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AUG 1 8. 1989.

Agricultural 5

Field Tests of

Experiment p
Station, 5

Fenvalerate for

JVka; Haven 5

Control of Black
Vine Weevil

BY JAMES L. HANULA

Bulletin 860
June 1988

STATE

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Field Tests of Fenvalerate

for Control of Black Vine Weevil

BY JAMES L. HANULA

The black vine weevil, Otiorhynchus
sulcatus (F.), is the major pest of ornamental
nurseries in the northeastern United States
(C. Staines, Maryland Department of
Agriculture, personal communication). The
highly polyphagous adults (Fig. 1) feed on more
than ICO plant species in 46 families (Masaki
et al. 1984). Adults are nocturnal, so they
are rarely seen. However, adult feeding
results in characteristic notches on leaves
(Fig. 1) that can be used to diagnose weevil
presence in a planting before damage occurs.
Although feeding by adults may cause aesthetic
damage to broadleaved evergreens it has very
little impact on plant vigor. On the other
hand, the larvae (Fig. 1 inset) feed on roots
and frequently cause mortality in greenhouse
and nursery plantings. Since effective soil-
applied insecticides are not available, control
efforts are aimed at killing adults before they
lay eggs.

Adults begin emerging from the soil in
late May, and new adults continue to emerge
throughout June, July and early August.
Newly emerged females require approximately
30 days for their ovaries to mature before
they begin laying eggs (Smith 1932). Eggs are
laid on or in the soil (Montgomery & Nielsen
1979), and females prefer to oviposit near
Taxus spp. (Hanula 1988). Newly hatched
larvae move through the soil and, begin feeding
on small roots. They continue to feed on
roots throughout late summer and fall until
soil temperatures become cold (>5.5 C; Smith
1932) and activity ceases. Larvae overwinter
in the soil and become active again in the
spring as soil temperatures rise. During this
time they move near the surface and feed on
any portion of the plant that is below ground,
often resulting in girdling of the stem just

beneath the soil line. Fully developed weevil
larvae transform into pupae in the soil and
emerge as adults several weeks later.

Larvae develop more quickly in container
grown plants maintained under plastic during
the winter. Observations of weevils developing
on container grown azalea, Rhododendron
kiusianum 'Hinocrimson' Makino, showed that
adults emerged approximately 2-3 weeks earlier
than weevils on field grown Taxus cuspitiata
Sieb. & Zucc. However, R. kiusianum was an
inferior food (Hanula 1988), so, consequently,
development may be faster on more favorable
hosts such as taxus.

Adult black vine weevils are unable to fly,
so they are dependent on man for long
distance transport. Therefore, limiting the
movement of infested plants helps slow the
spread of weevils within nurseries.

Acephate (Orthene) is the most widely used
insecticide for control of black vine weevil
adults in Connecticut. Other registered
insecticides such as bendiocarb (Ficam or
Turcam), oxamyl (Vydate), or azinphosm ethyl
(Guthion) have not been widely accepted
because of cost or high mammalian toxicity.
Although acephate is effective, several
applications are required because of its short
residual activity and the prolonged adult
emergence of the weevils. Therefore,
alternatives are needed. Nielsen and
Montgomery (1977) reported that the
insecticide fenvalerate (Pydrin or Asana)
provided control of adults for 4-8 weeks on
taxus foliage. In addition, Nielsen et al.
(1978) suggested that control could be achieved
with a single, well timed application of
fenvalerate, and that pitfall traps were the
most effective means of monitoring adult
activity for timing spray applications.

Connecticut Agricultural Experiment Station

Bulletin 860

This study was conducted to determine the
effectiveness of single and multiple applications
of fenvalerate under field conditions. In
addition, I tested a number of insecticides as
potential controls of late-instar larvae on the
roots of balled and burlapped plants.

MATERIALS AND METHODS

A randomized complete block design with
five treatments (10 replicates/treatment) was
used to test the efficacy of fenvalerate. In
April 1986, 200 Japanese yews, T. cuspidata

'Densa' (45 em diam. canopy), heavily infested
with larvae, were transplanted into a field of
five rows of 10 plots in Windsor, Connecticut.
Each plot contained four plants. Plants were
placed 0.6 m apart within plots, and the plots
were spaced 1.5 and 2.1 m apart within and
between rows, respectively. Each four plant
plot was surrounded by a barrier constructed
from aluminum lawn edging (15 em wide)
coated with Floun (a slippery material that
stops insects from climbing) to prevent adult
weevils from moving between plots. The
barrier was imbedded in the soil so that

mp*

Figure 1— Adult of black vine weevil feeding on foliage of T. cuspidata (left) and larva (inset);
(right) characteristic feeding damage on R. catawbiense.

Black Vine Weevil

10 cm remained above ground. The field was
irrigated with 2-3 cm water/week by overhead
sprinklers. All plots, except the controls,
received an application of fenvalerate at a
rate of 72 g AI/400 liters (0.15 lb AI/100 gal)
applied until runoff with a Solo backpack
sprayer (30 psi) on June 13, 2 weeks after the
first adults were caught in pitfall traps in a
nearby field. The treatments consisted of one
to four applications of fenvalerate applied at
2 week intervals beginning with June 13.
Treatment efficacy was evaluated in May 1987
by sifting the soil beneath the canopy of each
plant to a depth of 4C cm and examining it
for larvae.

A second study was conducted to test four
insecticides for control of larvae in balled and
burlaped plants in the spring. Ninety
T. cuspidata 'Capitata' (ca. 1 m height) were
dug from a weevil-infested field, and the
rootballs were wrapped in burlap and tied
according to standard nursery practice. The
plants were dug May 6, 1986 and treated the
next day by submerging the rootballs in
insecticide solution for 60 sec. Controls were
treated with water. The rootballs of three
plants, not included in the study, were treated
with water and examined immediately to insure
that the solutions penetrated throughout. The
following insecticides were tested at two rates
each: fenvalerate (48 & 96 g AI/400 liter),
oxamyl (Vydate; 119 & 239 g AI/400 liter),
carbofuran (Furadan; 60 & 120 g AI/400 liter)
and chlorpyrifos (Dursban; 478 & 861 g AI/400
liter). Larval mortality was evaluated 5 days
after treatment by removing the soil from the
roots and examining for larvae. Larvae were
considered alive if they moved when prodded
with a pencil point. Plants which contained
five or more larvae were included in the
analysis.

RESULTS

A single application of fenvalerate,
2 weeks after adult weevils began emerging
from the soil, was effective in reducing
subsequent populations of the black vine weevil
on taxus (Fig. 2). Control of summer adults
before they laid eggs resulted in an average
of less than one larva/plant compared to a

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June 13
July 2

Spray Dates

June 13
July 2.16

FIGURE 2— Mean numbers of black vine weevil
larvae recovered from roots of T. cuspidata
plants given none to four foliar applications of
fenvalerate to control adults.

mean of 5.2 larvae/plant in untreated plots.
In addition, one application was as effective as
two to four applications even though residues
were subjected to repeated overhead irrigation
throughout the summer. No phototoxicity was
observed on taxus.

TABLE 1— MORTALITY OF O. SULCATUS
LARVAE FROM T. CUSPIDATA 5 DAYS
AFTER THE ROOTBALL WAS SUBMERGED IN
INSECTICIDE FOR 60 SEC.

Rate

Insecticide

(g AI/

N

% Mortality

400 1.)

(S.E.)

Check

0

8

25.5

(5.98)

Chlorpyrifos

478

9

42.8

(7.34)

(Dursban 4E)

861

7

48.7

(6.85)

Oxamyl

119

6

19.3

(5.36)

(Vydate L)

239

7

41.7

(11.07)

Carbofuran

60

7

27.2

(7.74)

(Furadan 4F)

120

7

32.4

(4.13)

Fenvalerate

48

9

38.8

(6.70)

(Pydrin 2.U EC)

96

6

35.5

(4.42)

Means are not significantly different by
analysis of variance (P < 0.05).

Connecticut Agricultural Experiment Station

BuDetin 860

Larvae were difficult to control. None of
the four insecticides used in the present study
were effective in reducing the number of
mature larvae at the rates applied (Table 1).
The highest mortality (48.736) was achieved
with clorpyrifos but this was not significantly
higher than the controls (25.2%).

DISCUSSION

Fenvalerate was an effective residual
insecticide for the control of adult black vine
weevil. Its use should supplement other
insecticides currently registered for control of
this insect in Connecticut. Current control
efforts require three to four applications of
insecticide throughout July and August, and the
insecticides currently available require higher
rates of application to be effective.
Therefore, the use of fenvalerate should reduce
the amount of insecticide entering the
environment and the overall cost of control,
since only one application is required.
However, complete reliance on a single
insecticide may result in the development of
resistance in the treated population. Nielsen
et al. (1975) demonstrated black vine weevil
resistance to dieldrin in a population in Ohio.
Consequently, alternating the use of
fenvalerate with a second insecticide should
extend the periods of effective use for both
materials.

Some larvae were found on the roots of
plants that had been sprayed four times with
fenvalerate during the summer, even though
care was taken in this study to ensure
complete coverage of the foliage during each
application. Based on these results, it appears
that elimination of this insect from a field is
unlikely. Therefore, once a field is infested it
will probably require insecticidal treatment
until the plants are removed. Proper timing
and thorough coverage will maximize the
effectiveness of the insecticide used.

The relatively ineffective control of mature

larvae noted after plant roots were submerged
in insecticide demonstrates that control of this
stage is less effective than controlling adults.
For example, fenvalerate was effective against
adults but provided poor control of larvae. In
the field, larvae may be distributed to depths
of 40 cm or more, requiring large quantities
of insecticide to adequately treat the soil to
that depth. In addition, deep penetration of
the insecticide into the soil requires either
adequate rainfall or irrigation, which may be
limited or unavailable. Therefore, the most
effective management practice is to control
adult weevils before they lay eggs.

REFERENCES

Hanula, J.L. 1988. Oviposition preference and
host recognition by the black vine weevil,
Otiorhynchus sulcatus (Coleoptera:
Curculionidae). Environ. Entomol. In press.

Masaki, M., K. Ohmura and F. Ichinohe. 1984.
Host range studies of the black vine weevil,
Otiorhynchus sulcatus (F.) (Coleoptera:
Curculionidae). Appl. Entomol. Zool. 19: 95-106.

Montgomery, M.E. and D.G. Nielsen. 1979.
Embryonic development of Otiorhynchus
sulcatus: effect of temperature and humidity.
Entomol. Exp. & Appl. 26: 24-32.

Nielsen, D.G. and M.E. Montgomery. 1977.
Toxicity and persistence of foliar insecticide
sprays against black vine weevil. J. Econ.
Entomol. 70: 510-512.

Nielsen, D.G., M.J. Dunlap and J.F. Boggs.
1978. Progress report on research in black vine
weevil control. Ohio Report 63: 41-44.

Nielsen, D.G., H.D. Niemczyk, C.P. Balderston
and F.F. Purrington. 1975. Black vine weevil:
resistance to dieldrin and sensitivity to
organophosphate and carbamate insecticides.
J. Econ. Entomol. 68: 291-292.

Smith, F.F. 1932. Biology and control of the
black vine weevil. USDA Tech. Bull. 325. 45p.

^xcy^

)! The Connecticut Agricultural Experiment Station ,

founded in 1875, is the first experiment station in America. It is chartered
Hi • nC* by the General Assembly to make scientific inquiries and experiments

regarding plants and their pests, insects, soil and water, and to perform analyses for State
agencies. The laboratories of the Station are in New Haven and Windsor; its Lockwood
Farm is in Hamden. Single copies of bulletins are available free upon request to Pub-
lications; Box 1 106; New Haven, Connecticut 06504. ISSN 0097-0905

University of
Connecticut

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