Research on managing Fusarium head blight (scab) of wheat and barley with foliar fungicides

Carl A. Bradley, Kelsey Mehl, and Josh Duckworth, Department of Plant Pathology
University of Kentucky Research & Education Center, Princeton, KY

Tim Stombaugh, Department of Biosystems & Agricultural Engineering
University of Kentucky, Lexington, KY

Research trials funded by the Kentucky Small Grain Growers Association were conducted on soft red winter wheat and winter barley during the 2017-18 growing season at the University of Kentucky Research & Education Center in Princeton, KY. The overall objective of the research trials were to develop the best recommendations for managing Fusarium head blight (FHB; also known as scab) and the associated mycotoxin deoxynivalenol (DON; also known as vomitoxin) with foliar fungicides. The specific objective of each trial differed, and details and results of these trials are provided below.

PLEASE NOTE THAT SOME OF THE TREATMENTS EVALUATED ARE FOR RESEARCH PURPOSES ONLY AND MAY BE NOT BE REGISTERED FOR USE OR MAY HAVE BEEN AN APPLICATION THAT IS NOT IN ACCORDANCE WITH THE LABEL. ALWAYS READ AND FOLLOW LABEL DIRECTIONS AND REGULATIONS BEFORE MAKING A FUNGICIDE APPLICATION.

Soft red winter wheat fungicide trial. The objective of the soft red winter wheat trial was to determine if sequential applications of fungicides would provide better control of FHB and DON compared to a single application of a foliar fungicide. The treatments consisted of the fungicides Prosaro (applied at 6.5 fl oz/acre), Caramba (applied at 13.5 fl oz/acre), or Miravis Ace (applied at 13.7 fl oz/acre) applied at Feekes growth stage 10.3 (50% head emergence), or Prosaro, Caramba, Miravis Ace, or Folicur (applied at 4 fl oz/A) applied at Feekes growth stage 10.5.1 (beginning anthesis), or sequential applications of Prosaro (Feekes 10.5.1) followed by Folicur (4 days later), Caramba (Feekes 10.5.1) followed by Folicur (4 days later), Folicur (Feekes 10.5.1) followed by Folicur (4 days later), or Miravis Ace (Feekes 10.5.1) followed by Folicur (4 days later). A nontreated check also was included as a treatment. Each treatment was replicated 4 times, and a mist-irrigation system was used to help provide an environment that would be favorable for FHB. The FHB-susceptible variety AgriMaxx 446 was used for this trial.

All fungicide treatments significantly (statistically significant with 95% confidence) reduced FHB index when compared to the non-treated check (Table 1). For treatments applied at the Feekes 10.3 growth stage, Miravis Ace had the significantly lowest FHB index value. For treatments applied at the Feekes 10.5.1 growth stage, Caramba, Prosaro, and Miravis Ace had statistically similar FHB index values, which were significantly less than the FHB index value of Folicur applied at Feekes 10.5.1. All sequentially applied treatments had statistically similar FHB index values. When comparing solo treatments applied at Feekes 10.5.1 with sequentially applied treatments, all solo applied products were statistically similar to the corresponding treatment that was applied sequentially with Folicur (4 days later) except when comparing solo applied Folicur with sequentially applied Folicur + Folicur. In that case, the sequentially-applied Folicur + Folicur had an FHB index value significantly less than Folicur applied alone at Feekes 10.5.1. It is important to note that some of the sequentially-applied treatments were tested for research purposes only, and that some of them, including Folicur + Folicur, would be a treatment that would not be legal according to the current EPA label for Folicur.

All fungicide treatments significantly (statistically significant with 95% confidence) reduced DON in harvested grain when compared to the non-treated check (Table 1). When comparing a products applied at Feekes 10.3 with the corresponding products applied at Feekes 10.5.1, only Prosaro had a significantly lower DON value when applied at Feekes 10.5.1 vs. 10.3. However, numerically speaking, all DON values were lower when the corresponding product was applied at Feekes 10.5.1 compared to its Feekes 10.3 application. All sequential applications significantly reduced DON values compared to the non-treated check; however, solo-applied products at Feekes 10.5.1 did not significantly differ with their corresponding products when applied sequentially with Folicur.

Conclusions. As observed in past research trials, applying a fungicide for FHB management at Feekes 10.5.1 generally will be better than applying at an earlier growth stage. The exception to this was with Miravis Ace, which had similar FHB index values when applied at Feekes 10.3 compared to Feekes 10.5.1. Although not always significantly different, the Feekes 10.5.1 applications had lower DON values than Feekes 10.3 applications. In general, sequentially applied treatments, where either Caramba, Prosaro, or Miravis Ace was applied at Feekes 10.5.1 and then followed with a Folicur treatment 4 days later, did not greatly differ with the corresponding solo treatment applied at Feekes 10.5.1. This suggests that sequential applications likely would not be worth considering for management of FHB.

Winter barley fungicide trial. The objective of the winter barley trial was to determine the best growth stage to apply a foliar fungicide to achieve the best control of FHB and DON. Prosaro (6.5 fl oz/acre), Caramba (13.5 fl oz/acre), Folicur (4 fl oz/acre), or Miravis Ace (13.7 fl oz/A) was applied at either the boot stage, heading stage, or 5 days after heading. A nontreated check also was included as a treatment. Each treatment was replicated 4 times, and a mist-irrigation system was used to help provide an environment that would be favorable for FHB. The FHB-susceptible variety Thoroughbred was used for this trial.

For treatments applied at the boot stage or at the heading stage, all treatments except Folicur, significantly reduced the FHB index compared to the non-treated check (Table 2). All treatments applied at 5 days after the heading stage, significantly reduced the FHB index compared to the non-treated check. In general, the lowest FHB index values were observed when treatments were applied at 5 days after the heading stage.

No statistically significant differences were observed among treatments for DON in harvested grain. Although not statistically significant, treatments applied at 5 days after heading had the numerically lowest DON values (Table 2).

Conclusions. Applying a fungicide treatment at 5 days after heading appeared to be the best in managing FHB in ‘Thoroughbred’ winter barley.

Fungicide coverage in soft red winter wheat. The objective of this trial was to evaluate the coverage of the wheat head with different fungicide application systems. Three different nozzle tips and orientations were evaluated at three different speeds (Table 3). To evaluate coverage of the wheat head, water sensitive paper cards were wrapped around test tubes that were the approximate same size in diameter as wheat heads, placed on a metal rod at the approximate height of wheat heads, and water was applied through the different application systems. The research trial was conducted in a wheat field. Water sensitive cards were collected after water applications, digitally scanned, and special software is being used to determine the % coverage of the cards with water droplets. These % coverage measurements are still being processed. FHB severity index was measured at the soft dough stage from treated and non-treated areas.

As observed in Table 3, all treatments significantly reduced FHB index compared to the non-treated check. Within a nozzle tip, adjusting the angle orientation and ground speed did have a significant effect on FHB index in several cases.

Conclusions. Significant differences were observed in FHB index when adjustments to nozzle angle orientation and ground speed were made. When % coverage analyses are completed, it will be interesting to determine if coverage influenced FHB index. More analyses is needed to better understand the relationship of coverage and FHB index, as well as how ground speed and nozzle orientation affects these variables.

Table 1. Effect of different fungicide products applied to wheat at different timings and sequentially on Fusarium head blight (FHB) severity index and on deoxynivalenol (DON) in harvested grain. Trial was conducted at Princeton, KY in 2018.

Table 2. Effect of different fungicide products applied to ‘Thoroughbred’ winter barley at different timings on Fusarium head blight (FHB) severity index and on deoxynivalenol (DON) in harvested grain. Trial was conducted at Princeton, KY in 2018.

Table 3. Effect of different fungicide application variables on Fusarium head blight (FHB) severity index of wheat. Trial was conducted at Princeton, KY in 2018.