Air temperatures during February 3^rd and 4^th dropped well below freezing throughout the vegetable production areas in Yuma County, Arizona and Imperial County, California. According to Arizona Meteorological Network (AZMET) data, the duration of time with air temperatures below 32°F during February 3rd and 4th, respectively, was 4 and 6 hours at the Yuma Valley, 6 and 9 hours at the North Gila, and 7 and 9 hours at the Roll AZMET stations. Plants were subjected to additional time periods when temperatures were above but close to freezing. Freeze injury damages and kills plant cells. Chilling injury is more subtle, with symptoms not appearing for some time after the event. The damage sustained by crops is a function of temperature, duration of exposure, the physiological age of the plant, type and variety of plant, and the type of plant tissues affected. Freeze and chilling damage can result from physical damage of plant cells, disruption of plant photosynthesis and respiration, interruption of nutrient and water mobility, and accumulation of toxins. Plants weakened by exposure to freezing or chilling temperatures may become more susceptible to colonization by microorganisms that will cause additional damage.

To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.