Severe fire blight blossom blight risk for May 20-23

Risk of blossom blight infection in Michigan orchards will be extremely high for the next three days. Orchard blocks of susceptible varieties should receive full covers of Kasumin or streptomycin at two-day intervals.

As an update to the Michigan State University Extension articles posted last week on blossom blight control (“Fire blight risk increasing this week: treatment options in east Michigan and Benzie-Manistee area” and “Fire blight risk increasing: treatment options in counties affected by Section 18 for Kasumin”), the EIP values predictive of infection potential have gotten significantly higher in response to the very warm temperatures we experienced through the weekend (May 18-19, 2013).

EIP values are extremely high and as high as:

These numbers predicting fire blight infection have not been this high since 2005, our last major fire blight year. Thunderstorms are predicted beginning this afternoon (as of Monday, May 20) through Wednesday. The first rain event that occurs will trigger a fire blight infection as the water will enable the fire blight pathogen to migrate from flower stigmas to nectarthodes where it infects flowers. Rain will also facilitate spread of the pathogen among flowers and between trees. Any trauma associated with the storms will facilitate shoot infection.

Any orchard with open bloom will be under severe risk of fire blight infection. Orchards at petal fall will be at risk if the storms cause trauma injuries that facilitate infection.

Prior to today’s rains:

Ensure that a full cover of Kasumin (2 quarts per 100 gallons) is on trees in counties where the Section 18 is applicable. A full cover of streptomycin should be on trees in other counties. This is not the time to use an alternate row strategy.

Other considerations:

With conditions as they are, a second application of either Kasumin (Section 18 counties) or streptomycin (other counties) should be applied within two days. Thus, if you sprayed Sunday (May 19), make the next application Tuesday (May 21) or spray Monday and Wednesday. The second application is needed because fire blight bacteria will continue to grow rapidly over these next several warm days. Also, in northwest Michigan, new flowers will continue to open and need to be protected. SPRAY EVERY ROW!

Apogee should be or should have been applied at king bloom petal fall. It takes 10 to 14 days for the “Apogee effect” to take place and initiate tree growth inhibition and control of shoot blight infection.

Dr. Sundin’s work is funded in part by MSU’s AgBioResearch.

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