Macadamia Nuts in Hawaii: History and Production - ctahr ...

Figure 70. A badly P-deficient tree recovering with healthy regrowth
after P fertilization. Picture was taken nine months after
application of fertilizer.
symptoms are not severe, the less expensive
magnesium oxide or dolomite may be used. Leaf
analyses should be made to monitor the change.
Leaf analysis values for tetraphyllas can be
developed by using integrifolia val ues a t the
beginning and relating these to production and
nut quality. Changes in the integrifolia values can
be made upwards or downwards for the tetraphyllas,
depending on tree responses.
Weed Control
Weed control continues to be one of the more
important and expensive cultivation cost items. A
persistent and continuous effort needs to be maintained
in cultivation to reduce the competition
from weeds for moisture and nutrients so vital in
tree growth and production. Further losses through
poor weed control can be expected during the harvest
season when some nuts on the ground are lost
among the weeds and are not picked up regularly.
Unharvested nuts left too long on the ground can
become unacceptably moldy or can be eaten by
rats. In either case, losses to total production can
be substantial and very expensive.
During the past 50 years, as farm labor has
become increasingly scarce and, when available,
expensive, weed control using chemical herbicides
has become the standard practice. In spite of the
continued increase in cost, the use of herbicides,
with the continuing development of more specifically
effective chemicals, is now the cheapest and
most effective method of weed control.
One of the early problems in weed control was
the lack of effecti ve, selective, and cheap herbicides
approved for use on macadamia by the U.S. Food
and Drug Administration and the Hawaii State
Department of Agriculture. Some of the uncleared
herbicides used in the past were the many forms of
arsenicals, sodium chlorate, trichloroacetic acid,
pentachlorophenols, and aromatic oil. Due to the
lack of effective and approved herbicides in the
early 1960s, H. Ooka (59) experimentally used
flame weed control with butane and propane gases
at Keaau Orchard (Fig. 71). It was particularly
effective on small weeds and left no chemical
residues on the nuts or on the ground. The practice
was discontinued, however, after more herbicides
were cleared, particularly because fire risk and
insurance considerations were too high.
Weed control by mowing or beating with chain
segments or steel blades has been used extensively
Figure 71. Flamethrower experimentally used at Keaau Orchard in
the early 1960s.
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