Tolerância de milho tratado com inseticidas a herbicidas do grupo das imidazolinonas Maize tolerance to imidazolinone herbicides when treated with insecticides

Objetivou-se neste trabalho estudar os efeitos e as interações entre os herbicidas imazapyr + imazapic e os inseticidas thiamenthoxan, thiodicarb, clorpirifós e fipronil sobre a cultura do milho. O experimento foi conduzido a campo em Castro, Paraná, na safra de 2001/2002, sendo o híbrido DKB 909 CL, tolerante ao herbicida, cultivado em sistema de plantio direto. Os inseticidas thiodicarb (120 mL ha-1) e thiamenthoxan (32 g ha-1) foram misturados às sementes; clorpirifós (1.125 mL ha-1) e fipronil (96 g ha-1) foram aplicados no sulco de plantio. A aplicação dos tratamentos com os herbicidas imazapyr + imazapic nas doses de 0; 17,5 + 52,5; 35,0 + 105,0 e 52,5 + 157,5 g ha-1 foi realizada quando o milho apresentava cinco folhas (V5). As avaliações de toxicidade na cultura foram realizadas aos 7, 16, 25 e 30 DAA (dias após aplicação dos herbicidas); por ocasião da colheita, avaliaram-se o rendimento e a massa de mil grãos. Não houve interações entre os inseticidas aplicados no sulco de semeadura ou nas sementes de milho e as diferentes doses de herbicida. Todavia, o inseticida clorpirifós e a maior dose do herbicida provocaram os maiores sintomas de intoxicação (20,5 e 30,0 respectivamente), caracterizados por clorose inicial próxima do cartucho das folhas, observando-se recuperação da cultura aos 30 DAA. Nenhum dos tratamentos afetou o rendimento e a massa de mil grãos do milho DKB 909CL.<br>Chemical protective practices are commonly used in maize crop and negative interactions between insecticides and herbicides seem possible. Some of these negative interactions have been observed in other crops in Brazil with a few studies related with maize. The main objective of this work was to study the interaction between imazapyr + imazapic herbicides and thiamenthoxan, thiodicarb, clorpirifos e fipronil, insecticides in maize. The experiment was carried out at field conditions, at "Fundação ABC" experimental area, Castro, Paraná State, Brazil during 2001/2002 season crop. The herbicide tolerant hybrid DKN 909 CL, under a no-tillage system, was used. Thiodicarb (120 mL ha-1) and thiamenthoxan (32 g ha-1) were mixed with the seeds while clorpirifos (1125 mL ha-1) and fipronil (96 g ha-1) were applied to the sowing lines. The herbicide treatments (imazapyr + imazapic) were applied at the 5-leaves stage (V5) in the doses of 0, 17.5 + 52.5, 35.0 + 105.0, 52.5 + 157.5 g ha-1 Crop phytotoxicity was evaluated at 7, 16 and 25 days after application (DAA). Harvesting for yield analysis and 1000 kernels mass was done at 131 DAA. No interactions were observed between insecticide treatments and herbicide doses. Clorpirifos insecticide and a proportional increase of the herbicide to 52.5+157.5 g ha-1 induced phytotoxicity symptoms; nevertheless no injuries were observed from 30 DAA on. Yield and 1000 kernels mass were not reduced by the different treatments.