Update:
Objective 1: Compare new fungicide products with industry standards for foliar disease management and yield protection
Foliar fungicides were evaluated across seven Iowa State University research and demonstration farms to determine their performance for disease and yield response on soybean in 2022. These farms included the Northwest Research and Demonstration Farm (Sutherland), Northern Research and Demonstration Farm (Kanawha), Northeast Research and Demonstration Farm (Nashua), Central Iowa Research Farms (Ames), Armstrong Memorial Research and Demonstration Farm (Lewis), McNay Memorial Research and Demonstration Farm (Chariton), and Southeast Research and Demonstration Farm (Crawfordsville).
A total of 14 fungicides containing single and multiple active ingredients were evaluated at each location. Fungicide treatments were laid out in a randomized complete block design with four replications. Plot size ranged from 25–35 ft long and 10 ft wide (4 rows 30-inch inter-row spacing). Soybean cultivar NK28-T3XF was planted in all locations except in Crawfordsville, where Merschmans Arthur 2230E was planted and weed managed with standard pre- and post-emergence herbicides. Corn was planted in the previous year in all the locations. All fungicides were sprayed using a self-propelled research sprayer at recommended rates at the beginning of the pod (R3 growth stage) with nonionic surfactant (Induce at 0.3% v/v). Foliar diseases were assessed when soybeans reached the R6 (full seed) growth stage. Septoria brown spot (SBS caused by Septoria glycines) progression was assessed by measuring the height of the highest infected leaf in the canopy, and the disease severity was estimated as the percent of leaf area covered by the disease on the highest infected leaves. A total of two assessments, one in each row (couple of plants per row), were collected and averaged for a plot. Other foliar fungal diseases were also assessed, including frogeye leaf spot (FLS caused by Cercospora sojina) and Cercospora leaf blight (CLB caused by Cercospora species) if present on 10 leaves in the upper canopy of each plot. The two central rows were harvested per plot. Total seed weight/plot and moisture were measured with a 2009 Almaco SPC20 research plot combine. The seed weight was adjusted to 13 percent moisture, and yield was calculated in bushels per acre. At Central Iowa Research Farms (Ames), slide spore traps were placed from VE–R6 of statewide project collaboration and sent to the University of Wisconsin-Madison.
Objective 2: Monitor for fungicide resistance in major soybean pathogens in Iowa
We sampled leaves from fungicide trials across the state (both small plot and on-farm) and from demonstration farms of private companies that exhibit the foliar diseases FLS, CLB, and SBS. Fungal isolation of these three fungal pathogens is still underway. Cercospora leaf blight (CLB) was found in 3 locations with low disease pressure in Iowa State University research and demonstration farms such as McNay and Kanawha and a research farm in Gilbert. These CLB samples were shared with colleagues at Southern Illinois University to monitor for fungicide resistance.
We evaluate foliar fungicide products in seven locations across the state. This provides farmers annual updates on how effective different foliar fungicide products are. Our data are combined with other states to update the National Foliar Fungicide Efficacy Guide which is housed on Crop Protection Network. Each year's data also will be posted on ISU's ICM News Blog so farmers can see local data.
Fungicide resistance continues to be a huge issue. The two main fungi that foliar fungicides target (pathogens that cause frogeye leaf spot and brown spot) are now resistant to one of the main groups of fungicides (QoI or strobilurin). This matters because there are solo strobilurin fungicides still being used and they do not work at all. More importantly, the strobilurin fungicides are still being used as premixes in almost every product, and their inclusion in these premix products is also not helping farmers (in fact it is only hurting them because they have to buy a product that does not work at all and is misleading farmers into thinking they are spraying a premix (doing the right thing)). Our group is documenting what pathogens are becoming resistant to fungicides. We are working closely with other pathology labs across the nation to monitor for resistance in other fungicide classes as well.
We continue to evaluation other ways fungicides may be better used - for example, we have evaluated the importance of fungicide coverage and started looking at using predictive models to time fungicide application.