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

Figure 72. Macadamia racemes showing effects of Botrytis cinerea
infestation (right) compared with normal racemes (left).
Figure 73. Macadamia racemes showing Phytophthora capsici infestation.
(Normal racemes are shown in Fig. 72.)
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formed (Fig. 73). The infestation first appears
as minute necrotic spots on the racemes, but
it very rapidly develops to encompass the
total structure. Flowers and fruits do not develop
normally.
3. The Kretzschmaria clavus (34, 35, 37) root
and trunk rot symptom is especially noticeable
when the trees are about 15 to 25 years
old (Fig. 74). Its ecology has not been completely
established and further studies are
needed, but at this time, young trees planted
in the same spot where a tree has previously
succumbed seem to grow normally, probably
indicating that this organism develops very
slowly. The Kretzschmaria root rot is again
more prevalent in the wet areas of Hilo and
Pahoa. More work on this fungus has been
funded by the Governor's Agricultural Coordinating
Committee through the Hawaii
Macadamia Producers Association.
Phytophthora cinnamomi has been associated
with trunk canker in macadamia. However, this
infestation is rarely found and apparently does not
affect production (23, 36, 87). It probably exists
only as a harmless member of the microbial community
(36).
Figure 75 shows a nut-set picture of a tree in the
leeward area of Kona, where the high mountain
brings about a temperature reversal for most of
Kona, resulting in a dry winter when the flowers
are developing. This temperature situation in
Kona is very unlike the wet condition in Hilo and
the windward sides of the Islands, where the
flowering season is wet and cold. Under this dry
condition in Kona, Botrytis cinerea and Phytophthora
capsici develop slowly; nut set is conseq
uently very good.
With the advantage of hindsight after 30 years
of active macadamia production, the evidence
now on disease manifestation and control indicates
that a better alternative on land is the use of
areas that are cool and dry in the winter months.
This will reduce the bad effect of flower blights. If
economic considerations can be resolved, macadamia
planted in dry areas where irrigation water
is available and is applied will lend itself further
to better control of its serious diseases, including
Kretzschmaria root rot. Such a rethinking is a
better alternative and worth considering as a first
step in macadamia disease control and macadamia
production.
Rats. Without a thorough rat eradication pro-