THE ROLE OF PENDIMETHALIN IN THE INTEGRATED MANAGEMENT OF PROPANIL-RESISTANT ECHINOCHLOA-COLONA IN CENTRAL-AMERICA

Pre-emergence activity of pendimethalin on propanil-resistant jungle r ice (Echinochloa colona) was demonstrated in glasshouse trials. Both s usceptible and resistant populations, collected from Costa Rica, were controlled by 1.25 kg ha(-1), the usual application rate used in the f ield where Rottboellia cochinchinensis is also a problem. When applied post-emergence, propanil performance was improved by the addition of low doses of pendimethalin to the herbicide mixture. A propanil-resist ant selection was controlled by 0.23 kg ha(-1) pendimethalin + 0.54 kg ha(-1) propanil at the one-to-two leaf stage, and 0.23 kg ha(-1) pend imethalin + 1.08 kg propanil at the three-to-four leaf stage compared to 1.08 kg and 2.16 kg ha(-1) respectively when propanil was applied a lone. This suggests that pendimethalin improves post-emergence control in the field compared to the standard propanil treatment and can prov ide residual preemergence control of late-germinating individuals, so reducing the propanil selection pressure. For effective jungle rice co ntrol, growers apply propanil (3.84 kg ha(-1)) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop-P-ethyl (0.0 45 kg ha(-1)) at 35 DAP. Field experiments, conducted in dry-seeded up land rice in southern Costa Rica, demonstrated that under high jungle- rice population pressure, one application of pendimethalin at 1.5 kg h a(-1) provided an effective replacement for propanil, resulting in red uced weed-control costs.