Preventative Disease Control

Because this past spring was wetter and warmer than most, many plants are showing signs of fungus type diseases. Many homeowners have forgotten, because of dyer seasons, that these diseases are a natural occurrence in damp conditions.

Although these afflictions are normal and usually won't kill a plant during the first year they appear, they can destroy the plant, in time, if left untreated.

Fungus diseases thrive when days are cloudy, moist and the humidity is high or a lot of rainfall has occurred. The spores for maladies are transported through the air from many sources including debris, or on dead and diseased sections of the plant itself.

"Black Spot" on roses and "Apple Scab" on crabapples are two examples of characteristic fungus diseases. How they are prevented is essentially how similar blights are treated. However, what they are treated with varies. Your local garden center can show you which treatments will most likely prevent or, at least, help control which disease.

Black Spot appears as dark brown spots on the leaves of rose bushes. The leaves then yellow and drop off. It is caused by a fungus, which travels by way of spores in the air or splashed by raindrops. The best treatment is prevention. Even though it is too late to prevent the first attack this year, spraying now can help check subsequent infection for the balance of the year. Fungicide can be applied as either a dust or spray. Both work well, however spraying is likely to be more thorough and lasting. It should be applied after each rainfall for the remainder of the summer because the rain washes away the fungicide residue.

Even with no rain, the materials will break down and should be used every 10-14 days to prevent reinfection.

You can also prevent Black spot and others disease through selective pruning to open the plant up to better airflow. This allows the plants to dry more quickly in the early morning and after rains, which reduces the dampness in which most diseases thrive.

For roses, prune away entire stems growing in the center of the plant. Cut on a slight angle about one-eighth of an inch above an outside facing bud. This will promote the growth of new stems to the outside of the plant and away from the middle, opening the rose bush to better air circulation.

Apple Scab is also a fungus, which initially appears as dark brown spots on crabapple leaves, eventually turning the leaf completely yellow. It, too, is preventively controlled with fungicide, which should be applied every one to two weeks during the time from first bud break on through spring into the early summer season. When it is very rainy, it should be applied every three to five days.

Crabapples also need pruning in order to control the threat of disease. Many varieties of crabapples have very dense foliage. Pruning and thinning out the branches allows sunlight and air movement to reach the center of the tree, dry out the leaves and reduce the dampness in which Apple Scab thrives.

Fungus diseases are a natural occurrence under damp conditions, but you can combat them with appropriate preventive treatments and pruning. When selecting new plants, inquire about those that are naturally more resistant to fungus. Many new varieties are available.