HEy

this is just water that fell on the leave and burned the leave. How? a water droplet act like a magnifying glass: it emplifys the solar rays (like a magnifying glass on wood or pater it burns). So if its outside (it looks to me that this plant is outside) just be careful to not water the leaves and only the dirt. And dont do a leafe fertilisation, when you spray dissolved ferts in water on the leafes, very bad if not done propely and if its done in sunligt or MH/HPS ligts.

Anyway have fun i hope this will help and remember: if there is only one leafe that is affected (or less than 5 ) dont panic, otherwise, chek out for moving dots or something)

Have fun

Canna