Transplanted Weeds

Because grasses such as Echinochloa are not easily distinguished from rice seedlings during the early growth stage, they are often transplanted into the field with rice seedlings. Recently, IRRI researchers and farmers in Guimba, Neuva Ecija, Philippines, studied the dissemination of weed seeds and weed seedlings along with transplanted rice seedlings.

The farmers in the study area did not hand-weed or apply herbicides in rice seedling nurseries. As a result, weeds grew in association with the rice seedlings and were removed with them when the rice seedlings were pulled and bundled for transplanting. Weed seeds in the soil and those attached to the roots of the rice seedlings ranged from 271 to 683 per bundle.

During the wet season, grasses comprised 63% of the weed seedlings and 81% in the dry season. Fourteen weed species were recorded in the seedling bundles in the wet season and nine in the dry season.

Farmers of Guimba commonly use the same area in their fields for rice nurseries year after year. After the seedlings are removed, the area usually receives little care whether it is planted with a crop or not. This allows annual weeds to produce many seeds and perennial weeds to multiply vegetatively.

Several recommended practices will help farmers minimize the problems of transplanted weeds. First, start with weed free rice seed. By pre-germinating seeds (dapog method) on banana leaves, burlap or paper, farmers avoid weed seed contamination from the soil. Farmers should then prepare the seedling nursery thoroughly to reduce weed seed reserves in the soil.

By maintaining standing water in the seedling nurseries during the pulling of seedlings, farmers can clean the roots thoroughly before transplanting.

Finally, researchers advise farmers to shift the seedling nurseries each season to areas of the field that have been kept relatively weed free during crop growth. If rotation of the nurseries is impractical, farmers should attempt to grow a cover crop during the rest of the year to smother remaining weeds. Tropical Pest Management, 1988, 34(3):288-290.

For more information:

Dr. A.N. Rao
Department of Agronomy
Los Banos, Laguna