Fungicide efficacy on tar spot and yield of corn in the Midwestern United States

Tar spot of corn caused by Phyllachora maydis has recently led to significant yield losses in the eastern corn belt of the Midwestern United States. Foliar fungicides containing quinone outside inhibitors(QoI), demethylation inhibitors(DMI), and succinate dehydrogenase inhibitors(SDHI) are commonly used to manage foliar diseases in corn. To mitigate the losses from tar spot thirteen foliar fungicides containing single or multiple modes of action (MOA/FRAC groups) were applied at their recommended rates in a single application at the standard tassel/silk growth stage timing to evaluate their efficacy against tar spot in a total of eight field trials in Illinois, Indiana, Michigan, and Wisconsin during 2019 and 2020. The single MOA fungicides included either a QoI or DMI. The dual MOA fungicides included a DMI with either a QoI or SDHI, and fungicides containing three MOAs included a QoI, DMI, and SDHI. Tar spot severity estimated as the percentage of leaf area covered by P. maydis stroma of the non-treated control at dent growth stage ranged from 1.6 to 23.3% on the ear leaf. Averaged across eight field trials all foliar fungicide treatments reduced tar spot severity, but only prothioconazole+trifloxystrobin, mefentrifluconazole+pyraclostrobin+fluxapyroxad, and mefentrifluconazole+pyraclostrobin significantly increased yield over the non-treated control. When comparing fungicide treatments by the number of MOAs foliar fungicide products that had two or three MOAs decreased tar spot severity over not treating and products with one MOA. The fungicide group that contained all three MOAs significantly increased yield over not treating with a fungicide or using a single MOA.

Impacts of row spacing and fungicide timing on foliar disease, greenstem and yield in double cropped soybeans grown in the Chesapeake Bay region of the United States.

Double cropped soybeans are planted on approximately 1/3 of crop acres in the Chesapeake Bay region of the United States. Producers have asked if foliar fungicides are required to optimize yields in this region. We assessed the impacts of foliar fungicide application timing and row spacing on foliar disease, greenstem, and yield from 11 site years spanning 2017-2019. Foliar diseases only developed at rateable levels in one location. Fungicide application, regardless of timing, increased percent greenstem over non-treated controls. Fungicide application did not impact soybean yield. Yield was greater in 38.1 cm rows when compared to 19 cm rows. Our data do not support the use of foliar fungicides in double cropped soybean production in this region.

Diagrammatic scale for assessment the severity of Cercospora leaf blight on soybean (Glycine max) leaflets

Introduction. Cercospora leaf blight (CLB) caused by Cercospora kikuchii is an endemic soybean crop disease in Argentina. Objective. To develop and validate a scale to quantify the severity of CLB in leaflets of soybean (Glycine max) for the evaluation of foliar fungicides and cultivar trials. Materials and methods. A diagrammatic scale to assess the severity of CLB on soybean leaflets (Glycine max) was developed. The scale was based on the evaluation of 50 leaflets. The different severity levels of the leaflets were determined according to Weber-Fechner’s stimulus-response law. The proposed scale included severity levels of 1, 4.5, 17.5, 50, 82.2, 95, and 99 %. The validation of the scale was performed by 23 raters (3 experienced and 20 inexperienced) who assessed the severity of CLB on 50 leaflets with and without the use of the scale. Results. The results from the three experienced raters were more precise than those obtained by the inexperienced raters. The scale improved the visual interpretation to assess the severity of CLB for the inexperienced raters, who obtained estimated severity values close to the actual severity values. When the inexperienced raters used the proposed scale to estimate the severity of CLB on leaflets, they were accurate having determination coefficients (R2) between 0.74 and 0.91. According to the absolute errors, the greatest deviation was observed between -2.49 and 2.46. However, these deviations were not significantly different from the population average. To speed the process of cultivar evaluations we also propose the use of scales based on grades. Conclusions. The proposed scale to assess the severity of CLB on leaflets can be used for the assessment of foliar fungicide trials and soybean cultivars. The scale showed specificity for assessing the severity of Cercospora leaf blight (CFB) in soybean leaflets.

A machine learning interpretation of the contribution of foliar fungicides to soybean yield in the north‐central United States

Foliar fungicide usage in soybeans in the north-central United States increased steadily over the past two decades. An agronomically-interpretable machine learning framework was used to understand the importance of foliar fungicides relative to other factors associated with realized soybean yields, as reported by growers surveyed from 2014 to 2016. A database of 2738 spatially referenced fields (of which 30% had been sprayed with foliar fungicides) was fit to a random forest model explaining soybean yield. Latitude (a proxy for unmeasured agronomic factors) and sowing date were the two most important factors associated with yield. Foliar fungicides ranked 7th out of 20 factors in terms of relative importance. Pairwise interactions between latitude, sowing date and foliar fungicide use indicated more yield benefit to using foliar fungicides in late-planted fields and in lower latitudes. There was a greater yield response to foliar fungicides in higher-yield environments, but less than a 100 kg/ha yield penalty for not using foliar fungicides in such environments. Except in a few production environments, yield gains due to foliar fungicides sufficiently offset the associated costs of the intervention when soybean prices are near-to-above average but do not negate the importance of disease scouting and fungicide resistance management.

Impact of foliar fungicides on disease and silage quality of brown midrib (BMR) corn hybrids in Wisconsin

Corn, Zea mays L., is one of the most widely grown crops in the United States due to its importance as a feed, food, and fuel crop. Silage is a high energy, fermented feed that uses the entire corn plant and is important for feeding dairy cows. Any disease that affects the plant’s physiology can reduce silage quality. The goal of this study was to evaluate fungicide treatments on silage corn hybrids to determine their effect on fungal diseases, including those caused by Fusarium graminearum, on silage quality. Foliar fungicide trials were conducted in Arlington, Wisconsin in 2018 and 2019 and included two brown-midrib silage hybrids. In-field disease ratings were collected for foliar disease symptoms, ear rot severity, and lodging. Harvested silage was analyzed for yield, quality parameters, and mycotoxin (deoxynivalenol, DON) concentration. There were significant differences in all measured parameters between years and hybrids; however, only the foliar disease ratings were consistently reduced by the use of fungicide treatments. DON concentrations were significantly lower for two fungicide treatments in one hybrid in 2019. There were no significant differences among the treatments used on yield or any quality parameters in this study. More research needs to be done to find potential fungicides that can consistently reduce F. graminearum damage and DON concentration in silage corn.

Fungicide Sensitivity in Strawberry Powdery Mildew caused by Podosphaera aphanis in California

Field observations suggest that reduced fungicide sensitivity exists in field populations of Podosphaera aphanis, the causal agent of strawberry powdery mildew (SPM). SPM is one of the most common diseases in strawberry production and is controlled using foliar fungicide applications. This study characterizes the sensitivity of 19 P. aphanis isolates to the most common fungicides used against SPM in California. Isolates were collected from commercial fruit production fields in Oxnard, Ventura, Santa Maria, Salinas, and Watsonville, and from a plant nursery in Balico, California. Healthy, unfurled strawberry leaves (cv. Monterey) free of any visual disease symptoms were removed from actively growing plants and treated with one of six commercially formulated fungicides using the minimum labeled rate and inoculated with conidia of P. aphanis. Inoculated leaves were incubated at 20°C under 16/8 hours of day/night lighting and assessed for disease incidence (%) after 14 days. Pathogen growth on the treated leaflets constituted a measure of insensitivity to the fungicide. The six fungicide treatments and their average disease incidence on treated leaves for the 19 isolates are penthiopyrad (51.4%), quinoxyfen (41.5%), myclobutanil (39.8%), trifloxystrobin (19.8%), cyflufenamid (19.3%), and fluopyram + trifloxystrobin (3.5%). The average disease incidence for the trifloxystrobin treatment was raised significantly by two isolates considered to be resistant to the product (disease incidence > 66.6%). Two isolates collected from organic production systems were sensitive to all fungicides. We document compromised fungicide efficacy due to resistance to most of the fungicides currently used for control of SPM in California. This is the first report of resistance in P. aphanis to any fungicide in California and the first report of resistance in P. aphanis to penthiopyrad and quinoxyfen worldwide.

Chemical characteristics and digestibility of forage maize hybrids associated with foliar fungicide application

The objective of this study was to evaluate the effect of foliar fungicide application on the chemical characteristics and in situ digestibility of forage and silage in forage maize hybrids with different grain textures in two sowing seasons. A randomized complete block design was used with four replications, in a 4 x 2 factorial arrangement, 4 hybrids, with and without foliar fungicide application, in two sowing seasons. The hybrids used were DKB240PRO, AS1572PRO, 32R48YH and AG8690PRO3. Data were tested by analysis of variance; the means were compared by Tukey’s test at 5% probability and two non-orthogonal contrasts were performed. The application of fungicide on forage maize hybrids reduced the content of neutral detergent fiber (NDF), acid detergent fiber (ADF), soft dough stage and in the silage produced. The sowing season in December negatively influenced the chemical parameters of forage maize hybrids, compared to sowing in October. Hybrids with highly vitreous endosperm presented the highest contents of NDF and ADF, soft dough stage and in the silage produced. The application of fungicide (trifloxystrobin + prothioconazole) at the V8 and R1 stages positively influenced in situ digestibility soft dough stage and in the silage produced, depending of the sowing season.