By Mike Matheron, UA Extension Plant Pathologist

Air temperatures Feb. 3 and 4 dropped well below freezing throughout the vegetable production areas in Yuma County, Ariz. and Imperial County, Calif.  According to Arizona Meteorological Network (AZMET) data, the time duration with air temperatures below 32 degrees Fahrenheit was four and six hours at the Yuma Valley, six and nine hours at the North Gila, and seven and nine 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 the 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.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.