possible from properly looking after a smaller number.
PEST AND DISEASE RESISTANCEWHEN CHOOSING ROOTSTOCKS
With the industry movement toward integrated pest management, it is vital that we stay with
woolly apple aphid resistant rootstocks.At present, most of our orchard plantings are on tolerant
rootstocks.This means that the small proportion planted on susceptible rootstocks such as M.9,
M.26 and Mark are not under heavy infection pressure, thus making woolly apple aphid control
relatively easy. If the proportion of susceptible rootstocks increased markedly, we can anticipate
substantially more difficulty with woolly apple aphid infestation of susceptible rootstocks.
development.Until these rootstocks become commercially available, I believe trees propagated
using M.9 or Mark interstock on our standard rootstocks are our best option.
spectacular. A word of warning about fire blight infection of M.26.Over the years we have
heard stories from the USA of M.26 trees being killed by fire blight at the bud union as a result
of systemic infection travelling down the tree from a strike in the scion.This season I came
across this type of fire blight infection here.It appears as if it may become a problem where
susceptible varieties such as Gala are grown on M.26 in warmer districts which favor fire blight
activity.We, therefore, need to be very diligent about fire blight control for orchards planted on
this rootstock.
date, I have not come across reports of problems with tree deaths due to fire blight infection to
the union.Until we have something better, these M.9 or Mark interstocks with either MM.106 or
M.793 rootstocks look to be our best options.