Burrknot

Symptoms

A rough, warty growth occurs above the soil line on dwarfing rootstocks. The growth generally is circular or spherical. Bumps are root initials (the beginnings of new roots). Knots can increase in size during the growing season. Small, normal-looking roots may be present if the burrknot is partially buried. Trees with severe burrknot can be stunted or girdled or break off in high winds. Adjacent burrknots can increase in size faster than the normal trunk and can girdle the tree. A heavy crop load also can cause the tree to break at the knot. Burrknot has also been observed on the branches of susceptible cultivars in western Washington and Oregon.