Efficacy of entomopathogenic nematodes and polymer gel against flea beetle (Coleoptera: Chrysomelidae) on canola

Principal Investigator: Dr. Gadi V. P. Reddy.

Cooperators: Dr. Frank Antwi, Amber Ferda, John H. Miller, Julie Prewett

Western Triangle Agricultural Research Center,

Montana State University,

9546 Old Shelby Rd,

Conrad, P.O Box 656, MT 59425

Introduction

In North America, Canola (Brassica napus L.; Brassicales: Brassicaceae) is a major oilseed crop grown especially in the northern Great Plains of the United States and Canada. The crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae), is a significant and economically an important insect pest of canola in the Northern Great Plains. Adult flea beetles emerge from overwintering sites in the spring as air temperatures warm to 14.7-20oC. Overwintered adults initially feed on brassicaceous weeds, and as the crop emerges they move into canola fields. They immediately begin to feed on young cotyledons and leaves.Yield losses due to flea beetle damage each year, have been estimated to be tens of millions of U.S. dollars.

Figure-1: Canola crop (left) and flea beetles feeding on the canola leaves (right)

Crucifer flea beetle management is targeted at adults in early spring when the canola crop is in its seedling stage, the most vulnerable stage to flea beetle injury (Fig-1). The first line of defense against P. cruciferae, are chemical insecticides, as seed treatments or foliar sprays. Majority of canola acreages in the Northern Great Plains are planted to insecticide-treated seed since foliar chemical insecticides are effective against crucifer flea beetle, within a narrow window of opportunity. The reliance on chemical insecticide-based pest management increases the risk for crucifer flea beetle populations to develop resistance to these insecticides. The use of entomopathogenic nematodes applied in alternative treatment regimes or in combination with reduced rates of conventional insecticides may prevent or delay insecticide resistant development in crucifer flea beetle in canola. However, due to the concerns of insect resistance development to chemical insecticides, and impact of these chemistries on pollinators and beneficials, environmentally friendly pest management, drives the need to evaluate alternative insecticides that could be included in pest management programs for crucifer flea beetle.

Ecorational insecticides are products that are ecologically rational, with no or minimal effects on non- target organisms or the environment. Ecorational insecticides have been effective against numerous insect pests, and they may have potential in crucifer lea beetle management.

Ecorational insecticides have unique modes of action compared with chemical insecticides, and can be used in insecticide resistance management and in environmental conservation.

Entomopathogenic nematodes (EPNs) due to their ability to search for their hosts can serve as an alternative for used in managing soil dwelling pest, and flea beetles in Brassica crops. It has been reported in the literature that treatment of radish roots with Sternenema Capocapsae (250000-500000) reduced Phyllotreta striolata damage by 3 to 5 fold. The objective of our study was to evaluate reduced amounts of EPNs, their mixtures, and a polymer gel on crucifer flea beetle feeding injury to seedling canola and resulting yield.

Materials and methods

Trial Location

The trials were conducted at three field locations Cutbank (48o 50.22’N, 112o 17.746’ W), Sweet Grass (48o 57.831’N, 111o 40.801’ W), and at the Western Triangle Agricultural Research Center (48o 18.627’N, 111o 55.402’ W in the Golden Triangle Area of Montana. Experimental plots were seeded on April 13, 2015 at Western Triangle Agricultural Research Center, April 20, 2015 at Sweet Grass, and on May 30, 2015 at Cutbank. Hy-Class canola seeds were used for the three locations. The canola crop was seeded at a rate of 12 seeds per 30 cm using a four-row plot drill with a row spacing of 30 cm apart. The herbicide RT3 (glyphosate) at the rate of 2.5 L/ha was applied before seeding for weed control. Fertilizer N, P, K, and S ratio was applied at 134.5, 25.2, 61.6, at the time of seeding. Additional application of 12.3, 25.2, and 0 kg/ha was broadcasted through the seed plot drill. The trials were conducted under dryland conditions.

Treatments

The entomopathogenic nematode treatments used were Ecomask (Steinernema carpocapsae), Hi (Heterorhabditis indica), Scanmask (Steinernema feltiae), Heteromask (Heterorhabditis bacteriophora), Ecomask + Heteromask (Steinernema carpocapsae + Heterorhabditis bacteriophora), Ecomask + Scanmask (Steinernema carpocapsae + Steinernema feltiae), Gaucho + Scanmask (imidacloprid + Steinernema feltiae), Barricade (Barricade polymer 4%), Barricade + Scanmask (Barricade polymer 2% + Steinernema feltiae), Barricade + Scanmask (Barricade polymer 1% + Steinernema feltiae). The source and rate of the materials are presented in Table 1.

Plot design and data collection

The plot sizes were 3.6 m ×1.2 m, with a buffer zone of 1.2 m to avoid cross contamination from spray drift. The treatments were sprayed on the plots using SOLO backpack sprayer calibrated at

87.33 gallons per acre, after arrival of flea beetles, and when canola was in the cotyledon to one- leaf stage. Untreated plots with water served as the control. Before foliar applications, each plot was rated for flea beetle feeding injury. Along a 4.6-m section of row, plants nearest to 0.3-m intervals were selected for a total of 10 plants. Residual activity of treatment applications was determined by post application ratings for flea beetle injury at 7 and 14 d after the application date for foliar insecticides. The feeding injuries and yield from the plots were evaluated for comparison of treatment effects. The injury ratings were converted into percent leaf area injury with modification OEPP/EPPO (2002). The scheme used was 1 = 0%; 2 = 2%; 3 = 5%; 4 = 10%; 5 = 25% leaf area injury. Plots were harvested on August 5, 2015 at Western Triangle Agricultural Research Center, September 14, 2015 at Sweet Grass, and on October 3, 2015 at Cutbank when 50% of the canola seeds were dark in color.

The canola crop was swathed from each whole plot at 30% seed moisture, and seed yield (kilograms per hectare) was collected from each experimental unit at 8-10% seed moisture between August and October.

Data Analysis.

Data were analyzed using multivariate analyses of covariance. Analyses of covariance were used to account for and eliminate effects of prefoliar treatment ratings on change in flea beetle feeding injury across dates after treatments. Treatment means were compared by multiple t-test obtained by least square means statement of GLM at the 0.05 level. Main and interaction effects of location by treatment on flea beetle feeding injury ratings and yields were determined using PROC GLM procedure (SAS Institute 2015).

Results

Percentage of leaf area injury

Crucifer flea beetle feeding leaf area injury is presented in Table 2. Across the locations, the seed treatment Gaucho 600 resulted in the lowest percent leaf area injury at 7 to 14 DPT (Table 2). At WTARC the leaf area injury ranged from 1 to 3.3% at PT (Table 2). At 7 DPT Gaucho had a significant leaf area injury of 3.1% (Table 2). Among the treatment combinations or mixtures Gaucho + Scanmask was the only treatment that resulted in a lower leaf area injury of 5.8%, and this was not significant when compared to Gaucho and water (Table 2). At 14 DPT Gaucho resulted in significantly lowest leaf area injury of 8.0%. However, this was not significant when compared to Gaucho + Scanmask treatment which resulted in a leaf area injury of 9.8%. The rest of the treatments had leaf area injury which were either not significant or were significantly higher compared to the control.

At Sweetgrass the leaf area injury varied from 2.0 to 5.3% at PT (Table 2). Treatment of canola with Gaucho 600 and Gaucho + Scanmask resulted in a significantly lower leaf area injury of 4.7 and 6.0%, respectively at 7 DPT (Table 2). Ecomask, and Baricade (2%) + Scanmask with leaf area feeding injuries of 7.4% were the only treatments with flea beetle feeding that were not significant compared to Gaucho, the seed treatment (Table 2). The rest of the treatments had leaf area injuries which were not significant compared to the water control. The leaf area injury at 14 DPT showed that Gaucho 600 (12.4%), and Gaucho + Scanmask (14.3%) had leaf area injury that were significantly lower (Table 2). Except Ecomask, Scanmask, Ecomask + Heteromask, Ecomask + Scanmask all the treatments had leaf area injury which were significant compared to the control.

The leaf area injury at Cutbank ranged from 4.3 to 8.6% at PT (Table 2). Gaucho + Scanmask, and Gaucho treatments had leaf area injuries of 4.2 and 14.3%, respectively (Table 2). Except Ecomask + Heteromask which had leaf area injury of 20.2%, the leaf area injuries among the treatments were not significant at 7 DPT. At 14 DPT Gaucho 600 was the only treatment that had a significantly lower leaf area injury of 13.2% (Table 2). Gaucho + Scanmask treatment leaf area injury of 16.5% was not significant when compared to Ecomask (19.6%), Scanmask (19.2%), Ecomask + Scanmask (19.6%) (Table 2).

Yield traits

Canola yield is presented in Table 3. The yield (F= 2.69; df = 35, 143; P < 0.0001) and location (F= 28.97; df = 2, 22; P < 0.0001) effects were significant. However, treatment (F= 1.63; df = 11, 22; P = 0.1014) and location*treatment (F = 0.84; df = 2, 22; P = 0.6704) effects were not significant. Gaucho 600 the seed treatment resulted in the highest yield of 843.2 kg/ha at WTARC (Table 3). However, this was not significant when compared to the yields from Hi (804.0 kg/ha), Heteromask (669.1 kg/ha), Ecomask + Heteromask (665.3 kg/ha), Ecomask + Scanmask (801.8 kg/ha), Barricade (4%) (758.3 kg/ha), Barricade (2%) + Scanmask (669.5 kg/ha), and Barricade (1%) + Scanmask (739.5 kg/ha).

Baricade (1%) + Scanmask treatment resulted in the highest yield of 1020.8 kg/ha at Sweetgrass (Table 3). Except with Water (588.2 kg/ha), Heteromask (560.3 kg/ha), and Barricade (2%) + Scanmask (604.5 kg/ha), the yield among the treatments were not significant (Table 3).

Baricade (1%) + Scanmask treatment resulted in the highest yield of 670.2 kg/ha at Cutbank (Table 3). This yield was however not significant when compared to Barricade (2%) + Scanmask (469.5 kg/ha), and the Water treatment (427.1 kg/ha) (Table 3). Yields were not significant among the other treatments.

Summary and Conclusion

At WTARC we observed medium flea beetle feeding pressure (200 - 300 flea beetles per trap week). At Sweetgrass we observed high flea beetle feeding pressure (200 - 300 flea beetles per trap week), whilst at Cutbank extremely high flea beetle feeding pressure was observed (> 300 300 flea beetles per trap week. The data indicates that Baricade (1%) + Scanmask can serve as alternative to the seed treatment. Moreover, Scanmask can be used to complement the seed treatment when the protection period is exceeded.

Acknowledgements

This work was supported by the USDA National Institute of Food and Agriculture, Multistate Project S-1052, the Working Group on Improving Microbial Control of Arthropod Pests Covering Research in Montana. [Accession number # 232056]. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the National Institute of Food and Agriculture (NIFA) or the United States Department of Agriculture (USDA). We would like to thank Dawson Berg and Kristal Juisch for assistance with field work.

Table 1. Materials and rates of application in each treatment

Table 2. Crucifer flea beetle feeding leaf area injury to seedling canola treated with entomopathogenic nematodes in Montana

a, WTARC, Western Triangle Agricultural Research Center.

b, PT, pre foliar application.

c, 7 DPT, days after foliar and granular application.

d, 14 DPT, days after foliar and granular application.

Table 3. Canola seed yield after treatment of seedlings with entomopathogenic nematodes in Montana

a, WTARC, Western Triangle Agricultural Research Center.