical bomb you use as well.

Spray this every week and immediately after rains for complete coverage that will slow blackspot down to a dull and livable roar.

There is also some research suggesting Neem oil can be used  as an alternate spray (spray with the homemade spray one week, the neem the next).

Twist with Powdery Mildew

If your growing tips on your roses are twisted and curled, it is likely you have powdery mildew. You might never see the white powder that is evident on other plants infected with this problem but those twisted leaves are a dead giveaway on roses. Uncurl the leaves to make sure the curling is not an insect making a nest in there and if no insect is present, powdery mildew is the culprit.

Prune off the infected tips and start a weekly spray of the above recipe. Do not water the leaves if at all possible but apply water to the base of the plant.

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