Efficacy, cost-effectiveness, and residue levels of fungicides for managing panicle blight, fruit blight and anthracnose diseases of litchi

Litchi is affected by several diseases among which panicle blight, fruit blight and anthracnose are major diseases that affect yield and quality of fruits. Use of fungicides are the primary method for managing these diseases. Studies were conducted at Muzaffarpur in Bihar state of India during during 2022–2024 to assess the effectiveness of ten fungicides, including azoxystrobin, trifloxystrobin, pyraclostrobin, difenoconazole, tebuconazole, thiophanate methyl, metiram, carbendazim, mancozeb, and copper oxychloride, and various combinations. Residue levels of selected fungicides were also analyzed for safety standards compliance. The fungicides were applied at recommended dosages ranging from 0.3 to 2.0 g or ml per litre of water on litchi trees thrice-first after panicle initiation, second immediately after fruit set, and third at colour-break stage. Fungicides residue assay was carried out in a ‘planned experiment,’ and also in some ‘random retail samples’ from Muzaffarpur and Patna districts of Bihar, India. The results showed that fungicide application significantly reduced the incidence and severity of panicle blight, fruit blights, and anthracnose, thereby protecting both panicles and developing fruits in litchi trees. Thiophanate methyl was found to be the most effective, with a minimum percent disease severity index of 5.93 in 2022 and 7.81 in 2023. Thiophanate methyl-treated trees recorded the lowest incidence of fruit blight and anthracnose (0.0–0.50 %) during both years, compared to significantly higher levels in control trees (5.50–8.50 % fruit blight and 5.83–6.37 % anthracnose). Azoxystrobin was statistically at par with thiophanate methyl in disease control efficacy. Thiophanate methyl had the highest overall disease control and recorded the highest incremental cost benefit ratio (5.52–5.63) for the complete spray schedule targeting multiple diseases. Fungicide residues were mainly confined to peels, with only copper oxychloride and carbendazim detected in pulp; residue levels in all cases remained well below the maximum residue limits (MRLs) established by FSSAI, EFSA, and Codex standards. Residues in litchi pulp from fruit samples of trees sprayed with thiophanate methyl, difenoconazole, azoxystrobin, and untreated trees (control), applied 15 days, 10 days, and 5-days before harvesting of fruits were found below limit of quantification (0.01 mg/kg). The residue level was below MRL for thiophanate methyl and difenoconazole but not for azoxystrobin. Results of the studies will be useful for spray scheduling to manage panicle blight, fruit blight and anthracnose of litchi.