Watch out for weedy rice

By Sosimo Ma. Pablico

Rice farmers would do well to watch for the invasion of weedy rice in their farms, as this weed poses great competition for soil nutrients with the rice plants and could cause reductions in yield.

Research reports indicate that if 35 percent of a rice crop is composed of weedy rice plants, grain yield losses can reach 50 to 60 percent.  What’s more, greater weedy rice infestation can result in total crop loss because of competition and crop lodging.

If weedy rice grains are mixed with the crop harvest, the milled rice becomes contaminated with red to cream weedy rice grains, resulting in a great reduction of its market value. 

Dr. Madonna C. Casimero, acting deputy executive director for research of PhilRice [Philippine Rice Research Institute], said that since weedy rice is closely related to cultivated rice it is difficult to differentiate the two during the vegetative stage, most especially in direct-seeded rice.

“It could be a serious threat in direct-seeded rice, as it would be quite difficult to distinguish it during early vegetative growth,” according to the lady weed control expert.

The cost of controlling weedy rice could be staggering once it has invaded a community of rice fields, she added. 

Scientists claim that this weed could be a natural hybrid of cultivated rice and the wild rice species Oryza rufipogon and Oryza nivara.  It is known as padi angin in Malaysia, lua lon in Vietnam, lutao in China, akamai in Japan, sharei in Korea, khao pa in Laos, khao nok in Thailand, and jhora dhan in Bangladesh.  Its name in the Philippines is not known.

In areas where early maturing rice varieties are planted and harvesting is done with mechanical harvesters, the seeds of weedy rice could become part of the harvest.  If this happens, the grains of the weed seeds, which are red to cream, could reduce the quality of the milled rice.

Weedy rice seeds that fall on the ground do not germinate until some time later.  Its seed dormancy varies, but a large portion of the seeds normally germinates within three months after shattering.  In double cropping areas, the next crop would have severe weed problems.

Likewise, weedy rice can be taller or shorter or even as tall as cultivated rice.  The flag leaves are either erect or droopy.  The panicles can either be closed or open like those of cultivated rice.  The grains may not have awns, but some variants can have either short or long awns.  

Weedy rice also tends to grow vigorously and mature early.  Farmers, therefore, must learn to distinguish weedy rice from cultivated rice during its vegetative phase to be able to remove them before these could produce panicles.

To prevent weedy rice seeds from being introduced into rice fields, farmers are advised to:

* Use certified seeds or “clean seeds” from a source known to be not invaded by weedy rice. 

* Make sure that machinery or implements coming from infested fields must be thoroughly before these are used in uncontaminated fields.

* Clear irrigation canals of weedy rice infestation to prevent weedy rice seeds from invading clean fields.

If infestation is not avoided, remove the weed rice plants manually once these are recognized.  For those that have escaped manual weeding, remove them before these produce panicles or before the panicles mature.

Practice stale seedbed technique during land preparation to encourage the weedy rice seeds to germinate when irrigation water is allowed into the field or when it rains.  Plow the seedlings under the soil or apply nonselective herbicide.  Repeat this process several times to deplete the soil seed bank of weedy rice.

(For past columns, click http://sundaypunch.prepys.com/archives/category/opinion/harvest-time/)

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