Richard Evans, UGA Extension, Bryan County
After several years of drought we have really enjoyed having a wet spring/summer.
For some it has been a pleasure to sit on the porch and watch the rain fall. We have seen our rivers running full and the lakes/ponds filling. Many homes in Bryan county are on a shallow well and really like the idea of our groundwater recharging them. Unfortunately, all the news concerning our wet spring is not good. Warm temperatures and wet weather can provide the ideal conditions for plant diseases.
In order for a plant disease to occur you have to have a disease organism (pathogen), a susceptible host, and favorable environmental conditions.
Although plants can get bacterial infections and viral diseases, fungi are the most common cause of plant disease.
Most fungi reproduce by spores which can be spread by wind and splashing rain. Once a fungal spore lands on a leaf it has to germinate or sprout in order to infect the leaf tissue. Most fungi require water on the leaf surface in order to germinate. That is why we recommend that you minimize the amount of time plant leaves are wet. Fungal spores are also very sensitive to temperature. Most grow best at temperatures between 70 and 90° F. We are experiencing ideal temperatures for fungi growth now.
Rose bushes are among the first plants to show damage from fungal diseases.
Periods of afternoon thundershowers are often followed by rose leaves developing black spots on their leaves. As Black Spot disease progresses the leaves may turn yellow and fall. The spores produced by damaged leaves infect other nearby leaves.
Lawns can also suffer from wet weather. The most common disease of turf, Brown Patch, occurs when highly fertilized lawns are wet for extended periods during favorable temperatures. On centipede lawns, the recipe for decline is essentially too much moisture, mixed with too much nitrogen. Check your lawn for compaction issues and consider getting it’s soil tested to make sure you are fertilizing it correctly.
Tomato plants are easily attacked by fungi in the vegetable garden. Splashing rain or late afternoon watering that wets the leaves is often followed by problems.
The tomato leaves begin to develop spots and the lower leaves may begin to yellow. These are the classic symptoms of the fungal disease Early Blight.
With millions of spores of fungus swirling among us what can gardeners do to reduce the impact of fungal diseases? Well, there are several techniques we can use. First, minimize wetting plant leaves when we irrigate. Use drip irrigation, soaker hoses, or other techniques that reduce soaking the entire plant. In situations where a sprinkler system must be used, apply the water in the early morning when leaves are already wet from dew.
A second technique is to apply fungicides to protect plants. Fungicide sprays can help prevent diseases on roses, tomatoes, and many other plants. The fungicide will not “cure” damaged leaves but it will help to prevent fungi from infecting additional foliage. Of course, always read and follow all label recommendations whenever you use a pesticide.
Correct pruning can aid in reducing disease. Thinning cuts allow better air circulation so that plant foliage dries more quickly. Pruning overhanging limbs may open garden areas to the drying rays of sunshine.
When possible, you can also use resistant varieties. Some homeowners spray my roses at home to prevent Black Spot disease. The roses in front of my house, however, are resistant “KnockOut” roses that have remained healthy with no fungicide spray. It’s a good example of how a resistant variety can be used to reduce fungal pressures.
During periods of wet weather keep on the lookout for signs of plant disease.
Contact us at the Extension office if you need help with disease identification or fungicide recommendations. Then you can enjoy a rainy day without worrying about your plants.
Richard Evans is the Bryan County UGA Extension Coordinator. You can reach the Bryan County Extension Office at uge3029@uga.edu or call (912) 6532231