As a follow up to the discussion on last Monday’s Eco-Apple conference call, John Aue has this to say about when to start degree day models for apple scab:
Start your models January 1. The reason to start them at this time is because over 5% of ascospores may be mature by the time green tip begins.
For example, this year at Sauk County Orchard, we have the following data:
Jan 11- 1% of spores mature
March 10-2% of spores mature
March 21-5% of spores mature
Mar 26- 20% of spores mature
Apr 2 – 36% of spores mature
This indicates that we may have a lot of pressure of mature ascospores this season on some farms.