I would wager over-feeding too, but that one photo alone without more detailed information really prevents anyone from giving you an accurate diagnosis to be honest.
^^I tend to disagree on the feeding thing above, though...proper dosage from start to finish precludes the need for a "flush" with just about every medium other than soil, and so many people hit their girls with so many different products only to basically cancel them all out that I feel 95% of growers over-feed from the get-go and that is why they run into issues.
For example, I run only tap water (not even left out overnight to dechlorinate, just straight tap water), Canna A, and Canna B from the third week of veg throughout the end of flowering...I just yielded ~85g dry from one plant, looking to be at about 125g from another when it's fully dry, and at least 100 from the third, and did not flush at all...in fact, I literally fed directly up until the cut. Granted, this is coco, which is a soil-less medium and much more like hydro than soil, but I have buddies who slap a shit-ton of carbo-loads and silica blast and other such crap into their coco and then wonder why their plants look unhealthy and they yield half of what I do from the same strains and twice the wattage.
Sorry to go off on a tangent, I just think feeding as a whole should be approached differently in the interest of maximum yield and quality...hoping the OP posts some more detailed information so we can help him out a bit.
edit- when I say "more information," I'm talking about the specifics of your medium and environment, especially:
-pH
-EC
-ppm (if e&f/other hydro application as it appears)
-RH/temp
-Lighting intensity/spectrum
etc.
thank you for replying...
