black canker noun2 •Any of several plant diseases causing the formation of dark cankers. •The larva of the turnip sawfly (Athalia rosae), an agricultural pest having the appearance of a black caterpillar.In some seasons these pests are exceedingly numerous, and in the Eastern Counties the “Black Canker,” as it is called, lays waste entire fields of turnips. — 1869 formsblack cankers
