When the first of the dwarfing rootstocks were released, the testing procedures were not as elegant or elaborate as they are today. East Malling-Long Ashton researchers were looking largely for rootstocks that would grow smaller, more precocious trees with higher quality fruit. They accomplished those goals, but ended up with a bunch of other issues like fireblight, woolly apple aphid, cold susceptibility, replant issues, and more. Even so, they’ve survived for almost 75 years as very popular rootstocks that are used quite extensively to this day.
When the next major round of rootstock research was cranked up at Cornell, they knew they needed to address some of these issues in addition to searching for rootstocks that were equally or more productive. The Cornell-Geneva rootstock series was run through the gauntlet early in the process to eliminate any rootstocks that for the most part were susceptible to any and all of the above. Yes, some of the rootstocks are susceptible to some of the above issues. But their other benefits outweighed the negatives and so they were moved on through the selection process. In the end, there are approximately 13 Geneva rootstocks that are considered ‘elite’, because of their large combination of productivity, precociousness, and resistance to fireblight, woolly apple aphid, cold susceptibility, replant issues, and more.
Needless to say, I am generally impressed with the Geneva rootstock series despite the fact that they are still new to the industry and many aren’t fully field tested – especially on the potentially virus-laden cider varieties – there are a number of types that I can recommend. They provide many benefits to orchardists of all scale without the issues associated with rootstocks like the M9 series. Of course, while they may appear very good right now, it took years for the failings of the Malling rootstocks to come through. Of course, testing standards and rigor are much better than they were in the early 20th century, so hopefully we know what we need to know before planting.
The only true caveats with dwarfing stocks is that that they all need support. These rootstocks keep trees small because they have smaller, shallower root systems. Without support, and especially on a tall spindle type of training system, they will likely fall over. And they will also require more attention to soil moisture status – whether that is from irrigation or not, you’ll need to keep on top of it. Trust me on these two things.
- G41 – the smallest of the ones I’ll recommend here. Resistant to everything we’ve discussed above and its cold hardy. Similar in size to the industry standard M9 T337.
- M9 (T337) – the standard of the industry for almost 40 years now. It is dwarfing, precocious, easy to manage – everything you’d want as an orchardist. But it is highly susceptible fireblight and woolly apple aphid, two things that will likely keep away from using this stock unless you are up to the challenge of managing them.
- G935 – next up in the size sequence, while G935 seems to have the most potential as a dwarfing rootstock in cider orchards, there are concerns over its hypersensitivity to common apple viruses. It is a slightly larger tree than G41, susceptible to woolly apple aphid, but resistant to everything else we’ve discussed – and cold hardy. Similar in size to the industry standard M26.
- G202 – Basically A G935 with less cold-hardiness (maybe) and woolly apple aphid resistance. Similar in size to the industry standard M26.
- G222 – yet another step in size, very good cold hardiness, resistant to everything we’ve discussed here except replant complex. It doesn’t appear to be as strong as G935 or G30 in unfumigated sites, so allowing your land to rest between orchards is important. Similar in size to the industry standard M26/M7.
- G30 – another that’s been out there for a while. Seems to be working well, though it is not resistant to woolly apple aphid. Apparently is miserable to grow in the nursery, but makes a nice tree. Similar in size to the industry standard M7.
Know Your Roots 