Browsing by Author "Prewett, Julie"

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Developing nominal threshold levels for Phyllotreta cruciferae (Coleoptera: Chrysomelidae) damage on canola in Montana, USA
(2014-12) Tangtrakulwanich, Khanobporn; Reddy, Gadi V. P.; Wu, Shaohui; Miller, John H.; Ophus, Victoria L.; Prewett, Julie
The flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae) are serious pests infesting canola (Brassica napus L.; Brassicales: Brassicaceae) in the Northern Great Plains of the United States. In Montana, P. cruciferae is the only flea beetle species that attacks canola during the crop growing stage. Management of P. cruciferae is usually focused on treating adults feeding on canola seedlings, which is the stage most vulnerable to flea beetle damage. In the Golden Triangle area in Montana, canola growers traditionally use seed treatments or calendar based spraying to control P. cruciferae. Here, we compared calendar-based spraying with seed treatment and threshold-based treatment. The experiment treatments included threshold levels (15–20, 25, 45% of leaf area damaged), calendar based sprays (15, 30 and 45 day intervals after plant emergence), seed treatments (imidacloprid), and untreated controls. The trials were done at two locations (Conrad and Western Triangle Agricultural Research Center). We found that calendar-based spraying at a 15-day interval did not differ significantly in yields from threshold-based treatment at 15–20% leaf damage. Also, the seed treatment did not give significantly higher yields compared to calendar-based sprays. A negative correlation was detected between leaf damage and yield in each treatment. Overall, calendar-based and threshold-based treatments were most effective in improving yields. However, treatment made at the threshold of 15–20% leaf area damage is recommended in order to reduce the number of chemical applications and also to reduce the possibility of selecting for resistance in flea beetles.
Efficacy of Entomopathogenic Fungi and Nematodes, and Low Risk Insecticides Against Wheat Stem Sawfly, Cephus cinctus (Hymenoptera: Cephidae)
(2014-04) Tangtrakulwanich, Khanobporn; Reddy, Gadi V. P.; Wu, Shaohui; Miller, John H.; Ophus, Victoria L.; Prewett, Julie
Entomopathogenic nematodes, fungi, and low risk insecticides were evaluated for the management of the wheat stem sawfly, Cephus cinctus Norton, in winter wheat at two locations (Devon and Western Triangle Ag Research center) in the Golden Triangle area of Montana (USA) in 2013. Two fungi (Beauveria bassiana and Metarhizium brunneum), four nematodes species (Steinernema carpocapsae, Steinernema kraussei, Steinernema feltiae, and Heterorthabditis bacteriophora), an insect growth regulator (diflubenzuron/dimilin), and a botanical-based chemical (azadirachtin/Aza-direct) were used as foliar sprays. These control agents significantly reduced damage caused by C. cinctus larvae, compared to the untreated control or treatment with water alone. No yield differences were observed among entomopathogenic fungi, nematodes, and low risk insecticides. The effectiveness of azadirachtin, diflubenzuron, the entomopathogenic fungi, and the nematodes persisted at the 28th day post application, by which time the wheat had been harvested. Stubbles collected after harvest showed significantly fewer sawfly larvae in the plots treated with entomopathogenic fungi, nematodes, diflubenzuron, and azadirachtin compared to the untreated and water spray plots, indicating that these biorational pesticides have potential to be used as alternatives to conventional pesticides for controlling the wheat stem sawfly larvae.
Evaluation of the effectiveness of entomopathogens for the management of wireworms (Coleoptera: Elateridae) on spring wheat
(2014-07) Reddy, Gadi V. P.; Tangtrakulwanich, Khanobporn; Wu, Shaohui; Miller, John H.; Ophus, Victoria L.; Prewett, Julie; Jaronski, Stefan T.
Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are serious soil dwelling pests of small grains, corn, sugar beets, and potatoes. Limonius californicus and Hypnoidus bicolor are the predominant wireworm species infesting wheat in Montana, particularly in the ‘Golden Triangle’ area of north-central Montana. Wireworm populations in field crops are increasing, but currently available insecticides provide only partial control, and no alternative management tools exist. In our study, three entomopathogenic fungi were tested for their efficacy against wireworms in spring wheat at two field locations (Ledger and Conrad, Montana, USA) in 2013. The three fungi (Metarhizium brunneum F52, Beauveria bassiana GHA, and Metarhizium robertsii DWR 346) were evaluated as seed-coat, in-furrow granular, and soil band-over-row drench applications in addition to imidacloprid (Gaucho® 600) seed treatment (as a chemical check), the approach currently being used by growers. Wireworm damage in these treatments was evaluated as standing plant counts, wireworm population surveys, and yield. The three fungi, applied as formulated granules or soil drenches, and the imidacloprid seed treatment all resulted in significantly higher plant stand counts and yields at both locations than the fungus-coated seed treatments or the untreated control. Significant differences were detected among the application methods but not among the species of fungi within each application method. All three fungi, when applied as granules in furrow or as soil drenches, were more effective than when used as seed-coating treatments for wireworm control, and provided an efficacy comparable or superior to imidacloprid. The fungi used in this study provided significant plant and yield protection under moderate wireworm pressure, supporting their value in the management of this pest.
Sustainable Management Tactics for Control of Phyllotreta cruciferae (Coleoptera: Chrysomelidae) on Canola in Montana
(2014-04) Reddy, Gadi V. P.; Tangtrakulwanich, Khanobporn; Wu, Shaohui; Miller, John H.; Ophus, Victoria L.; Prewett, Julie
The crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae), has recently emerged as a serious pest of canola (Brassica napus L.) in Montana. The adult beetles feed on canola leaves, causing many small holes that stunt growth and reduce yield. In 2013, damage to canola seedlings was high (≈80%) in many parts of Montana, evidence that when flea beetles emerge in large numbers, they can quickly destroy a young canola crop. In the current study, the effectiveness of several biopesticides was evaluated and compared with two insecticides (deltamethrin and bifenthrin) commonly used as foliar sprays as well as seed treatment with an imidacloprid insecticide for the control of P. cruciferae under field conditions in 2013. The biopesticides used included an entomopathogenic nematode (Steinernema carpocapsae), two entomopathogenic fungi (Beauveria bassiana and Metarhizium brunneum), neem, and petroleum spray oils. The control agents were delivered in combination or alone in a single or repeated applications at different times. The plant-derived compound neem (azadirachtin), petroleum spray oil, and fatty acids (M-Pede) only showed moderate effect, although they significantly reduced leaf injuries caused by P. cruciferae and resulted in higher canola yield than the untreated control. Combined use of B. bassiana and M. brunneum in two repeated applications and bifenthrin in five applications were most effective in reducing feeding injuries and improving yield levels at both trial locations. This indicates that entomopathogenic fungi are effective against P. cruciferae, and may serve as alternatives to conventional insecticides or seed treatments in managing this pest.