Rashi on Exodus 9:31/רש"י על שמות ט׳:ל״א

1והפשתה והשערה נכתה AND THE FLAX AND THE BARLEY נכתה — i. e. were broken; it has the same meaning as in, (2 Kings 23:29) “Pharaoh-Necho (נכה)”, which denotes Pharaoh the lame i. e. broken in so far as the power of his legs is concerned (cf. II Samuel 9:3); (Isaiah 16:7) “brocken (נכאים)”, and so too לא נכו (v. 32), “they were not broken”. It would not be correct to explain that it is connected in meaning with the word that signifies “smiting”, הכאה, for a נ cannot take the place of a ה that one may explain נֻכָּתָה as being equivalent to הֻכָּתָה, and נֻכּוּ to הֻכּוּ, but the נ is a root-letter in the verb, and the word נֻכּוּ is of the same grammatical form as the verb in, (Job. 33:21) “and all his bones are laid bare” שֻׁפּוּ (i. e. Pual of כי השערה אביב

2כי השערה אביב FOR THE BARLEY WAS IN THE EAR — it had produced its first ears and it stood on its stalks; these were therefore broken and fell. So, too, the flax had already grown and had become hard enough to stand in its capsules.

3השערה אביב means [THE BARLEY] STOOD IN RIPE STATE, similar in meaning to, (Song 6:11) “[to look at] the ripe plants (באבי] of the valley”.