84F + and you are loosing yield without the supplementation of co2. That is the highest I ever see without complications.
As the heat increases, so do the plants metabolism. They need higher levels of co2 to sustain that temp. They basically start to eat themselves alive, and photosynthesis comes to a halt.
As far as recomendations to reduce your heat, there isn't much we can say without knowing about your setup and ambient temps. Ambient temps are something people don't consider much, the temp outside of your cab or room also dictate what is going on inside. Whatever your situation is big or small, you can:
Increase exhaust and intake
lower your ambient temps aka intake air
add an AC (not effcient in a non sealed setup but will help if you can throw some dollars at it)
Be creative, is there a place in your house where you can pull cool air from?
Are you exhausting the hot stale air outside I hope?
If its a decent sized setup just throw some money at it to get it right. Either way 98F and your yield and quality will suffer, if you finish your plants at all. We are having a crazy heat wave this year, but I just pulled down some of the highest quality herb I have ever produced, it can be done. June, July, August eat new growers alive.
I started having problems WITH CO2 in the 94-98F range. Obvious heat stress symptoms. I never had heat problems before I used CO2. Different set up. The only real atmosphere problems I've had atmospherically are high humidity during the light off cycle. That shits a bitch.
Although the high 90's will diminish your yields, you can still pull successful harvests in that environment.
open the door to your cab, get the air moving w/in the room the cab is in, open windows, etc etc or get A/C.
pretty damn obvious, but there's only so much you can do when you're blasting a de facto space heater within a very small space in the middle of summer.
