Insecticide Management of Spotted Wing Drosophila on Small Fruits in Washington State
LYNELL K. TANIGOSHI, BEVERLY S. GERDEMAN & HOLLIS SPITLER
Washington State University, Mount Vernon Northwestern Washington Research & Extension Center, Mount Vernon WA USA 98273
INTRODUCTION
RESULTS
When applied to strawberries, bifenthrin, malathion and
spinetoram caused 100% adult D. suzukii mortality, acetamiprid
was intermediate, whereas thiamethoxam was not significantly
different from the untreated check (F = 101.90; df = 4, 5; P =
0.001; Table 1). All four pyrethroids (bifenthrin – two
formulations, zeta-cypermethrin, esfenvalerate), malathion and
spinosyn (spinetoram) applied to blueberries resulted in the
highest levels of mortality, while imidacloprid and thiamethoxam
provided intermediate control and acetamiprid, while
significantly greater than the control, resulted in the lowest level
of mortality (F = 22.49; df = 8, 9; P = 0.0001; Table 1). All four
pyrethroids (bifenthrin – two formulations, zeta-cypermethrin,
esfenvalerate), spinosyn (spinetoram) and malathion cause
significant adult mortality compared with the neonicotinoids and
the untreated check when applied to red raspberry fruit (F =
53.65; df = 9, 16; P = 0.0001; Table 1).
Our 2010 research efforts at the WSU Mount Vernon
Northwestern Washington REC to manage spotted wing
drosophila in conventional strawberry, red raspberry and
blueberry production systems were to identify and develop use
patterns for currently labeled insecticides.
MATERIALS AND METHODS
Exposure of flies to blueberries after one day field exposure to
malathion resulted in the greatest levels of adult mortality,
followed by intermediate activity of spinetoram, bifenthrin, zetacypermethrin and imidacloprid (F = 14.74; df = 7, 14; P =
0.0001) (Fig. 4). Thiamethoxam and acetamiprid did not cause
greater levels of mortality as the untreated check. D. suzukii
mortality after exposure to field aged residues after seven days
for malathion and spinetoram were significantly greater from all
of the remaining treatments which themselves were not
significantly greater than the untreated control (F = 2.58; df = 7,
14; P = 0.062).
100
90
80
Fig 2.
1 DAT
7 DAT
% Mortality
70
60
50
40
30
20
10
Fig 1.
0
Brigade WSB Mustang Max Provado 1.6
Fig 3.
Laboratory evaluations
of field-aged residues on
100 berries/sample
70
60
1 DAT
7 DAT
50
40
30
20
10
0
Mustang Max Mustang Max Mustang Max Mustang Max
Assail
Entrust
Six commercial blueberry fields in Skagit and Whatcom
counties were monitored within 1 DAT of being aerially
treated with low volume applications of Mustang Max,
Assail and Entrust (Fig. 5). Samples of one hundred
ripening fruit were taken at 1 and 7 DAT at each site.
These were placed in individual 2 oz condiment cups with
one S. suzukii adult each and held for 24 hours to record
contact mortality. As expected, the residual of Mustang
Max had declined to 17, 11, 9 and 4 percent for their
respective fields above after 7 DAT. However, residual
mortality was 52 and 40 percent for Assail and Entrust after
7 DAT. The rapid knockdown character of the pyrethroids
when coupled with the slower MOA and systemic potential
of neonicotinoids to eggs/larvae, suggest aerial and ground
application tank mixes will provide enhanced activity and
residual for D. suzukii population control.
OBJECTIVES
Research included laboratory fruit dip bioassays (Fig. 1) and
evaluating field-aged residues utilizing field treated berries
and Potter Spray Tower applications (Figs. 2, 3) .
Helicopter applications on mature blueberry were also
evaluated.
Fig. 5
% Mortality
Spotted wing drosophila, Drosophila suzukii (Matsumura) was
first detected in the United States in California beginning in
2008 and by 2009 it had spread northward into the Pacific
Northwest, which includes Oregon and Washington in the
United States, as well as British Columbia in Canada and as far
east as Florida, North Carolina, New Jersey and Michigan.
Spotted wing drosophila is now the key pest for both red
raspberry and blueberry in the state of Washington. Red
raspberry industry consensus, following the 2010 season,
concluded management options were adequate and susceptible
gaps could be eliminated through adjustments in timing of
insecticide applications to ensure future season-long
protection. Successful management requires early season
detection of adult SWD in apple cider vinegar traps followed
by rapid application of labeled insecticide to ripening fruits.
Subsequent applications of protective treatments will be
necessitated when traps indicate post-application populations
approaching provisional economic tolerance levels as
determined by growers for their respective cultivars and
associated horticultural and environmental conditions.
Grower’s must rotate chemical classes through a D. suzukii
generation of ~14 days to delay resistance development while
being cognizant of REI, PHI and MRL’s for their target
markets.
Actara
Assail 30SG
Delegate
Malathion 8EC
UTC
Fig. 4. Efficacy of field-aged residues of various modeof-action chemistries in blueberry (cv. ‘Liberty’).
DISCUSSION
Our laboratory bioassays and field trials identified a
number of insecticides representing various modes of
action, which are effective in managing D. suzukii.
Products that performed well in the laboratory bioassay
also performed well in the field indicating that screening of
new chemistries in the laboratory is a worthy exercise.
Field application of pyrethroids, organophosphates or
spinosyns provided 5-14 days of residual control of D.
suzukii. Follow-up applications should be applied when
apple vinegar cider traps indicate increasing D. suzukii
populations. Depending on the D. suzukii pressure in the
field and the length of harvest, 1-3 additional sprays may
be required to maintain fruit infestation levels near zero.
While growers do have chemical tools available to them to
manage D. suzukii, a difficult challenge for them is to
maintain a protective residue throughout harvest periods
while complying with restricted entry interval, pre-harvest
interval and maximum residue limits regulation. Because
of the presence of multiple generations of D. suzukii each
growing season, growers should apply insect resistance
management techniques by rotating compounds from
different mode of action groups to prevent or delay
resistance development.