Chorothalonil based fungicides can cause rind burn on the upper side of mature watermelon fruit before harvest (typically indicated in the product label as do not use starting 21 days before harvest).

Small discolored light green patch on watermelon rind. Intense heat and sunlight, drought, poor vine canopy and other environmental conditions that favor sunburn increase damage.

A light green and large discolored patch on upper side of watermelon fruit. The symptoms are typically seen on fruits not fully covered by leaves.

Burning and yellowing of the rind of mature watermelons sprayed with chlorothalonil. Exposed fruits tends to be more at risk to the damage and hence careful use of the fungicide is critical.