A common trait of many plant diseases is an affinity for moist, humid conditions. When plants are able to naturally dry out quickly, they are less vulnerable to diseases.
Try to place plants that are particularly susceptible in areas that tend to receive ample sunlight, and place enough space in between them so air circulates to dry them quickly. This practice also prevents diseases from spreading between plants.
Sometimes, the weather does not cooperate, as is often the case this time of year with late afternoon thunderstorms. Such conditions are ideal for diseases to strike even the most well-planned gardens.
Carefully monitor your plants during these times, and consider using a broad-spectrum fungicide as a preventative measure or at the first sign of a problem. Two particular disease problems that are active now are powdery mildew and gray mold.
Though it generally won't kill a plant, powdery mildew can significantly detract from the natural beauty and overall healthy appearance of a number of ornamental plants. It is caused by a variety of closely related types of fungi, and gets its name from the grayish-white powdery coating the disease causes on leaves, stems and blossoms.
Excessive watering and shade also can contribute to the problem. Some plants are more susceptible to powdery mildew than others, such as rose and crape myrtle. Place these plants in a location that gets plenty of sunlight and drains well, and keep an eye on them when conditions are favorable to powdery mildew.
Fortunately, controlling powdery mildew is pretty simple. On particularly sensitive plants, consider a preventative spray with a broad-spectrum fungicide, such as Ortho Garden Disease Control, Immunox, Funginex or Bayer Advanced. Begin spraying in the springtime just before buds begin to appear and continue every couple of weeks through the early summer.
In addition to powdery mildew, many home gardeners are familiar with gray mold, or Botrytis blight. This disease infects a wide variety of ornamentals as well as a significant number of fruits and vegetables. There are several species of Botrytis fungi that can cause blight. Some varieties can attack a number of plants while others are host-specific.
Gray mold can affect any part of the plant except the root system. However, it tends to only infect one part per plant. For example, on onions or violets, the pathogen generally causes damage to the leaves, while on tomatoes it tends to attack the fruit. Telltale signs of the disease include spotted plant material accompanied by powdery gray spores.
Infections occur most frequently during rainy spring or summer weather. Outbreaks are particularly common when such conditions persist for several days to a week.
Keeping plants clean and dry is an important step to preventing gray mold. Garden cleanup at the end of the growing season is also important to prevent the disease from carrying over to next year.
Billy Skaggs is an agricultural agent and Hall County extension coordinator. Phone, 770-531-6988; fax, 770-531-3994.