Resistance and Tolerance Screening of Spring Wheat Cultivars to Cereal Cyst Nematode (Heterodera avenae) in Southeastern Idaho.

Increased populations of Heterodera avenae in southeastern Idaho are associated with increased planting of susceptible cereal cultivars and lack of crop rotation. Identifying high-yield, resistant spring wheat cultivars with tolerance requires testing new genotypes and susceptibility assessments of marketed cultivars. We conducted two experiments to determine whether cultivars with putative resistance could maintain acceptable yield in the presence of H. avenae. We also evaluated the tolerance response in relation to previously tested cultivars. Seven spring wheat cultivars were planted in two irrigated commercial fields that were naturally infested with high populations of H. avenae. Measures of resistance, tolerance, and grain yield were assessed in aldicarb-treated versus nontreated plots. In aldicarb-treated plots in both years, grain yield of the susceptible cultivars Snow Crest, WestBred 936, WB9411, Patwin-515, and WB9668 was significantly increased. The expected yield increase with aldicarb was limited for the moderately susceptible Expresso due to water stress. 'WB-Rockland', carrying the Cre5 resistance gene, maintained its standard yield, while none of the other cultivars in the experiment showed resistance or tolerance. Our results indicated that aldicarb improves wheat grain yield in irrigated crop production systems, and although removed from the market, it is effective and has utility for research. The results also support the hypothesis that high yield susceptible cultivars can mask the effect of H. avenae on grain yield when managed appropriately.

Efficacy of Naturally Occurring and Commercial Entomopathogenic Nematodes Against Sugar Beet Wireworm (Coleoptera: Elateridae).

Wireworms are the larval stage of click beetles (Coleoptera: Elateridae), and some of their species are serious pests of many crops. In the present study, we evaluated the efficacy of naturally occurring and commercial entomopathogenic nematode species against the sugar beet wireworm, Limonius californicus (Mannerheim), in the laboratory. First, efficacies of Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) collected from an irrigated (S. feltiae-SSK) and a dryland (S. feltiae-SSC) field and the two commercial entomopathogenic nematode species, S. carpocapsae (Weiser) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were examined. Efficacies of the two field-collected S. feltiae isolates were also compared against a commercial S. feltiae strain. In the first bioassay, S. feltiae-SSK caused 63.3% wireworm mortality, followed by 30% caused by S. carpocapsae, 23.3% by S. feltiae-SSC, and 6.7% by H.bacteriophora. In the second assay, S. feltiae-SSK killed 56.7% of the wireworms, ≈2.1- and ≈5.7-fold higher than S. feltiae-SSC and the commercial isolate, respectively.

Soil Type Mediates the Effectiveness of Biological Control Against Limonius californicus (Coleoptera: Elateridae).

Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are a considerable threat to cereal and vegetable production in the Pacific Northwest and Intermountain regions of the United States. As insecticides are generally ineffective, alternative controls are needed to improve wireworm management. Wireworms are continuously exposed to a wide range of subterranean pathogenic organisms in the soil; identifying these organisms and determining their impact would contribute to the development of biological control for wireworms. Here, we evaluated the efficacy of an entomopathogenic nematode, Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), and a fungus, Metarhizium brunneum Petch (strain F52) (Hypocreales: Clavicipitaceae), for control of the Pacific Northwest predominant wireworm species Limonius californicus, in two different soil media. We also examined whether diatomaceous earth (DE) increases the efficacy of entomopathogens through facilitating their penetration into the host integument. Treatments containing M. brunneum (F52) resulted in the highest rates of wireworm mortality, indicating that the fungus may be more effective than the nematode at reducing population size. However, results were impacted by soil media. In peatmoss-dominated medium, M. brunneum-containing treatments were more effective in reducing feeding damage than treatments containing S. carpocapsae. However, in sand-dominated medium, treatments with S. carpocapsae provided relatively better seedling protection. No consistent effect of DE was detected. Our results suggest that the effectiveness of wireworm biological control agents depends on soil media, such that the application of biological control against wireworms must be made with knowledge of field soil type.