Field experiments were conducted at four locations in the Central Pacific region of Costa Rica between 1994 and 1996 to determine suitable tactics for integrated control of propanil-resistant junglerice in rain-fed rice. Stubble incorporation within 3 mo after rice harvest did not affect the density of junglerice that emerged with the crop at the beginning of the rainy season at any location. However, the elimination with glyphosate of the first junglerice seedling population emerging before rice planting consistently reduced the in-crop infestation of junglerice and resulted in increased grain yields. The positive effect of eliminating the first junglerice flush remained even after the in-crop treatments were applied and lasted after rice harvest. Substitution of the two customary applications of propanil (3.8 kg ha−1 each) with a single application of pendimethalin (0.75 to 1.5 kg ha−1), preemergence or early postemergence, also reduced junglerice infestation and improved grain yield. Both propanil, in mixture with the synergist piperophos, and quinclorac controlled propanil-resistant junglerice and increased grain yields. Control of the initial junglerice population and improved in-crop weed management can serve as the basis for integrated management of herbicide-resistant junglerice in rain-fed rice.
Nomenclature: Glyphosate; pendimethalin; piperophos; propanil; quinclorac; junglerice, Echinochloa colona (L.) Link. ECHCO; rice, Oryza sativa L. ORYSA.