PCC January/February 2018

Managing Navel
Orangeworm on Two
Million Acres
By Emily J. Symmes | Sacramento Valley Area IPM Advisor, UC Statewide IPM
Program and Cooperative Extension
Navel orangeworm (NOW) populations
exploded in 2017, costing
growers tens of millions of dollars in
reduced quality and lost yields. In a year
where double-digit damage estimates
from nut processors were not uncommon,
the question heading into the coming
growing season (and future seasons
beyond 2018)—how do we limit damage
from this pest? Is our current arsenal
of integrated pest management (IPM)
tactics enough to keep damage in the
desired one to two percent range given
the two million (plus) acres of commercial
nut crop habitat in California (not to
mention the myriad other crop and noncrop
plants that play host to NOW)?
This article covers the “tried-and-true”
strategies, as well as where we need to
head in the future of NOW management
to ensure clean, safe, and profitable nut
crops for years to come.
A four-pronged approach to NOW
management in nut crops has been
suggested for years based on University
research and field success stories. These
include: sanitation, minimizing damage
by other sources, timely (early) harvest
to avoid late generation flights, and
insecticide treatments as deemed necessary
by monitoring pest activity and
crop phenology.
Sanitation
By now you have certainly received
the message—SANITIZE! This single activity
is the absolute backbone of all pest
management targeting NOW, no matter
the nut crop. This practice results in direct
destruction of overwintering worms,
as well as destruction of spring habitat
for any part of the population that
survived the winter (those remaining
in the orchard or those migrating into
the orchard from external
sources outside of your
control). In many
cases, it’s simply
not enough to
get nuts on the
ground, but
additional
destruction
of the nuts
is required
in order to
achieve maximum
reduction
in emergence,
population build-up,
and damage (NOW will lay eggs on and
develop in ground mummies if that is all
that is available).
Plenty of research summarizes the
effectiveness of sanitation practices (e.g.,
Higbee and Siegel 2009, California Agriculture,
Volume 63). Research has also
suggested that females prefer to oviposit
(lay eggs) on nuts previously damaged
by NOW, and that development rate and
survival success are both also positively
correlated with previous kernel damage
(Hamby and Zalom 2013, Journal of
Economic Entomology, Volume 106).
Therefore, all mummies are not created
equal. Clearly, a mummy with live
overwintering worm(s) is a
bigger threat in the coming
season than one without
live worm(s). Live moth-
(s) will emerge from
these mummies and
give rise to subsequent
generations, which will
ultimately target the
Adult navel orangeworm.
Credit: University of California
Statewide IPM Program.
4 Progressive Crop Consultant January/February 2018