Letters to the Editor
As the weather is getting hotter and more humid, the presence of diseases is increasing as well. One particular disease that is showing up in a variety of production systems is Powdery Mildew. I’ve seen this fungus on vegetables, trees, and ornamentals over the past few weeks.
Powdery Mildew is actually a group of diseases caused by a few different closely related fungi.
However, the disease is pretty easy to spot because they produce white or gray spots on leaves, stems, or flowers. These gray spots are the fruiting bodies or mycelium of the pathogen. Once spores are produced they can be transmitted through wind or splash from rain or overhead irrigation to nearby plants. Oddly enough, Powdery Mildew is less common during the hottest part of the summer, but it is present nonetheless.
While this disease is not considered as fatal to the plant, it can cause damage to the plant. The fungi attached to the plant cells in order to take in nutrients, and in severe or untreated cases the plant experiences decline.
This decline can be a reduction in plant growth or leaves will appear as yellow or brown. In turn, as the plant declines that provides the opportunity for other pathogens cause infections that could lead to plant death.
For example, this week I examined a powdery mildew sample that had both Powdery Mildew and Alternaria structures when viewed under the microscope. This combination could lead to plant death in the vegetable it was sampled from.
However, as mentioned above, Powdery Mildew is a few different fungi, and what that means is that just because you find the fungus on your oak tree does not necessarily mean that it will spread to all of your plants. Each of these fungi have a fairly limited host range that includes several ornamentals like azaleas, dogwoods, roses, oak trees, pecan trees, and vegetables such as cucumber and squash.
The accompanying picture is squash where you can see the multiple sites of infection on the leaf surface, however, the nearby peppers and blackberries are unaffected.
Management of this disease can take on a few different forms. First, when planting make sure the plants are not overcrowded, are healthy, and receive the light, soil, and moisture requirements that are necessary. If you happen to find Powdery Mildew before it is widespread, then removing the infected leaves can help control the spread.
By the end of the growing season or harvest, remove leaves that have fallen or were infected so that the disease has less opportunity to overwinter and cause issues next year. There are also several fungicides that can be utilized if necessary that include the following active ingredients: Myclobutanil, Propiconazole, Thiophanate-methyl, Chlorothalonil, Neem Oil, Cooper or Tebuconazole.
When selecting a fungicide be sure to select one labeled for your production system such as vegetables, flowers, etc.
For more information about managing diseases or other agricultural issues, please contact the Extension office by stopping by, calling 478-9863958 or email brennan4@uga.edu.
