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.