Establishment and Management of Compact Apple Trees 



William J. Lord and Joseph Costante 

 University of Massachusetts 



Part 2 



Rootstocks 



Commercial interest in size-control rootstocks developed in 

 the early 1950's in Massachusetts. Presently, those in most 

 common use are the clonally propagated Mailing (M.) and 

 Malling-Merton (MM) rootstocks. The degree of dwarfing 

 induced by these rootstocks is shown in Table 9. A descrip- 

 tion of these rootstocks and seedlings follows as well as a 

 summary in Table 10 of the characteristics of the common 

 and less commonly planted rootstocks. 



Table 9. Apple rootstocks presently used in Massachusetts 

 and their relative degree of dwarfing. 



Apple rootstock 



Dwarfing (%) 

 of seedling trees^ 



M.9 

 M.26 

 M.7 



MM 106 

 MM 111 

 Seedlings 



30-50 

 45-60 

 55-75 

 75-90 

 80-90 

 100 



-Degree of dwarfing will vary with variety and soil type. 



M.9. This is a true dwarf rootstock (Table 9) and can be use- 

 ful for specialized orchard culture by commercial growers. 

 It is a century old, thus well known. This rootstock has a 

 brittle root system which means each tree will need to be 

 supported by a post or by a trellis. It is a very suitable root- 

 stock for high density plantings. Interest in this rootstock is 

 increasing for use in "pick-your-own" orchards. On a good 

 site, with good soil and management, cultivars on M.9 can 

 be productive. 



Virus-tested M.9 rootstocks (free of all known viruses) are 

 becoming available. Preliminary data from the Netherlands 

 show that; (a) cultivars on virus-tested M.9 rootstocks grow 

 more vigorously than those on virus-infected M.9's; (b) virus 

 tested trees usually produce larger yields than virus-infected 

 trees; (c) the yield efficiency (poundsof fruit/unit of growth) 

 of the virus-tested trees is equal to or higher than virus-infect- 

 ed trees; and (d) fruit quality is also usually better for the 

 virus-tested trees. The stronger growth of virus-tested trees 



could be advantageous on poorer soil but a disadvantage for 

 high density plantings on strong soils. 



Cultivars on M.9 are well suited for trellising or the slender 

 spindle type of training with a single post parallel to the 

 trunk for support. Apple varieties differ in vigor on M.9 with 

 weaker growing types like Idared, Empire, Golden Delicious, 

 and probably MacSpur easier to train as slender-spindles than 

 Red Delicious, Mcintosh or Cortland. Slender-spindle trees 

 will be described elsewhere. 



M.26. This is one of the new clones from East Mailing from 

 a cross of M.I 6 and M.9 and introduced to the U.S.A. about 

 1 958. Its roots are brittle like the M.9 but trees on this root- 

 stock have better anchorage. Whether or not trees on M.26 

 are going to require support is still questionable. At present, 

 we have found temporary support necessary on windy sites 

 and when nursery stock quality was poor. 



An overgrowth of M.26 forms below the graft union and 

 burr knots (adventitious roots) form on the stock. It does 

 not suckei as much as M.7. Trees on M.26 produce earlier 

 than those of M.7 and it propagates well in stool beds. It is 

 not resistant to wooly aphids or to collar rot. It is reported 

 to be very winter hardy. M.26 requires well-drained soil for 

 optimum performance. 



M.26 is gaining popularity in Massachusetts orchards but 

 many questions about this roostock remain unanswered: 

 anchorage, soil requirements, whether loss from fireblight 

 will be a problem, and scion/rootstock effects on growth and 

 fruiting. Therefore, it is suggested only for trial. We have 

 observed no serious problems but our experience is limited 

 to 6 years. 



M.26 looks very promising in Michigan. They have lost a 

 few trees in commercial plantings, but these have been on 

 low, wet heavy soils. Michigan reports that M.26 will sup- 

 port a free standing tree. To the contrary, researchers in 

 western New York are rather "cool" toward M.26 because 

 of its susceptibility to fireblight and its sensitivity to "wet 

 feet." It requires a well-drained sandy, loamy soil without 

 the tendency to drought (Table 8). 



M.7 is the best stock we have to give a semi-swarf tree. 

 Twenty years of commercial experience with M.7 has proven 

 its reliability under our conditions. Cultivars on this root- 

 stock come in bearing early and continue to produce good 

 annual crops. M.7 is not without its faults-it produces suck- 

 ers from the roots, it tends to lean, particularly when budded 

 to Red Delicious, and it is susceptible to wooly aphids. 



