Nathan Kleczewski Ph.D
Extension Specialist- Plant Pathology
Department of Plant and Soil Sciences
The 2013 full season soybean disease report is now available and can be found by clicking the link below:
Soybean Variety Trial Writeup 2013
This report will be posted under the soybean variety trial results on the University of Delaware Field Crops Resources page soon. http://extension.udel.edu/ag/field-crop-resources/variety-trials-corn-hybrids-small-grains-soybeans/
Disease severity was evaluated at full season soybean variety trials located in Newcastle and Sussex counties. The variety trials tested the adaptability soybean to Delaware growing conditions and susceptibility to common diseases in the region. Frogeye leaf spot spot was present at all sites but only in sufficient amounts to rate at the irrigated site located in Georgetown, DE. Brown spot (Septoria glycenes) and downy mildew (Peronospora manshurica) were present at all sites but not in sufficient quantities to rate. Alternaria leaf spot was only observed at the Georgetown site.
The disease ratings were conducted at the Newcastle County and Sussex County locations on September 4th, 2013 and September 6th 2013, respectively. The Sussex County trial in Georgetown was irrigated. Ratings were made from a 1 ft2 portion of the center of each plot. Ratings were made on a 5-point scale as follows: 0 = 0-1% disease; 1 = 1-10% disease severity; 2 = 11-20%; 3 = 21-30%; 4 = 31-40%; 5 = 41-50%. Frogeye leaf spot was rated on the upper most fully expanded leaves in the canopy. Severity of frogeye leaf spot in individual plots ranged from 0 to 30%. Severity of Alternaria leaf spot was estimated in the middle canopy on four fully expanded leaves. Severity of Alternaria leaf spot in individual plots ranged from 0 to 50%. Disease levels were too low to differentiate treatments the unirrigated site in Newcastle County. Plants were at R5-R6 when rated. Data presented here represent the plot averages (N=4) based on the aforementioned rating scale. Data were transformed to the midpoint of the range and analyzed statistically using non-parametric Kruskal-Wallis tests. Analysis indicated that significant differences between varieties existed (P <0.001). Means were separated using student’s t-tests at α=0.05.
In general the amount of frogeye leaf spot was low and infection was not severe enough to result in defoliation often associated with yield loss. Alternaria leaf spot was only found at the irrigated Georgetown site. This disease was moderate in some cultivars and caused some defoliation into the mid-upper canopy in some varieties. In Georgetown no differences in disease were noted in early maturing varieties. Conversely, six late season varieties contained significantly more Frogeye leaf spot severity than the most resistant variety. Twelve late season varieties had significantly greater amounts of Alternaria leaf spot than the most resistant variety. The data are summarized in Tables 1 and 2. Soybeans were planted into conventionally tilled ground and therefore inoculation was dependent on airborne spores from other areas. Therefore disease levels are likely lower than what would be expected in no-till or minimal-tillage fields.”
Source : udel.edu