Regular Pecan Bearing
Why don't fruit and nut trees produce every
year? This phenomenon is referred to as alternate bearing.
One of the main reasons why a poor fruit year follows a year
of abundant harvest is improper leaf maintenance.
Early defoliation of pecan trees can be the
result of a combination of problems including disease, stress,
Scab and downy spot are the diseases that may
cause defoliation. Scab appears as small black lesions that
later enlarge and completely blacken the pecan leaf, eventually
killing it and causing defoliation. Scab will also attack
and kill the shuck or outer covering of the pecan, which results
in a poorly filled or hollow pecan. Downy spot causes the
leaves to drop in August prohibiting the from filling the
Water stress and various foliar feeding insects
that compound leaf drop problems can also be associated with
disease. Such insects as aphids and mites attack pecan leaves,
contributing to early defoliation.
The variety of pecan dictates the severity
of the disease problem. Many of the older varieties, such
as Burkett, Delmas, Success and Mahan, are very susceptible
to disease. On the other hand, varieties such as Desirable,
Choctaw, Cheyenne and Shawnee are quite disease resistant.
Pecan varieties that are not considered to
be disease resistant can only be kept in production through
the spray application of pesticides throughout the growing
season. However, pecan trees are too large to be sprayed with
conventional garden equipment. Most homeowners do not have
spray equipment that will reach the top of a 30-foot tree.
Therefore, for homeowners who want to produce
pecans in the backyard, the most logical solution is to plant
the disease resistant varieties listed above. Those varieties
have sufficient inherent disease resistance to make spraying
less essential. These varieties may, however, require some
insect control throughout the season.
Pecan producers with established trees that
are more susceptible to disease may consider "top working"
(grafting) trees to a more resistant variety. This should
be done in early spring.
Spraying backyard trees is not considered to
be very economical. The cost of pesticides and the length
of the spray schedule make it very impractical and costly
to spray and maintain pecan trees on a commercial basis.
Another factor essential to maintaining productive
pecan trees is an annual application of fertilizer. Pecan
producers should fertilize in February with one pound of a
slow?release lawn fertilizer (such as 19?5?9) per each diameter
inch of trunk, measured 3 feet from the ground. Fertilizer
should be applied at the drip line of the tree and lightly
incorporated if possible. This is in addition to lawn fertilization.
Trees must also have adequate amounts of zinc.
Soil applications containing zinc have proven ineffective,
so foliar sprays should be used. Two to 3 applications of
a zinc product such as zinc sulfate or NZN should be made
at 2- to 3-week intervals beginning at bud break. NZN should
be used if sprays contact peach or plum trees since defoliation
can be caused if zinc sulfate is used.
In late August and early September, aphids
and mites may cause premature shredding of leaves. Premature
defoliation will certainly affect the quantity and quality
of this year's crop, as well as next year's harvest. Aphids
and/or mites cause a general yellowing of the leaves. A severe
infestation of either or both of these pests can completely
defoliate the trees in mid- and late-summer.
With this information, those homeowners who
have nonproductive pecan trees can do something about it.
Homeowners who want to plant a pecan tree in or around the
yard should carefully consider the location of such trees-they
get big! Many folks mess up the future beauty of their lawns
by planting "cute little trees" in the wrong place.
The problem arises when the "cute little tree" grows
into such a monster that swings can be hung on limbs growing
through the living room! A pecan tree can be a productive
asset or a perpetual liability.