Diversity Of Weed And Their Integrated Management Practices In Paddy Rice (Oryza Sativa) Production

Abstract

Weed has become a major threat in rice cultivation and its effects continue to cause enormous yield, quality and quantity loss. The above has over time been a major concern for a rice farmer since the advent of agriculture not to mention the potential danger weeds being hosts to many opportunistic rice diseases. Most practices employed by farmers to eliminate these weeds in lowland rice ecology have proved to be unsuccessful. Farmers in some instances, allow weeds to reduce huge portion of the crop through deprivation of nutrients, moisture content, resting place for insect pests and diseases and acting as a cover crop in relatively few instance among others. This trial was conducted at Mwea Irrigation Agricultural Development Centre through a field experiment. The experiment was done for two consecutive seasons of 2013-2014 while a survey to evaluate the diversity of weeds in the expansive scheme was achieved during the off season of 2015. In this study the effect of lowland paddy field weeds on rice crop establishment and corresponding integrated weed management strategies employed were evaluated and compared with regard to major weeds within the scheme. These weeds included the grass family, broad leaf and the sedges. Barn yard grass (E. Crus-galli L.), Red sprangletop (Leptochlo chinensis L.)., Umbrella sedge (Cyperus difformis spp L.) and Monochoria (Monochoria vaginalis Burm.f) among others were found to be the most problematic in rice production. The outcome of the trial became clear that weeds reduce up to 30% of rice crop yield per unit area. Farmer practice in weed management also became evident is enough to give significantly (P<0.05) optimum yield of rice produced per unit area. Common practice by these farmers of weeding twice by hand and a spot weeding at maturity stage per cropping season is costly and time consuming. Chemical weed control done for each of the three varieties suggests a quicker option and less expensive way to achieve same results. The two methods of weed management in irrigated rice cultivation need further evaluation to determine economic and environmental effect. The lower tillering variety Basmati 370 performed better with contact type of weed control chemical (herbicide) application while high tillering varieties of BW 196 and IR 2793-80-1 showed preference of systemic herbicide application to manage weeds. Diversity of weeds in paddy fields indicated the extent at which these weeds have covered per species and an inventory of these species. Survey done across the expansive scheme indicated that there are 17 major weeds with presence from the upper part of the scheme down to the lower areas x which experience perennial water shortage. The survey to determine this diversity was done during long rains of 2015 when the scheme is mixed with activities with some areas either having a main crop/ratoon/left fallow. Their frequency being the percentage of the total number of fields surveyed in which a species occurred in at least one quadrate showed Eclipta prostrata (False daisy) at a score of 16% being least present while Cyperus difformis (Small Flower umbrella nut-sedge) at 100% presence in every quadrate. Recommendation of best practices to manage weeds of paddy field should start at land preparation as shown in the diversity of these weeds that some of them are carried over during off season to the main season. The study therefore opens up more work to be done in the scheme to determine both phenotypic and genotypic variation of major lowland paddy field weeds in Mwea.