The latest Lunch ‘N Learn webinar on July 3rd heard Dr David Rosenberger, Plant Pathologist and Professor Emeritus from Cornell University speak on summer disease management in apples, particularly flyspeck, sooty blotch and bitter rot. The presentation can now be downloaded below.
Key take home messages:
- Preventative fungicide programs should continue later into the summer on 2-3 week intervals depending on product used and residue wash-off, especially with late-maturing varieties and ahead of conditions conducive to disease development.
- If symptoms appear prior to harvest, that is likely a sign that fungicide residues were totally depleted 14-21 days prior. The appearance of symptoms may even occur after harvest.
- If using sensors to determine leaf wetting hours for flyspeck and sooty blotch management, use 185 hours, not 270 hours from the original developmental model as most sensors are now electronic rather than string. If not using sensors, consider risk of these diseases starting typically late June or early July.
- Bitter rot, on the other hand, favours hot, humid weather so is often of greater concern mid to late summer.
- Ideal fungicide programs tend to use mancozeb early summer before switching to captan (high rate alone or mixed with Senator or Inspire Super as long as scab is not an issue) and Pristine as a late summer / preharvest choice.
- pH can affect activity of captan; read all labels carefully as mixing with products that require higher or more neutral pH such as Phostrol (compared to the US registered phosphite fungicide, ProPhyt) could reduce captan’s effectiveness.
- Cultural management is important to reduce inoculum: 1) remove nearby wild or alternate hosts such as raspberries or blackberries which harbour flyspeck and sooty blotch; 2) clean up rotten fruit, dead wood and prunings and move them to row middles to be shred by flail mower; 3) reduce tree stress by irrigating, especially ahead of a heat wave.
Click on the following links to download this presentation:
Accessible format: Ontario Apple Webinar_Summer Disease Management_2019 07 03_accessible