Evaluation of Insecticides for the Economic Control of Root Weevils in Red Raspberry and Strawberry, 2002

L. K. Tanigoshi and J. R. Bergen
Washington State University
Vancouver Research and Extension Unit
Vancouver, WA 98665-9752

Several promising biorational or reduced risk insecticides and those EPA call OP alternatives were tested in the laboratory at recommended field rates on the black vine, strawberry and rough strawberry root weevils. This was the third year weconducted these bioassays with a precision Potter spray tower (Fig. 1; not shown). This year’s bioassays further reinforced our understanding that the root weevil complex in Washington red raspberry respond differently to the recommended field rate for Capture® and several promising new experimental insecticides (Table 1, Table 2 & Table 3).

Field efficacy for Brigade® (bifenthrin) at the recommended rate of 0.1 lb (AI)/acre and its timing regimens for adult control of the black vine weevil were studied at a 4 year-old ‘Totem’ strawberry field in Woodland, WA. This replicated treatment was applied in 160 gallons of water per acre with a tractor mounted plot sprayer equipped with a 3 row boom equipped with 3, 8006 TeeJet nozzles calibrated at 100 psi (Fig. 2; not shown). The timing regimens were a 7 June preharvest and 25 June postharvest application. Failure, in part, may be associated with root weevil tolerance, timing when root weevils are not actively present or effective residual activity less than the claimed 7 to 14 days posttreatment. The prebloom application of Brigade provided significant reduction of black vine weevils at 4 days posttreatment compared with the untreated check of about 14-fold (Table 4). However, after 11 days field exposure, there was no significant difference for adult weevil counts between the treatment and untreated check (Fig. 3; not shown). These results corroborate associated experiments that indicate 4-5 days is the maximum field control for Brigade at its registered rate on strawberry. A second application of Brigade was applied at postharvest to the numerically increasing weevil population 18 days after the preharvest treatment. Compared with the untreated check, the second application showed significant differences 2 and 7 days posttreatment. Brigade provided good commercial control of black vine weevil because the grower applied Brigade when and where there were actively feed adults after a pretreatment, evening monitoring plan. This grower experienced first hand the shorter residual interval with Brigade and the importance of sampling and timing as the keystone of adult weevil management.

Table 1. Black Vine Weevil

Treatment	lb(AI)/acre	Mean Mortality
		1DAT	3DAT	7DAT	10DAT	14DAT
Means within columns followed by the same letter are not significantly different (Tukey HSD test, P<0.05).
Actara 25WG	0.06	0.1ab	0.8a	0.8a	0.9a	1.0a
Assail 70WP	0.15	0.3ab	0.4ab	0.6a	0.7a	1.0a
Capture 2EC	0.1	0.0b	0.8a	0.8a	0.8a	0.8a
DeltaGard 5SC	0.05	0.4ab	0.5ab	0.5ab	0.6a	0.8a
DeltaGard 5SC	0.05
W/Tactic	8 fl.oz.	06.a	0.6a	0.6a	0.7a	0.7a
Guthion 50 WP	0.5	0.4ab	0.9a	1.0a	1.0a	1.0a
Untreated Check		0.0b	0.0b	0.0b	0.0b	0.0b

Table 2. Rough Strawberry Root Weevil

Treatment	lb(AI)/acre	Mean Mortality
		1DAT	3DAT	7DAT	10DAT	14DAT
Means within columns followed by the same letter are not significantly different (Tukey HSD test, P<0.05).
Actara 25WG	0.06	0.3ab	1.0a	1.0a	1.0a	1.0a
Assail 70WP	0.15	0.5ab	0.7ab	0.7ab	0.7ab	0.7ab
Capture 2EC	0.1	0.7a	1.0a	1.0a	1.0a	1.0a
DeltaGard 5SC	0.05	0.5ab	0.6ab	0.9a	0.9a	0.9a
DeltaGard 5SC	0.05
W/Tactic	8 fl.oz.	02.ab	0.3bc	0.8ab	0.8a	0.8a
Guthion 50 WP	0.5	0.7a	0.7ab	0.7ab	1.0a	1.0a
Untreated Check		0.0b	0.0c	0.0b	0.3b	0.3b

Table 3. Strawberry Root Weevil

Treatment	lb(AI)/acre	Mean Mortality
		1DAT	3DAT	7DAT	10DAT	14DAT
Means within columns followed by the same letter are not significantly different (Tukey HSD test, P<0.05).
Actara 25WG	0.06	0.0a	0.4a	0.6a	0.8a	0.8a
Assail 70WP	0.15	0.4a	0.4a	0.4ab	0.8a	0.8a
Capture 2EC	0.1	0.6a	0.6a	1.0a	1.0a	1.0a
DeltaGard 5SC	0.05	0.0a	0.2a	0.4ab	0.4a	0.4a
DeltaGard 5SC	0.05
W/Tactic	8 fl.oz.	02.a	0.2a	0.4ab	0.4a	0.4a
Guthion 50 WP	0.5	0.0a	0.7a	0.7ab	1.0a	1.0a
Untreated Check		0.0a	0.0a	0.0b	0.2a	0.2a

Table 4.

Treatment	Mean No./Treatment
	Precount	4DAT1	11DAT	2DAT2	7DAT
Means within columns following by the same letter are not significantly different (Tukey test, P<0.05).
1 1st spray, 7 June
2 2nd spray, 25 June
Brigade WSB	84a	8b	127a	28b	28b
Untreated check	116a	109a	234a	147a	88a