In Ethiopia, maize has been selected as one of the national commodity crops to satisfy the food self-sufficiency program of the country, to feed the alarmingly increasing population because maize has a great promise for higher yield and easier cultivation than any other cereal crop and if managed properly can go a long way in increasing food production in Ethiopia. Unfortunately and despite its great yield potential, the average maize grain yield (2.29 tons ha^-1) in Ethiopia (CSA, 2010) is still less than that of the yield (5.14 tons ha^-1) in other important maize-growing countries of the world(http://faostat.fao.org/site). Weed infestation is of supreme importance among biotic factors that are respon-sible for low maize grain yield. Worldwide maize production is hampered up to 40% by competition from weeds which are the most important pest group of this crop (Oerke and Dehne, 2004). Generally, weeds reduce crop yields by competing for light, nutrients, water and carbon dioxide as well as interfering with harvesting and increasing the cost involved in crop production. Kebede (2000) reported that most farmers in Ethiopia commonly lose up to 40% of yield in maize due to weed infestations. Weeds not only cause severe crop losses but also require farmers and their families to spend a considerable amount of their time on weeding. More than 50% of labor time is devoted to weeding, and is mainly done by the women and children in the farmer’s family (Ellis-Jones et al., 1993; Akobundu, 1996). 

Control of weeds in maize is, therefore, very essential for obtaining good harvest. Weed control practices in maize resulted in 77 to 96.7% higher grain yield than the weedy control (Khan et al., 2003). Different weed control methods have been used to manage the weeds but mechanical and chemical methods are more frequently used for the control of weeds than any other control methods. Mechanical methods including hand weeding are still useful but are getting expensive, laborious and time-consuming. Chemical control is a better alternative to manual weeding because it is cheaper, faster and gives better control (Chikoye et al., 2002, 2004). Weed control in maize with herbicides has been suggested by researchers (Correa et al., 1990; Owen et al., 1993). Ali et al. (2003) also reported that herbicides significantly increased maize yield and decreased the weed density. Therefore, the present re-search work was carried out to evaluate the effect of different weed control methods on weeds and yield and yield components of maize and to assess economics of herbicides under field conditions at Guder of Toke Kutaye and Ambo district, West Shoa, Ethiopia.

The field experiment was conducted at two different areas, Guder and Ambo in West Showa, Ethiopia during the main cropping season of 2013. Guder and Ambo district has total geographical area of 78887 km² and are located at 8° 57’ North latitude and 38° 07‘ East longitude at an average elevation of 1800-2300 m. a. s. l. The annual rainfall ranges from 1000 -1588.06 mm and the temperature of the district ranged between 9.4 and 21.9°C with average of 15.7°C. The soil of the experimental site is light red in color (Guder), clay loam (Ambo) in texture and with pH value of 6.8. 

Where, M is the measured moisture content in grain and D is the designated moisture content. Relative crop yield loss was calculated using:

, Where, MY = maximum yield from a treatment, YT = yield from a particular treatment.

Weed density was subjected to square root transformation  to have normal distribution. Data were subjected to the analysis of variance. Mean separation was conducted for significant treatment means using least significance differences (LSD) at 5% probability level using SAS computer software version 9.1. 

Weed floral composition of the experimental sites

The experimental site at Ambo was infested with 12 different weed species belonging to 8 different families. Out of the total weeds, 91.7% were broadleaved weeds whereas the remaining 8.3% were grasses weeds (Table 2). This indicated that indicating a species-rich weed community in the experimental field. Similarly at Guder, 10 weeds species belonging to 9 families were identified. Out of the total weeds 70% were broadleaved weeds whereas the remaining 10 and 20% were grasses and sedges weeds, respectively (Table 2).

Density and dry weight of weeds

Effect of different weed control methods on weed density both at Ambo and Guder were significant (p<0.05). As shown in Table 3, the lowest weed density (0.71 and 4.99 m^-2) was recorded in plot treated with hand weeding followed by Nicosulfuron at 0.09 kg ha^-1 (3.68, 5.92 m^-2) whereas the maximum was recorded in weedy check (14.16 and 24.24 m^-2) in Guder and Ambo, respectively. Similar finding was reported by Mehmeti et al. (2012) who found highest weed density in weedy check.

The weed control methods significantly affected the dry weight of weeds at both locations (p<0.05). The lowest dry weight of weeds (0.0, 26.67 gm^-2) was recorded in plot treated with hand weeding followed by Nicosulfuron at 0.90 kg ha^-1 (2.13 and 65.60 gm^-2). No significant differences existed among treatments in Guder, whereas the highest was observed in weedy check (170.93, 382.13 gm^-2) in Guder and Ambo, respectively. These results are in agreement with those reported by Hassan et al. (2010) who reported reduced weed biomass due to use of selective pre-emergence and post emergences herbicides for controlling different maize weed species.

Weed control efficiency

Weed control efficiency at both locations was also significantly affected (p< 0.05). As described in Table 4 in Guder, the minimum weed control efficiency was observed in weedy check (0.00%) whereas the highest (100.0%) was recorded in a plot treated with hand weeding and hoeing which was not significantly different from Nicosulfuron at 0.90 kg ha^-1 (98.8). Similarly, in Ambo the maximum weed control efficiency (93.0%) was recorded in hand weeding and hoeing followed by Nicosulfuron at 0.90 kg ha^-1 (82.0), whereas the minimum was in weedy check (0.0%).  This result further indicated that herbicides are more effective in reducing density and dry weights of weeds when compared with hand weeding and hoeing which are more effective than weedy check. This result was in accordance with Mehmeti et al. (2012) who reported that herbicides reduced the weed infestation in maize in comparison with the control plots.

Yield and yield components

All the weed control treatments proved significantly superior to weedy check with respect to yield attributes and yield of maize. At Guder, cob number per plant, ear length and diameter were significantly affected by weed control methods, whereas plant height was not (p< 0.05).

The maximum number of cobs per plant (1.9) was observed in hand weeding and hoeing followed by Nicosulfuron at 0.90 kgha^-1(1.8); the lowest was recorded in weedy check (0.47). Similarly at Ambo site, weed control methods significantly affected the yield component of maize (p< 0.05).

Weed control methods also significantly affected the ear length and ear diameter of maize at both locations. The highest ear length (16.3, 19.2 cm) was in hand weeding and hoeing which was not statistically different from Nicosulfuron at 0.90 kg ha^-1, s-metolachlor 1.50 kg ha^-1 and Primagram 3.00 kg ha^-1, whereas the lowest was recorded from weedy check (12.1, 12.9cm) in Guder and  Ambo, respectively. Hundred kernel weigh, grain yield and relative yield losses were significantly affected by weed control methods. The highest thousand kernel  weight was recorded with hand weeding (45.33, 49.7 g) whereas the lowest was recorded with weedy check (33.8, 29.8 g) in Guder and Ambo, respectively. These results are in accordance with work of Patel et al. (2006) who stated that all the weed control treatments proved significantly superior to weedy check with respect to yield attributes and yield of maize.

Maximum grain yield (6989.8, 7223.1 kg ha^-1) was recorded in plots treated with hand weeding and hoeing and Nicosulfuron at 0.90 kg ha^-1 (6883.3, 6883.3 kg ha^-1). The lowest was recorded in weedy check (2312.4, 2612.4 kg ha^-1) in Guder and Ambo, respectively (Table 5). The efficiencies of various chemicals and other weed control practices in enhancing grain yield have previously been observed by Toloraya et al. (2001). The highest relative yield loss (63.7 and 75.7%) was recorded from weedy check whereas the lowest relative yield losses was observed from hand weeding and hoeing (0.0, 0.0%,) followed by Nicosulfuron at 0.90 kg ha^-1 (4.7, 6.3%) in Guder and Ambo, respectively (Table 6). All yield and yield parameter of maize were best in weed control methods as compared to weed control (check), this may be due to lowest weed density and dry weight.

The results from both locations suggest that the density and dry weight of weeds was lower in hand weeding and hoeing followed by Nicosulfuron at 0.09 kg ha^-1, whereas the maximum was recorded in weedy check in both locations. Weed control efficiency was also high in these treatments. Like density, the minimum dry weight of weeds was observed in hand weeding and hoeing followed by Nicosulfuron at 0.09 kg ha^-1. Moreover, those treatments also increased the yield and yield component of maize in both locations. 

The author(s) have declared that there is no conflict of interests.