John Dominic Crossan
Crossan does not discuss this cluster in [The Historical Jesus].
Some of the Fellows were willing to concede that Jesus may have spoken something along these lines (partly due to the similarity with Matt 3:10: "Even now the axe is aimed a the root of the trees. So every tree not producing fruit gets cut down and tossed into the fire.") However, the saying could also be a proverb better attributed to the common lore of the Second Temple Jewish community. [Five Gospels] (202)
Luedemann [Jesus] (192) notes the way this saying accentuates the criticism of Jesus' Jewish opponents, but does not address the question of its provenance until he treats Thom 40:1-2. There (page 610) he attributes Matt 15:13 to the Matthean redactor, and concludes that Thomas is dependent on Matthew for this saying.
John P. Meier
Meier does not discuss this saying in the first three volumes of A Marginal Jew.