what's wrong with my plants?? HELP please!

i am growing these two plants in a greenhouse and they are about 3 weeks into flowering. the leaves are turning yellow/brown and dying. not sure what the problem is. help would be greatly appreciated!

Dude, on that entire grow I spotted what, 4 yellowing leaves on 2 plants that are about half way through flowering. You are fine. That is natural this time of the grow. The plant is extracting stored nitrogen from the oldest growth (bottom leaves) and it will work it's way up slowly as the buds mature.

Look at your first pic.... all the surrounding leaves look great, causing that one leaf to stand out and grab your attention. If you look at the overall condition of your plants, you'll see that you only have a few yellowing leaves. It is my opinion that your grow is doing fine.

Because it is only a few select leaves, you may want to examine for signs of pests in their early stages as a precaution. Make sure to look at the bottom of the affected leaves as well.

Good luck, hope your harvest is plentiful and something to be thankful for.

nothings wrong they do that in flowering