Sunday, June 10, 2012

Fire Blight Damage on Flowering Pear

Homeowners continue to question me concerning management of fire blight in flowering pear, crabapple, cotoneaster, hawthorn, and pyracantha.  Shepherd’s crooks and spur dieback occurred in March or April, as pathogenic bacteria infected flowers or young shoots.  Often, homeowners do not notice damage until later in the season, and inquiries continue for weeks after damage occurred.

There is no management option during this time of year, as the fire blight bacterium is not currently active.  Hot summer temperatures suppress bacterial growth, and plants are able to compartmentalize and wall off spread.  Thus, visible symptoms are the result of early infections. 

Current recommendations indicate that pruning of blighted twigs and cankered branches should be delayed until winter when risk of disease spread is lowest.  Under certain circumstances, homeowners or commercial landscape contractors may choose to prune infected branches during the growing season.  Only young, vigorous trees should be considered, and care should be taken to prevent bacterial spread.  Always avoid working with wet plants.  Cut branches at least 6 to 8 inches below cankers, disinfesting pruners between each cut (10% Lysol disinfectant, 10% bleach, or rubbing alcohol).  Ideally, winter pruning is recommended. 

Disease management includes both cultural practices and preventative bactericides.  Because the fire blight bacterium overwinters in cankered branches, removal of diseased plant tissue before bud break (mid to late winter) is critical.  Copper applied as buds swell (late dormancy or silver tip) reduces build-up of bacterial cells, especially during warm rainy spring seasons.  Streptomycin applications are only recommended for fruiting apple and are not labeled for use in the landscape. 

See earlier posts for more information on the biology of the fire blight bacterium and for management in orchards.


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