CO2 continues to not ravage US crops: This year, only as many as 14 amateur growers have been able to raise pumpkins topping 1,500 pounds; "they speed photosynthesis by spraying their plants’ leaves with carbon dioxide"

The Race to Grow the One-Ton Pumpkin - NYTimes.com

This fall’s pumpkin contests have begun, and as many as 14 amateur growers have won regional weigh-offs with entries tipping the scales at more than 1,500 pounds. The contests are far from over — they continue in force over the next two weekends — but already one pumpkin, raised by Dave Stelts of Edinburg, Pa., has come within three pounds of beating the 1,810-pound record set last year. Rumor has it that a record-breaker may emerge in California.
...they speed photosynthesis by spraying their plants’ leaves with carbon dioxide.