Effect of fungicide and timing of application on management of Phoma black stem of cultivated sunflowers in the United States

Phoma black stem (PBS), caused by Phoma macdonaldii Boerema (teleomorph Leptosphaeria lindquistii Frezzi), is the most common stem disease of sunflower (Helianthus annuus L.) in the Northern Great Plains (NGP) region of the United States (US). However, the impact of PBS on sunflower yield in the US is unclear, and a near complete absence of information on the impact of fungicides on disease management exists. The objectives of this study were to determine the impact of PBS on sunflower yield, the efficacy of available fungicides, the optimal fungicide application timing, and the economic viability of fungicides as a management tool. Fungicide timing efficacy was evaluated by applying single and/or sequential applications of pyraclostrobin fungicide at three sunflower growth stages in ten field experiments between 2017 and 2019. Efficacy of ten fungicides from FRAC groups 3, 7, and 11 were evaluated in four field experiments between 2018 and 2019. The impact of treatments on PBS were evaluated by determination of incidence, severity, maximum lesion height (MLH), disease severity index (DSI) and harvested yield. Nine of the ten fungicides evaluated, and all fungicide timings that included an early bud application, resulted in disease reductions when compared to the non-treated controls. The DSI was negatively correlated to sunflower yield in high-yield environments (p=0.0004; R2 = 0.3425), but not in low- or moderate- yield environments. Although FRAC 7 fungicides were generally most efficacious, the sufficient efficacy and lower cost of FRAC 11 fungicides make them more economically viable in high-yielding environments at current market conditions.

Increase of Bacterial Leaf Streak in Hard Red Spring Wheat in North Dakota and Yield Loss Considerations

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa, has increased in both prevalence and severity in the major hard red spring wheat (HRSW)-producing state North Dakota. The disease is readily observed after flag leaf emergence and can quickly lead to defoliation and severe yield loss. The objectives of this research were to document the prevalence and incidence of BLS in North Dakota and provide estimations of yield and economic losses. Trained field scouts determined the incidence and prevalence of BLS in ND on HRSW plants between Feekes growth stage (FGS) 8 and FGS 11.2 from 2015 to 2021, and data were used to determine BLS-affected hectares. Yield data in combination with BLS ratings were obtained from HRSW performance trials to estimate the impact of BLS on yield. The combination of variety identity, hectarage data, BLS-affected hectarage estimates, and yield loss estimates was used to estimate economic losses from BLS in 2019 and 2020. Our data suggest that BLS-affected hectares ranged from 747 to 141,680 between 2015 and 2021. Yield loss was observed at multiple HRSW performance trial locations, with estimated yield losses as high as 60% on susceptible varieties. The amount of BLS-affected hectares was the highest in 2019 and 2020, and direct economic losses for North Dakota HRSW producers were estimated to be as high as $4.7 and $8.0 million, respectively. These data highlight the importance of BLS in HRSW and the need to procure resources for breeding efforts and grower education on management of BLS.

Meta-Analysis of Soybean Yield Response to Foliar Fungicides Evaluated from 2005 to 2018 in the United States and Canada

Random-effect meta-analyses were performed on data from 240 field trials conducted between 2005 and 2018 across nine U.S. states and Ontario, Canada, to quantify the yield response of soybean after application of foliar fungicides at beginning pod (R3) stage. Meta-analysis showed that the overall mean yield response when fungicide was used compared with not applying a fungicide was 2.7% (110 kg/ha). Moderator variables were also investigated and included fungicide group, growing season, planting date, and base yield, which all significantly influenced the yield response. There was also evidence that precipitation from the time of planting to the R3 growth stage influenced yield when fungicide was used (P = 0.059). Fungicides containing a premix of active ingredients from multiple groups (either two or three ingredients) increased the yield by 3.0% over not applying a fungicide. The highest and lowest yield responses were observed in 2005 and 2007, respectively. Better yield response to fungicides (a 3.0% increase) occurred when soybean crops were planted not later than 21 May and when total precipitation between planting and the R3 application date was above historic averages. Temperatures during the season did not influence the yield response. Yield response to fungicide was higher (a 4.7% increase) in average yield category (no spray control yield 2,878 to 3,758 kg/ha) and then gradually decreased with increasing base yield. Partial economic analyses indicated that use of foliar fungicides is less likely to be profitable when foliar diseases are absent or at low levels.