Improving fungicide application recommendations for managing Fusarium head blight of wheat and barley
Carl A. Bradley*, Kelsey Mehl, and John Walsh
Department of Plant Pathology, University of Kentucky Research & Education Center, Princeton, KY
*Contact information for C. A. Bradley: tel: 859-562-1306; email: carl.bradley@uky.edu.
Tim Stombaugh*
Department of Biosystems & Agricultural Engineering, University of Kentucky, Lexington, KY
*Contact information for T. Stombaugh: tel: 859-218-4351; email: tim.stombaugh@uky.edu
Research trials funded by the Kentucky Small Grain Growers Association were conducted on soft red winter wheat and winter barley during the 2018-19 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), Miravis Ace (applied at 13.7 fl oz/acre), Folicur (applied at 4 fl oz/acre), or Proline (applied at 5.7 fl oz/acre) applied at Feekes growth stage 10.3 (50% head emergence), Feekes 10.51 (beginning flowering), or 4 days following Feekes 10.51, or sequential applications of Prosaro (Feekes 10.51) followed by Folicur (4 days later), Caramba (Feekes 10.5.1) followed by Folicur (4 days later), Folicur (Feekes 10.51) followed by Folicur (4 days later), Miravis Ace (Feekes 10.51) followed by Folicur (4 days later) or Proline (Feekes 10.51) 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 trial was no-till planted into corn stubble, and the FHB-susceptible variety AgriMaxx 446 was used for this trial. Plots were harvested with a small plot combine, and yields were determined. Grain samples from each plot were collected and sent to the University of Minnesota DON testing laboratory for DON analysis.
All fungicide treatments significantly (statistically significant with 95% confidence) reduced FHB index when compared to the non-treated check, except for Feekes 10.3 applications of Prosaro and Folicur (Table 1). In general for single-applied treatments, the applications at Feekes 10.51 tended to result into the lowest FHB index values, but were not always significantly lower than treatments applied at Feekes 10.3 or 4 days after Feekes 10.51. All sequentially-applied treatments had very low FHB index values (ranging from 0.4 to 1.4), but were not significantly lower than many of the single-applied treatments. 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). Despite being significantly lower than the non-treated check, many treatments were still above the grain elevator threshold of 2 ppm. Treatments that resulted into DON values less than 2 ppm included Proline applied at Feekes 10.51 and at 4 days after Feekes 10.51, and all sequential applications except Folicur followed by Folicur and Proline followed by Folicur.
When comparing a products applied at Feekes 10.3 with the corresponding products applied at Feekes 10.51, only Miravis Ace and Prosaro had significantly lower DON values when applied at Feekes 10.51 vs. 10.3. However, numerically speaking, all DON values were lower when the corresponding product was applied at Feekes 10.51 compared to its Feekes 10.3 application.
No significant differences among treatments were observed for yield (Table 1) or test weight (data not shown). In general, test weights for all treatments were very low due to delayed harvest because of consistent heavy rainfall during harvest season.
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. Although not always significantly different, the Feekes 10.51 applications had lower DON values than Feekes 10.3 applications. In general, sequentially applied treatments, where either Caramba, Prosaro, Miravis Ace, Folicur, or Proline 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 10.51. 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. In addition, Quadris fungicide (6 fl oz/acre) was applied at boot stage by itself or followed by a Miravis Ace application 5 days after heading. The Quadris treatment was included to determine if strobilurin fungicide applications to winter barley can potentially increase DON similar to what has been reported in winter wheat. 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. Plots were harvested with a small plot combine, and yields were determined. Grain samples from each plot were collected and sent to the University of Minnesota DON testing laboratory for DON analysis.
All treatments significantly reduced FHB index compared to the non-treated check (Table 2). For boot applications, only Miravis Ace significantly reduced DON compared to the non-treated check. For heading applications and 5 days after heading applications, all treatments significantly reduced DON compared to the non-treated check except Folicur. Treatments that resulted into DON values less than 2 ppm included Miravis Ace applied at boot, Prosaro, Caramba, and Miravis Ace applied at either heading or 5 days after heading.
No statistically significant differences were observed among treatments for yield Table 2 (Table 2).
Conclusions. Applying a fungicide treatment at either heading or 5 days after heading appeared to be the best in managing FHB in ‘Thoroughbred’ winter barley. As observed in previous years, applying fungicides at boot stage is too early to achieve the best control of FHB and DON 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. FHB severity index was measured at the soft dough stage from treated and non-treated areas. In addition, grain samples were collected from fungicide-treated areas and from non-treated areas for DON analysis.
As observed in Table 3, simulated head coverage ranged from 9% to 14.6%. Additional analyses of the water-sensitive cards is ongoing to determine differences in coverage of front and rear portions of the simulated wheat head. All treatments resulted into FHB index values numerically less than the non-treated check. Nearly all treatments resulted in DON values that were numerically less than the non-treated check. Interestingly, there was a minor trend of applications made at 15 mph of having DON values than were potentially above the grain elevator threshold of 2 ppm. Additional analyses of the data are ongoing to determine statistically significant differences among treatments.
Conclusions. In general, most applications of fungicides, regardless of method, resulted in lower FHB index values and DON values compared to the non-treated check. This was an important finding, in that fungicides are working regardless of application type. However, the range of FHB index values and DON values in fungicide-treated plots showed that optimizing spraying system can result into additional control of FHB and DON. The analyses are still ongoing for this project to better detect and understand potential statistically significant differences among treatments.