- Author: Sally A Logan
In my research for a solution to save the Bartlett Pear trees; first treatment was ‘pruning back’ to 12 inches below the infected area and still the trees might not survive!! Oh my!! After seeing the beautiful Bartlett Pears from the two trees, I could not bear to have them die! What to do?! Research revealed that the recommended treatment was a European mixture called ‘Bordeaux’. Named for the discovery of its effectiveness in the vineyards of France. ‘Bordeaux’ is a mixture of copper sulfate & calcium hydroxide (slaked lime). This Bordeaux mixture, although considered ‘organic’, has many disadvantages along with a reputation as one of the few solutions to stop ‘fire blight’ in Bartlett Pears. One of the suggestions in our research was also to choose another type of pear; Bartletts are particularly susceptible to Fire Blight, while other types are more resistant.
Some of the disadvantages of the ‘Bordeaux’ mixture are the following:
- Must be mixed just before use.
- Copper in the mixture can stain everything touched, a blue color
- Copper can build up in the soil, if used too often and kill any earthworms present
- Can injure leaves if used after the trees break dormancy
- Not compatible with most other pesticides
- Longer time to prepare and safety precautions must be taken
- Corrosive mixture
- Raw ingredients not readily available in smaller quantities for the home gardener
Just because it’s considered ‘organic’ does not mean it is the safest possible means of treating for ‘Fire Blight’.
Another, lesser problematic solution is, ‘fixed copper fungicide spray’. Possibly less effective, but the disadvantages are also much less than the ‘Bordeaux’ mixture. Fixed copper sprays would be; tribasic copper sulfate, copper oxychloride sulfate and cupric hydroxide. These preparations don’t stain blue and don’t last thru winter rains the way the ‘Bordeaux’ mixture will. These sprays are considered to be the most effective for use after winter rains in the spring.
If you choose the ‘Bordeaux’ mixture; there is a recipe and instructions on the IPM website at the following URL address; www.ipm.ucdavis.edu; look for publication #7481. Whether you choose ‘Bordeaux’ or one of the fixed coppers, covering the tree thoroughly is very important for the best results. Another publication with #7414 on the website discusses the disease itself, and gives detailed descriptions of the path of the Fire Blight organism. Publication #7414, titled simply, FIRE BLIGHT, gives some hope for our Bartlett Pear Trees; “In general, trees are more susceptible when young and suffer less damage as they age”, according to the authors. The ‘Fire Blight’ publication recommends the following for ‘managing’ the disease:
- Excess nitrogen fertilization & heavy pruning should be avoided, since young tender shoots are the most vulnerable
- Remove and destroy fire blight infections thru pruning.
- If fire blight infections have been a problem in the past, apply blossom sprays
Should chemical control be needed, use one of the copper products listed above or a Bordeaux mixture of .05%, very weak. Apply as blossoms open and apply as blossom period continues to the end; possibly 5-12 applications.
Fire Blight has no easy answers, but planting less susceptible varieties, pruning back infected areas and copper sprays seem to offer some hope for the backyard orchard.
**University of California ANR, Publication 7257; Pamela M. Geisel is UCCE Farm Advisor of Fresno County, Carolyn L. Unruh, UCCE staff writer and Paul Vossen, UCCE Farm Advisor in Fruits, Vegetables, and Marketing for Sonoma and Marin counties
***Sunset Garden Book
****UCIPM-ANR (Agricultural and Natural Resources) website; Publication 7481, ‘Bordeaux Mixture’, also Publication # 7414 and Publication 74126