Upland Rice - The Importance of Weeds

The Importance of Weeds

Weeds are the most serious biological constraint to upland rice production. IRRI scientists are pursuing projects on managing weeds with less herbicide use. One approach is to search for rice plant species that exhibit a characteristic known as allelopathy. Allelopathic plants can affect the growth of nearby plants through the production of biological compounds they release into the environment. If an allelopathic rice -- or other plant species -- could be found that could inhibit the growth of weeds important in rice production, it might be possible through genetic engineering to develop rice cultivars that would provide their own weed control.

Most weed species also are victims of their own diseases. Purposeful application of the agents of such diseases to weed pests among rice crops could constitute another approach to weed control.

Researchers from IRRI, Maejo University and Chiang Mai University launched a study in 1993 of the interactions between weeds, crop environmental conditions, and farmers' practices in upper northern Thailand. The goals are to understand the diversity of farmers' practices and decisionmaking processes and to grade the factors that limit rice crop yields.

IRRI scientists are also studying how fertilizer and cultural practices influence weed communities. In one project on phosphorus management, they are investigating how weed communities change as soil fertility is improved over time in the Philippines, Indonesia, and Thailand.

Riceplant cultivars differ in their ability to compete with weeds in the field. Scientists in the Philippines tested the competitiveness of a dozen cultivars against weeds to help farmers choose the most highly competitive one. By planting this cultivar and enhancing its competitive ability through good management practices, farmers should be able to reduce the number of handweedings necessary while achieving maximum yields.