M9-337 Produces a tree that is approximately 30/35% the size of standard seedling. Trees grown on M9-337 do require support due to brittle root systems that lead to poor anchorage. This rootstock tends to produce large fruit and is tolerant to heavy soils. It does show resistance to collar rot, but is susceptible to fire blight. This rootstock is not recommended for light soils as it does struggle under drought conditions. M9-337 is recommended for high-density plantings.