Efficacy of Insecticides to Citrus Thrips on Lemons in Yuma Arizona 1997
David L. Kerns, Assistant Specialist, Entomology, Yuma Agricultural Center
Tony Tellez, Research Specialist, Yuma Agricultural Center
Three small plot efficacy trials were conducted evaluating different insecticide
rotation regimes using commercially available insecticides and the effectiveness of new
insecticide chemistries to control citrus thrips. Because of its long residual activity,
and ability to control post-application egg hatches, Carzol appears to be the product that
best fit the petal fall application window. Agri-Mek, Baythroid, Dimethoate or Vydate are
probably good follow-up insecticides. However, Agri-Mek and Baythroid will probably provide
greater control, especially under hotter conditions. If temperatures are cool, Agri-Mek looks
good at reduced rates. The best insecticide for subsequent applications depends on temperatures
and what was previously applied. Avoid making back-to-back applications of the same materials,
and Dimethoate or Vydate applications should probably be followed by Carzol to catch post-application
egg hatches. Overall, Vydate appear very similar to Dimethoate in efficacy and residual activity,
while Baythroid appear slightly better. Although the addition of Lannate to Dimethoate does
slightly enhance thrips control, the additional cost probably does not justify the tank mix.
Of the new chemistries (Alert, Success, Ni-25, and M-96-015) evaluated, Success and M-96-015
appeared to offer the best fruit protection. However, M-96-015 does not appear to be very
effective in killing the thrips, but very effective in repelling them. Also, M-96-015 will
need to be applied at a high gallonage, i.e. 500 gal/A. None of the new products tested
appear to fit the petal fall application window very well. Ni-25, Alert and Success appear
to lack the residual activity of Carzol, and M-96-015 should not be used as a clean-up material
but preventively following Carzol at petal fall.
Citrus thrips, Scirtothrips citri (Moulton), is the most severe insect pest attacking
citrus in the low desert areas of Arizona, and are far have the more severe than elsewhere in the
United States. Presently, pest control advisors (PCA's) and growers rely primarily on Carzol,
Agri-Mek, Baythroid or Dimethoate, often tank-mixed with Lannate or other insecticides for control
of this pest. Although these products have proved efficacious under cool conditions, except for
Carzol, they will often provide only knock-down control and suppression under hot conditions.
Recent investigations suggest that insecticide resistance may be a contributing factor in poor
insecticidal control. Additionally, there is concern that highly toxic and non-specific products
such as Lannate and other carbamate and organophosphorus insecticides, are being targeted by the
Environmental Protection Agency for discontinuation. Identifying alternative control measures for
control is critical.
Within recent years, several new insecticides have begun development for citrus thrips control
in citrus. Unlike many of the products developed in the past, these insecticides tend to be more
target-specific and more mundane to the environment. Alert, chlorfenapyr (American Cyanamid), is in
a novel class of insecticide and has a unique mode of action. It acts as a mitochondrial poison, and
disrupts the electron transport chain. Basically, it shuts down the insect's power generating
capabilities. Although Alert has contact activity and a rapid knockdown, it is most toxic after
consumption. Once ingested, the insect converts the molecule into a more toxic structure. Alert
is translaminar and will move into the leaf tissue where contacted, but is not systemic. Alert appears
to be toxic to a broad range of Lepidopterous pests, thrips and mites. Ni-25, acetamiprid, is a new
product being developed by Rhone Poulenc. It belongs to the chloronicotynl class of insecticides.
Although, Ni-25 is noted for its activity towards whiteflies and aphids it has demonstrated some
activity to thrips. Success, spinosad (Dow), is a fermentation by-product produced by the bacterium
Saccharopolyspora spinosa. Success has demonstrated good activity against a broad range of
Lepidopterous pests, leafminers and thrips. Like Alert, it has translaminar activity and will
move into the leaf tissue, and is most active after ingestion. It is thought to act at the GABA
site and also at the nicotinic receptor on the nerve synapse. Success is very safe to beneficial
insects and is low in toxicity to mammals. M-96-015 is a new product being developed by Engelhard.
Unlike most products currently being developed for insect control in citrus, M-96-015 is thought to
act primarily as a repellent.
The purpose of this research was to evaluate the efficacy new insecticides and insecticide
currently available for citrus thrips control, for their potential for use in the unique growing
conditions of the low desert citrus production areas of Arizona. The following report represents
citrus thrips control data collected during 1997 from three separate small plot efficacy trials.
Materials and Methods
Nine year old lemon trees managed by Glen Curtis Inc. in Yuma, AZ were treated with insecticides
for control of in three separate efficacy trials during 1997. All small plot tests were randomized
complete block designs consisting of four replicates. Each plot (30 ft by 90 ft) consisted of three
trees in a row spaced 30 ft apart. Applications were made using a backpack air-blast sprayer
calibrated to deliver 100 gal/acre.
Temperature data was obtained from the AZMET weather database system, from the weather station
located at the University of Arizona Yuma Mesa Station, ca. 300 yd from the test site. Temperature
data are presented as an average maximum daily temperature in °F for each 24 hr period following
the most recent insecticide application. Percent infested fruit were estimated by sampling ten
fruit per tree for the presence or absence of immature citrus thrips. In addition to thrips,
products were evaluated for their tendency to flare or control twospotted spider mite, Tetranychus
urticae Koch. Fruit sampled for thrips infestation were also evaluated for mite infestation.
Fruit damage was estimated on by rating the degree of scarring to the rind. Scarring was rated
as 1=no scarring, 2=slight scarring around the calyx, 3=significant scarring around the calyx,
4=slight scarring on the side of the fruit and 5=major scarring on the side of the fruit.
Fruit with a damage rating of 2, are not considered to be scarred heavy enough to cause a
downgrade in quality. Fruit with 3 or higher damage ratings, are considered significantly
scarred and subject to downgrading. Percentage fruit infested with immature citrus thrips or
twospotted mites were transformed using a square-root transformation for analysis. Percentage
of fruit with no scarring and significant scarring were transformed using an arc-sine transformation,
while the percentage of fruit with slight scarring was transformed using a square-root transformation
for analysis. Percentage values are presented in the tables. Differences among treatments were
separated using ANOVA and an F protected LSD.
Agri-Mek was evaluated for its efficacy at normal (10 oz. /A) and reduced rates (5 oz. / A) in
a rotation with Dimethoate and Carzol. These treatments were compared to standard rotations of Carzol
and Dimethoate. Applications were initiated at petal fall. Agri-Mek applications included NR-415
spray oil at 1.0 gal / A, and Carzol and Dimethoate treatments included Kinetic spreader-sticker at
0.1% v/v and Neutralizer buffer at 0.125% v/v. Treatments were applied on an as needed basis,
when the number of fruit infested with immature citrus thrips was greater than or equal to 10%.
Application dates and rates are displayed in Table 1.
Commercial Insecticides Test
Various rotation regimes including: Dimethoate and Carzol; Danitol, Dimethoate and Carzol;
Baythroid, Dimethoate and Carzol; Dimethoate, Carzol and Dimethoate + Lannate; Agri-Mek, Dimethoate
and Carzol; and Dimethoate, Vydate and Carzol were evaluated for efficacy towards citrus thrips and
twospotted spider mites. Applications were initiated at petal fall. Agri-Mek applications included
NR-415 spray oil at 1.0 gal / A. Other treatments included Kinetic spreader-sticker at 0.1% v/v.
Applications including Carzol or Dimethoate included Neutralizer buffer at 0.125% v/v. Treatments
were applied on an as needed basis, when the number of fruit infested with immature citrus thrips
was greater than or equal to10%. Application dates and rates are displayed in
Experimental insecticides were evaluated for their potential for controlling citrus thrips and
twospotted spider mites on lemons. Treatments included two rates of Ni-25, Alert, Success, M-96-015
and a standard rotation regime of Dimethoate and Carzol. All treatment applications included Kinetic
spreader-sticker at 0.1% v/v. Applications including Carzol or Dimethoate included Neutralizer buffer
at 0.125% v/v. Treatments were applied on an as needed basis, when the number of fruit infested with
immature citrus thrips was greater than or equal to10% or if thrips numbers were moderate and substantial
time had elapsed since the last application . Application dates and rates are displayed in
Results and Discussion
Agri-Mek Test (Tables 1, 2, 3, 4)
Following the first application at petal fall on Mar 21, of the treatments applied, only Carzol
provided more than 1 week of control. (Table 2). Citrus thrips populations at this time were no doubt
unsynchronized, meaning there were many life stages present and eggs were continually hatching.
The long residual activity of Carzol allowed this product to control thrips that had hatched after
the application, Agri-Mek and Dimethoate are fairly short-lived materials. Because of the long
residual activity of Carzol, it has a good fit for the first application, especially if it is warm,
because it can pick up post-application hatches. The second application was applied on Mar 26, treatment
6 which was Carzol didn't require re-treatment. Following application 2, temperatures cooled and
populations remained below 10% infestation in all treatments until April 22. On April 22, only the
plots spray with Dimethoate or skipped during application 2 required re-treatment. If a period of cool
weather is expected, Carzol and Agri-Mek, even at reduced rates, appear to offer the best control.
During the period of applications 3 and 4, temperatures began to warm, with average maximum daily
temperatures beginning in the lower 90s and ending in the upper 90s
(Table 2 and 3). During this period,
Carzol provided about 3 weeks control, while Dimethoate provided only 1 week. For the most part,
temperatures for the remainder of the season were hot, in excess of 100°F
(Tables 3 and 4).
Under these extreme conditions, Agri-Mek at 5 oz/A did not provide sufficient control, while the 10-oz
rate did. For the most part, Carzol was still performing well, and Dimethoate was performing marginally,
especially if it followed a weak material the previous week, i.e. Agri-Mek at 5 oz/A.
Differences among treatments in the number of twospotted spider mites were detected only on May 3.
None of the rotation regimes seemed to flare mites, relative to the untreated, and it was evident that
those rotations containing Agri-Mek had fewer mites.
All of the treatment regimes evaluated contained a lower percentage of significantly scarred fruit
(fruit that would be downgraded). The only treatment regime that did not differ from the untreated in
the percentage of fruit with no scars, was when Dimethoate was sprayed at petal fall, followed by a
reduced rate of Agri-Mek. Treatment regimes that included Agri-Mek at 10 oz/A required 4 applications
to get through the season, relative to 5 or 6 applications for the other regimes. This reflects the
increased efficacy over Agri-Mek at the low rate and Dimethoate.
This trial demonstrated the importance of achieving good thrips control at petal fall. Carzol appears
to fill this niche nicely. During periods of cooler temperatures, Agri-Mek, Dimethoate and Carzol all
performed well, however Carzol and Agri-Mek were the better products. During this time it is feasible
to use Agri-Mek at reduced rates without jeopardizing control. Under hot conditions, it is important
to avoid using weaker materials so the thrips don't spread out their egg lays. Once egg lays are
spread out in time, even the more efficacious insecticides will appear weak. Avoid using Dimethoate
or reduced rates of Agri-Mek is temperatures are 95°F or greater. Based on these data and considering
only those products used in this trial, although we didn't test this specific regime, a good treatment
regime might be Carzol, followed by Agri-Mek at 5 oz/A, followed by Carzol, then followed by Carzol, or
Agri-Mek at 10oz/A or Dimethoate if temperature aren't too hot and most the fruit is near 2.0 inches in
Commercial Insecticides Test (Tables 5-8)
Application 1 was made at petal fall on 19 March. Neither Dimethoate, Baythroid nor Danitol
offered extend control at this period, probably because of post-application egg hatches
Neither Carzol nor Agri-Mek required re-treatment within a week, however Carzol appeared to offer
better residual control. Following application 2, temperatures cooled and all treatments provided
good thrips control and numbers remained low for about 4 weeks. All treatment regimes required an
insecticide application by April 24. Because of the long period since the second application, the
thrips egg hatch was probably unsynchronized. Thus similar to the first application, following
application 3 Carzol was the only product to offer good residual activity. All treatment regimes
except the no. 8, which had been treated with Carzol during application 3 and didn't require re-treatment,
were treated with Carzol at application 4 (Table 7). Following application 4, there was no clear cut
distinction as to why two of the Carzol treatments (regimes no. 2 and 6) provided only 1 week of control
and required an application on May 8. Otherwise Carzol provided 2 to 3 weeks control. Although I haven't
been able to sort out the intricacy of the rotation relationships, it appears that weaker insecticides may
reduce the apparent efficacy of insecticide applications 2 to 3 weeks latter, especially under hot
conditions. The few thrips that survive the applications of the weaker materials probably spread out
the egg hatch, resulting in overlapping generations, and control difficulty. When comparing efficacy of
Dimethoate alone to Dimethoate + Lannate at application 5, statistically the addition of Lannate does not
significantly enhance the activity under hot conditions. Adding Lannate is probably not cost effective.
Additionally, under hot conditions, Carzol appeared to offer the best control relative to Dimethoate,
Vydate or Agri-Mek (Tables 7 and 8).
None of the treatment regimes evaluated appeared to flare mite over the untreated check.
Based on the amount of significant fruit scarring, all of the treatment regimes offered fruit
protection over the untreated control. Treatment regime no. 5 contained the smallest amount of
significantly scarred fruit. This regime contained Baythroid rotated with Dimethoate and Carzol.
The efficacy of the pyrethroids appears to fall between Dimethoate and Carzol (see
Table 6, April 30)
which explains the lower amount of scarring compared to regimes with more frequent applications of
weaker materials. Regimes that consisted of Carzol rotated with Dimethoate and non-pyrethroid products,
similar in efficacy to Dimethoate, i.e. Vydate or Dimethoate + Lannate, appeared to be the weaker regimes.
Overall, Vydate appears very similar to Dimethoate in its activity, and should be treated as an alternative
Experimentals Test (Tables 9-11)
All treatments were applied at petal fall on March 19 (Table 9). At 2 days after treatment M-94-015
was the only treatment that did not differ from the untreated. By 6 days after treatment there were no
differences among any of the treatments and the untreated (Table 10), suggesting that none of the products
evaluated provided enough residual activity to control the post-application eggs hatches. All treatments
were again treated on March 26. However, Carzol was substituted for Dimethoate, and M-96-015 was applied
using a hand-gun sprayer instead of the air-blast sprayer. M-96-015 requires full coverage to be effective.
The air-blast sprayer was not providing sufficient coverage (100 gal/A) of this material, the hand-gun was
calibrated to deliver 250 gal/A. Additionally, M-96-015 is not thought to have strong insecticidal
properties but acts primarily as a repellent. In retrospect, this treatment should have probably had the
thrips killed with Carzol before the M-96-015 was applied. Following the second application the
temperatures cooled and another application was not necessary until late April. The third application
was made on April 24, none of the treatments changed except Dimethoate was rotated with Carzol. All of
the products evaluated appeared equally efficacious. The only products that required spraying at application
4 were Carzol, which followed Dimethoate at application 3, Alert, and Ni-25
(Table 11). Success and
M-96-015, appeared to offer greater residual activity, than Alert, Ni-25 or Dimethoate, especially when
temperatures >90°F. Following application 4, thrips
populations became stagnant throughout May, the
hottest portion of the season, which is usual. No further applications were necessary. It is possible
that the products evaluated were so efficacious that overlapping generations were eliminated and the
populations never fully recovered. Thrips populations in the Dimethoate/Carzol and untreated plots did
not build probably because of inter-plot interactions (the effect of highly efficacious materials used
nearby). Although mites were present, none of the products evaluated flared them in this study.
Damage ratings indicated that all of the treatments were equally effective at protecting the fruit.
However, the commercial standard, Alert, and Ni-25 required an additional application to achieve this
protection. Overall, Success and M-96-015 appeared to be the most efficacious materials evaluated.
However, Carzol, or a similarly efficacious material should precede applications of both products,
especially M-96-015 at petal fall. Alert and Ni-25 also appeared to be very effective materials,
but similarly to Success and M-96-015 probably do not fit the petal fall application window as effectively
This is a part of publication AZ1051:
"1998 Citrus and Deciduous Fruit and Nut Research Report," College of
Agriculture, The University of Arizona, Tucson, Arizona, 85721.
This document located at http://ag.arizona.edu/pubs/crops/az1051/az10511.html
Return to Table of Contents