Over the years, we discuss plant disease problems and talk about the fact that stressed plants are more susceptible to insect and disease problems. Now that gardening demands have slackened, why not spend some time improving plant health? Plant health is a very important management tool for disease and insect problem prevention. Taking the part of the devilís advocate, I suppose we wonít ever really know our actions did any good. If we donít see the disease or insect, then we assume it must never have been a threat. Research has shown over and over again that stressed plants are more susceptible to disease, more likely to be injured by insect infestations, and more likely to decline than vigorous plants that are not under stress.
Many disease problems are best controlled with preventive measures. Chemical rescue treatments may act as temporary Band-Aids but are usually not the answer for long-term disease control. These fall lawn and garden cleanup procedures will help prepare plants for winter while discouraging development of disease problems.
- Keep grass mowed until it stops growing. This helps prevent winter injury and damage from fungal snow mold diseases. If you donít have a mulching mower, remove leaves from grass in the fall, also to prevent fungal snow mold development.
- Prune oak trees in the dormant season to reduce the risk of oak wilt. Pruning from September to early March is recommended because pruning during the growing season causes sap flow, attracting bark beetles, which in turn may transmit the oak wilt fungus.
- Prune trees and shrubs to remove all dead and seriously cankered wood, as well as any crossing and interfering branches. Opening up the center of woody plants helps promote faster drying, lets in more light, and reduces foliar and stem diseases. This is a common practice to help prevent fire blight on rosaceous hosts, anthracnose and fungal leaf spots of trees, bacterial leaf spot of Prunus species, as well as many other diseases.
- Provide winter protection for roses, evergreens, thin-barked young trees, and other sensitive plants. Winter injury causes wounds that become infected with secondary canker fungi. Many of the rose cane cankers infect such injuries. Check with local Extension specialists about timing for applying winter protection.
- Prune tree and bush fruits according to recommendations by Extension horticulturists. Pruning at the wrong time can cause more cankering and dieback.
- Remove and burn (where possible), compost, or bury plant debris to help reduce foliar and stem disease next year. It is usually safe to compost any leaf material; but diseased stem and root tissues should be burned or buried, not included in a compost pile. A tree infected with Verticillium wilt should not be chipped or composted. It should be burned or removed from the site.
- Look over a variety of seed and nursery catalogs. Select resistant varieties and plant them where youíve had problems in the past but have no rotation options. Choosing disease-resistant hybrids, varieties, and species is usually the least expensive and best long-term method of disease control. If you have had problems with scab on crabapple, consider replacement with a scab-resistant variety showing flower and fruit color that you prefer as well. Try to obtain a variety that is also resistant to powdery mildew and rust.
- Make a map of your flower and vegetable gardens. Rotate annuals to another area of the garden to reduce soil-borne pathogens that cause Rhizoctonia and Fusarium root rots. Now is also a great time to make soil amendments to improve soil drainage. Phytophthora and Pythium root rots are known problems in poorly drained areas.
- Divide perennial flowers (where appropriate), remove rotted or diseased parts, and replant in a new location. Let the cut edges dry a day before replanting to avoid soft rot bacteria and other soil-borne root rots.
- Water stressed trees and shrubs periodically until hard frost. Much of Illinois experienced severe drought this summer, and we will be seeing the effects of that drought this fall, winter, and next spring. Trees and shrubs suffer root injury in those times but may not show wilting. Plants that exhibited early fall color, leaf rolling, or dieback are stressed plants. Water these to promote root growth now. Late-fall or early-spring fertilization with a balanced fertilizer will help promote growth on these stressed plants.
Of course, these measures will not guarantee no plant disease in your garden, but they will help reduce disease incidence.