Controle de Pyricularia grisea e Bipolaris sorokiniana em sementes de trigo mediante tratamento com fungicidas

Laboratory, greenhouse and field experiments were carried out in order to evaluate the effectiveness of fungicides, in wheat seed treatment, to control Pyricularia grisea Sacc., anamorphic state of Magnaporthe grisea (Hebert) Barr and Bipolaris sorokiniana (Sacc.) Schoemaker (Helminthosporium sativum Pammel, King & Bakke), anamorphic state of Cochliobolus sativus (Ito & Kurib.) Drechs.: Dastur. Seeds of Anahuac and Batuira cultivars were treated with 20 fungicides, in four consecutives fases, and analised for health, in laboratory, by the deep-freezer method. In greenhouse, emergence and seedlings symptoms were evaluated; in the field, besides these parameters, yield was also evaluated. According to the results obtained, most of the fungicides were efficient for controlling both fungi. The products evaluated, in the doses below (g of a.i./100 kg seeds) can be put in 4 groups, in decreasing order of effectiveness for the control of P.grisea and B. sorokiniana in wheat seeds: 1° group – iprodione+carbendazin (52,5+26,2), carbendazin+mancozeb (50+160) and triflumizole+methyl tiophanate (45+135); 2° group - iprodione+thiram (50+150) and carboxin+thiram (93.7+93.7); 3° group – iminoctadine (62.4), thiram (210), prochloraz (50) and carboxin + prochloraz (82.5+22.5); 4° group – triadimenol (67.5), guazatine+imazalil (60 + 4) and prochloraz (40). Thiabendazole (60), benomyl (125) and tricyclazol (75) controlled efficiently P.grisea, but did not control B. sorokiniana while flutriafol (7.5) and ethyltrianol (4.9), that were efficient to control this fungus, did not control P.grisea. There was a significant negative correlation between H. sativum seed incidence and emergence and a positive correlation between emergence and yield. Nevertless, there was no correlation between P.grisea seed incidence and emergence. This fungus was transmitted by seeds in a transmission rate (seed infection/seed transmission) which ranged from 7.3:1 (13.6%) in the winter, to 1.8:1 (55.5%) in the summer, that indicates the influence of the temperature on its seed transmission.