- Pamela Corle-Bennett Contributing Writer
It’s not surprising that several diseases on plants are beginning to show up. We have had perfect weather conditions for disease to develop.
One of the most common diseases that we see every year is apple scab, and this year is no exception.
Many cultivars of apple and crabapple are susceptible to this disease. The leaves develop olive-colored blotches. These spots turn blackish, and the leaves eventually turn yellow and drop.
If the weather conditions are perfect (wet and cool) during leaf development in the early spring, the damage can be quite heavy.
However, this disease doesn’t kill trees. I have seen it on crabapples year after year, and they still survive.
The trees can sometimes look really bad when the entire tree drops its leaves.
On apple trees, apple scab can become a major problem on the fruits. It’s safe to eat the fruit, but they look horrible.
Apple scab makes it really hard for fruit growers in Ohio. Given our weather conditions, growers need to be on top of fungicide spray programs to have clean perfect apples.
Another disease on apples and crabapples is frogeye leaf spot. The symptoms pretty much look like a frog’s eye. Again, this is another disease that is cosmetic on crabapples but can cause problems for apple growers.
I am beginning to see symptoms of powdery mildew on perennials such as tall phlox and bee balm. This disease is very common on these plants and won’t kill the plants.
I simply cut my plants back to the ground after they finish blooming and let them come back with clean foliage for the rest of the season.
Another weather-related disease also showing up on roses is called black spot. If you are a rose grower, you are very familiar with this disease and the symptoms.
The leaves begin to develop black spots as the name suggests on the foliage. Areas around the black spots begin to yellow and the leaves eventually drop.
Continual infection on roses can lead to weakened plants that are more susceptible to other problems, including lack of overwintering ability.
The fungus that causes the symptoms likes a wide range of conditions, and we sometimes see symptoms develop all season. What you are seeing now is the early spring leaves affected with black spots.
Control of this disease is a bit challenging because of timing. Fungicide applications have to be on the leaf surface prior to infection. This means that you should be protecting any new growth from the disease every seven to 14 days.
Keeping irrigation water off the leaf surface helps to reduce the spread of the fungal spores as does planting them in the sun so that early morning dew dries off quickly.