Fusarium Head Blight of Small Grains in Pennsylvania: Unravelling Species Diversity, Toxin Types, Growth, and Triazole Sensitivity.

Fusarium graminearum is the main causal species of Fusarium head blight (FHB) globally. Recent changes in the trichothecene (toxin) types in the North American FHB pathogens support the need for continued surveillance. In this study, 461 isolates were obtained from symptomatic spikes of wheat, spelt, barley, and rye crops during 2018 and 2019. These were all identified to species and toxin types using molecular-based approaches. An additional set of 77 F. graminearum isolates obtained from overwintering crop residues during winter 2012 were molecularly identified to toxin types. A subset of 31 F. graminearum isolates (15 15-acetyl-deoxynivalenol [15ADON] and 16 3-acetyl-deoxynivalenol [3ADON]) were assessed for mycelial growth, macroconidia, perithecia, and ascospore production, and sensitivity to two triazoles. Ninety percent of isolates obtained from the symptomatic spikes (n = 418) belonged to F. graminearum, with four other species found at a lower frequency (n = 39). The F. graminearum isolates from symptomatic spikes were mainly of the 15ADON (95%), followed by 3ADON (4%), nivalenol (0.7%), and NX-2 (0.3%) toxin types. All F. graminearum isolates obtained from overwintering residue were of the 15ADON type. The toxin types could not be differentiated based on the multivariate analysis of growth and reproduction traits. All isolates were sensitive to tebuconazole and metconazole fungicides in vitro. This study confirms the dominance of F. graminearum and suggests ecological and environmental factors, to be further identified, that lead to similar composition of toxin types in the northern United States. Our results may be useful to assess the sustainability of FHB management practices and provide a baseline for future FHB surveys.

Evaluating the Profitability of Foliar Fungicide Programs in Mid-Atlantic Soft-Red Winter Wheat Production.

In mid-Atlantic soft-red winter wheat (SRWW) production, the standard timing for a fungicide application is between flag leaf emergence (Feekes growth stage [FGS] 8) and heading (FGS 10.5). However, two-pass and anthesis (FGS 10.5.1) applications are becoming common, although these programs have not been thoroughly evaluated for disease control, yield, and profitability. Experiments were conducted in the mid-Atlantic in 2015 and 2016 to evaluate fungicide programs with applications at FGS 8, FGS 10.5.1, and two-pass programs with an early application at green-up (FGS 5) followed by (FB) applications at either FGS 8 or FGS 10.5.1. Fungicide programs that included an application at FGS 10.5.1 resulted in the highest probability of no disease on the flag leaf (0.29 to 0.40). The estimated mean yield increases ( D¯ ) relative to the nontreated check ranged from 253.65 to 634.16 kg ha-1. Using a grain price of $0.18 kg-1 ($5 bushel-1), probabilities were similar between applications at FGS 8 (0.49 to 0.56) and FGS 10.5.1 (0.53). The probability of profitability ranged from 0.48 to 0.57 for FGS 5 FB FGS 8 applications and 0.52 to 0.59 for FGS 5 FB FGS 10.5.1 applications, indicating limited benefit to two-pass programs.