With warm temperatures and further rainfall expected, the second spray should be applied within two days of the first a late afternoon, early evening application on Sunday or Monday would be optimal. Your first application may need to be today on high-risk cultivars. (Although, note that there is a chance of rain even today, Friday, May 22, and EIPs are in the 90s on the Ridge. The first spray should be applied prior to the first rain event, predicted to occur on Saturday, May 23. This current situation will require a minimum of two to three antibiotic applications for successful blossom blight management. Your fire blight risk will also be extreme as flowers open. In orchards further north where flowers are not yet open, the occurrence of many consecutive warm days leading into bloom is very concerning. Free water from rain enables the fire blight bacteria to “swim” down the style from stigmas to the nectaries at the base of the flower where these bacteria cause an infection.įire blight risk will be extreme this weekend on the Fruit Ridge as orchards are coming into full bloom. Rain events will trigger fire blight infection events on flowers that harbor very large populations of the fire blight pathogen. At these temperatures, populations of the pathogen can double in size every 45 minutes on stigmas during overnight growth. Temperatures in the high 70s to low 80s are optimal for growth of the fire blight pathogen on apple flower stigmas. The EIP value is telling us the potential is there for significant fire blight infection. The MaryBlyt model on Michigan State University Enviroweather is predicting EIPs (Epiphytic Infection Potential) for fire blight as high as: Also, the forecast of intermittent rain showers is concerning remember, only 0.01 inch of rain is needed for a blossom blight infection to occur. Our work has shown that the fire blight pathogen mostly grows at night on apple flower stigmas. Three other factors will contribute to this major fire blight risk: daily low temperatures in the high 60s and high relative humidity favor extreme overnight growth of the fire blight pathogen. Forecast temperatures in the low to mid-80s for the next week have significantly increased the risk of blossom blight infection in orchards with open bloom. Temperatures over the past several days, from May 20 to 22, 2020, have been in the 60s and could have allowed the initial buildup of the fire blight pathogen.
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