Combining melon varieties with chemical fungicides for integrated powdery mildew control in Tunisia

Powdery mildew is one of the most important diseases that causes significant economic losses in melon. Chemical fungicides and tolerant melon varieties, which may reduce pathogen severity and encourage positive plant responses, are viable techniques for controlling this disease. The study objectives were to investigate the effectiveness of contact fungicides, systemic fungicides and a combination of both in four commercial fields at various sampling times [30, 90 and 120 days after the first fungicide application (DAFA)]. Both fungicide mixture azoxystrobin + chlorothalonil and fungicide thiophanate-methyl reduced the disease index of powdery mildew on melon varieties compared to the untreated control (disease index 1.70–2.13 and 0.83–1.75, respectively at 120 DAFA), reduced the disease severity (24.79–31.5% and 19.06–21.88%, respectively at 120 DAFA) and the percentage of leaf area covered by powdery mildew (27–43.75% and 8.25–39%, respectively at 120 DAFA). Furthermore, melon plants treated with azoxystrobin + chlorothalonil showed a larger yield increase (63.31–71.40%), polar (15.43–17.59 cm) and equatorial (24.71–29.61 cm) diameter, yield (2.23–3.18 fruits number/plant; 27.67–52.22 t/ha) and mean weight (2411.25–3289.5 g). Azoxystrobin + chlorothalonil and thiophanate-methyl not only reduced the disease index and disease severity index, but also promoted a yield increase of all melon varieties. More attention should be given to the effectiveness of chemical fungicide control in view of expected climate changes. But fungicides continuous application following a fixed schedule is unsustainable and could lead to high resistance development in PM fungi.