This is the
VOA Special English Agriculture Report.
Alternate
bearing is a widespread problem for growers of citrus and other fruit trees. It
can affect a large area or just individual trees or even part of a tree. No, it
is not a disease. Alternate bearing is when a tree produces a heavy crop one
year, called an "on-crop," followed by an "off-crop" the
next year.
On-crop trees produce a
large number of small fruit with little value. Off-crop trees produce no fruit
or a small number of large fruit that often have thick, unappealing skins.
 |
| Mandarin trees heavy with fruit in an on-crop year |
Citrus
growers know that the number of fruit in their current crop has an inverse
effect on the number of flowers in the return bloom. In other words, if one
number is big, the other number will be small.
Two researchers recently did a study to
understand how this happens. Johannes Verreynne is now at Stellenbosch
University in South Africa. Carol Lovatt is at the University of California,
Riverside. They studied "Pixie" mandarin trees in the Ojai Valley of
California. Mandarin oranges are also known as tangerines.
The study showed that fruit on the tree
reduces the next bloom by stopping buds from appearing. This limits the number
and length of summer and fall shoots. As a result, there is a reduction in the
number of nodes, or joints, that produce groups of flowers along stems. Fruit
on the tree during spring bloom stops the growth of flowering shoots.
During
an on-crop year, growers often treat the fruit so it can stay on the tree
longer. The purpose is to extend the harvest season. Yet Carol Lovatt says holding
fruit on the tree makes alternate bearing worse. The researchers advise growers
to investigate the effects of thinning or pruning to reduce the number of fruit
in early summer of the on-crop year.
The findings appeared in
the Journal of the American Society for Horticultural Science.
Other kinds of trees that can experience alternate
bearing include nut trees. Scientists recently studied the effects of
mechanical thinning on two kinds of pecan trees in the southeastern United
States. The results from the University of Georgia appeared in HortTechnology,
also published by the society.
The study compared trees
that had been thinned by machine with those that had not been thinned. The
findings suggest that thinning during the on-crop year can increase the value
of off-year pecan crops.
And
that's the VOA Special English Agriculture Report, written by Jerilyn Watson. I'm Bob Doughty.
E-mail
Print
