02-15 August 20, 2002

Acaricide Trial for Watsonville Strawberries, Summer, 2001

Frank Zalom, David Limburg and Doug Shaw Department of Entomology and Department of Pomology, UC Davis

Introduction. This field experiment was intended to evaluate several registered and non-registered acaricides for their effectiveness in controlling twospotted spider mites on strawberries. Acaricides were evaluated against an untreated control, and also included the currently registered acaricides Agrimek (abamectin, Syngenta), Valero (cinnamic aldehayde, Mycotech), Savey (hexythiozox, Gowan) and Acramite (bifenazate, Uniroyal). Non-registered chemicals evaluated include Secure (etoxizole, Valent), Mesa (milbemectin, Gowan), Pyramite (pyridaben, BASF), rosemary oil (Ecosmart) and TM- 41301 (Tomen Agro). Danitol, a Pyrethroid insecticide, was Report Highlights applied in combination with a reduced rate of Secure. Danitol • Mite densities can reach very high is registered for spider mite control, but we only recommend its levels if left untreated. use for Lygus control to preserve its effectiveness for that • Acramite and Savey, both recently important use. In addition, use of both Danitol and the other registered on strawberries, gave registered pyrethroid insecticide, Brigade, can also result in later control similar to that of Agrimek. • season spider mite outbreaks. Following the loss of Omite Several unregistered acaricides show promise for mite control. (propargite, Uniroyal) for use in production fields, Agrimek was the only effective remaining acaricide in most major production regions. The resulting inability for growers to rotate acaricides with different modes of action presented the serious likelihood of resistance development in Agrimek. Use of newly registered acaricides at optimal rates and timing in rotation with Agrimek will delay the development of resistance in all strawberry acaricides.

Materials and Methods. Clone/runner plants (cv. Diamante) were transplanted to the UC Strawberry Research Facility near Watsonville, CA, in November, 2000. Our plot design consisted of 4 replicates of 20 plants with treatments applied in a completely randomized design. Acaricides were applied with an Echo D9 Duster-Mister (air-assisted sprayer) at a volume of 200 gpa. Mite abundance was determined by leaf brushing 10 midtier leaflets per replicate, counting the mites, and averaging on a per- leaflet basis. Plots were harvested and yield and fruit size and quality assessments were calculated from 6 April through 21 August.

Results and Discussion. The pre-application mite counts on 8 June indicated no significant difference between plots assigned to the different treatment. By the third week after nitial sprays were applied, all acaricides except Pyramite, Valero, and the low rate of Ecosmart (rosemary oil) significantly suppressed spider mites when compared to the untreated control (p < 0.05) (Table 1). These differences compared to the untreated control continued through the fifth week. Residual spider mite control comparable or better than that of our standard treatment, Agrimek, was afforded by all rates and mixes of Secure, both of the single application rates of Acramite (the 2 applications one week apart treatment is not a legal use), Mesa, Savey, the tank mix of Mesa and Savey, and all rates of the numbered Tomen Agro product. We have evaluated Pyramite on a number of occasions, and have found control to be variable, sometimes quite effective and at other times less so. The combination of Secure and Danitol was not more effective than the Secure alone, but the rate of Secure needed to achieve the same level of control was less. There was no significant difference (p < 0.05) between the combination of Mesa + Savey and Mesa alone applied at the same rate. Although not significant, a dose response was observed for both Acramite and TM-41301. All of the acaricides tested in 2001 are currently being evaluated again at Watsonville, as well as a new chemical Oberon from Bayer. We anticipate that Mesa will be registered in time for the next production season, and that registrations for Pyramite, and Secure will also become available on strawberries in the next year or two. Table 1. Miticide efficacy comparison, Watsonville, CA, June, 2001. Mean number of spider mites per midtier leaflet (± standard error).

No. Rate Pre-treat Week 1 Week 2 Week 3 Week 4 Week 5 Treatment apps. (a.i./acre) 6/8/01 6/15/01 6/22/01 6/29/01 7/5/01 7/12/01 Untreated - - 16 ± 9 31 ± 8 50 ± 31 57 ± 39 78 ± 43 149 ± 51 2 1 * * * * * Omite (winter) 1x 6.0 lb 7 ± 35 ± 1 7 ± 4 4 ± 1 9 ± 5 20 ± 3 +Agrimek + 1x + 0.0188 lb (summer) Agrimek 2x 0.0188 lb 17 ± 5 10 ± 2* 8 ± 4* 11 ± 5* 9 ± 4* 22 ± 11* 2 * Pyramite 2x 0.3 lb 17 ± 7 18 ± 6 29 ± 28 26 ± 22 33 ± 27 41 ± 26 2 * * * * Secure 1x 0.09 lb 18 ± 9 16 ± 12 7 ± 3 8 ± 2 7 ± 3 17 ± 9 2 * * * * * Secure 1x 0.135 lb 20 ± 9 10 ± 4 8 ± 4 9 ± 4 14 ± 8 21 ± 12 2 * * * * * Secure 1x 0.045 lb 20 ± 96 ± 2 6 ± 3 6 ± 3 9 ± 6 20 ± 11 + Danitol + 0.2 lb Acramite 1x 0.38 lb 11 ± 56 ± 3* 4 ± 1* 6 ± 1* 7 ± 2* 27 ± 8* Acramite 2x3 0.38 lb 14 ± 5 10 ± 6* 3 ± 2* 2 ± 1* 2 ± 1* 4 ± 2* Acramite 1x 0.50 lb 13 ± 55 ± 2* 7 ± 6* 5 ± 1* 4 ± 2* 10 ± 7* 2 1 * * * * * Mesa 2x 32 oz 17 ± 4 11 ± 5 4 ± 3 3 ± 2 3 ± 0 5 ± 1 2 1 * * * * * Mesa 1x 32 oz 10 ± 25 ± 3 3 ± 2 4 ± 2 3 ± 0 4 ± 2 1 + Savey + 6 oz Savey 1x 6 oz1 17 ± 10 13 ± 68 ± 4* 6 ± 3* 10 ± 7* 10 ± 6* Rosemary oil 2x 1.25% 34 ± 19 28 ± 16 71 ± 38 68 ± 44 79 ± 44 148 ± 60 Rosemary oil 2x 2.5% 4 ± 24 ± 1* 6 ± 3* 8 ± 2* 22 ± 6* 35 ± 14* Valero 2x 0.2% 5 ± 29 ± 3* 13 ± 6 16 ± 3 21 ± 12* 45 ± 12* 2 1 * * * * TM-41301 1x 15 oz 14 ± 37 ± 3 9 ± 53 ± 1 13 ± 8 18 ± 11 2 1 * * * * * TM-41301 1x 30 oz 17 ± 13 8 ± 7 3 ± 1 3 ± 1 4 ± 3 9 ± 5 2 1 * * * * TM-41301 1x 60 oz 18 ± 94 ± 2 9 ± 64 ± 3 4 ± 2 8 ± 5 * Spider mite density for this date is significantly different from the untreated control plots by pairwise t-tests at p<0.05. 1 These chemicals applied at formulated amount. 2 Not currently registered for use on strawberries. 3 Not registered as a paired application.