black canker

Noun

black canker (countable and uncountable, plural black cankers)

1. Any of several plant diseases causing the formation of dark cankers.
   • Scab and black canker is rapidly destroying Salix vitellina in Nova Scotia. Ten per cent of the trees surviving from previous years were killed. The damage caused by these two diseases can not be estimated separately.1927, Plant Research Institute (Canada), Annual Report of the Canadian Plant Disease Survey
2. The larva of the turnip sawfly (Athalia rosae), an agricultural pest having the appearance of a black caterpillar.
   • Among the numerous enemies to which turnips are liable, none have proved more fatal here than the black canker (a species of caterpillar) which in some years have been so numerous as to cut off the farmer's hopes in a few days.1783, William Marshall, Account of the black canker caterpillar, which destroys the turnips in Norfolk, Royal Society, page 1
   • 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, author unknown, Hardwick's Science Gossip, page 232

   Synonyms:

   black jack, black palmer, nigger