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Hello all:

     From my experience here in SE Pennsylvania I can not recommend Mark rootstock.  I have had a number of Greenmantle red/pink fleshed varieties on Mark, purchased as benchgrafts.  I planted them in pots for a year and then moved them to the orchard about 1998 or 1999.  Everything was fine until 2007 when I had my first experience with fireblight.  I lost about 1/4 of the 60 or so trees I had, and the vast majority were on mark or M26.  This year, even spraying with streptomycin, I lost a couple more trees-again on Mark.  
     The trees on M26 included fireblight succeptible varieties (Mott Pink, Webster Pink Meat, Esopus Sptitzenberg) and some that were not supposedly too succeptible (Cortland comes to mind).  They died from the top down.  I kept cutting back strikes until there were virtually no limbs to cut back and the trunk showed infection.  They were then dug out. 
     In both 2007 and 2008 the varieties on Mark where I had not seen strikes or  cut them out seemed to be OK until late July or August, when the leaves turned brown almost overnight.  The branches showed symptoms of drying out.  When I dug up the trees, the Mark rootstock was dead.  The trees are all staked so there are no graft union breakage issues.
     I've since tried to graft surviving varieties on Mark and M26 to less succeptible rootstock.  M9 is supposedly a little less succeptible so I've tried some M111/M9 interstems.  I also grafted onto Geneva16 and Bud9.  I will be grafting more onto Geneva16 and 30 next spring.
     Interestingly, I have a Gala on a Geneva rootstock that I bought from Rocky Meadow about 10 years ago.  Although Gala is supposed to be fieblight succeptible, the tree has not had any visible strikes and no dieback. Just lucky I guess.  In Spring 2007 I also planted a Caville Blanc on Bud 9 as a replacement for one on M7 that blew over when loaded with apples (trees on M7 do need staking in heavy clay soils).  Fireblight hit the tree and I had to cut it back to a stub about 6" above the graft union.  I thought it was shot but this past spring it pushed out from a latent bud and regrew a leader.  In late June deer nibbled the leader down to the top of the trunk guard so I had to put an additional guard above the first.  It continued growing so I will be interested to see how it does next year.  The survival of the tree seems to confirm my suspicion that Bud9 is much less succeptible to fireblight than Mark. I hope my emperical experience helps in deciding what rootstocks to choose and use.  Chris Patterson

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