Disease fungi are microscopic plants that take their energy from the plants on which they live--they parasitize the plants in the landscape. Fungal diseases exhibit a number of distinctive symptoms, often indicated by their names. Downy mildew and powdery mildew create pale patches on the leaves of the plants. Rusts can be identified by their rusty color on leaves. Leaf spot causes round, yellow spots on the leaves that darken over time. Many fungal diseases can be controlled or even eliminated by proper yardcare practices. Not all fungal diseases are found in all parts of the country. When you spot a problem in a plant, rule out possible environmental problems before looking for a fungal cause.
Symptoms of Fungal Diseases
The following symptoms may indicate a fungal disease of some kind:
Pale patches on leaves.
Chlorosis (yellowing of leaves), specifically round spots or irregular yellow-green spots that darken with time.
Dead spots or sections on leaves.
Water-soaked or greasy appearance on leaves or stems.
Sudden death of small seedlings.
Fungal diseases tend to spread over the entire plant somewhat slowly, occurring over weeks rather than days, whereas problems caused by viruses or bacteria spread quite quickly. This does not mean you can wait to confirm you have a fungal problem, because the low toxic fungicides are not very effective in controlling the disease if it is well established in the plant.
Control of Fungal Diseases
What is very important to understand is FUNGAL DISEASES CANNOT BE CURED! You cannot bring back that part of the plant that has turned brown or yellow or lost its leaves. FUNGAL DISEASE CAN BE STOPPED FROM SPREADING ANY FURTHER AND IT CAN BE PREVENTED NEXT YEAR IF YOU KNOW WHEN IT IS LOOMING.
Treatment of fungal diseases varies depending on the disease. In some cases, you should simply remove the affected leaves. However, in most cases, you should leave the plant alone and begin some control strategy using fungicidal sprays or dusts. Discussions of the diseases in the individual plant files in Yardener’s Helper offer specific control steps, but in general, once you've decided your plant has one of the fungal diseases, such as rust or black spot, it often can be arrested by the application of an appropriate fungicide. Fungicides are not a cure. They are a tool to stop the spread of a fungal disease that has occured or they are a tool to use to prevent an expected fungal disease from getting started. For detailed information about the fungicide products commonly found in garden centers go to Fungicides in Yardener's Tool Shed
Preventing Fungal Diseases
The best way to prevent fungal diseases in your yard and garden is to use varieties of plants that have been bred to be resistant to those diseases. Resistant varieties are not always available, but when they are, try the plant to see how you like it. Some varieties of plants are susceptible to certain fungal diseases and should be avoided if those diseases are problems in your landscape.
Most fungal spores are spread by the wind and by rain bouncing them up onto plants from the soil. Using mulch around your shrubs and in your gardens prevents this by acting as a barrier. Use drip irrigation to avoid the splashing of water that occurs with overhead watering. If you must water overhead, then do it before noon so the sun will dry off the moisture on the leaves, eliminating the moist environment the spores need to multiply.
If fungal diseases are a serious problem in your area, especially if you live in a hot, humid climate, provide maximum spacing between the plants in your landscape to encourage good air circulation around those plants. Fungal diseases thrive in hot, damp areas with poor air circulation. The better the air circulation, the faster the plants will dry after a rain or after overhead watering. This rule also applies to shrubs and trees. If fungal disease is a problem with those plants, they should be pruned so that the tree canopy allows light and air to reach the interior of the tree.
Critical to preventing any serious fungal disease is a very thorough yard and garden cleanup in the fall, which reduces the overwintering sites for fungal spores.
It is always wise, if fungal diseases are a problem anywhere in your yard or garden, to keep your tools clean. Some homeowners keep handy a covered 5-gallon pail with a common household bleach solution made of one part bleach to four parts water or a copper fungicide solution mixed according to the directions on the container. Dip shovels, rakes, and hoes in either of these solutions after working in the yard and garden around vulnerable or infected plants. After disinfecting your tools, coat them with oil to avoid any rusting.