Resumo

DELGADO, Maryory; ORTIZ DOMINGUEZ, Aída  e  ZAMBRANO, Cástor. Populations of Rottboellia cochinchinensis (Lour.) W.D. Clayton cross resistance to foramsulfuron + iodosulfuron. Agronomía Trop. [online]. 2008, vol.58, n.2, pp.175-180. ISSN 0002-192X.

Itchgrass (Rottboellia cochinchinensis (Lour,) W,D, Clayton) is one of the most noxious weed in corn crops in Venezuela. The objective of this research was to evaluate the effect of six increasing doses of foramsulfuron + iodosulfuron in six nicosulfuron resistant itchgrass accessions and susceptible population, It was establishes a trial under completed randomized block design with 4 replications. This experiment was realized in a greenhouse. When the plants had of 3 to 4 leaves, It was were sprayer foramsulfuron + iodosulfuron a rates of 0, 18.6, 37.2, 74.4, 148.8 and 297.6 g,i,a,ha-1. Were analyzed the data of fresh weight of plants in a log-logistic regression model, establishing the required dose to inhibit growth in 50% (RC50) in each biotype and the threshold of resistance index (RI). All nicosulfuron resistant populations harvested in Portuguesa evaluates under this experimental conditions showed crossed resistant to foramsulfuron + iodosulfuron too. Also, We found degrees resistant indexes (RI), Phaller, García, Gómez, Cedeño and Esteger showed highest values of RI, 26.91, 24.64, 23.85, 22.58 y 21.01, respectively, whereas Luchi has smallest RI, with 12.6. In agreement with these results, we must design a management to itchgrass resistant populations in corn farms in region of this study.

Palavras-chave : Dose-response biossay; herbicide resistance; cross-resistance; foramsulfuron + iodosulfuron; nicosulfuron; ROTCO; ZEAMA.