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How to Prevent Plant Disease

October 8, 2003

Most of us readily accept the notion that, if we take care of ourselves, we are less likely to have health problems. Of course, there is no guarantee that we wonít become ill; but our own actions often prevent disease problems. Why then is it so difficult to convince homeowners that action now can help prevent plant disease problems next year in their plants? Plant health is an 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. Please trust horticulture and plant pathology specialists on this topic. 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 gardeners wait until a problem occurs, then scramble to correct it. The next step usually involves asking for a quick chemical cure (which usually does not exist). Consider instead what can be done now to help prevent future disease problems in the lawn and garden. 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 help prepare plants for winter while discouraging development of disease problems.

  1. Keep grass mowed until it stops growing. This helps prevent winter injury and damage from fungal snow mold diseases. Remove leaves from grass in the fall, also to prevent snow mold development.
  2. 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 may transmit the oak wilt fungus.
  3. 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.
  4. 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.
  5. Prune tree and bush fruits according to recommendations by University of Illinois Extension horticulturists. Pruning at the wrong time can cause more cankering and dieback.
  6. 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.
  7. 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. Try to obtain a variety that is also resistant to powdery mildew and rust.
  8. Make a map of your flower and vegetable gardens. Rotate annuals to another area of the garden to reduce soilborne 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.
  9. Divide perennial flowers (where appropriate), remove rotted or diseased parts, and replant in a new location. Let the cut edges dry a day or two before replanting to avoid soft rot bacteria and other soilborne root rots.
  10. Water stressed trees and shrubs periodically until hard frost. Much of Illinois experienced 6 to 8 weeks of drought in the summer of 2002, a dry fall and winter, and additional drought stress this past summer. Trees and shrubs suffer root injury in those times but may not show wilting. Plants exhibiting early fall color, leaf rolling, or dieback are stressed plants. Water them to promote root growth now. Late-fall or early-spring fertilization with a balanced fertilizer helps promote growth on these stressed plants.

Of course, these measures cannot guarantee a lack of plant disease in your garden, but they can help reduce disease incidence.


Author: Nancy Pataky

 

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