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Act Now to Prevent Diseased Plants

October 24, 2001

It is so hard to convince homeowners to act now to prevent disease problems next year. After all, how do we know last year's actions did any good? We don't see the disease, so it must never have been present. Please trust me on this one because I see plenty of samples each year that do have problems. If you decide to do nothing, then I may be hearing from you next May when you send samples to the Plant Clinic.

Many gardeners wait until a problem occurs, then try to correct it by asking for a quick chemical cure (which usually does not exist). Ask instead: What can be done now to help prevent disease problems in the lawn and garden? Many problems are best controlled with preventive measures. Chemical rescue treatments may act as temporary Band-Aids, but they are usually not the answer for long-term disease control. These fall lawn and garden cleanup procedures help prepare plants for winter and discourage disease problems.

1. Keep grass mowed until it stops growing. This practice helps prevent winter injury and damage from fungal snow mold diseases.

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 that may transmit oak wilt fungus.

3. Prune trees and shrubs to remove dead and seriously cankered wood and any crossing or interfering branches. Open up the center of woody plants to promote faster drying, let in more light, and reduce foliar and stem diseases. This practice helps prevent fire blight on rosaceous hosts, anthracnose and fungal leaf spots of trees, bacterial leaf spot of Prunus species, and many other diseases.

4. Provide winter protection for roses, evergreens, thin-barked young trees, and other sensitive plants. Winter wounds often become infected with secondary canker fungi, such as rose cane canker.

5. Prune tree and bush fruits according to the recommendations of Extension horticulturists.

6. Remove and burn compost where possible, or bury plant debris to help reduce foliar and stem disease next year. It is usually safe to compost leaf material, but diseased stem and root tissues should be burned or buried, not included in a compost pile.

7. Look over seed and nursery catalogs and select resistant varieties. Plant them where you've had problems 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 that shows a flower and fruit color 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 to reduce soilborne pathogens that cause Rhizoctonia and Fusarium root rots. This is also a great time to amend soil to improve soil drainage. Phytophthora and Pythium root rots are problems in poorly drained areas.

9.Divide perennial flowers where it is appropriate, remove rotted or diseased parts, and replant them in a new location. Let the cut edges dry a day or two before replanting to avoid soft rot bacteria and other soil-borne root rots.

Taking these measures does not guarantee a lack of disease in your garden, but it will help reduce the incidence of disease.

Author: Nancy Pataky


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