Hi all. I thought that I would post my results from my 2016 rootstock trial. This trial was for my own use, but I thought that someone else might find it useful. Zone 4b Maine growing conditions are quite different than much of the country, and rootstocks grow different than is often reported in warmer climates.
I trialed 4 newer rootstocks against the old standard Malling 4, which is becoming extremely difficult to find for some reason. If someone knows of a source of M4 in wholesale quantities, please let me know. To give perspective on how M4 grows in my area, it will easily grow 30+ feet tall if you let it.
This past spring, I grafted 5 different cultivars on each of these 5 rootstocks, and grew them in a row a couple feet from each other. The soil was not irrigated, but the water level is only about 10 feet below the surface. All of the the trees have now gone into dormancy, so I took measurements and took a few notes. Inches are rounded to the nearest quarter inch.
Average height increase = 29.75 inches
Notes: New wood is very flexible, which is a commonly known issue of M4, and should be staked for the first few years.
Average height increase = 25.25 inches
Vigor: 85% of M4
Notes: New wood is very flexible, similar to M4.
Average height increase = 25.5 inches
Vigor: 86% of M4
Notes: New wood is stiff, but can be bent without any feeling like it will crack. Bend it down and it snaps right back like a spring.
Average height increase = 15 inches
Vigor: 50% of M4
Notes: New wood is stiff, but flexible to a point. Bend it too much and it feels like it will crack.
Average height increase = 23.75
Vigor: 80% of M4
Notes: New wood is stiff, but flexible up to a point like Geneva 935. 4 out of 5 roots had black lesions on them, which look to me like early stages of canker. Nowhere have I read that B118 is susceptible to canker, so maybe this is something else. Picture below.