January 21, 2002	Monday	Ziqa’ad 6, 1422

Barnyard grass, locally known as “dhidden,” is a troublesome weed found in rice because in early stages of growth, it resembles rice plants and cannot be easily separated from rice seedlings.

A similar ecological requirement of rice crop and barnyard grass makes the latter the worst weed of rice crop. Barnyard grass removes huge amount of nutrients, especially nitrogen at higher doses, as compared to rice.

Similarities in morphology, physiology, and growth of barnyard grass with rice, pose double-edged control problem in terms of stiffer competition and development requirements and of similar vulnerable stages to control (germination to four leaf stage), resulting in narrow margin of selectivity where post-emergence control measures are used.

The grass have almost identical growth and growth requirements, and hence the practices which benefit rice will also benefit this weed, while practices which harm barnyard grass will harm rice. With proper management practices, it can be manipulated to make growing conditions more favourable to rice and less favourable to barnyard grass.

Considering huge loss in terms of rice yield reduction (90 per cent) caused by the grass, and the significant contribution of rice crop to the economy of Pakistan, a two-year research study was conducted at the University of Agriculture, Faisalabad. This contains the salient findings of the research.

In laboratory trials, it was observed that water extract of rice husk significantly inhibited germination and seedling growth of barnyard grass while water extract of barnyard grass suppressed the germination and seedling growth of rice, indicating inter-alleopathic behaviour of both, the crop and weed. Moreover strong allelopathic effect of ‘sorgaab’ (sorghum water extract) was observed on germination and seedling growth of both, providing the possible manipulation of sorghum alleopathic properties for managing barnyard grass.

It was found that barnyard grass, up to the first 28 days of transplanting, does not influence rice yield (fine rice cv. Basmsti-385) but after this period, till maturity, it compete vigorously reducing rice yield up to 38 per cent while 4 plants m-2 of barnyard grass had non-significant effect on rice yield indicating that 4 plants m-2 as the economic threshold level irrespective of the nitrogen levels.

While 16 barnyard grass plants m-2 reduced the rice yield from 16-32 per cent under different nitrogen levels (0,60,120,180 kg ha-1). After determining the competitive capability and the competition duration of barnyard grass in rice the strategy adopted for its control must be sustainable, economical and environment friendly. To achieve these objectives weed control methods prevalent in Pakistan as hand weeding and chemical weed control were compared with a new technology evolved at weed science lab. Uni. of Agric. Faisalabad which is foliar spraying of Sorgaab (sorghum water extract containing naturally produced allelochemicals in mature sorghumi plants.)

The common practice of controlling weeds with standing water was not included in the study because of the soil conditions prevailing at Faisalabad, where it is not possible to ensure standing water.

The findings of this field study revealed that hand pulling (20 days after transplanting) provided effective control of barnyard grass (90%) and increased rice yield by 30% but was uneconomical due to higher cost of hand pulling. Chemical control with herbicide as butachlore (60 EC) @ 1.2 kg a.i ha-1 applied at 3-4 days after transplanting, gave effective control of barnyard grass up to 94% and increased yield by 35%, while the marginal rate of return for herbicide was 570% where as the use of one foliar spray of Sorgaab 20 days after transplanting controlled barnyard grass up to 38% and increased rice yield by 20% with highest marginal rate of return (2750%).

From the results of the investigation it could be concluded that barnyard grass is a serious weed of rice and it must be controlled to ensure higher rice crop yields. For controlling barnyard grass, environment friendly, sustainable and economical approaches like naturally produced products as Sorgaab (sorghum water extract) may be sued because the herbicide cause environmental and health hazards. However, studies to improve effectiveness of natural products by mixing different crop/plant water extracts as sunflower, neem, tobacco, eucalyptus and sorghum and relatively non-toxic organic compounds may be continued.