- Author: Richard Smith
- Author: Steven Koike
During this time of year, there are various weather issues that affect lettuce. Frost damage can often occur during the cold, clear nights in the winter and spring. Interestingly, frost damage on lettuce causes some classic symptoms that are easily recognizable and some that are a bit surprising. Different types of symptoms can be caused due to differences in the severity and duration of low temperatures, as well as the age and location of the leaf tissue. One of the more common symptoms of frost damage on lettuce is when the outer leaf cuticle separates from the underlying cell tissue; this can result in a bronzed look to the leaf, which is probably due to the death or damage of the surface epidermal cells (Photo 1). More severe frost conditions may cause necrotic interveinal lesions as well as necrotic spotting on the leaves (Photos 2 and 3); such symptoms could resemble those caused by heat damage or pesticide burn. Occasionally the tips of young leaves are killed, and as the leaf continues to grow, the leaf may curl around this dead area (Photo 4). Sublethal frost damage tends to occur towards the edges of the leaves and causes thickening and roughening of the texture of the leaf tissue (Photos 5 and 6). Lettuce is mostly tolerant of temperatures near freezing for a short period of time, though plants will grow more slowly. Freeze damaged leaves that are not removed from heads may break down, decay, and cause post harvest issues.
Growers and others in the field should be aware of how very low temperatures can also damage other crops, such as cauliflower transplants (Photo 7), that are present during this time of year.