1. RAMMOHAN R. BALUSU and HENRY Y. FADAMIRO*
Field Evaluation of Some Biorational Insecticides against Yellowmargined Leaf Beetle, Microtheca ochloroma (Chrysomelidae) in Organic Crucifer Vegetables
RAMMOHAN R. BALUSU and HENRY Y. FADAMIRO*
Department of Entomology and Plant Pathology, Auburn University, 301 Funchess Hall, Auburn, Alabama 36849, U.S.A., *
Abstract
Field trials were conducted to evaluate the efficacy of select OMRI-approved biorational insecticides against yellowmargined leaf beetle (YMLB), Microtheca ochroloma in two commercial organic crucifer vegetable fields in Alabama during The following treatments were evaluated: PyGanic® (pyrethrum), Aza-Direct® (azadirachtin), PyGanic® + Aza-Direct®, Entrust® (organic formulation of spinosad), and Mycotrol O® (organic formulation of Beauveria bassiana). Treatments were applied at field recommended rates on a weekly schedule. Insecticide efficacy was determined by comparing densities of YMLB larvae and adults, and crop damage ratings. Entrust® consistently provided the lowest pest densities and mean damage ratings and was the most promising treatment. The other treatments were not effective in reducing YMLB infestations. A B C
Fig. 1. Adult (A), egg (B), and larval (C) stages of yellowmargined leaf beetle (YMLB)
Fig. 2. Dead YMLB adults on turnip treated with Entrust® A B A B
Introduction
The yellowmargined leaf beetle (YMLB), Microtheca ochroloma Stal (Coleoptera: Chrysomelidae) is an introduced pest of cruciferous vegetable crops in southeastern U.S. Major field infestations of YMLB have been reported in AL, FL, LA, MS, SC, OK and TX (Ameen and Story, 1997). Both adults (Fig. 1A) and larvae (Fig. 1C) feed on the foliage of crops such as turnip, mustard, radish, napa cabbage, cabbage, collards and watercress, with the potential for major economic loss (Fig. 3). In particular, YMLB poses a major threat to organic vegetable production since organic farmers cannot use effective synthetic insecticides. Currently, there are no published results on the efficacy of insecticides approved by the Organic Materials Review Institute (OMRI) against this beetle. The goal of this study was to evaluate the field efficacy of select OMRI-approved insecticides against YMLB.
Control
Enturst®
Fig. 3. Defoliation of napa cabbage (A), defoliation & root damage of turnip (B) caused by YMLB
Fig. 4. Turnip plants damaged by YMLB in untreated control plot (A) versus Entrust®-treated plot (B)
Materials and Methods
The experiment was conducted in two commercial organic crucifer vegetable farms in Alabama (Snow Farm and Red Root Farm) during spring 2007 and The following biorational insecticides were evaluated at field recommended rates against YMLB: i) PyGanic® EC 1.4 II (Pyrethrum, at 2 pints/acre), ii) Aza-Direct® (Azadirachtin, at 2 pints/acre), iii) PyGanic® EC 1.4 II + Aza-Direct® each at half rate), iv) Entrust® (organic formulation of Spinosad, at 2 oz per acre), v) Mycotrol O® ES (organic formulation of Beauveria bassiana, at 1 quart/acre), and vi) untreated control.
Trials were conducted in long rows (80 m) of turnip. Plots were 0.6 m beds wide by 10.6 m long for a total of ~80 plants, and separated by 3 m. Treatments were arranged in randomized complete block design and each treatment was replicated four times. Pre-treatment and post-treatment densities of YMLB adults and larvae were collected by sampling at 3 days intervals 5 randomly selected plants per plot. Treatments were applied weekly with a hand-sprayer calibrated to deliver about 25 gpa at 40 psi. Damage ratings were based on a scale of 1 to 6.
Statistical Analysis: Data were analyzed by using ANOVA to determine significant differences among treatments. Means were separated by using Tukey-Kramer HSD test. A B C
Results and Discussion
In 2007 at both locations, Entrust® provided significant suppression of larval and adult (Fig. 2) populations of YMLB on the crop as early as 3 days after treatment and throughout the study, which resulted in significantly lower damage ratings (Fig. 5). None of the other treatments was significantly different from the control in reducing insect density and damage. Similar trends were observed in 2008 in both locations. Entrust® has been reported to provide significant suppression of another chrysomelid, the tuber flea beetle, Epitrix tuberis (Lena Syrovy and Meberg, 2006). The reduced efficacy of slow acting insecticides (e.g., Aza-Direct® and Mycotrol O®) against YMLB may be due to its short life cycle and high fecundity. Future studies will determine the potential use of Entrust ® in alternation or rotation with slow acting biorational insecticides for managing YMLB.
Fig. 5. Suppression of YMLB larvae (A), adults (B) and damage rating (C) in turnip plots treated weekly with various biorational insecticides in a commercial organic vegetable farm in Alabama in 2008
Acknowledgements
Funding was provided by an IPM Enhancement grant from the Southern Region IPM Center and USDA/IR-4 Biopesticide grant to HYF.
Industry collaborators: Novozymes Biologicals Inc. (Salem, VA); Laverlam International Corporation; Gowan Co. (Yuma, AZ); Dow AgroSciences (Indianapolis, IN), and MGK Co. (Minneapolis, MN).
References
Ameen, A. O., and R. N. Story Biology of the yellowmargined leaf beetle (Coleoptera: Chrysomelidae) on crucifers. Journal of Entomological Science 32:
Lena Syrovy, J. C, and H. Meberg The effect of Novodor® (Bacillus thuringiensis subsp. tenebrionis) and Entrust® (Spinosad) on reproduction and feeding activity of Epitrix tuberis (Coleoptera:
Chrysomelidae) in potato. Report to Certified Organic Association of British Columbia.