Outdoor grow problem please help

1st outdoor grow without nutrients at all and regular soil . Moved plant from side of garage (concrete) to middle of grass for more sunlight.My Gardner came by and may have put something in the grass to kill weeds. From September 20th to now there has been a drastic change. I've slowly noticed that about 75% of the leaves are yellowing. Could that be due to the Gardner or nature taking its course? What should I do? Please help. See attached pics.

looks like a severe lack of food to me.

That's just nature taking it's course and it's a little more intense in your situation because lack of food .....but that's normal just more pronounced in your situation because you
Opted not to feed them that's all

nature doing its thing using up all the sugars etc in the leaves