 Plant Diseases in Arkansas
Black Spot
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Dr. Steve Vann - Extension Urban Plant
Pathologist
Roses are perhaps one of the most common ornamentals that we see here in
Arkansas. Many homeowners grow these for hobby. However some of the varieties
are particularly susceptible to a fungus disease called Black Spot. Black
Spot
can be a very devastating disease to some of our rose cultivars.
Anytime you mention the words Black Spot to a rose grower, this usually brings
on a lot of frowns and headaches to many rose growers across the state.
As you can see the spot are very characteristic for this particular disease.
Often times they will be very dark purple to black and the edges of the spots
tend to be a little feathery, or not nice and round and discreet. They tend to
feather out. And as you can see, when we have a lot of spots that grow together,
often times the individual leaflets will become yellow and then they’ll drop.
They’ll fall off the plant. And this is one of the biggest things about this
particular disease; it can cause severe defoliation, so this is a good way to
recognize Black Spot.
As you can see here from this particular leaf, the spots sometimes will not
have the yellow area around them, they’ll be nice and dark, but again look for
those feathery edges around the spot. It’s very characteristic.
So it’s real important to control this particular disease as best as
possible, especially in our Arkansas climate, because we tend to see this
problem more common during the hot temperatures of the year, the summer
temperatures.
And one of the things that makes this disease bad is the fact that we get
quite a bit of rain leading to wet leaves and this is very important for disease
control is to try and keep those leaves as dry as possible. So one of the best
ways we can do that is to actually water those plants from below. Or if we water
them from above, it’s best to do it early in the morning.
This particular fungus also has the ability to grow on dead plant tissue. So
just doing a good cleanup prior to springtime can be very beneficial to the
homeowner as far as controlling Black Spot.
But again, keeping those leaves dry, you want to keep these plants full sun,
the more sun the better. Anything to encourage leaf drying is very helpful.
Also, one of the better methods of controlling this particular disease is
selecting resistant varieties. You can actually select varieties that don’t get
the disease as bad under our environmental conditions here.
The Cooperative Extension Service also offers more detailed information about
this particular disease on roses. We have a very nice
fact
sheet that is located on our extension website and I would encourage
homeowners to take a look at this because it will give more detailed information
about this particular disease that we see very commonly on roses and it will
also outline some of the more popular control practices. It even talks about
some of the fungicides that can be used to control this particular disease.
Announcer
To learn more,
contact your county Extension agent, and follow the links in this section.
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