Fireblight (apple, pear, see above right) and Apple Scab (apple, see below) diseases are normally reproducing and spreading this time of year. We have been more concerned about Apple Scab. The cool weather has really reduced the activity of fireblight bacteria but the risk of fireblight will increase with temperatures >18C.
Continue to protect new growth for Apple Scab sincemore wet weather is on its way, with fungicides (such as Banner, Captan/Maestro, Dithane, Luna, Fontelis) Mix single-site fungicides such as Luna or Fontelis with a general fungicide such as Captan or Dithane to reduce possibility of resistance. Protect new foliage with fungicide before rain events.
Keep an eye out for powdery mildew as it can overwinter in the buds. If you haven’t been putting on Captan/Maestro or Dithane, try mixing Nova or Fontalis or Manzate with Captan or Dithane in your next fungicide application to help manage powdery mildew on nursery crops.
The Fireblight prediction models are showing low-medium levels of caution this week based on the weather forecast but the possibility of fireblight increases dramatically if the weather becomes warmer and wetter. Foliar (floral) applications of products for Fireblight (such as copper, Kasumin, streptomycin) should continue to reduce numbers of fireblight bacteria on floral structures (stigmas) throughout the bloom period. The floral stigmas are the main entry point for fireblight into the tree.
Fireblight is a lower concern right now because the crop is not in full bloom yet and we’ve had cool temperatures. The Ontario Fireblight Prediction Models can be found below: