They are heat stressed. It also looks like you might have spider mites (or some other type of infestation). Give them some shade for the hottest part of the day (if above 90 degrees). Buy some neem oil for the pest (if you can) if you want to go the cheep way for the pests. Mix up 2 cloves of garlic, 1 table spoon of chili powder and 2-3 drops of dish soap with 2 gallons of water. Put into spray bottle and use in the morning. Let it sit for 2-3 hours and then respray them with clean water to wash them off. Do this everyday for a week and you should see them improve.