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| Interveinal (between the veins) chlorosis (yellowing) |
In desert regions, we
sometimes notice that plants growing under higher temperatures develop
yellowing of the leaves when exposed to intense sunlight for long periods of
time. This yellowing does not appear to be associated with a lack of any
particular type of nutrient such as iron or manganese, a common problem in desert soils. We don’t see the typical
micronutrient deficiency symptoms such as interveinal chlorosis; yellowing
between the veins while the veins remain green. I have talked about this in
previous postings, probably relating to intense sunlight. Usually, growing
tomatoes under light shading (no more than 30%) during times of intense
sunlight helps to alleviate this problem.
the University of California, Hunter Johnson, explains it much better. He is talking to green house growers but the message is the same. Reduce intense sunlight on tomatoes for better color development. I
borrowed this posting from a University of California publication several years
ago. http://vric.ucdavis.edu/pdf/TOMATO/tomatoes_HomeGarden.pdf
occurs beginning in the late spring months under greenhouse conditions, or from
that period on through the summer in the open field in inland areas where
daytime temperatures regularly exceed 85OF. An accurate term for
this condition is “solar yellowing” because the source of the problem is
the sun. It isn’t only the heat of the sun or the temperature increase in the
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| Tomatoes not developing good red color in heat |
fruit that creates the problem, but also high light intensity. This was shown
by Dr. Werner Upton, who coined the term “solar yellowing” in
research he conducted on the subject in 1970. His treatments involved shading
or painting the fruit either black or white. Black-painted fruit were higher in
temperature than exposed fruit, but discoloration was highest in the exposed fruit.
His conclusion was that short-wave radiation was largely responsible for
defective coloration.
yellow-orange color, rather than the normal red, is that the red pigment
(lycopene) fails to form above 30OC (86OF). This phenomenon was
first described by researchers in 1952 and was later confirmed by others. When
lycopene fails to form, only carotenes remain for fruit color. In the field,
some red color forms when day temperatures rise above 85OF because
of fluctuation in noninhibiting temperatures during other parts of the day or
night. An orangey-red color results.
not exceed 85OF, much higher red color develops.
develop, high temperatures should be avoided and fruit should be protected from
short-wave radiation in high light intensity areas.
sprays of non-phytotoxic whitewash will help. In greenhouses, growers who
intend to mature fruit in May and June should begin to alter their pruning practices
in March by allowing two leaves to develop on axillary branches instead of the
standard practice of removing these branches.
retired University of California Cooperative Extension Vegetable Specialist,
Riverside Campus.