Pear and Apple Fire Blight: Maryblyt Predictions Can Aid in Disease Management

Bob Mulrooney, Extension Plant Pathologist;

Adapted from an article in Ky Pest News April 6, 2010 #1224 by John Hartman, Extension Plant Pathologist, University of Kentucky.

Flowering pears (Pyrus calleryana), grown in many landscapes, are in full bloom in most of Delaware. Pears grown for fruit in backyards and orchards in the region are also in flower now. Fire blight can be a devastating disease of nursery and landscape flowering pears and can also damage pears (both Asian and European) in fruit orchards.

Fire blight primary infections occur during bloom. During warm spring weather, the causal bacteria (Erwinia amylovora) grow on the surface of flower parts such as the stigma. After several warm days, high populations of bacteria become available to be washed by rainfall or even heavy dew into the nectaries at the base of the flowers. Once inside the flower, the bacteria continue to grow, killing the fruit spur and spreading into the subtending twigs and branches. Disease build-up from these infections leads to shoot infections, the most noticeable part of this disease, which appears later.

This year, a new version of a computer program called Maryblyt has become available to help nursery growers and orchardists make decisions to manage fire blight disease. This new version of the program, called Maryblyt 7, utilizes Windows-based computers and was updated by plant pathologists Dr. A. R. Biggs (Tree Fruit Research and Education Center, Kearneysville West Virginia) and Dr. W. W. Turechek, (USDA-ARS, Florida). They have indicated that it is free for the downloading by growers, extension agents and crop advisors.

Go to the following link to download a copy of the new Maryblyt 7 program.

This is a good time for growers to get the program running for the 2010 season. Growers can enter the data themselves and the program automatically provides a chart and graph of fire blight status. Growers only need to provide date, growth stage, daily maximum and minimum temperatures, and rainfall (or heavy dew) for their nursery or orchard. Weather data are entered into the program starting at green tip (perhaps sometime between March 21-24 this year) so weather data from recent weeks will need to be found. Growers wanting weather data specific to their orchard or nursery can purchase a maximum/minimum thermometer and a rain gauge at the hardware store. By knowing when infection is expected, preventive orchard and nursery applications of streptomycin can be used in a timely way.

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