All products were applied at R3 soybean growth stage. Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required.
This article was originally published on December 2, The information contained within may not be the most current and accurate depending on when it is accessed. Daren Mueller is an associate professor and extension plant pathologist at Iowa State University. Mueller earned his bachelor's degree from the Univ You are here Home.
Septoria brown spot was also observed at all locations. Heavy rainfall in September and October challenged timely harvest in many locations. Average yield in untreated plots was Yield response to fungicide was statistically significant, and the yield response ranged from 0. Figure 1. Soybean yield response to fungicide products combined across all seven experiment locations in Means followed by the same letter are not statistically significant from one another.
Treatment effect was statistically significant for both diseases Figures 2 and 3. The QoI fungicides were not effective, however, the fungicides with new chemistries and with multiple mode of actions showed better performance than QoI fungicides alone for disease management and yield response.
Figure 2. Frogeye leaf spot severity in upper soybean canopy in fungicide treatments combined across all seven experiment locations in Figure 3. Fungicides with solo QoI active ingredients had limited efficacy against frogeye leaf spot and provided less yield benefit compared with fungicides with multiple chemistries, especially some of the newer chemistries.
An integrated method of disease management that does not depend only on fungicides should be employed to maximize disease management to preserve efficacy of existing fungicides. The answer to this question calls for an important consideration: Several foliar diseases occur each year in soybean in Missouri, yet their level of intensity and resulting impact on yield in a growing season depend on the susceptibility of a given soybean cultivar and the suitability of the environmental conditions for disease development.
Early-season diseases like Septoria brown spot, for example, may have a significant negative impact on the yield of a susceptible or moderately resistant cultivar if weather conditions are favorable for disease early in the season and towards the reproductive stages R4 to R6. Late season foliar diseases like frogeye leaf spot, Cercospora leaf blight and soybean rust can significantly reduce yield if weather conditions are favorable for epidemics towards mid- to late season.
Generally speaking, fungicide treatments are justifiable when they reduce disease impact on yield such that the profit from the gained yield advantage is much greater than the cost associated to the fungicide application. Many commercial fungicides are available for control of foliar diseases of soybean, and treatments are typically recommended for the beginning of blooming and later reproductive stages.
Timing and rate of application are important when a decision to do a fungicide treatment has been made. This report summarizes the results of two fungicide trials carried out in West Central Missouri in the growing season. The purpose of the trials was to evaluate the effect of several fungicides applied at different timing and application rates on the development of foliar fungal diseases and yield in soybean.
Description of the site and experimental design The trials were conducted in a non-irrigated, conventional till field Plots were planted to the soybean cultivar AsGrow at a seeding rate of , seeds per acre. Agronomic management of the plot followed the recommended practices for soybean in Central Missouri. The experimental plots consisted of four ft long rows, spaced at 30 inches. Plots were delimited by mowing two-foot alleys when plants were at the developmental stage V2.
The treatments were assigned to the experimental units in a randomized complete block design with four replications per treatment. Treatment Applications and Disease Assessment The fungicide treatments in both trials were applied at reproductive stages R1 and R3 and at different application rates Tables 1 and 2.
Intensity of foliar diseases was assessed in early August in both trials. The amount of disease per plot was determined in two inch wide x inch long x inch tall cubic quadrats that were placed systematically on each of the center rows of each plot. Septoria brown spot SBS; Septoria glycines incidence was measured in the lower, inner side plant canopy of the center row on which the quadrat was placed. Assessment of bacterial blight was done as an extra to the trial.
However, fungicide treatments were not aimed at controlling this disease.
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