Blight means anything which obviously damages (the crop), by rain, hail, locust, blast of wind, or fire.
Sunan Abi Dawud Book 24, Hadith 56
← Previous Hadith The Messenger of Allah (ﷺ) as saying: If you were to sell dried dates to your brother and they were smitten by blight, it will not be allowable for you to take your brother's property unjustly.

Sunan Abi Dawud Book 24, Hadith 55 Next Hadith → Blight is not effective when less than one-third of goods are damaged. Yayha said: That has been the established practice of Muslims.

Sunan Abi Dawud Book 24, Hadith 57