Apple Scab Moving Right along with Tree Development
As trees in the warmest parts of the state are either at or fast approaching green tip, it is time to start thinking about scab. To gauge maturity, we made observations from last year's scab-infected leaves, collected from under unsprayed trees. The good news is the vast majority of leaves we have sampled in the Amherst area have undeveloped ascal sacs. You can't even see the beginnings of ascospores. The bad news is that a few leaves have immature but developing ascospores. Based on this, we feel that we are from 1 to 2 weeks from the time when there will be enough mature spores to cause scab infections. In areas where trees are at 1/2 in. green or more today (4 April) then continued warm weather could generate mature inoculum as early as next week. In other areas, it will be somewhat longer, again depending on temperatures.
