Abstract
Workneh, F., G.L. Tylka, X.B. Yang, J. Faghihi, and J.M. Ferris. 1999. Assessment of soybean brown stem rot, Phytophthora sojae, and Heterodera glycines in the northcentral United States using area-frame sampling: prevalence and effects of tillage. Phytopathology 89:204-211.
The prevalence of brown stem rot (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae in the northcentral United States was investigated in the fall of 1995 and 1996. Soybean fields were randomly selected using an area-frame sampling design in collaboration with the National Agricultural Statistics Service. Soil and soybean stem samples, along with tillage information, were collected from 1,462 fields in Illinois, Iowa, Minnesota, Missouri, and Ohio. An additional 275 soil samples collected from Indiana were assessed for H. glycines. For each field, the incidence and prevalence of brown stem rot was assessed from 20 soybean stem pieces. The prevalence and recovery (expressed as the percentage of leaf discs colonized) of P. sojae, and the prevalence and population densities of H. glycines were determined from the soil samples. The prevalence of brown stem rot ranged from 28% in Missouri to 73% in Illinois, with 68 and 72% of the fields in Minnesota and Iowa, respectively, showing symptomatic samples. The incidence of brown stem rot was greater in conservation-till than in conventional-till fields in all of the states except Minnesota, which had few no-till fields. Phytophthora sojae was detected in two-thirds of the soybean fields in Ohio and Minnesota, whereas Iowa, Missouri, and Illinois had 63, 55, and 41%, respectively, of the fields infested with the pathogen. The recovery of P. sojae was significantly greater (P < 0.05) in conservation-till than in conventional-till fields in all the states except Iowa. Heterodera glycines was detected in 83% soybean fields in Illinois followed by Iowa (74%), Missouri (71%), Ohio (60%), Minnesota (54%), and Indiana (47%). Both the prevalence and population densities of H. glycines were consistently greater in tilled than no-till fields in all states for which tillage information was available.