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 rice (Echinochloa colona) was demonstrated in glasshouse trials. Both susceptible and resistant populations, collected from Costa Rica, were controlled by 1·25 kg ha‐1, the usual application rate used in the field 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‐resistant selection was controlled by 0·23 kg ha‐1 pendi‐methalin+0·54 kg ha‐1 propanil at the one‐to‐two leaf stage, and 0·23 kg ha‐1 pendimethalin+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 alone. This suggests that pendimethalin improves post‐emergence control in the field compared to the standard propanil treatment and can provide residual pre‐emergence control of late‐germinating individuals, so reducing the propanil selection pressure. For effective jungle rice control, growers apply propanil (3·84 kg ha‐1) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop‐P‐ethyl (0·045 kg ha‐1) at 35 DAP. Field experiments, conducted in dry‐seeded upland rice in southern Costa Rica, demonstrated that under high jungle‐rice population pressure, one application of pendimethalin at 1·5 kg ha‐1 provided an effective replacement for propanil, resulting in reduced weed‐control costs. ©1997 SCI