Definition from Wiktionary, the free dictionary
cornstalk (plural cornstalks)
- (botany) The tough, fibrous stalk of a corn (maize) plant, often ground for silage after harvest.
- (botany) A single specimen of a corn plant once past the seedling stage and which may, at maturity, bear multiple ears of corn.
- (Australia, slang, obsolete) A non-indigenous person born in Australia. 
- (Australia, slang, pejorative) a non-indigenous native of New South Wales. 
- He's a bloody cornstalk.
- 2001 December 21, Peter Marshall, The Cambridge Illustrated History of the British Empire, Cambridge: Cambridge University Press, ISBN 978-0521002547, page 272: A few decades earlier he[a non-indigenous person of Australian birth] would have been nicknamed a ‘cornstalk’, a sarcastic reference to the way in which Australian children, like colonial wheat, grew fast and gangly; but labels could change with great rapidity, and by 1882 ‘cornstalk’ had become a caustic term for the New South Welsh.