Are modified/controlled atmospheres useful for pumpkins and winter squash? We want to store pumpkins longer than we can achieve currently with just ambient temperature storage.
First there are many factors that affect the postharvest storage potential of pumpkins and winter squash. Production conditions, variety, careful harvest to avoid injury to the stem end and fruit surface, and adequate curing all contribute to obtaining good storage life. For short periods (1-2 months), pumpkins and winter squash can be stored in the range of 10-25C (50-77F), but after this initial period, chilling symptoms may appear on those stored as low as 10C and excessive water loss and surface drying will appear on those stored at 20-25C. The recommended storage temperature is 15C (59F).
Long before exploring the use of a more costly technology such as controlled atmospheres, you should work on optimizing the storage temperature of the pumpkins—15C is a good target storage temperature. After doing that, the focus should be on managing relative humidity. Generally about 70% RH will provide a good balance between minimizing weight loss and favoring decay organisms. To my knowledge, controlled or modified atmospheres are not used on winter squash and pumpkins. There is limited research in this area. A recent study at the University of Georgia compared CA (3%O2 + 5%CO2) stored fruit with ambient conditions (air) and found the former to yield more marketable fruit after 2-3 months. However, the CA was conducted at 10C, so the positive effect was a combination of temperature and CA. In other tests on winter squash, atmospheres with about 7% CO2 helped reduced degreening, but this would be of little benefit to pumpkins harvested at full color.