Herbicide seed treatment for weed control in wet‐seeded rice

Abstract

One laboratory and two field experiments were conducted at the International Rice Research Institute (IRRI) to determine the effect of herbicides applied as seed treatments on crop safety and weed control in wet‐seeded rice (Oryza sativa L.). In the laboratory experiment all the herbicides tested, except butachlor‐2,4‐D, did not affect rice seed germination. Butachlor‐2,4‐D reduced root growth the most, while thiobencarb caused the greatest reduction in shoot growth. In the first field experiment all the seed treatments except bensulfuron reduced crop stand. The same herbicides poured directly onto flooded fields several days after sowing did not decrease plant stand significantly. Plant heights were reduced significantly by seed treatments with both butachlor formulations and pretilachlor + fenclorim. The best weed control was observed with pretilachlor + fenclorim applied either as a seed treatment or poured onto water. In the second field experiment, pretilachlor + fenclorim at 0.45 kg a.i./ha reduced crop stand and slightly stunted plant height when applied to the seed. Weed weights were generally less, and crop yields were increased, in the herbicide‐treated plots compared with the untreated plots, regardless of application method. Seed treatment with herbicides appears to be a promising technique for controlling weeds in wet‐seeded rice.

Keywords:

• Application method
• herbicide concentration
• phytotoxicity
• germination
• growth