IPM practitioner Joe Barcinas with IPM researcher Joseph Morse

During the first time period, 1972-
1991, broad-spectrum organophosphate,
carbamate, and pyrethroid insecticides
were used in the SJV and in the test
areas of this field at Lindcove for citrus
thrips control. Many pest control advisors
mentioned to us that spraying thrips
“only makes them mad”. They found
that if the first spray did not control
them well, they “came back” at very high
levels and were more difficult to control.
We believe that what was happening
was that citrus thrips populations
had developed resistance in some areas
and to varying degrees to organophosphates,
carbamates, and/or pyrethroids.
The level of resistance varied greatly
depending on how often and which
chemicals had been used in the past and
how long thrips had NOT been exposed
to that chemistry so that resistance
could revert.
When citrus thrips are sprayed with
a broad-spectrum insecticide (as is the
case for most products in these three
classes of chemistry, see Table 1) these
sprays reduce most natural enemies that
might help hold the thrips in check. If
the thrips are somewhat resistant, they
are not completely killed.
Hormoligosis is the term used to
describe the stimulation of insects or
mites when they are exposed to sublethal
rates of pesticides or other toxins.
As pesticide residues drop to sub-lethal
rates, citrus thrips can be stimulated
(depending on pesticide and dose) to
lay more eggs, contributing to a “resurgence”
of the thrips population several
weeks later.
Hormoligosis — the stimulation of insects
or mites when they are exposed
to sub-lethal rates of pesticides or
other toxins.
What happened to contribute to
lower thrips levels over 1992-2003 The
relatively “soft” insecticides Agri-Mek
and Success (Entrust is the organic version)
were registered for use on California
citrus in 1994 and 1998, respectively,
and growers largely switched to using
those products, especially Success, for
citrus thrips control (see Figure 4). In
addition, growers switched to Esteem
or Applaud for red scale control, in both
cases replacing broad-spectrum organophosphate,
carbamate, and pyrethroid
treatments with softer insecticides
that allowed more natural enemies to
survive.
Thus, although citrus thrips can still
cause economic damage when weather
conditions are conducive, in general,
citrus thrips is less of a problem than it
used to be. Whereas citrus thrips insecticide
screening trials at LREC were
quite productive prior to 2003, once the
“organophosphate era” ended, it was
difficult to consistently see differences
between fruit scarring on trees treated
with the standard, effective product
versus levels on untreated control trees.
We shifted in 2004 to screening
experimental pesticides on what we
believe is one of the major natural hosts
of citrus thrips in California (before
citrus was introduced), laurel sumac,
in greenhouse trials (see Morse 1995).
Treatments on non-bearing citrus
Some growers and PCAs believe
that treating citrus thrips on non-bear-
Table 1. Pesticides that might be used in rotation for citrus thrips control.
Trade name Common name Pesticide class Mode of Action a Critical as part Resistance situation with Comments and application
of future ACP citrus thrips methods to improve efficacy
control
Dimethoate (and Dimethoate Organophosphate 1B Yes Resistance in some areas Moderately systemic material
generics)
depending on the degree of
past organophosphate use
Carzol Formetanate Carbamate 1A No Resistance in some areas
hydrochloride
depending on the degree of
past carbamate use
Veratran D Sabadilla alkaloids Botanical unclassified No Resistance not yet seen Adding 1-2 gallons of
with citrus thrips (seen with molasses/acre assists with
avocado thrips)
efficacy and persistence;
Critical to reduce spray tank
pH to 4.5 prior to adding
material; Works poorly in
cold weather (active only as
a stomach poison)
Baythroid XL Beta-cyfluthrin Pyrethroid 3A Yes Resistance in some areas
Danitol Fenpropathrin depending on the degree of
Mustang Zeta-cypermethrin past pyrethroid use
Agri-Mek (and Abamectin Chloride channel 6 Somewhat Possible cross-resistance Translaminar, add oil (1/4%
generics) activator (adults) with class 5 or more) to aid leaf
penetration and persistence
Success Spinosad Spinosyn 5 Delegate – Possible cross-resistance Translaminar, add oil (1/4%
Entrust Spinosad (organic) Yes with class 6 or more) to aid leaf
Delegate Spinetoram penetration and persistence
Movento Spirotetramat Inhibitor of acetyl 23 Yes Resistance management Highly systemic; add oil to
CoA carboxylase critical to protect this improve leaf penetration
material’s efficacy for ACP, (surface residues are NOT
red scale, and citrus thrips active)
control
a
The IRAC MoA (mode of action) for each class of chemistry (see www.irac-online.org).
26 Citrograph March/April 2012