Vol. 8, Issue 11, Part H (2024)

Onion (Allium cepa L.) is one of the most important commercial vegetables. Onion is a cool season crop. However, it can be grown under a wide range of climatic conditions. It grows well under mild climate without extreme heat or cold or excessive rainfall. Onions are susceptible to various pathogens, including viruses, phytoplasmas, bacteria, and fungi, each presenting distinct challenges to onion cultivation. Fungal pathogens, in particular lead to diseases such as downy mildew, powdery mildew, white rot, and purple blotch, which can significantly harm the health of onion plants, ultimately affecting both their yield and quality. Among the fungal diseases purple blotch of onion incited by Alternaria porri is one of the most economically important in all regions wherever onion is grown. Therefore, research was carried out in the Rabi seasons of 2023–24 at the Research Farm, Department of Plant Pathology at the Naini Agricultural Institute, Sam Higginbottom University of Agriculture, Technology and Sciences, Prayagraj, U.P. The biocontrol, botanicals and fungicides were applied in field. The experiment was laid out in RBD (Randomized block design) with 3 replications. Treatments were applied after the appearance of the disease symptoms in the three sprays at the interval of 15 days. Treatments comprised of T₀ (Control); T₁ {Trichoderma harzianum @ 1% (SD) + (FS)}; T₂ {Trichoderma harzianum @ 1% (SD) + Aloe vera leaf extract @ 10% (FS)}; T₂ {Trichoderma harzianum @ 1% (SD) + Garlic Clove extract @ 10% (FS)}; T₄ {Trichoderma harzianum @ 1% (SD) + Lemon leaf extract @ 10% (FS)}, T₅ {Trichoderma harzianum @ 1% (SD) + Neem leaf extract @ 10% (FS)}; T₆ {Trichoderma harzianum @ 1% (SD) + Dhatura leaf extract @ 10% (FS)} and T₇ {Mancozeb (DM-45) @ 0.2% (SD) + (FS)}.

Among the different treatments applied T₅ {Trichoderma harzianum @ 1% (SD) + Neem leaf extract @ 10% (FS)} showed minimum percent of disease intensity (6.86, 12.23 and 18.28%) at 45, 60 and 75 DAT respectively. T₅ {Trichoderma harzianum @ 1% (SD) + Neem leaf extract @ 10% (FS)} showed maximum bulb yield per hectare (17.49 t/ha) and highest cost benefit ratio (1:2.68). Hence, T₅ {Trichoderma harzianum @ 1% (SD) + Neem leaf extract @ 10% (FS)} proved to be the most effective treatment against purple blotch of onion compared to other treatments and the untreated control.