Monday, May 19, 2008

Nursery and Landscape - What to do About Fire Blight Infections

Fire blight strikes are evident in landscape plantings. Fire blight affects rose family plants, most commonly apple and pear, but also crabapple, hawthorn, mountain ash, cotoneaster, pyracantha, and spirea. What should be done with fire blight infections? The following are recommendations.

Growers and landscapers dealing with infected trees are often tempted to remove fire blight infected branches as soon as they see them. In many cases, this would be the wrong strategy, because removing branches can encourage new shoots to develop and these new shoots would also be susceptible to new infections. If fire blight strikes are discovered early, before leaves have turned completely brown, timely removal of infected shoots can help slow the spread of the disease. However, most growers do not discover the disease early enough for this to be helpful. So what is to be done with infected trees now?

Growers should just let the disease run its course, allowing the tree defenses to stop fire blight spread within the tree. Dead shoots and branches should be removed later in summer, after the plant has stopped the infection or better in winter when there is little chance of spreading the disease.

Some growers may feel compelled to cut out fire blight infections, possibly for cosmetic or aesthetic reasons. What then? If pruning is begun after obvious symptoms appear, cut back in the direction of a healthy internode of at least two-year-old wood, leaving a stub several inches long. Rely on the tree's natural defenses to prevent further movement into the branch. If needed, paint the stub with bright paint to make it more obvious. This stub can then be safely removed in the winter. Leaving infected stubs rather than pruning all the way back to the main branch reduces the chances for development of undesirable water sprouts in response to pruning.

The reason not to prune infected branches back to a spur or crotch in summer is because it may not be noticed in winter and could be overlooked. It should not be necessary to sterilize cutting tools between cuts if only blighted shoots are being removed.

Do not engage in normal summer pruning and training at the same time as fire blight removal without wiping the cutters with sterilizing solutions like Lysol, 70% alcohol or 10% bleach. Don't forget to remove the infected stubs along with dead shoots and cankers next winter.
Do not apply chemical controls such as streptomycin. They are only effective if used during the normal bloom period. Remove trailing blooms to prevent late spring and summer infections.

Fire Blight Symptoms. Photo by Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services,

Adapted from "FIRE BLIGHT-WHAT NOW?" By John Hartman in the May 31, 2005 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.

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