Efficacy of Cruiser Maxx™ and Actara™ for tuber flea beetle control on potato

L. K. Tanigoshi, G. Hollis Spitler and Beverly S. Gerdeman
Washington State University
Mount Vernon Northwestern Research and Extension Center

Tuber flea beetle (TFB), Epitrix tuberis Genter bioassays

This bioassay was conducted at the Washington State Northwestern Research and Extension Center, Mount Vernon, WA to evaluate major neonicotinoid compounds and experimental formulations applied as residual leaf dip bioassays under laboratory conditions. Actara was compared with the neonicotinoids Venom™, Assail™, Leverage™ and experimental Allectus™ SC (imidacloprid-bifenthrin), Success™ (spinosad) and experimental IGR Aza-Direct™ (azadirachtin). Residual leaf dip bioassays were conducted using the terminal leaflet of ‘Yukon gold’. Leaflets were dipped in respective deionized water-insecticide-X-77 solutions for approximately five sec and air-dried. Five adult TFB were obtained from a manageable number of adults held in a quart size plastic container that was placed in the freezer for about one minute to temporarily immobilize them before individually placing them in a bioassay unit with a camel hairbrush. The upper surface of each leaflet was sandwiched between the 4 cm diameter plastic cap and the top opening of a 1 fl oz clear plastic condiment cup. Each cup was ventilated near the inverted bottom of the cup with the tip of a hot dissecting probe. These treatment units were placed in a ventilated salad crisper unit to maintain ambient relative humidity for both the beetles and the leaf’s integrity. Given this lab setup, the potato leaf disc began to deteriorate after four days. A better isolation unit will be researched next year. Each treatment was replicated 10× and 6× for the two treatment dates shown in Table 1 and Table 2.

Within 24 hours, 96% and 83% of the adult TFB were dead for the Actara treated leaves for both treatment times. By the fourth day, 90% or more of the adults were dead given the conditions of this bioassay. There were no significant differences between the five neonicotinoid or combination formulations through the sixth day of each bioassay. The foliar condition of the leaflets was problematic by six days posttreatment. Flea beetle control should be listed on the Actara label and the PNW Insect Management Handbook as a foliar application at 3-4 oz product/acre.

Tuber flea beetle (TFB) grower farm trials

Flea beetle farm trials were established at three farms on ‘Yukon Gold.’ These farms were located within a radius of seven miles from the NWREC. The trials were planted on 22 May 2007 at each farm in plots consisting of four rows ten feet long with 38 inch spacing and 9 inch seed spacing. The experimental design for the three fields consist of five non-replicated plots (i.e., Actara, Leverage, Vydate™, Cruiser Maxx™, untreated check). Each farm represented a block with each treatment or plot replicated 3 times across these farms. Weed control and blight treatments were similar to the schedule presented for the on-station trials. Adult flea weevil populations were assessed with a 15” × 15” beating tray consisting of three taps per tray and three trays/plot.

The Cruiser Maxx seed treatment used weight of cut seed tubers to determine application rate of 0.23 fl oz/100 cwt mixture with a hand sprayer adjusted to apply a misting spray over the cut pieces contained in a black plastic garbage bag. The seed pieces were tumbled and rolled in the sealed bag until seeds were uniformly covered and then placed on butcher paper an allowed to dry over night. These seed pieces were planted the next day in plot rows and covered. In-furrow treatment with Vydate was applied with a Solo™ backpack sprayer at 2 gal/acre in 20 gal water. The application was applied in an 8-inch band with a TeeJet TP8003 nozzle at 40-50 psi. Foliar treatments of Leverage at 3.75 fl oz/ac and Actara at 4 oz/ac were applied with a Solo backpack sprayer at 100 gal/ac at 50 psi. This pressure gave good coverage to the top and some directional coverage to the underside foliage as the canopy was very dense by mid-summer.

Foliar sprays of Ambush™ at 12.8 fl oz/ac for Cruiser Maxx and Vydate plots were applied on farms 1 and 2 at 85 days postplanting (16 August) and repeat foliar applications of Leverage and Actara were made on 27 July (66 days) and 17 August (86 days) on farm 1, 19 July (58 days) and 17 August on farm 2 and 17 August on farm 3.

Natural infestations of TFB never established in the four commercial sites selected for our 2007 field trials until low levels were detected in these spatially separated field on 10 July. Flea beetles were obtained from a ‘field insectary’ consisting of mixed cultivars of potatoes grown organically about a quarter mile from the NWREC field site.

In Farm 1, TFB were present mainly in volunteer potatoes until 20 insects per plot were introduced from the field insectary on 20 July. The first foliar applications of Actara and Leverage were applied on 27 July and delayed population increases until 10 August when TFB counts indicated numerical increase of TFB (see attached table). A second foliar spray for both treatments was applied on 16 August and a foliar spray of Ambush™ on the Cruiser Maxx and Vydate plots at 85 day after planting. The Cruiser Maxx plot gave the highest yield and most marketable ‘Yukon gold’ potatoes at harvest. Vydate and UTC plot showed similar yields, while both foliar application plots gave lower yields at this location.

At Farm 2, natural infestations of TFB were mainly found on volunteer potatoes until 20 insects again were introduced in each plot on 20 July. The first foliar sprays of Leverage and Actara were applied on 19 July and late timing resulted in unsatisfactory foliar control of an increasing TFB resulting from our field release (attachment). At least 0.5 inches of rainfall occurred late afternoon-evening of 19 July and probably affected uptake of both foliar neonicotinoid compounds. These population trends followed those recorded for the UTC from 27 July to 10 August. A second poorly timed application of Actara and Leverage was applied on 16 August that seemingly provided good knockdown 24 hours posttreatment and held until plant defoliation. Foliar sprays of Ambush were applied on 16 August on the Cruiser Maxx and Vydate plots. Field residual activity of the latter systemic compounds at Farm 2 was about 80-87 days for adult TFB suppression. The late second treatments respectively control TFB adult populations compared with the UTC through 30 August. Yield data showed the Vydate plot to have nearly twice the marketable potatoes as Cruiser Maxx while Actara, Leverage and UTC yields were less than a third of Cruiser Maxx. The high beat tray counts reflected these results that were the result of late timing and high economic treatment levels far exceeding the suggested a 5-6 adults per 25 sweeps threshold.

Farm 3 never developed a natural or introduced field population of TFB despite introductions of 20 adults per plot on 20 and 28 July 2007 (see attached table for farm 3). Yield data were problematic and reflected a tillage practice that mechanically disrupted the Cruiser Maxx plot.

NWREC trials

Two attempts to introduce TFB from an organic potato site a quarter mile from this site in July never established in any of the 55 RCBD plots which included Cruiser Maxx and Cruiser Maxx + Dynasty™. Despite the lack of obvious foliar feeding injury, the Cruiser Maxx + Dynasty plot showed highest yield, followed by Vydate, Cruiser Maxx, UTC and other treatments. Foliar treatment yields were generally lower, however, yields were not significantly different after SAS analyses.

Chris, Table 3 represents the combined data obtained from the three farms, each treated as a replicate. As is obvious from the SD values and simply looking at the data from Farm 3, average beat tray counts for TFB populations were very low compared with Farms 1 and 2.

Based on the results of four different TFB levels we monitored above and the lack of grower reports of flea beetle problems to our Skagit County extension agent, we conclude that flea beetle incidence for the 2007 growing season was very light and spotty. We speculate that overwintered adults were possibly impacted by freezing temperatures in mid-January that have not been the norm for the past 6-8 years in this region and an unseasonable rain on 19-20 July affected Actara uptake and residual as well.

Table 1. Tuber flea beetle bioassay, 2 Aug. 2007.

Treatment	lb(AI)/acre	Percent adult mortality
		1DAT	2DAT	3DAT	4DAT	5DAT	6DAT
Mean within columns followed by the same letter are not significantly different (Fisher’s protected LSD, P<0.05), PRC ANOVA SAS.
Actara 25WG	0.0625	96ab	96ab	96a	96a	96a	96a
Allectus	0.135	94ab	100a
Assail 30SG	0.05	98a	98ab	98a	98a	98a	98a
Aza-Direct	0.04	10c	32c	36b	40b	40b	40b
Leverage 2.7SE	0.08	100a
Success	0.094	16c	16d	16c	24c	36b	38b
Venom 20SG	0.066	82b	88b	96a	96a	96a	96a
Untreated check		2c	6d	6c	10d	10c	10c

Table 2. Tuber flea beetle bioassay, 10 Aug. 2007.

Treatment	lb(AI)/acre	Percent adult mortality
		1DAT	2DAT	3DAT	4DAT	5DAT	6DAT
Mean within columns followed by the same letter are not significantly different (Fisher’s protected LSD, P<0.05), PRC ANOVA SAS.
Actara 25WG	0.0625	83a	83a	87a	90a	100a
Allectus SC	0.135	93a	97a	97a	97a	100a
Assail 30SG	0.05	83a	100a
Aza-Direct	0.04	80a	80a	90a	93a	97a	100a
Leverage 2.7SE	0.08	90a	93a	97a	97a	97a	100a
Success	0.094	87a	87a	87a	100a
Venom 20SG	0.066	73a	80a	87a	90a	97a	100a
Untreated check		7b	7b	7b	7b	7b	7b

Table 3. Mean tuber flea beetles per 3 beat trays across three locations, August, 2007.

Treatment	lb(AI)/acre	Appl. Method1	Mean adult TFB/plot
			3-Aug	10-Aug	17-Aug	24-Aug
Mean within columns followed by the same letter are not significantly different (Fisher’s protected LSD, P<0.05), PRC ANOVA SAS.
1 FT (foliar treatment), SP (seed pieces), PF (planting in-furrow).
Actara 25WG	0.0625	FT	19.7b	32.7ab	1.3b	0.3b
Cruiser Maxx	0.23 fl oz/cwt	SP	10b	19.3ab	0b	0.3b
Leverage 2.7SE	0.08	FT	10.3b	24.7ab	0.7b	0.7b
Vydate L	4	PF	12.7b	10.7b	0b	0.3b
Untreated check			34.3a	38.3a	59.3a	18.3b