Unleashing the synergistic effect of promising fungicides: a breakthrough solution for combating powdery mildew in pea plants

Abstract

Pea powdery mildew, caused by Erysiphe pisi, is a major limitation to global pea production. The emergence of fungicide-resistant pathogen populations due to frequent and injudicious pesticide application highlights the importance of exploring the synergistic properties of fungicide combinations. This study investigated the efficacy of difenoconazole, thiophanate-methyl, and sulfur, both individually and in mixtures, against powdery mildew and assessed the interaction types between these fungicides. The results demonstrated that the combination of difenoconazole, thiophanate-methyl, and sulfur was the most effective in reducing, reducing disease severity to 6.10% and minimizing conidial production on foliage. Additionally, this fungicide combination reduced conidial germination by 89.26% in vitro and by 87.50% in a detached leaf assay compared to the control. The treatment also positively impacted leaf chlorophyll content (55.18), green pod yield (22.21 tons ha^-1), seed yield (12.29 tons ha^-1), and other yield-related parameters. Although statistically significant, this ternary fungicide combination was closely followed by the binary combination of thiophanate-methyl and sulfur, which was the only combination exhibiting synergism in both laboratory and field trials with a synergy factor (SF) > 1. In conclusion, this approach offers improved disease control as part of integrated disease management (IDM) while minimizing the risk of resistant pathogen strains.

Keywords: Erysiphe pisi; Fungicides mixtures; disease control; pea; synergism.

Figure 1

Effect of fungicides on the conidial⁻¹ in the treatment. (A) Effect of fungicides and their binary and ternary combinations on inoculum load (Log transformed conidia mL⁻¹) of powdery mildew of pea following 7 days of fungicide application. Dots and error bars represent means and standard error mean, respectively, at a significance level of 0.05. DF, TM, and S stand for difenoconazole, thiophanate-methyl, and sulfur, respectively, whereas DF + TM, DF + S, TM + S, and DF + TM + S stand for a binary fungicide mixture of difenoconazole with thiophanate-methyl, difenoconazole with sulfur, thiophanate-methyl with sulfur and a ternary mixture of difenoconazole with thiophanate-methyl and sulfur, respectively. (B) A regression and correlation curve between the severity of powdery mildew and conidia mL⁻¹ of Erysiphe pisi.

Figure 2

Effect of fungicides and their binary and ternary combinations on pea plants. (A) control with no fungicide (B) difenoconazole, (C) thiophanate-methyl, (D) sulfur, binary mixture of (E) difenoconazole and thiophanate-methyl, (F) difenoconazole and sulfur, (G) thiophanate-methyl, and sulfur, and (H) ternary mixture of difenoconazole, thiophanate-methyl and sulfur on Area Under Disease Progress Curve (AUDPC) of powdery mildew of pea when recorded at a weekly interval for four weeks. AUDPC means followed by different letters are significantly different at a p-value of 0.05.

Figure 3

Status of chlorophyll content in plant leaves of the pea plant. (A) control plot with no fungicide application, (B) binary combination of thiophanate-methyl and sulfur, and (C) ternary combination of difenoconazole, thiophanate-methyl, and sulfur.

Figure 4

Effect of fungicides and their binary and ternary combinations on pea plants. (A) chlorophyll content (SPAD) of pea infected by powdery mildew. Bars and error bars show means and standard error mean, respectively, at a significance level of 0.05. DF, TM, and S stand for difenoconazole, thiophanate-methyl, and sulfur, respectively, whereas DF + TM, DF + S, TM + S, and DF + TM + S stand for binary fungicide mixtures of difenoconazole with thiophanate-methyl, difenoconazole with sulfur, thiophanate-methyl with sulfur and a ternary mixture of difenoconazole with thiophanate-methyl and sulfur, respectively. (B) A regression and correlation curve between powdery mildew severity and chlorophyll content following 28 days of initial fungicide application.

Figure 5

Effect of fungicides and their binary and ternary combinations on pea plants. (A) number and biomass of pods per vine, (B) number of seeds per pod, number and biomass of seeds per vine, (C) green pod yield and seed yield, and (D) shoot biomass, plant height, and root length. Symbols and error bars show means and standard error mean, respectively, at a significance level of 0.05. DF, TM, and S stand for difenoconazole, thiophanate-methyl, and sulfur, respectively, whereas DF + TM, DF + S, TM + S, and DF + TM + S stand for a binary fungicide mixture of difenoconazole with thiophanate-methyl, difenoconazole with sulfur, thiophanate-methyl with sulfur and a ternary mixture of difenoconazole with thiophanate-methyl and sulfur, respectively.

Figure 6

A correlation curve between the Area under the Disease Progress Curve (AUDPC) of powdery mildew with (A) green pod yield and (B) seed yield of pea.

Figure 7

Pea plant of (A) control plot with no fungicide application, (B) treated with a binary combination of thiophanate-methyl and sulfur, and (C) ternary combination of difenoconazole, thiophanate-methyl, and sulfur.

Figure 8

Root of pea plant of (A) control plot with no fungicide application, (B) treated with a binary combination of thiophanate-methyl and sulfur, and (C) ternary combination of difenoconazole, thiophante-methyl, and sulfur.