Fire Blight Spray Considerations with Recent and Oncoming Warm Weather
With the extreme heat wave we have experienced in the recent several weeks, pears have been in active bloom for some time and were under risk from infection by fire blight on 22 March. The NEWA’s Infection Potential EIP value reached over 100 on March 22 and the EIP color field was changed to dark red indicating infection on pear flowers was possible with wetting event(s) in Rustburg, Charlotsville, Roseland, Madison, Red Hill, and Sperryville, VA. Please check the fire blight model at: https://newa.cornell.edu/fire-blight/ RIMpro Erwinia model also reported infection was possible on 22 March in Roseland VA.
Early apple cultivars like Pink Lady are at 30% bloom in Roseland VA as of yesterday, and south of it other early cultivars are also in bloom, especially crab apples. The risk for fire blight infection is predicted with wetting event on 27 March in Rustburg, VA. Check for your location by selecting closest NEWA weather station to your farm. You must keep an eye on NEWA’s fire blight model every day from now on and apply streptomycin prior to the day when Infection Potential EIP value reaches 100 and the color field around this number turns into dark red. That means all conditions for fire blight infection have been met. Make sure you select the accurate First Blossom Open Date in its specific box in the model so as to make the model work correctly. You also have a function to select Streptomycin Spray Date so you can see how the model re-calculates the EIP risk of infection.
Remember, a wetting event can be heavy dew, rain, or spray water when you apply fungicides (if you did not add antibiotic into the tank). Therefore, since the risks are wetting event dependent, apply your streptomycin in mix with LI700 or Regulaid within 24 h before a wetting event triggering an infection (dark red field and EIP at or over 100). Also, add streptomycin with surfactant when you plan a fungicide spray application during the periods when the EIP field is orange and EIP value is at or above 100. Orange filed and EIP 100 means that one condition for infection out of four is missing, and it might as well be a wetting event. That is why if you spray, the water you provide can create that necessary condition for infection to occur. Add fungicide(s) to streptomycin to make the spray more economical. To determine your next streptomycin spray application, use the spray date selection function in the NEWA’s EIP Fire Blight model – scroll down on the page and you will find it – it is placed below the Wetness Events Table and looks like this:
In periods of extreme risk for infection for several days continuously, which is EIP of 100 or above and dark red fields around it, make sure to use this function, as when you enter the spray date, it will re-calibrate the model and it will tell you when next infection will occur and when you must apply the next streptomycin. With the oncoming warm weather, new flowers will be opening every day and these newly open flowers are not protected with a previous streptomycin application if they were closed when you applied it the first time. Be very careful to not underestimate fire blight in this way as blocks of 4-7 days during bloom with infection events predicted every day have occurred in previous years and in these cases you need to apply streptomycin almost every second day. To determine exact day when to spray next you should use this streptomycin date function in the model. Please open the NEWA’s EIP model available here: https://newa.cornell.edu/fire-blight. It is the right column of colored rectangles under the string “Infection Potential EIP value, Risk Levels:” Here are previous risks of infection for 22 March for pears in bloom and oncoming risk for 27 March in Rustburg, VA, and Westfield, NC, shown below. The reason why some locations have infection predicted on 27 March and some don’t is because of patchy rain predictions in the weather forecast:
