Effects of Modification of the Plant Canopy Environment on Sclerotinia Blight of Peanut

Abstract

The development of Sclerotinia blight, caused by Sclerotinia minor Jagger under various environmental conditions, was studied in field plots of peanuts (Arachis hypogaea L.). The peanut plant canopy was modified to produce desired environmental parameters. The m&cations included the thinning of canopy foliage to allow air circulation that would decrease canopy humidity and the addition of water-filled troughs under an unthinned canopy &at would increase humidity. Canopy relative humidity and soil moisture under the canopy was decreased by canopy thinning. Following infection by S, minor, the number of infection foci and disease development was reduced in the thinned canopy; however, thinning also reduced pod yield. Disease development was not increased, nor was yield affected by the addition of the water-filled troughs which increased humidity levels in the canopy. Soil moisture and canopy light interception were important variables in multiple linear regression models for the disease severity index and longest lesion length in the thinned and unthinned-trough plots.

An Assessment of Environmental Conditions Preceding Outbreaks of Sclerotinia Blight of Peanut in Virginia1

“…Plants with open canopies had a warmer and drier microclimate within the plant canopy as a result of more air circulation and light penetration, whereas plants with dense canopies had a cooler and wetter microclimate because ofless air circulation and light penetration. The observations of Sclerotinia blight of peanut over a 16-yr period in the current study agree closely with those of others (3,6,10,14) which collectively provide evidence that plant growth has a primary role in determining the time of disease onset.…”

“…New flushes of succulent plant growth at branch tips after irrigation are also a likely source of increased vulnerability to infection by S. minor (2,15). Observations in the current study and those of others (5,6,12) have indicated that mycelia from germinating sclerotia at the soil surface and near plant tissues (branches, pegs, leaves, etc.) were responsible for initiating infections in peanut fields.…”

“…Both air and soil temperature along with available moisture have been implicated as primary factors in determining disease onset in the field (5). Vine growth or specifically the covering of middles between rows and the density of the foliar canopy are thought to be important host factors (3,6). With regard to plant cultivars, it seems that the architectural characteristics of cultivars are responsible for much of the differences in susceptibility.…”

Fluazinam: A New Fungicide for Control of Sclerotinia Blight and Other Soilborne Pathogens of Peanut1

“…Unfortunately, the advisory program often calls for sprays late in the season when applications of chlorothalonil may trigger increases in severity ofSclerotinia blight. A dense peanut canopy has been implicated as a factor favoring Sclerotinia blight (5). However, in peanut plots lacking significant differences in defoliation, plots sprayed more frequently with chlorothalonil still had higher incidence of Sclerotinia blight (11), which suggests a direct role for chlorothalonil in triggering an increased severity of the disease.…”

Planting Density Influences Disease Incidence and Severity of Sclerotinia Blight in Peanut

“…Okrun 5.2 aA 5.0 aA 5.9 aA 5.9 aA Flavor Runner 458 2.4 bA* 4.1 abAB* 4.9 abAB* 6.3 aB* Southwest Runner 3.5 abA* 2.9 abA* 3.3 bA* 3.5 bA* Tamspan 90 3.2 abA* 2.3 bA* 2.2 cA** 1.9 bA* * Significant at the 0.05 probability level for rate within a cultivar given as an uppercase letters (rows) and among lines for a given seeding rate given by lowercase letter (columns). Significant interaction of year 3 cultivar (p # 0.0001) was obtained (Table 5), which may have been due to the quantitative nature of the disease resistance (Wildman et al, 1992;Wildman et al, 1992) and the large degree environment influences the infection process of S. minor (Dow et al, 1988a;Dow et al, 1988bPhipps, 1995 also seen with disease incidence scoring. consistent with the increased differences between cultivars as spacing increased for disease incidence and disease severity (Table 6).…”