کارایی قارچ‌کش اورتیوا تاپ® در کنترل بیماری لکه برگی سرکوسپورایی چغندر قند در مقایسه با قارچ‌کش باویستین® در شرایط مزرعه

Cercospora leaf spot, caused by Cercospora beticola, is the most important leaf pathogen of sugar beet worldwide including Iran. The management of the disease is primarily achieved through the application of the synthetic chemical fungicides and carbendazim is widely used. Carbendazim residues are frequently found in food, soil and water and it is classified in the hazardous category of chemicals by World Health Organization. Furthermore, carbendazim is a systemic fungicide with a site-specific mode of action, and its repeated use leads to resistance development among pathogen populations. Hence, this study aimed at validating the combination of azoxystrobin + difenconazole as an alternative to carbendazim and identifying the lowest effective dosage by assessing its field efficacy against cercospora leaf spot in terms and effect in yield. The trials were carried out in Khuzestan province, Iran, where the incidence and severity of the disease is commonly very high. Experiments were designed as completely randomized blocks with five treatments and four replications. The efficacy of the fungicide was assessed under natural inoculums of the pathogen. Experimental plots were subjected to foliar spays of azoxystrobin + difenconazole (Ortiva top® 32.5 SC) and carbendazim (Bavistin® 60 PW) fungicides after the appearance of the disease symptoms followed by three sprays at one month intervals. Application of fungicides was carried out at three doses of 0.75, 1 and 1.25 L/ha for azoxystrobin + difenconazole fungicide and at the recommended dose of 0.5 Kg/ha for carbendazim fungicide. Disease severity was measured two weeks after the last spraying using a scale of 0 to 5 as described by Rossi et al. (1995). Based on the results of this study, azoxystrobin + difenconazole fungicide significantly reduced the disease severity compared with carbendazim fungicide and untreated plots and significantly increased the yield per hectare. The lowest effective dosage for azoxystrobin + difenconazole fungicide against cercospora leaf spot was determined as 1 L/ha under field condition. These results showed that the inclusion of the optimal dosage of azoxystrobin + difenconazole in the cercospora leaf spot management can offer an appropriate alternative to carbendazim even under high inoculum pressure of the pathogen.