But agriculture experts were unable to explain why chemical-free melons were exploding. They cited the weather and abnormal size of the melon as factors... [One farmer] said he had used chemicals to boost their growth on 6 May, and the following day more than 180 melons exploded. Mr Liu was reported to be the only farmer from the 10 households who used chemicals.

Wang Dehong, who has been farming watermelons for 20 years, couldn't understand why his fruit also exploded as he had not used any chemicals.
B.B.C. News