Can someone help identify my problem

[Kurtweb]

This yellow stuff started appearing on some of my fan leaves and the pistils are turning brown very early I’m Growing Autoflowers in coco can someone please help thanks

 

[ArtfulCodger]

If the "yellow stuff" wipes off, then I have no idea. If it's just interveinal yellowing of the leaves, you might be over-lit.

 

[GNick55]

yep could be your light or calmag def or etc? more pictures of all the plant?
coco been buffered?
what you feeding it?

 

[Ponky]

If you look on the underside do you see black dots and silver streaks?