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Group Title: Research Report - University of Florida Central Florida Research and Education Center ; 90-08
Title: Evaluation of selected Bacillus thuringiensis insecticides for the control of Diamondback moth, Plutella xylostella (Linnaeus) in cabbage
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Title: Evaluation of selected Bacillus thuringiensis insecticides for the control of Diamondback moth, Plutella xylostella (Linnaeus) in cabbage
Series Title: Research Report - University of Florida Central Florida Research and Education Center ; 90-08
Physical Description: Book
Language: English
Creator: Leibee, Gary L.
Savage, Kenneth E.
Publisher: University of Florida, Central Florida Research & Education Center
Publication Date: 1989
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Bibliographic ID: UF00075872
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 122930258

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HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





100

CFS


I .: Li


University of Florida
J CENTRAL FLORIDA RESEARCH & EDUCATION CENTER
S ianford, Florida

Research Report SAN 90-08 December 19

Evaluation of selected Bacillus thuringiensis insecticides for the
Scontrol" of "diamondback moth, Plutella xylostella (Linnaeus), in cabbage
Central Scence
Library Gary L. Leibee and Kenneth E. Savage


89


JAN 11 1990
Introduction
University of Elorida I
Diamondback moth (DBM),, Plutella xylostella (L.), populations have become
veryfl~flTTYTcutlto control with pyrethroids, organophosphates, and carbamates in
the last four years in central Florida (personal observation). Laboratory
studies have indicated a high level of resistance to fenvalerate and methomyl
in central Florida (Leibee, unpublished data). Bacillus thuringiensis (Bt) based
products are currently the principle insecticides being used.

The objective of this study was to evaluate two new Bt insecticides, MYX
7275 (Mycogen Corp.) and EG 2371 (Ecogen, Inc.), for the control of DBM.

Methods and Materials

'Golden Acre Yellows Resistant' cabbage was grown in Myakka fine sand at
the Central Florida Research and Education Center in Sanford, FL. The cabbage
was transplanted on April 18 and 19, 1989, from seedbeds sown on March 15, 1989.
No insecticide was used in the seedbed to allow the build up of insect pests.
Plots consisted of four 50-ft rows with a 2.5-ft row-spacing and about a 11-in
plant spacing. Four rows were left unplanted between each plot to provide a
separation of 12.5 feet. Plots were arranged in four blocks and the blocks were
separated by 25-ft alleyways. Treatments were assigned to the plots in a
randomized complete block design with four replications. Nemacur 15G 2 lb
ai/acre was applied pretransplant in 15" band for nematode control. Randox 4EC
and Vegedex 4EC, both at 2 Ib ai/acre, were applied for weed control two days
after transplant. Sprays were applied with a tractor-mounted, compressed-air
sprayer. Three nozzles (D2-25) were used per row; one overhead and one drop on
each side. The delivery rate was 50 gpa with a boom pressure of about 45 psi
and a speed of 2 mph. Application dates were May 4, 10, 18, 25, 30, and June
5. The Bt insecticidal treatments (expressed as amount of formulation per acre)
consisted of MYX 7275 (Mycogen Corp.) at 523, 2095, and 2095 ml, MYX 7275 at 2095
ml plus 950 ml of Coax Flowable (CCT Corp.), MYX 2222 (Mycogen Corp) at 1960 ml,
EG 2371 OF (Ecogen, Inc.) at 0.5, 1.0, and 2.0 qt, EG 2371 WP at 0.5, 1.0, and
2.0 Ib, Dipel 4L (Abbott Labs) at 1047 ml, Dipel 2X (Abbott Labs) at 0.5 lb, and
Javelin (Sandoz Corp.) at 326 and 1304 ml. To compare the MYX 7275 with the MYX
2222, Dipel 4L, and Javelin, the amounts of formulation used per acre in the MYX
2222, Dipel 4L, and Javelin treatments were adjusted to deliver amounts of toxic
protein (toxic protein levels determined by Mycogen) equivalent to that delivered
by the low and high rate of MYX 7275 (5 and 18 g, respectively). Pydrin 2.4EC
* (E. I. duPont deNemours & Co.) at 0.2 lb ai., Lannate 1.8L (E. I. duPont de
Nemours & Co.) at 0.9 lb ai, and an untreated check were included. Bond
(Loveland Industries, Inc.), a sticker-extender-deposition agent, was used with


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the Lannate!, Dipel 2X,' and EG 2371 OF and WP at 9.5 ml per gallon of spray. I
PlyacI(Hopkins Agric. Chem. Corp.), a spreader-sticker, was usediat the rate'of
1.2 ml per,gallon of spray with the MYX 7275, MYX 2222, Pydrin, Dipel 4L, and
Javelin treatments. ., I i :

Plants were sampled; on May, 24 and June 12, .,1989, to determine larvAl
numbers. i;Four randomly selectediplants per plot. (two from.the middle of eadh
center row) were sampled by carefully cutting the stem below the portion of the
plant containing the bud or head and the next four youngest leaves (wrapper
leaves in the head stage). The stem was cut below all the foliage if only four
leaves were present. The four plants were placed in a plastic bag for transport
back to the processing area. Each sample of four plants was placed into a
Berlese funnel and subjected to heat for 24 hrs. When heads were present, the
infested head leaves were carefully pulled away from the head and the uninfested
portion of the head was cut out to reduce the amount of plant material that went
into the funnel. Larvae were collected into 70% ethyl alcohol. Cabbage looper,.
Trichoplusia ni (Hubner), and imported cabbageworm, Pieris rapae (L.), larvae
were categorized according to size (small, medium, and large). DBM larvae were
categorized according to instar by head capsule width. Ten mature plants were
rated for damage on June 10, 1989, using a scale of 1-6 similar to that of Greene
et al., Jour. of Econ. Entomol. 62(4):798-800: 1 no apparent insect feeding;
2 0-1% defoliation of wrapper leaves only; 3 2-5% defoliation of wrapper
leaves only; 4 6-10% defoliation of wrapper leaves and minor feeding damage
on head, head unmarketable during normal market conditions; 5 11-30%
defoliation of wrapper leaves, moderate number of scars on head; 6 over 30%
defoliation of .wrapper leaves and numerous feeding scars on head. Percent
marketability was based on the proportion of plants having damage ratings less
than or equal to 3 for normal market conditions.

Results and Discussion

Damage ratings, percent marketability, and counts of DBM larvae (second
through the fourth instar combined) per four plants for two sampling dates are
presented in Table 1. The DBM infestation was very heavy. Cabbage looper,
imported cabbageworm, and cabbage webworm, Hellula rogatalis (Hulst), were also
present. The numbers of cabbage looper and imported cabbageworm larvae were too
low to yield any significant results. The cabbage webworm counts were low,
but persisted throughout the season, which was considered unusual. The first
instar DBM larva was not included in the counts because it generally feeds inside
the leaf as a leafminer and would not be subject to retrieval by heat extraction.
Not all the data were entered into the analyses of variance, as indicated in
Table 1, because an area at one end of the field contained stunted plants which
yielded low larval counts and low damage ratings regardless of insecticide
treatment. Apparently these stunted plants were less attractive to the insects
than the plants in the rest of the experiment. The stunting was apparently
caused by excessive soil moisture from nearby ponds and the build up of soluble
salts in the root zone. Excluding these plots resulted in number of missing data
points in the experiment. Data for a treatment were analyzed only if there were
at least 3 replications not in the area of stunted plants. As a result, the data
for EG 2371 OF at 2.0 lb, Javelin at 1304 ml, and Lannate 1.8L were not included
in the analysis. Also, larval count data from June 12 for the untreated check
* were removed from analysis because the counts were abnormally high in one
plot in addition to one plot being stunted. This high larval count was obviously
due to its proximity to a Pydrin plot from which many DBM adults had apparently










migrated. The means for data not included in the statistical analyses were
included in Table 1 if they were considered typical and therefore useful
information. Also, yield data were not taken due to the uncontrollable variation
in plant size. No problems with formulations were encountered and no
phytotoxicity was observed.

The only treatment that reduced damage to an acceptable level was the high
rate of MYX 7275. The addition of Coax to the high rate of MYX 7275 caused a
significant (P <0.05) increase in the level of damage over the high rate of MYX
7275 alone. Even though the remaining treatments did not reduce damage to an
acceptable level, several treatments effectively controlled the DBM. The highest
level of DBM control was achieved with EG 2371 OF and MYX 7275. The OF
formulation of EG 2371 was superior to the WP formulation in reducing damage even
though the larval counts were not statistically different (P > 0.05). The low
levels of marketability were due to head damage resulting from feeding activity
of the cabbage webworm and the cabbage looper. Even though these two species
were present in very low numbers their activity was concentrated on the head
which rendered the plant unmarketable even though there was effective control
of the DBM. The lack of control of DBM in this experiment by fenvalerate
indicated that a highly insecticide resistant population was present. Larval
counts taken up to and including May 24 showed that Pydrin was controlling the
DBM, indicating that there were susceptible individuals in the population at the
beginning of the season. Based on the larval counts of May 24, it appears that
the initial population consisted of mostly susceptible individuals. The
individuals remaining after the Pydrin treatments were probably resistant and
were the source'of the large build up of resistant individuals that were present
* in the Pydrin plots by June 12. It is interesting to note that there were more
larvae in the fenvalerate treatment than in the untreated check on June 12 which
is the reverse of that found on May 24. The lower number of larvae in the
untreated check on June 12 was probably due to the activity of predators
(spiders, wasps, dragonflies, earwigs, carabids) and parasites (Diadegma spp.
and some unidentified chalcids) that were observed to be in the untreated plots
and not in the pyrethroid plots.










Table 1. Effects of selected
diamondback moth in cabbage on damage
larval counts (2-4 instar combined).


insecticidal treatments for control of
rating (DR), percent marketability, and


Treatment and Damage8 %Mrktbla
formulation/A rating (DR<3) 2-4 instar DBMa
(unless AI) 6/10 6/10 5/24 6/12


Untreated check
Pydrin 2.4EC 0.2 lb AI
Lannate 1.8L 0.9 Ib AI
Dipel 4L 1047 ml
Javelin 326 ml
Javelin 1304 ml
Dipel 2X WP 0.5 lb
MYX 7275 523 ml
MYX 7275 2095 ml
MYX 7275 2095 ml +
Coax (19 ml/gallon)
MYX 2222 1960 ml
EG 2371 OF 0.5 qt
EG 2371 OF 1.0 qt
EG 2371 OF 2.0 qt
EG 2371 WP 0.5 lb
EG 2371 WP 1.0 Ib
EG 2371 WP 2.0 Ib


5.7 a
5.3 a
3.9 b


3.9 b
4.0 b
3.7 -
3.8 be
3.8 bc
2.4 f


3.0 e
3.1 de
3.4 cde
3.0 e
2.7 -
3.8 be

3.5 bd
3.5 bed


0.0 g
0.0 g
7.5 efg
7.5 efg
5.0 fg
20.0 -
17.5 def
22.5 cd
80.0 a


57.5 ab
57.5 ab
40.0 bc
56.7 ab
65.0 -
17.5 cde
_-- b

32.5 bcd


16.0 a
2.8 b
0.3 -
1.3 bc
1.8 bc
0.8 -
2.7 b
1.8 be
1.0 bc


0.8 be
0.5 be
0.8 bc
0.0 c
0.0 -
1.0 bc
1.3 bc
1.0 bc


8.0 -
42.3 a
2.3 -
4.8 bc
7.5 b
2.0 -
2.7 cd
1.5 d
1.0 d


1.5 d
1.3 d
2.5 cd
1.3 d
0.5 -
1.7 d
1.0 d
3.0 cd -


aMeans in the same column followed by
different at the .05 level by DMRT.


the same letter are not significantly
Analyses of variance performed on


transformed data except for damage ratings. Larval count data were transformed
to sq. rt. (X + 1.5). Percent marketability data were transformed to arc
sine. A dash indicates that data were not included in the ANOVA because there
were less than 3 replications (see text).

bDamage ratings for marketability not valid due to all 4 replications being
located in an area of stunted cabbage due to excessive soil moisture and high
salts content of soil (see text).




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