Vermont Apple IPM Alert
L.P.Berkett, IPM Specialist
April 24, 2001
Stage of Bud: Green Tip at UVM HRC
Apple Scab Ascospore Maturity: Upon examining 15 pseudothecia dissected out of about five scabby, overwintered leaves from underneath non-sprayed McIntosh trees at the UVM HRC, I did not see any mature ascospores and saw no discharged asci (sacs). What I did see were many robust looking asci per pseudothecia (i.e., the fungus overiwntered well). Only in two pseudothecia did I start to see the outlines of ascospores within the sacs, and in only one ascus did I see ascospores that started to approach maturation (i.e., their cell walls were thicker and spores started to turn yellowish).
It must be remembered that this is a very, very small sample. However, based on what I saw I would say that the fungus overwintered well underneath the blanket of snow and the snow perhaps kept the fungus "chilled" so that we do not have a high percentage of mature spores to contend with just yet -- but they will be here !
Remember -- pseudothecia from orchards in warmer locations than the UVM Hort. Res. Center are probably further along. UMass is reporting 5% mature at Groton, MA and Amherst, MA.