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vigorous. To establish the best anchorage, early practices
must encourage vigor; otherwise trees on M-26 will need
support. With good early management, trees with M-26
rootstock are early and heavy bearing. M-26 is susceptible
to fire blight and woolly aphids and is only moderately
tolerant to collar and root rot. Trees on M-26 are not
drought-tolerant.  M-26 acclimates slowly and, like
MM106, is susceptible to low, early winter temperatures
but very hardy during mid- and late winter.
M-26 rootstock is recommended only with
fireblight-tolerant varieties and only to growers
willing to provide intense management. Plant in deep,
well drained soils only. It is not recommended for
course textured soils.
M-9. This rootstock is propagated by layering and
stool beds and is multiplied from one clone. Vigorous
varieties on M-9 are 35 to 45 percent the size of those on
seedling rootstock. Spur varieties and less vigorous
varieties on M-9 are smaller and very dwarf. While M-9
may be more vigorous on deep, well-drained, loamy soils
than on sandy loam or shallow soils, the roots are very
brittle, and trees on M-9 are poorly anchored. All varieties
with M-9 need support in the form of a stake or trellis.
Trees on M-9 are early bearing and very efficient. M-9 is
the most resistant stock to collar rot and tolerates low
temperatures throughout the winter. It is not drought-
tolerant and is very responsive to irrigation. It is
susceptible to woolly aphids, and it suckers freely,
making it also susceptible to fire blight and mice.
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M-27. This rootstock is propagated by layering and
stool beds. Vigorous scion varieties are suggested on M-
26 because of its dwarfing habit of growth. Most scion
varieties on M-27 are 25% or less the size of these same
varieties on seedling rootstocks. Less vigorous or spur
type varieties may be "runty," very small, and poorly
anchored. Intense management and supplemental soil
moisture is needed to grow trees on M-27. All varieties
on M-27 are very precocious bearing the second year of
planting. Trees on M-27 rarely send out root suckers.
M-27 is susceptible to woolly aphids, powdery
mildew, fire blight, and early winter low temperatures.
Mailing 27 is very small and therefore not
recommended for commercial orchards unless special
conditions pertain.
MARK or MAC 9was developed at Michigan State
University. It is propagated by layering and stool beds.
Stamen, Jonagold, Braeburn and Granny Smith have not
done well on MARK because of the brittle union. When
planted with the union, well exposed aerial burr knots
have been observed. This will enhance disease and insect
injury. MARK is susceptible to fireblight, woolly aphids
and droughty soils. It is fairly tolerant of root rot.
Trees on MARK have developed potentially
damaging growth at the soil line and have ceased to
be supported by the commercial nurseries and fruit
programs.
Virus-Free Rootstocks. Trees indexed and
maintained free of known harmful apple viruses may be
slightly larger but are healthier and more productive.
Only virus-free trees and rootstocks are recommended.
Interstems. Grafting a 10- to 14-inch stem piece
scion to a rootstock makes interstem trees. The stem
piece scion recommended is Malling-9, and the rootstock
is MM111. The scion variety is budded 7 to 12 inches
above the union of the interstem piece and the rootstock.
The advantages and weaknesses of all three pieces are
combined.
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