Tag Archives: Flower Diseases

Flower Diseases ~ Black Spots

Black Spots on Roses

It makes you want to cry when you see your prime roses covered with black spots. What on earth is happening to your prize roses you ask. Black spot disease is yet another evil villain of our beloved flowers and another common fungal disease. And roses are its biggest victim.

The disease typically begins as black spots on the foliage. They are most prevalent on upper leaf surfaces, and may be up to ½″ across. The leaves will eventually turn yellow around the spots, then become all yellow and fall off. The spots may also appear on rose canes, appearing first purple and then turning black.

Again, the culprit for this disease is too wet of conditions for too long of a time frame. It only takes seven hours for infection to set in, so when watering your roses be sure to water early in the morning to give ample sun time for drying and avoid watering on known cloudy days. Also, make sure to water from the ground avoiding all foliage and flowers. Use proper spacing so your roses can get good circulation. These things will help to minimize the disease and or prevent it totally.

Black spot fungus overwinters in fallen leaves and infected canes. Prune out infections and rake the fallen leaves at the end of the season.

Rose varieties vary greatly in their resistance to black spot, so choose resistant ones. If this information is not indicated on plant labels, you can research the variety online or check with experts at your local nursery. Several of the shrub roses show resistance to black spot—and powdery mildew. Many of the other shrub roses and old-fashioned roses are resistant as well.

To help control black spot disease, dust roses infected with black spot with sulfur powder. Sulfur will not kill the fungus spores, but it will prevent a new generation from germinating. You can also use a spray solution of 1 tsp. baking soda mixed in 1 qt. warm water in the early morning hours on your roses foliage. In addition, when your plants are in the dormant season, spray your roses with a dormant oil or Bordeaux mixture.

Flower Diseases ~ Gray Mold

Gray Mold on rose flowers

Gray mold is one of the most common types of diseases that afflict flowers. It is more prevalent during periods of high rainfall and cool temperatures. It has an appearance of a powdery mildew that is gray in color, thus its name. It appears primarily on old and dying leaves and flowers. When water sits on plants without the natural ability to dry within a reasonable time frame a gray fuzzy coating begins to appear – gray mold.

Gray Mold on Marigold leaves

To care for plants and flowers affected with gray mold, remove all diseased flowers and or leaves right away and spray with a beneficial bacterial control. To prevent gray mold keep your garden bed flowers spaced to allow for plenty of air circulation and well weeded. Also avoid overhead watering.

gray mold on strawberries

Gray mold can also present on trees, shrubs, and small fruits like strawberries. Recommended disposal of affected leaves, flowers, and fruits is burning, but since many urban areas do not allow for burning, burying the affected plants is also acceptable.

Common Flower Diseases ~ Powdery Mildew on Leaf

Phlox ~ You can see the mildew on the leaves. This is after two treatments of baking soda water mix. Before the leaves were fully covered with the fungus.

We got a request to answer a flower problem one of our readers asked. The reader was questioning what a powdery mildew was on her phlox leaves. I took this as an opportunity to answer that question for anyone who may be dealing with this in their flower beds.

In Mid to late summer is when gardeners will begin to see signs of plant diseases. Powdery mildew on your plants leaves is just one of the diseases you may encounter. Over a period of seasons, this mildew will weaken your plant until it no longer produces or dies.

This condition can be isolated to just the flowers leaves, but if severe can move onto the plant stem and flower as well. Although not instant detrimental to your plant, it isn’t very attractive and if left unattended will eventually kill off your plant.

Annual flowers that are particularly susceptible to powdery mildew include zinnias, snapdragons and verbena. Perennials that are commonly infected include delphiniums, lungwort, bee balm and garden phlox.

This fungal disease is spread by wind and splashing water. To help prevent the onset of this fungus avoid getting water on the leaves and flowers, water in the early am to give leaves plenty of time to dry during daylight hours.

Most fungal diseases are spread by microscopic structures called “spores” that are transferred on wet foliage. However, powdery mildew flourish in high humidity. By keeping plants well-spaced and removing weeds will help ensure good air circulation and reduce the humidity around plants thus lowering risks of this fungus. .

To control this fungus there are several different things you can try – use a horticultural oil, insecticidal soap or another spray. Begin applications at the early onset of the disease and when treating make sure to treat all foliage. Repeated applications are usually necessary right through the duration of the growing season

A home remedy that works for some is a mixture of baking soda and warm water. Mix 1 teaspoon baking soda per quart of warm water and spray on plants every seven to 10 days.

If you have a gardening question, feel free to ask! If we don’t have an answer for you we will get one!