Selecting Pome Fruit Crops and Varieties - Growing Organic Orchard Fruits - page 165

Geneva 30 (G30) is more precocious and productive than M7, has good dis-
ease resistance, and is probably a better choice for organic growers, espe-
cially in eastern North America. Do not use G30 with 'Gala'. Avoid Ottawa
3 (O3), which has proven susceptible to fire blight, wooly apple aphids, and
tomato ringspot virus and has been reported to provide poor rooting.
Large Trees (16 to 25 feet tall)
Large orchard trees are seldom recommended today, due to pest and disease
problems, high labor requirements, poor labor efficiency, and poor yields per
acre. The following rootstocks produce large trees, typically 16 to 25 feet
tall in ideal conditions (25 feet being considered a full size or standard tree).
Some organic growers continue to use these vigorous rootstocks in areas
where cold, adverse climates cause poor tree growth on more dwarfing root-
stocks. Some organic growers who maintain grass sod throughout their orch-
ards and up to the tree trunks also prefer these vigorous rootstocks, which
compete better against the sod than more dwarfing rootstocks.
The MM106 rootstock produces trees 65 to 75 percent standard size and
is resistant to wooly apple aphid. While the tree is vigorous and has good an-
chorage, its susceptibility to root rot and damage from fall frosts makes this
a poor choice for organic growers.
The MM111 rootstock produces trees 80 to 85 percent standard size,
is well adapted to droughty soils, is moderately productive, and comes into
bearing rather slowly. This rootstock is best used for adapting to droughty
sites and with an interstem for size control. An M9 interstem on an MM111
rootstock produces a medium-sized, freestanding tree.
The M4 rootstock provides slight to moderate size reduction, resists collar
rot, and can be used for freestanding, spindle-trained trees. This rootstock
has been popular in Denmark, Holland, Germany, and British Columbia.
Alnarp2(A2) rootstock is used mostly in Sweden, but it occasionally appears
in North American nurseries. This rootstock provides good anchorage.