Impact of Management Practices on Prevalence of Soybean Sclerotinia Stem Rot in the North-Central United States and on Farmers' Decisions Under Uncertainty

Abstract

Regional prevalence of soybean Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, was modeled using management practices (tillage, herbicide, manure and fertilizer application, and seed treatment with fungicide) and summer weather variables (mean monthly air temperature and precipitation for the months of June, July, August, and September) as inputs. Logistic regression analysis was used to estimate the probability of stem rot prevalence with disease data from four states in the north-central region of the United States (Illinois, Iowa, Minnesota, and Ohio). Goodness-of-fit criteria indicated that the resulting model explained well the observed frequency of occurrence. The relationship of management practices and weather variables with soybean yield was examined using multiple linear regression (R 2 = 0.27). Variables significant to SSR prevalence, including average air temperature during July and August, precipitation during July, tillage, seed treatment, liquid manure, fertilizer, and herbicide applications, were also associated with high attainable yield. The results suggested that SSR occurrence in the north-central region of the United States was associated with environments of high potential yield. Farmers' decisions about SSR management, when the effect of management practices on disease prevalence and expected attainable yield was taken into account, were examined. Bayesian decision procedures were used to combine information from our model (prediction) with farmers' subjective estimation of SSR incidence (personal estimate, based on farmers' previous experience with SSR incidence). MAXIMIN and MAXIMAX criteria were used to incorporate farmers' site-specific past experience with SSR incidence, and optimum actions were derived using the criterion of profit maximization. Our results suggest that management practices should be applied to increase attainable yield despite their association with high disease risk.

Susceptibility of winter rape cultivars to fungal diseases and their response to fungicide application

“…Meteorological conditions were conducive to fungal diseases in 2010 and high pressure of alternaria black pod spot and sclerotinia stem rot were recorded during that season. This is in agreement with other reports that meteorological conditions can greatly affect the spread and severity of alternaria black spot (Hong et al, 1996;Shrestha et al, 2005) and sclerotinia stem rot (Mila et al, 2003;Kutcher and Wolf, 2006). During our research, fungicide application significantly reduced the severity of alternaria black spot on stems and pods.…”

Incidence and severity of white mold for soybean under different cultural practices and local meteorological conditions

“…According to Mila et al (2003) and Chad et al (2005), a diminution in plant populations of soybean constitutes an effective management practice to control white mold at the crop level. By studying the same disease for common beans under different plant population treatments, Vieira et al (2010) determined that the severity of white mold plummeted linearly, with a reduction of 15 to 5 plants per meter, or from 16 to 4 plants per meter High plant populations as a cultural practice can reduce the intensity of light captured by soybean plants.…”

“…Moreover, under high plant population conditions, crop canopy will shut down earlier and consequently there will be less circulation of air within the canopy, along with an attenuation of the interception of solar radiation by the leaves and branches of the plants. Such attenuation will, in turn, raise the relative humidity in both the air and soil, and air temperature will plunge; consequently LWD will rise in such a way as to create a microclimate favorable to the development of the pathogen (NAPOLEÃO et al, 2006).…”

“…Microclimatic conditions inside the canopy of the crop can be modified, depending on the management practices adopted in compliance with different sowing dates, reductions in row spacing, rises in plant populations, the use of genotypes with a greater height, and usage of irrigation systems (PENNYPACKER;RISIUS, 1999). Different management practices can interfere both with the disease control measures and its intensification in production fields (WORKNEH;YANG, 2000;MILA et al, 2003;DEL RIO, 2008). Hartman et al (1998) observed that there is an increase in the incidence of white mold when soybean is grown under small spacing, ranging from 0.25 to 0.38 m, as opposed to spacing of 0.96 m. Among 68 production fields of soybean, 46 were carried out under row spacing equals to 0.76 m, and showed a disease incidence corresponding to 48%.…”

“…According to Chad et al (2005), depletions in plant population for soybean crop is a more efficient method to control white mold compared to row spacing treatments. In addition, Mila et al (2003) associated the high incidence and severity of S. sclerotiorum to high plant populations for the crop in study.…”