neighborhood garden for july 16, 2016
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HEAT PROBLEMS IN THE garden
by george edgar
With the extreme high temperatures
we have been experiencing in Nebraska, we can expect some problems with
vegetable fruit set and quality. The ground around green beans may be
littered with aborted flowers. Flower and fruit abortion are common
responses to heat stress as a result of the general failure of
successful pollination and fertilization. Many people are concerned most
about their tomatoes and cucumbers. Another problem can be a lack of
female flowers, often noticed in summer squash.
As the heat increases, the ratio of male to female flowers
changes to more, or exclusively, male flowers. When cooler weather
prevails the plants will shift back to a more normal ratio.
A lot of
research has been done on tomatoes and especially FRUIT SET in tomatoes.
Day temperatures over 90 degrees F and night temperatures over 70
degrees F reduces fruit set.
Another problem
related to heat stress in tomatoes is LEAF ROLL. During mild spring
weather, top growth is more vigorous than root growth. When drier summer
weather occurs, the abundant foliage transpires water faster than the
root system absorbs it. The plant compensates by rolling its leaves to
reduce surface area. Also the leaves may become thickened. The symptoms
may occur after cultivation, heavy rains, or a sudden change in weather.
This condition is usually temporary and the plant will recover on its
own. To prevent leaf roll, keep soil evenly moist (not too wet, not too
dry) and avoid cultivation that damages roots.
Also tomato
problems related to high temperature are SUNSCALD and SOLAR YELLOWING
(yellow shoulders). Sunscald occurs when previously covered fruit are
exposed to direct sunlight, e.g. when foliage wilts or a branch breaks
off in the wind. Cultivars with sparse foliage may be more prone to
sunscald, or plants that have lost foliage to any of the numerous tomato
foliage diseases including early bight and septoria.
Solar yellowing
or yellow shoulders is a type of sun scald and occurs when lycopene (the
red pigment in tomato fails to develop and leaves only the carotene
(yellow) pigment to show at the shoulder. This occurs when tissue
temperature rises about above 86 degrees F.
Heat stress can
also cause bitterness in many vegetables. For example, broccoli,
zucchini, and lettuce form bitter compounds as a result of heat stress.
Generally, fruit that sets and develops later, after the more moderate
temperatures return, are ok. Also, fruit that became fully sized prior
to heat stress may not develop bitterness. Muskmelon may also turn
bitter but this is more closely related to bacterial wilt or other
diseases that affect healthy leaf development.
The last
problem I want to mention is BLOSSOM END ROT. Blossom end rot causes
sunken, water soaked lesions near the blossom end of the fruit that
eventually turns black. It is most often seen on tomatoes but can also
be a problem on other vegetables such as squash and cucumbers. It is
caused by a shortage of calcium in rapidly developing fruit. This
problem can occur even though the soil has an abundance of calcium. It
is associated with rapid plant growth and quick fluctuations in soil
moisture. In Nebraska it is typically most severe during periods of hot
daytime temperatures, low humidity, and windy conditions. The disease is
also more serious when excess nitrogen fertilizer has been applied.
During rapid growth the calcium in the soil is used by the plant for
growth and does not provide enough for the fruit.
This problem
usually happens to the first fruit. The condition is temporary and the
plant will recover and produce good fruit later. Copyright 2016 |