Chemical Control of Synthetic Pesticides on Garlic Germination and Performance

Background: Global garlic production has steadily increased over recent decades, with major producing countries including China, India, South Korea, and several Latin American nations contributing significantly to international markets. Among the most significant fungal diseases affecting garlic cultivation is rust, caused by Puccinia allii (Pers.) Rudolphi, which represents a major constraint to garlic production in many regions worldwide. Aim: The objective of this study was to evaluate the efficiency of fungicides and bactericides, applied weekly as single treatments, in controlling garlic diseases. Methodology: A randomised complete block design (RCBD) field trial was conducted with weekly applications of fungicides and bactericides, totalling 11 applications for each treatment, to compare their effects on disease incidence, severity, and crop performance. The experiment was carried out in garlic fields (26°49'16.8"S, 50°59'10.4"W) during one crop season, with evaluations performed from planting until 165 days after planting. Treatments included mancozeb (2.4 kg a.i./ha), difenoconazole (0.125 L a.i./ha), pyraclostrobin (0.1 L a.i./ha), propineb (2.1 kg a.i./ha), metiram+pyraclostrobin (1.1 kg a.i. + 0.1 kg a.i./ha), copper hydroxide [liquid formulation: 403.08 mL a.i./100 L (262.5 mL metallic copper); fluazinam (500 g a.i./ha), cuprous oxide (1.548 kg a.i./ha (1.35 kg metallic copper)), copper oxychloride (168 g a.i./100 L (100 g metallic copper)), and kasugamycin (0.07 L a.i./ha). Insect pests were managed using imidacloprid, formetanate hydrochloride, acetamiprid+etofenprox, or spinetoram, rotating active ingredients every two weeks. At 165 days, rust severity, bulb weight, and the percentage of green leaves were measured. Results: Pyraclostrobin, mancozeb, metiram+pyraclostrobin, and propineb showed the lowest rust incidence and severity. For bacterial control, propineb and mancozeb were the most effective. The highest bulb weights were obtained from treatments with mancozeb, propineb, pyraclostrobin, metiram+pyraclostrobin, and fluazinam. The efficacy of some fungicides against bacteria may be related to indirect effects, such as plant resistance induction or interference with secondary infection establishment. Fluazinam, for example, possesses a unique mechanism of action that may interfere with energy metabolism in both fungi and some bacteria. Moreover, integration of cultural practices, such as planting in well-drained soils, crop rotation, and elimination of infected crop residues, should complement chemical control to maximise management efficacy. Conclusion: The results demonstrate that multisite fungicides, particularly propineb and mancozeb, are effective tools for managing garlic diseases, contributing to improved plant health, yield, and bulb quality. Future management strategies may be designed focusing on fungicides with proven efficiency.