Agriculture Reference
In-Depth Information
pounds per acre in the 1920s to 1,348 pounds per acre in the 1990s.
Almonds are currently the most extensively planted tree crop in the state,
and account for nearly 5 percent of California's irrigated cropland. The
labor efficiencies achieved by harvest machinery have made almonds an
attractive crop for small and medium-size growers.
2
Increased production did not come without costs. Almonds develop
inside a shell enclosed by a hull. This double jacket protects the nuts but
is not impermeable, and it can offer shelter to the pest. Chemical nitro-
gen plus irrigation boosted tree growth and increased nut size, making
vegetation and the developing nut more attractive to pests. Almond hulls
are analogous to fruit flesh of their plant cousin, the peach. In the late
summer, a few weeks prior to harvest, hullsplit occurs, meaning that the
hull peels back to reveal the nutshell. Simultaneously the fibers holding
the nut to the stem begin to degrade. Trees require not too much and not
too little moisture for hullsplit to proceed properly. Overly vigorous trees
will delay hullsplit, and the trees stressed by inadequate moisture misfire
the ripening sequence, with hulls failing to release the shelled nut.
Larvae of the navel orange worm and the peach twig borer sniff out
the developing almond oil and try to penetrate the sealed hull through-
out the spring. Several of the new, high production cultivars have softer
shells, meaning that peach twig borer larvae chewing through the hull
easily work their way straight through to the nut. During his 40-year
career, UC Farm Advisor Lonnie Hendricks watched the NOW become
more of a pest as almonds became a widely planted and highly fertilized
monocrop, in part because the shell and hull seal began to open more
readily. As almond acreage grew, so did NOW food and habitat. The
NOW is a non-native insect, and thus has no native natural enemies to
dampen explosive population growth. As the 1960s drew to a close, the
NOW surpassed the peach twig borer as the chief economic pest in
almonds.
More and more pesticides were applied, but to little effect. The typical
pest-management program in the 1970s consisted of “holiday sprays” by
the calendar. New Year, Memorial Day, and July 4 roughly approximate
the times NOW larvae moved about, but variations by year in heat units
could make those sprays worthless. Nut damage rates due to the NOW
began to climb from the single digits up to 20, 30, even 40 percent
(figure 5.1).