Resumen

DELGADO, Maryory; ORTIZ DOMINGUEZ, Aída  y  ZAMBRANO, Cástor. Resistance of Rottboellia cochinchinensis (Lour.) W.D. Clayton to nicosulfuron in maize crops. Agronomía Trop. [online]. 2006, vol.56, n.2, pp.171-182. ISSN 0002-192X.

The control of Itchgrass, Rottboellia cochinchinensis, one of the most important weeds of maize in Venezuela is based on nicosulfuron, a postemergent herbicide. However, levels of control have been low, which may suggest resistance of the weed to the herbicide. Resistance of itchgrass, collected in different farms of Portuguesa State, to nicosulfuron was evaluated. The resistance of mature seeds of itchgrass collected from 13 farms was compared against the resistance of itchgrass collected in the botanic garden of the Department of Botany of the Faculty of Agronomy where nicosulfuron had never been used. Two experiments were carried out in a greenhouse, in a completely randomised block design with 4 replications, 1) to select resistance to the commercial recommended dose of nicosulfuron (30 i.a. g ha^-1), and 2) to evaluate the resistance of itchgrass to increased doses of nicosulfuron (0, 7.5, 15, 30, 60 and 120 i.a. g ha^-1) with selected plants from experiment 1 where there was low control of itchgrass (<30%) by nicosulfuron. In both experiments nicosulfuron was sprayed using a calibrated CO₂ constant flow sprayer set to 250l/ha, when itchgrass had 3 to 4 leaves. Seedlings were placed in pots with 3 kg of soil. The dose of nicosulfuron which inhibits growth of itchgrass in a 50% (RC50) was estimated through the threshold of resistance index (RI), using the log-logistic model of regression in accordance with Seefeld et al. (1995). We found that 3 of the evaluated populations were susceptible and 11 resistant to nicosulfuron. Resistance index fluctuated between 2.1 and 600.1: Randal (19.7), Phaller (17.4), Esteger (30.7), Gómez (600.1), Luchi (34.4), Cedeño (8.6), Gaester (9.4), Hhaller (2.1), Giacobucci (6.6), Jiménez (39.8) and García (2.5).

Palabras clave : Zea mays; Rottboellia cochinchinensis; resistance; biotype.