Agriculture Reference
In-Depth Information
crops. On the positive side, the required amount of vegetation-free space
around the fruit trees is smaller than most conventional herbicide strips. The
need for aggressive weed control also diminishes during the course of the
growing season and as the trees mature.
In orchards consisting of large, established trees that essentially form an
unbroken canopy across the entire orchard floor, weed control is often a
rather minor concern. The trees have extensive root systems capable of ob-
taining water and nutrients far beyond the reach of shallow-rooted under-
story vegetation. The dense shade produced by the trees also greatly reduces
the establishment and growth of other vegetation in the orchard.
While weed problems are often minor in a mature orchard with large
trees, it is important to manage vegetation throughout the life of high-dens-
ity orchards if you want to produce high-quality fruit and high, sustainable
yields. Orchard systems that confine the trees to narrow, trellised rows have
a particular need for careful vegetation management for two reasons: First,
the trees are kept small, often with weak trunks and relatively little foliage.
These trees are designed and maintained to produce high yields of fruit, not
structural wood and extensive root systems that provide abundant nutrient
and carbohydrate reserves. Large trees are better able to compete with orch-
ard floor vegetation for nutrients and water. Second, an abundant amount
of sunlight penetrates the orchard floor, greatly increasing the amount, di-
versity, and growth of competing vegetation.
For young trees just getting started, in any type of orchard, weed control
is a major concern. One of the greatest challenges in establishing an organic
orchard is weed pressure. Perhaps 90 percent of the young trees' root sys-
tems are in the top foot of soil, placing them in direct competition with
“weeds.” Most young fruit trees and bush fruit plants are rather poor compet-
itors.
In Washington State trials, trees in organic plots where weed pressure
was high had far lower survival and growth rates than those in conventional
plots with few weeds. The situation is worst in areas with ample summer
rains, where vegetation is naturally abundant, varied, and vigorous. An old
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