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MANAGEMENT OF SPIDER MITES ON MINT
Research Progress Report - 1992Prepared
by Mark Morris
Note: this information is considered unpublished work
and should not be used as final or finished results. It has been included in IPMP 3.0
because it may not be available from other sources, and in some cases may include
information that may not reach final publication.
The Twospotted Spider Mite, Tetranychus urticae
Koch (TSSM), is a key pest of peppermint in all mint production areas in Oregon
(Hollingsworth and Berry 1982) and the Northwest (Morris et al. unpublished data 1991 and
1992). During the fall, propane flaming in the Willamette Valley reduces populations of
spider mites and delays population increases the following season (Hollingsworth and Berry
1982). Spring flaming is also widely practiced in the Willamette Valley to manage rust of
mint (Puccinia mentha) and reduces populations of spider mites as well; often to
such low levels that acaricide applications are unnecessary (Morris and Fairchild,
unpublished data).
In central Oregon, spider mites are more serious because of the warm dry climate. Growers
rarely propane flame in the spring in central Oregon because mint rust is not an economic
problem and because there is a greater chance of crop damage. However, studies have shown
that spring flaming in central Oregon will significantly reduce spider mite populations
throughout the growing season (Morris, et al 1991 unpublished).
Predator mites are effective regulators of spider
mite populations in a number of crops (Croft and McGroarty 1977) (Helle and Sabalis 1985).
The predator mite, Amblyseius fallacis Garmen, appears to be widely distributed
throughout the mint growing areas of Oregon (Hollingsworth and Berry 1982) (Morris et al.
1991 unpublished). Populations of T. urticae appear to be regulated by A.
fallacis under certain field conditions in central Oregon (Hollingsworth and Berry
1982, Morris et al. 1991 and 1992). However, predators are often absent, or present at
such low densities, that effective biological control is not realized. This suggests that
they may be disrupted by pesticides or other agronomic practices used on mint. For
example, disruption of predator mites by pesticides is widely documented in the literature
(Croft and McGroarty 1977) Helle and Sabalis 1985).
The goal of this project is to identify reasons why TSSM is becoming a more serious
problem to mint production in the Pacific Northwest and to provide practical solutions to
this problem.
The objectives of this study are to: 1) determine
whether acaricide resistance is present in TSSM populations in Oregon and the Pacific
Northwest; 2) investigate the overwintering behavior of A. fallacis in central Oregon, 3)
investigate the population dynamics of A. fallacis and TSSM in central Oregon; 4) survey
mint fields in Oregon and the Pacific Northwest for predator mite species; 5) evaluate the
effects of insecticide applications on A. fallacis in central Oregon, and 6) evaluate the
effectiveness of new as well as registered acaricides for managing TSSM on mint.
Resistance to Acaricides in TwoSpotted Spider Mite in Mint
This season we continued the acaricide resistance study that was started in 1991. The
objectives of this study were to: 1) measure the levels and magnitude of Kelthane
(dicofol) resistance in populations of TSSM collected from peppermint fields in the
Pacific Northwest, and 2) to determine if TSSM populations have developed resistance to
Comite (propargite) in mint.
Materials and Methods
Pesticide toxicity bioassays were run on populations of T. urticae collected in Oregon and
on one population collected in Montana. For comparative purposes, toxicity bioassays were
run on a population collected from a susceptible laboratory colony which has never been
exposed to pesticides.
Tolerance to pesticides was determined by leaf disc
bioassays using a Potter spray tower (Sabelis and helle 1985). Six concentrations each of
Kelthane and Comite were tested, ensuring a wide range of responses. Water only was
applied to one replication to assess control mortality. Three replications of > 25
adult female spider mites each were tested at each of the concentrations.
Mortality was assessed at 48 hours by lightly touching mites with a fine camel's-hair
brush; significant movement by the spider mite was considered survival. Results were
analyzed using standard low-dose probit-mortality analysis (Finney 1971).
Results and Discussion
Resistance to Kelthane MF was detected in four fields in the Pacific Northwest: one in the
Willamette Valley, two in central Oregon and one in Montana. Three fields were judged to
be susceptible and were not different than the laboratory susceptible strain. The data for
Comite are in the process of being analyzed.
Predator Mite Survey
Materials and Methods
Peppermint and spearmint fields in Oregon, Washington, Idaho and Montana are continuing to
be surveyed for the presence of predator mites. Fresh mint foliage is first examined with
a 16X hand lens; plants observed to have predator mites are collected and placed in either
plastic "zip lock" storage bags or brown paper bags, depending on the mint stage
of growth. The samples are placed in a large plastic garbage bag which is stored in a
cooler with "blue ice" and transported back to the laboratory. Predator mites
are collected from the foliate with a camel's-hair brush that has been pre-moistened with
70% ethyl alcohol (ETOH). Specimens are placed into 70% ETOH until they can be cleared,
mounted and identified to species.
Results and Discussion
Predator mites have been found in the majority of the peppermint fields surveyed, often at
levels above 0.05/leaf. However, in several fields predator mite populations were either
absent, present only at low levels or were restricted to small areas of the field. The
specimens will be identified to species during the fall of 1992 and winter of 1993.
Overwintering habits of Amblyseius fallacis
To determine the effectiveness of predator mites at maintaining below economically
damaging levels, it is necessary to understand their life history and behavior throughout
the year. This information is useful for tailoring agricultural management practices to
encourage the continued availability of healthy populations of predator mites in and
around mint fields.
The objective of this study was to determine whether
or not A. fallacis was able to over winter in peppermint fields in central Oregon
during 1991-1992.
Materials and Methods
Sections of three peppermint fields in central Oregon that exhibited significant
populations of A. fallacis were identified in the fall of 1991. Two of the fields
were located in Lower Bridge and the third field was located two miles south of Madras.
These field sections were sampled on a monthly basis beginning on December 16, 1991.
Twenty plants were selected and examined with a 16X hand lens. The number of spider mites
and predator mites that were present on the bottom four leaves were recorded.
Results and Discussion
Predator mites were detected on the lower leaves in all the fields except for Lower Bridge
(field 2) on January 3, 1992, and Lower Bridge (field 7) on February 20, 1992. These data
demonstrated that predator mites were able to over winter in peppermint fields in central
Oregon during 1991-92. For this reason, mint growers need to consider the effects of
agronomic practices on predator mites throughout the year.
Population Dynamics of T. urticae and A. fallacis in Peppermint
in Central Oregon
The first objective of this study was to observe the population dynamics of A.
fallacis and twospotted spider mites (TSSM) in mint fields in central Oregon during
the 1992 growing season. The purpose was to learn more about the relationship between
these two organisms and how effective A. fallacis would be to regulate populations in
peppermint.
Because spider mite populations are often aggregated
in peppermint fields (Hollingsworth and Berry 1982), they may be clumped in areas of the
field known as "hot spots". The second objective was to investigate the
relationship between TSSM and A. fallacis within "hot spots" of intensive
activity over time (small plot analysis).
Another objective was to make careful observations on the effects of field applied
pesticides on TSSM and A. fallacis.
Materials and Methods
Entire Field Sampling
One 30 acre peppermint field located 1 mile south of
Madras, Oregon, was sampled on a weekly basis beginning on May 7, 1992 and continuing
through August 8, 1992 (study no. 1)(for brevity, only the results of study no. 1 are
reported below).
Three additional fields were studied during 1992: a
30 acre peppermint field located in Gateway, Oregon sampled between June 13, 1992 and July
22, 1992, and two 40 acre peppermint fields located in Lower Bridge, Oregon sampled on a
weekly basis beginning on May 20, 1992 and continuing through August 8, 1992 (the results
of these three field studies were similar to study no. 1 and the small plot studies
reported below).
Thirty samples were collected using a method developed by Hollingsworth and Berry (1982).
The fields were sampled using a "zig-zag pattern. Five peppermint plants were
collected within a 10 foot radius at each of 30 sampling locations. The number of TSSM
motiles, TSSM eggs, predator mite motiles and predator mite eggs were recorded from the
top, middle and bottom leaves of each of five plants.
Small Plot Analysis
Several small plots were studied in 1992 to determine
TSSM and A. fallacis population dynamics. For brevity, only the results from plot
no. 4 are reported below.
Small Plot No. 4. Beginning on May 20, 1992, a section of a field located in Lower Bridge,
Oregon, was divided into three plots. The West plot was 30 feet x 200 feet and had been
treated with Asian (esfenvalerate 0.06 Ibs ai/A) the previous year to eliminate predator
mites; the plot was then disked in the spring of 1992. The middle plot consisted of a
strip of unplowed mint running the length of the pivot road; this plot was 10 feet x 200
feet and was not treated with Asian or disked in the spring. The East plot was 30 feet x
200 feet and was also disked in the spring of 1992. Sampling began on May 20,1992 and
continued through July 30, 1992. Sampling consisted of collecting 10 plants/plot and
placing them in plastic "zip-lock" storage bags which were put in coolers with
blue ice. Samples were transported back to the laboratory where TSSM and predator mites,
on all leaves, were counted with a dissecting microscope.
Results
Entire Field Analysis
Study no. 1. The results of the field study in Madras
are summarized in Table 4 and Figs. 4 and 5. Populations of TSSM motiles remained well
below the treatment threshold of 5.0/leaf during the course of this study. Comite (2.5
pints/acre) and Thiolux (sulfur 3.0 Ibs/acre) were applied to suppress TSSM on May 30; the
same rate of Comite and Thiolux at 5.0 Ibs/acre was applied on July 20 to suppress TSSM.
Populations of TSSM motiles declined after the first applications but were not observed to
change after the second application. The field was harvested on August 10.
Predator mite motiles and eggs increased to a high of 0.09 and 0.06/leaf on June 18,
respectively, then declined rapidly on June 24 following the crash of the TSSM population
on June 18. Predator mite motiles and eggs increased until July 17, then declined on July
24. All of the predator mite motiles observed on July 24 and July 31 were juveniles. This
result may have been related to the high rate of Thiolux (5.0 Ibs/acre) that was applied
on July 20.
The ratio of TSSM motiles to predator mite motiles declined from a high of 250:1 on May 19
to a low of 1.55:1 on June 18 (Table 4). This ratio remained below 10:1 after June 8,
except for 26:1 on June 24.
Table 4. Mean number of motile TSSM, TSSM eggs, motile predator mites, predator mite eggs
and TSSM/predator mites ratios obtained from sampling an entire peppermint field located
near Madras, Oregon 1992.
___________________________________________________________________________
TSSM
Predator Mite
Sample
Mean no. Mean no. Mean no. Mean no.
Ratio
Date
Motiles Eggs
Motiles
Eggs TSSM/Pred
___________________________________________________________________________
May 7
0.17 0.82
0.003
0.030
56.67
May 14
0.30 1.51
0.020
0.003
15.00
May 19
1.25
1.34
0.005
0.020
250.00
May 26
1.74 5 49
0.020
0.030
87.00
Jun1
1.42 8.09
0.010
0.040
142.00
Jun 8
0.40 2.21
0.030
0.060
13.33
Jun18
0.14 0.42
0.090
0.060
1.55
Jun 24
0.26 0.79
0.010
0.020
26.00
Jun 30
0.12 0.46
0.060
0.040
2.00
Jul 10
0.31 1.17
0.040
0.040
7.75
Jul 17
0.11 0.97
0.070
0.080
1.57
Jul 24
0.14 0.58
0.050
0.010
2.80
Jul 31
0.18 0.73
0.040
0.010
4.50
Aug 8
0.20 1.01
0.040
0.060
5.0
___________________________________________________________________________
Small Plot Analysis
Study no. 4. West Section. Populations of TSSM
motiles fluctuated around the treatment threshold of 5.0 mites/leaf from May 20 until June
26 (Table 5, Figs. 6 and 7). After this date TSSM declined to levels well below the
treatment threshold for the remainder of the study. TSSM eggs followed a similar trend,
although at higher levels. The plot was treated three times with Comite (2.5 pints/A) and
Thiolux (sulfur 4.0 Ibs/acre) to suppress populations of TSSM on May 25, June 22 and July
17. Populations of TSSM resurged after the first Comite application on May 25 but declined
after June 26.
Predator mite adults and eggs increased after June 19 and the number of motiles remained
above 0.10/leaf for the duration of this study. Predator mite adults continued to increase
until July 30.
The ratio of TSSM motiles to predator mite motiles
declined steadily from the point where no predators where detected on May 20, to 256.5:1
on June 3, 128.6:1 on June 19 to a low of 0.80:1 on July 30 (Table 5).
Table 5. Mean number of motile TSSM motiles, TSSM eggs, adult predator mites, juvenile
predator mites, predator mite eggs and the ratio of TSSM motiles/predator mite motiles
observed in a 30 foot by 200 foot section peppermint field located in Lower Bridge, Oregon
1992. Small plot no. 4, West section.
___________________________________________________________________________
TSSM
Predator Mites
Sample Mean no. Mean no.
Mean no. Mean no. Mean no
Ratio
Date Motiles 1/
Eggs Adults
Juveniles
Eggs TS/Pred 2/
____________________________________________________________________________
May 20 8.15
36.37
0.00
0.000
0.000
NPD 3/
Jun 03 5.13
27.32
0.01
0.000
0.010
256.50
Jun 13 4.16
22.45
0.01
0.000
0.010
138.66
Jun 19 6.43
28.29
0.02
0.002
0.020
128.60
Jun 26 4.92
31.37
0.10
0.000
0.100
27.33
Jul 03 1.15
13.35
0.23
0.030
0.230
4.11
Jul 07 0.25
5.86
0.12
0.002
0.120
1.39
Jul 13 0.91
3.82
0.12
0.000
0.120
4.78
Jul 23 0.37
1.71
0.16
0.020
0.160
1.09
Jul 30 0.05
0.68
0.11
0.040
0.110
0.80
____________________________________________________________________________
1/ TSSM Motiles = juveniles + adults
2/ Ratio = TSSM motiles/predator mite motiles: predator motiles = juveniles + adults
3/ NPD = no predators were detected
Study no. 4. Middle Section. The results of this study are shown in Table 6 and (Figs. 8
and 9). TSSM motiles remained well below the treatment threshold of 5.0/leaf during this
study. No acaricides were applied during the study period. Predator mite motiles ranged
from a low of 0.01 / leaf on July 7 to a high of 0.25/leaf on July 30. The ratio of TSSM
to predator mites declined from a high of 33.22:1 on May 20, to 15.33:1 on June 3, and
below 10:1 thereafter (Table 6 ).
Table 6. Mean number of motile TSSM motiles, TSSM eggs, adult predator mites, juvenile
predator mites, predator mite eggs and the ratio of TSSM motiles/predator mite motiles
observed in a 10 foot by 200 foot section peppermint field located in Lower Bridge, Oregon
1992. Small plot no. 4, Middle section .
__________________________________________________________________________
TSSM
Predator Mites
Sample Mean no. Mean
no. Mean no. Mean no. Mean
no. Ratio
Date Motiles
1/ Eggs
Adults Juveniles Eggs
TS/Pred
__________________________________________________________________________
May 20 2.99
13.30
0.080
0.010
0.080
33.22
Jun 03 0.46
1.35
0.030
0.000
0.020
15.33
Jun 13 0.82
3.39
0.100
0.000
0.030
8.20
Jun 19 0.21
1.28
0.070
0.010
0.050
2.63
Jun 26 0.23
0.99
0.100
0.000
0.080
2.30
Jul 03
0.05
0.23
0.050
0.010
0.020
0.83
Jul 07
0.02
0.06
0.002
0.000
0.002
3.33
Jul 23
0.20
0.60
0.040
0.002
0.010
4.00
Jul 30
0.06
3.08
0.190
0.050
0.340
4.17
__________________________________________________________________________
1/ TSSM Motiles = juveniles + adults
2/ Ratio = TSSM motiles/predator mite motiles: predator motiles = juveniles + adults
Study no. 4. East Section. The results of this study are shown in Table 7. Populations of
TSSM motiles remained below the treatment threshold of 5.0/leaf during this study and
dropped to below 1.0 motiles / leaf after June 26, and remained at low levels through July
30, at which time sampling was discontinued. Comite (propargite 2.5 pints/acre) and
Thiolux (sulfur 4.0 Ibs ai/acre) was applied on May 25, June 22 and July 17 to suppress
populations of TSSM. Populations of TSSM motiles and eggs resurged after the May 25
application and were not maintained below 1.0/leaf until after June 26 when predator mite
populations reached their highest levels. Predator mite motiles began to increase after
June 13 and remained at high levels until July 13, after which they declined following the
reduction of TSSM on July 7. The ratio of TSSM motiles to predator mite motiles reached a
high of 53:1 on June 3, but then declined to below 5:1 after June 19 (Table 7).
Table 7. Mean number of motile TSSM motiles, TSSM eggs, adult predator mites, juvenile
predator mites, predator mite eggs and the ratio of TSSM motiles/predator mite motiles
observed in a 30 foot by 200 foot section peppermint field located in Lower Bridge, Oregon
1992. Small plot no. 4, East section.
________________________________________________________________________________
TSSM
Predator Mites
Sample Mean no. Mean
no. Mean no. Mean no. Mean
no. Ratio
Date Motiles
1/ Eggs Adults
Juveniles Eggs
TS/Pred 2/
_________________________________________________________________________________
May 20 2.75
17.14
0.08
0.030
0.070
25.00
Jun 03 1.06
14.00
0.02
0.000
0.040
53.00
Jun 13 1.74
14.91
0.08
0.000
0.040
21.75
Jun 19 3.19
23.05
0.12
0.020
0.190
22.78
Jun 26
1.78
15.17
0.44
0.000
0.280
4.05
Jul 03
0.34
5.54
0.23
0.060
0.230
0.94
Jul 07
0.12
1.30
0.39
0.140
0.360
4.33
Jul 13
0.10
0.51
0.23
0.020
0.070
0.37
Jul 23
0.04
0.01
0.02
0.003
0.000
2.00
Jul 30
0.01
0.09
0.02
0.020
0.000
0.50
_________________________________________________________________________________
1/ TSSM Motiles = juveniles + adults
2/ Ratio = TSSM motiles/predator mite motiles: predator motiles = juveniles + adults
Discussion
Entire field analysis
The results of the population dynamics studies in
entire fields suggest that predators are effective regulators of TSSM under some field
conditions. Within entire fields where predators were detected on all sampling occasions
and the ratio of TSSM motiles to predator mite motiles was consistently below 100:1,
acaricide applications were required less frequently than in fields where predators were
either not detected or where the ratio of TSSM motiles to predator mite motiles were
frequently above 100:1. Ideally this ratio should be below 30:1 as populations of TSSM
decline over time.
Applications of Comite were more effective against populations of TSSM in fields with
predator mite motile populations above 0.03/leaf. Applications of sulfur at rates above
3.0 Ibs/A appeared to reduce populations of predator mite adults and eggs; this may delay
the increases in predator mites that are necessary to effectively regulate TSSM
populations.
Populations of TSSM were not effectively regulated in
fields where predator mite populations were low, or not detected, until predator mite
populations increased. At the Madras site predators appeared to regulate TSSM throughout
the season (Table 4). In fields where predator mite populations were above 0.03/leaf, TSSM
and predator mites followed a typical predator to prey relationship. In these situations,
populations of predators declined about two weeks after the decline of TSSM.
Small Plot Analysis
TSSM populations increase in various sized
"hotspots" in mint fields during the growing season. As spider mites increase in
these "hotspots", it is important that predator mites colonize them in order for
effective regulation to occur. Predator mite motiles tend to increase in numbers as
populations of TSSM decline, which suggests a typical predator to prey relationship.
Predator mite motiles appear to work most effectively
at regulating TSSM below the treatment threshold in "hotspots" when the TSSM to
predator mite ratio is below 50:1 (Tables 5, 6, and 7). For this reason, it is important
to carefully and frequently monitor fields to detect changes in the ratio of TSSM motiles
to predator mite motiles. Given the opportunity, predators were able to increase to
effective levels even in those plots which initially had low levels of predator mites.
Comite applications appear to work most effectively when the density of predator mites
increase suggesting that predators may enhance the efficacy of Comite in mint in central
Oregon. However, applications of sulfur at rates above 3.0 Ibs/A may disrupt predator
mites and reduce the rate at which predator mites increase to effective population levels.
Disruption of Amblyseius fallacis by Pesticides
The predator mite A. fallacis, appears to be widely distributed throughout the
mint growing areas of central Oregon (Hollingsworth and Berry 1982) (Morris et al. 1991
unpublished). Populations of twospotted spider mite (TSSM) appear to be regulated by A.
fallacis in central Oregon (Morris et al. 1991 and 1992 unpublished). However,
predators are often absent or present at such low densities that effective biological
control is not realized (Hollingsworth and Berry 1982)(Morris et al. 1991 and 1992
unpublished). This suggests that they may be disrupted by pesticides and other
agricultural practices used in mint production. Because predator mites are known to be
adversely affected by a wide range of agricultural pesticides, it would be advantageous to
evaluate a number of those that are currently registered for use on mint for their effects
on predator mite populations: new pesticides for which the mint industry in seeking
registration, should also be tested.
An appropriate bio-assay program should include testing under field conditions because
pesticides that are demonstrated to be disruptive in some laboratory bioassays, may be
selective under actual field conditions (Jebson and Mead-Briggs in press).
The objective of this study was to evaluate the
affect of three insecticides registered for use on mint, and two non-registered
insecticides, on A. fallacis in central Oregon using a semi-field technique.
Materials and Methods
For all three tests, the plots were established by placing a PVC pipe enclosure (6 inch
diam., 10 inch high) over mint plants that were observed to have a mixed population of
TSSM and predator mites. A completely randomized design with four replications was used
for each test. Plots were treated with a CO2 pressurized backpack sprayer using a single
nozzle boom with a 9503 nozzle.
Plots were evaluated by collecting a number of plants
from within the PVC plot and placing them in a plastic 'ziplock' storage bag. Samples were
then placed in a cooler and transported back to the laboratory. All leaves were removed
from the stems and the number of TSSM motiles, TSSM eggs, predator mite motiles and
predator mite eggs were counted with the aid of a dissecting microscope to obtain the
number of TSSM and predators/leaf.
Disruption Study no. 1
In this study, we evaluated two registered
insecticides, Orthene (acephate 75 S (1.0 Ib ai/A)) and Lorsban (chlorpyrifos 4E (2.0 Ibs
ai/A), and one unregistered insecticide, Asana (esfenvalerate 0.66EC (0.05 Ibs ai/A)), for
their affects on TSSM and A. fallacies. Acaricides were mixed in a solution
equivalent to 100 gallons/acre (GPA) and the foliage was sprayed to wet.
This trial was conducted in a four year old field of
peppermint (variety Todd's Mitchum) located one mile south of Madras, Oregon. PVC pipe
enclosures were placed over plants that had natural populations of both TSSM and A.
fallacis. The top two inches of the pipes were coated with 'stickum' and the bottom of the
pipes were sunk in the soil two inches to prevent escape or immigration by predator mites.
Treatments were applied on May 1, 1992 at 6:30 pm. The temperature at the time of
application was 75°F, wind speed was 0-1 NW and the mint stage of growth was 1-4 tall.
Treatments were evaluated twice; once on May 6 and
again on May 13, 1992. Four plants were collected from each plot on May 6 and 10 plants
were collected from each plot on May 13.
Disruption Study no. 2
This trial was set up in the same field and used the
same set of treatments and procedures as in study no. 1, with the exception that the
foliage in the pots was not treated to wet, but rather, the pesticides were applied at the
actual field rates in 100 GPA total spray solution.
Treatments were applied on May 8, 1992, at 8:00 a.m. Temperature at the time of
application was 55°F, wind speed 1-3 mph NW and the mint stage of growth was 2-5 inches.
Treatments were evaluated twice; once on May 15 and
again on May 26, 1992. Four plants were collected from each plot on May 15 and 9 plants
were collected from each plot on May 26, 1992. Disruption Study no. 3
This trial was conducted in the same field as in study no. 2. In this experiment we
evaluated one registered insecticide, Vydate (oxamyl 2L (1.0 Ib ai/A) and one unregistered
insecticide, Capture (bifenthrin 2EC (0.06 Ibs ai/A), for their affects on TSSM and A.
fallacis. All treatments were applied at actual field rates in 100 GPA total spray
solution. Plots were treated on June 12, 1992, at 7:00 pm. The temperature at the time of
application was 69°F, wind speed 0-2 mph from the NW and the mint stage of growth was 1
5-20 inches.
Plots consisted of 10 inch diam PVC pipe enclosures cut to a height of 15 inches. The
larger PVC pipes were used to accommodate the expanded mint growth.
Because Vydate and Capture have acaricidal activity,
treatments were applied after the TSSM populations had declined but prior to decline of
the predator mites. By doing this, a reduction in predator mite populations in the treated
plots, when compared to the untreated plots, would not be correlated with a reduction in
TSSM populations in the treated plots, but would be related to a treatment effect
resulting from application of the pesticides.
Plots were evaluated once on June 20, 1992 by collecting six plants from each plot.
Results
Disruption Study no. 1
Results of the first disruption study comparing three
different Insecticides for their effect on populations of T. urticae to A. fallacis
are shown in Tables 8 and 9. None of the pesticides tested significantly (P < 0.05)
reduced populations of TSSM motiles or eggs compared to the untreated check (Table 8).
On May 6, 1992, there was a significant (P<0.05)
reduction in the mean number of predator mite motiles detected in the Lorsban and Asana
treatments compared to either the Orthene treatment or the untreated check (Table 9).
Predator mites were reduced by 63% in the Lorsban treatment and 100% in the Asana
treatment when compared to the untreated check. There was no significant (P<0.05)
difference in the mean number of predator mites observed between the Orthene treatment and
the untreated check. There was a significant (P<0.05) reduction in the mean number of
predator mite eggs in plots treated with Lorsban and Asana when compared' to the untreated
check: 88% and 91% respectively (Table 9).
On May 13, 1992, significantly (P<0.05) fewer predator mite motiles were detected in
the Lorsban and Asana treatments compared to either the Orthene treatment or the untreated
check. Compared to the untreated check, Lorsban reduced populations of motiles by 94%
while Asana reduced populations by 100%. Predator mite eggs were significantly (P<0.05)
reduced in plots treated with Orthene, Lorsban and Asana, resulting in reductions of 68%,
94% and 100% respectively.
Table 8. Evaluation of insecticides on populations of T. urticae (TSSM), Madras,
1992.
___________________________________________________________________________
Mean No. / Leaf
May 6 Post Treatment May 13 Post Treatment
Rate TSSM
TSSM
TSSM TSSM
Treatment Ibs ai/A No. Motile No.
Eggs No. Motile No. Eggs
____________________________________________________________________________
Untreated -
2.16a 5.36a
0.69a
2.31a
Orthene 75S 1.00
2.21a
2.47a
1.64a
3.62a
Lorsban 4E 2.00
2.91a
5.28a
1.33a
5.6 a
Asana .66E 0.05
2.26a
5.70a
0.58a
4.31a
____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Table 9. Evaluation of insecticides on populations of A. fallacis, Madras 1992.
____________________________________________________________________________
Mean No. / Leaf
May 6 Post Treatment May 13 Post Treatment
Rate Predator
Predator Predator
Predator
Treatment Ibs ai/A
No. Motile No. Eggs
No. Motile No. Eggs
____________________________________________________________________________
Untreated
-
0.16 a 0.25 a
0.25 a
0.21 a
Orthene 75S 1.00
0.15
a 0.11 ab
0.13 ab
0.02 b
Lorsban 4E 2.00
0.06
b 0.03 bc
0.02 bc
0.01 b
Asana .66E 0.05
0.00
b 0.02 bc
0.00 bc
0.00 b
____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Disruption Study no. 2
Results indicate that there were no significant
differences in the mean number of TSSM motiles or eggs between pesticide treatments (Table
10). Predator mite motiles were significantly (P<0.05) reduced in the Asana treatment
when compared to the untreated check; by 100% in this study. There were no significant
differences in the mean number of predator mites motiles detected between the Orthene,
Lorsban and control treatments. Significantly (P<0.05) fewer predator mite eggs were
detected in the Orthene and Asana treatments when compared to the untreated check; 79% and
100% respectively.
Table 10. Impacts of insecticides on populations of T. urticae (TSSM) and A.
fallacis in Madras, Oregon, 1992.
____________________________________________________________________________
Mean No. / Leaf
May
26, Post Treatment
Rate TSSM
TSSM
Predator Predator
Treatment Ibs ai/A No. Motile No.
Eggs No. Motile No. Eggs
____________________________________________________________________________
Untreated -
1.73a
4.07a
0.32a
0.2a
Orthene 75S 1.00
1.16a
7.96a
0.20a
0.06bc
Lorsban 4E 2.00
1.21a
2.96a
0.20a
0.21ab
Asana .66E 0.05
1.27a
4.75a
0.00b
0.00cd
SE = 0.05 SE =0.06
____________________________________________________________________________
Means with same letter are not significantly
(P<0.05) different. FPLSD.
Disruption Study no. 3
Results of the third predator mite disruption study
showed that there were no significant differences between treatments in the mean number of
TSSM motiles or eggs detected (Table 11).
There were significant (P<0.05) reductions in the mean number of predator mite motiles
observed in the Vydate and Capture treated plots when compared to the untreated check
plots; 84% and 100% respectively. There were no significant differences in the mean number
of predator mite eggs detected between treatments.
Table 11. Evaluation of insecticides on populations of T. urticae (TSSM) and A.
fallacis in Madras, Oregon, 1992.
___________________________________________________________________________
Mean No. / Leaf
June 20 Post Treatment June 20 Post Treatment
Rate TSSM
TSSM
Predator
Predator
Treatment Ibs ai/A No. Motile
No. Eggs No. Motile No
Eggs
___________________________________________________________________________
Untreated
--
0.000a 0.01a
0.13a
0.0075a
Vydate 2L 1.00
0.000a
0.00a
0.02b
0.0025a
Capture 2E 0.06
0.005a
0.00a
0.00b
0.0000a
SE = 0.02
__________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Discussion
These data suggest that applications of Orthene and Lorsban adversely affected predator
mites, and should only be applied when target pest populations (i.e., cutworms, adult
strawberry root weevils) are determined to be above the economic threshold. However,
Orthene appears to be less toxic to A. fallacis than Lorsban when the foliage was sprayed
to wet. When Orthene and Lorsban were both applied at field rates, only Orthene
significantly reduced predator mite eggs under these test conditions. These results agree
with evaluations of Orthene and Lorsban in larger field plots.
Both Asana and Capture were very toxic to A. fallacis motiles and eggs under these test
conditions, and if registered, could disrupt A. fallacis and result in secondary outbreaks
of TSSM. However, no resurgence of TSSM was observed in this study; perhaps because of the
short evaluation period.
At present, two large field plots are being studied
in central Oregon to evaluate the possible disruption of A. fallacis, in the fall, by
Vydate, Asana and Furadan (carbofuran). These studies will investigate the effects of
these treatments on both A. fallacis and TSSM through the fall of 1992 and into the winter
and spring of 1993.
Acaricide Efficacy
Because of documented resistance in twospotted spider mite (TSSM) in mint to dicofol, and
the potential this product has for disrupting predator mites, the mint industry should
begin developing alternative selective acaricides to Kelthane that are complimentary to
Comite. If Comite is relied upon as the mint industry's only effective acaricide,
resistance to this product may soon follow; if it has not already occurred.
The objective of this series of experiments was to
begin screening perspective selective acaricides for possible inclusion into a spider mite
management program on mint. A second objective was to determine the effectiveness of
currently registered acaricides that the mint industry depends on to manage TSSM
outbreaks.
Materials and Methods
Six acaricide efficacy trials were conducted on peppermint in Marion, Deschutes and
Jefferson counties during 1992. The acaricides that were evaluated were: (1) Kelthane MF
(dicofol) registered for use on mint, (2) Comite (propargite 6.55 EC) registered for use
on mint and relatively non-toxic to predator mites; (3) abamectin which is presently not
registered for use on mint but may be worth pursuing because preliminary results indicate
that low rates of abamectin are "soft" on predator mites; (4) Apollo
(clofentezine 4 SC) which is currently not registered for use on mint, however, this
acaricide would be a valuable tool for mint production because it is "soft" on
predator mites and has ovicidal activity; (5) Vendex (fenbutatin oxide 4L) which is not
registered for use on mint, but is selective for predator mites; and (6) Capture
(bifenthrin 2EC) which is not currently registered for use on mint but has been reported
to disrupt predator mites.
For all tests, acaricides were applied in 30 GPA using a CO2 pressurized backpack sprayer
equipped with a four nozzle boom with Teejet 9504 nozzles. Treatments were replicated four
times in a randomized complete block design; untreated plots served as checks. Plots were
evaluated by collecting 10 plants from each plot and placing them into a brown paper bag
which was then put into a plastic garbage bag. The plastic garbage bags were placed in a
cooler with blue ice and transported back to the laboratory. Three leaves from each plant,
one from the top, middle and bottom, were removed from each of the ten plants collected
from each plot, and examined under a dissecting microscope. The number of TSSM motiles,
TSSM eggs, predator motiles and predator eggs were counted.
Acaricide Efficacy Study no. 1
In this study, the objective was to determine how
well six acaricide treatments, applied in the early spring, would effectively manage
spider mites on mint. The acaricide treatments were: (1) Kelthane 40.0 oz/A, (2) Comite
40.0 oz/A, (3) abamectin 8.0 oz/A, (4) Apollo 16.0 oz/A, (5) Comite 40.0 oz/A + Apollo 8.0
oz/A, and (6) Comite 20.0 oz/A + Apollo 8.0 oz/A.
The trial was conducted in a peppermint field located
in Gateway, Oregon. Treatments were applied on May 1, 1992, at 8:30 a.m. The temperature
at the time of application was 48°F, wind was 0-1 mph from NW and the mint stage of
growth was 1-4 inches.
Acaricide Efficacy Study no. 2.
The objective of this study was to evaluate the
effectiveness of several acaricide treatments that are selective for TSSM and
"soft" on predator mites. The acaricide treatments were: (1 ) Apollo 16 oz/A,
(2) Comite 40.0 oz/A, (3) Comite 20.0 oz/A + Apollo 8.0 oz/A, (4) Vendex 48 oz/A, (5)
Vendex 48 oz/A + Apollo 8.0 oz/A, and (6) Vendex 32 oz/A + Apollo 4.0 oz/A.
The trial was conducted in a peppermint field located
near Lower Bridge, Oregon. Treatments were applied on June 19, 1992, at 8:00 a.m. The
temperature at the time of application was 73°F, wind was 0-1 mph from NW and the mint
stage of growth was 5-12 inches.
Acaricide Efficacy Study no. 3
The objective and set of treatments for the third
acaricide efficacy study were the same as for acaricide efficacy study no. 2, with the
exception that the trial was conducted in the Willamette Valley.
The trial was conducted in a peppermint field located
two miles east of Jefferson, Oregon. Treatments were applied on June 19, 1992, at 8:00
p.m. The temperature at the time of application was 76°F, wind was 2-4 mph from NNW and
the mint stage of growth was 24-36 inch long mint stems that had lodged.
Acaricide Efficacy Study no. 4
The objective of this study was to do a general
screening of different acaricides to see how well they managed populations of TSSM in
mint.
The study was conducted in a peppermint field located
in Gateway, Oregon. Treatments were applied on June 17, 1992, at 7:30 a.m. The temperature
at the time of application was 70°F, wind was 0-1 mph from the west and the mint stage of
growth was 8-16 inches.
Results and Discussion
Because resistance to Kelthane has been documented in TSSM on mint, and because Kelthane
has been found to be disruptive to predator mites, it would be advantageous to register
several new selective acaricides for use on mint. Also, if the mint industry continues to
depend solely on Comite to manage outbreaks of TSSM, then resistance to this acaricide is
likely to occur; if it has not already done so.
During 1992, the performance of four acaricides were
evaluated for their effectiveness to reduce populations of TSSM on mint in central Oregon
and the Willamette Valley: 1 ) abamectin, 2) Apollo, 3) Vendex, and 4) Capture. Results of
these experiments are summarized in Tables 12 through 18. Abamectin was very effective at
reducing populations of TSSM in mint (Tables 12, 13, 17, 18). Apollo, while it was not
often effective alone, was consistently among the best treatments when applied in
combination with a one half rate of Comite or mixed with Vendex (Tables 12, 13, 14, 15,
16). Vendex was not as effective as either abamectin or Comite when applied by itself
(Tables 14, 15, 16, 17, 18), however, it was quite efficacious in combination with Apollo
(Tables 14, 15, 16). Because Vendex is known not to disrupt predator mites, this product
may be worth pursuing if a registration for Apollo is also possible. Capture also
significantly reduced populations of TSSM (Tables 17, 18), however, this product has also
been shown to be very disruptive to predator mites (Table 1 1 ) and could result in
resurgence of TSSM following application.
Table 12. Efficacy of acaricides on populations of T. urticae (TSSM) motile
growth stages infesting a peppermint field near Gateway, Oregon, 1992.
__________________________________________________________________________
Mean No. TSSM Motiles / Leaf
Evaluation Dates 1992
Rate Pre-Treat Post-Treat
Post-Treat Post-Treat
Treatment oz's/A April 30
May 17
May 29
June 10
__________________________________________________________________________
Untreated -
6.19a
10.44a
6.91a
4.10a
Kelthane 40.0
4.65a
1.61b
2.13a
3.64ab
Comite 40.0
4.51a
1.86b
2.08a
2.67abc
Abamectin 8.0
2.82a
1.67b
1.21b
2.59abc
Apollo 16.0
2.62a
14.23a
6.45a
2.21bc
Com + Apol 40 + 8 3.23a
1.84b
1.03b
1.13c
Com + Apol 20 + 8 2.47a
1.28b
1.02b
1.44c
SE =1.36 SE =1.97 SE =
0.52 SE = 0.61
__________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Com = Comite, Apol = Apollo.
Table 13. Efficacy of acaricides on populations of T. urticae (TSSM) eggs in a
peppermint field located near Gateway, Oregon, 1992.
__________________________________________________________________________
Mean No. TSSM Eggs/ Leaf
Evaluation Dates 1992
Rate Pre-Treat
Post-Treat Post-Treat Post-Treat
Treatment oz's/A April
30 May 17
May 29 June 10
__________________________________________________________________________
Untreated -
51.37a 14.76a
19.36a
6.10bc
Kelthane 40.0
37.64a
8.08abc
13.48a
10.86a
Comite 40.0
36.69a
3.2bc
9.64a
9.41ab
Abamectin 8.0
26.66a
1.12c
4.86a
4.58abc
Apollo 16.0
46.09a
14.5a
12.50a
4.03c
Com + Apol 40 + 8 37.36a
5.44bc
7.03a
3.39c
Com + Apol 20 + 8 35.80a
9.3ab
9.13a
2.29c
SE =16.9 SE =2.40
SE = 3.69 SE = 1.36
__________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Com = Comite, Apol = Apollo.
Table 14. Efficacy of acaricides on populations of T. urticae (TSSM) motile
growth stages infesting a peppermint field in Lower Bridge, Oregon, 1992.
___________________________________________________________________________
Mean No. TSSM Motiles / Leaf
Evaluation Dates 1992
Rate Pre-Treat Post-Treat
Post-Treat Post-Treat
Treatment oz's/A June 19
July 3
July 14
July 28
___________________________________________________________________________
Untreated -
3.78a
7.78a
13.64
2.36a
Apollo 16.0
2.18a
1.33cd
10.48
1.12a
Comite 40.0
2.63a
1.44cd
5.70
0.55a
Com + Apol 20 + 8 3.67a
0.44d
2.18 *
1.42a
Vendex 48.0
4.41a
4.56b
12.77
1.65a
Ven + Apol 48 + 8 2.68a
2.19cd
3.72
1.05a
Ven + Apol 32 + 8 3.61a
3.08bc
6.68
1.00a
SE = 0.74 SE =0.80 SE =
3.43 SE = 0.62
____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
* Significantly different than the untreated check (LSD P<0.05).
Com = Comite, Apol = Apol, Ven = Vendex
Table 15. Efficacy of acaricides on populations of T. urticae (TSSM) eggs in a
peppermint field in Lower Bridge, Oregon, 1992.
____________________________________________________________________________
Mean No. TSSM Eggs / Leaf
Evaluation Dates 1992
Rate Pre-Treat Post-Treat
Post-Treat Post-Treat
Treatment oz's/A June 19
July 3
July 14 July 28
____________________________________________________________________________
Untreated -
23.84a
46.09a 34.85a
4.70a
Apollo 16.0
17.09a
29.06ab
33.97a 10.14a
Comite 40.0
19.24a
18.00b 19.94a
8.65a
Com +Apol 20 + 8 20.83a
28.33ab 20.91a
19.65a
Vendex 48.0
23.05a
42.16a 39.43a
5.33a
Ven +Apol 48 + 8 17.53a
30.45ab 25.38a
5.19a
Ven +Apol 32 + 8 19.94a
42.68a 28.03a
7.77a
SE = 4.36 SE =6.08 SE = 5.35
SE =3.83
____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Com = Comite, Apol = Apollo, Ven = Vendex.
Table 16. Efficacy of acaricides on populations of T. urticae (TSSM) motile
stages and eggs in a peppermint field located near Jefferson, Oregon, 1992.
_____________________________________________________________________________
Mean No. TSSM / Leaf
Evaluation Dates 1992
Rate Pre-treatment-June
16 Post-treatment- July 8
Treatment oz's/A Motiles
Eggs
Motiles
Eggs
_____________________________________________________________________________
Untreated -
2.78a
9.54a
5.31a
9.60a
Apollo 16.0
4.58a
19.96a
3.18a 9.99a
Comite 40.0
4.87a
17.30a
0.87cd 3.27a
Com + Apol 20 + 8 5.37a
13.71a
0.27d
1.27a
Vendex 48.0
3.10a
14.09a
2.50bc 9.46a
Ven + Apol 48 + 8 3.40a
11.71a
0.67cd 4.70a
Ven + Apol 32 + 8 3.97a
17.65a
1.34bcd 4.87a
SE = 0.57 SE=2.35
SE =0.69
SE = 2.26
_____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
Com = Comite, Apol = Apollo, Ven = Vendex.
Table 17. Efficacy of acaricides on populations of T. urticae (TSSM ) motile
developmental stages infesting a Peppermint field in Gateway, Oregon, 1992.
_____________________________________________________________________________
Mean No. TSSM Motiles / leaf
Evaluation Dates 1992
Rate
Rate Pre-Treat
Post-Treat Post-Treat
Treatment oz's/A Ibs ai/A
June 17
July 1
July 18
_____________________________________________________________________________
Untreated -
12.25a
6.95 0.25a
Kelthane 40.0
15.28a
0.04* 0.01a
Comite 40.0
12.74a
0.31* 0.03a
Abamectin 4.0
13.65a
2.24 0.90a
Abamectin 8.0
15.57a
0.83* 0.09a
Vendex 32.0
10.07a
3.84
0.46a
Vendex 48.0
8.84a
4.15 0.64a
Capture 3.8
0.06
8.11a
0.81*
1.00a
Capture 6.4
0.10
14.15a
0.34*
0.69a
SE=2.84 SE =1.72 SE = 0.36
_____________________________________________________________________________
Means with same letter are not significantly (P<0.05) different. FPLSD.
*Means are significantly different from the untreated check (LSD P<0.05).
Table 18. Efficacy of acaricides on populations of T. urticae (TSSM) egg stages
in a peppermint field in Gateway, Oregon, 1992.
______________________________________________________________________________
Mean No. TSSM Eggs / Leaf
Evaluation Dates 1992
Rate Rate
Pre-Treat Post-Treat Post-Treat
Treatment oz's/A Ibs ai/A
June 17
July 1
July 18
______________________________________________________________________________
Untreated -
6.78a
16.87a 0.65
Kelthane 40.0
7.97a 1.07b
0.45
Comite 40.0
11.69a
2.28b 0.17
Abamectin 4.0
7.31a
9.73ab 2.53
Abamectin 8.0
7.52a 1.91b
0.32
Vendex 32.0
6.76a
3.84ab 1.51
Vendex 48.0
9.34a 13.32a
3.23
Capture 3.8
0.06
6.46a
7.17ab
6.17*
Capture 6.4
0.10
7.83a
2.54b
4.08
SE = 2.03 SE = 3.55 SE = 1.54
______________________________________________________________________________
Means with same letter are not significantly (P~0.05) different. FPLSD
*Means are significantly different from the untreated check (LSD P<0.05) |
