MATERIALS AND METHODS

A field experiment was conducted to determine the effect of post emergence herbicides on the growth and yield of cotton at Students Farm, Sindh Agriculture University, Tandojam, Pakistan during Kharif, 2005. The suitable seed bed was prepared for seed germination and root penetration. Homogenous seed of a standard commercial cotton variety Shahbaz-95 was drilled in rows 75 cm apart in a four replicated randomized complete-block design. The description of various treatments is as under:

The thinning for proper plant distance was performed before first irrigation. NP fertilizers were applied as per the recommendations of Agronomy Department. Herbicidal spray as post emergence was applied 4 weeks after sowing of crop to all treatments except untreated/control. Data on various weed and crop parameters were compiled and statistically analyzed using Fihser’s analysis of variance technique and the Least Significant Difference (LSD) test at p≤ 0.05 for comparing the treatment means to determine their efficacy for different parameters (Steel and Torrie, 1980).

RESULTS

Weed population density (m^-2) before treatment: About twelve weed species appeared in the cotton field. Among them, Trianthema portulacastrum was the dominant specie (29.56%), followed by Cyperus rotundus (17.24%) and Portulaca oleracea (14.78%), while other weed species were less in number and ranged between 1.23 to 10.47%, respectively (Table 1).

Weed count (m^-2) before weed management: The population of weeds recorded m^-2 before treatment was more or less same in all the treatments and ranged between 63.71 to 65.13 m².

Table 1:	Species, population density (m-2) and density percentage of weeds observed in cotton field

Table 2:	Weed and crop traits as affected by various weed control methods
Values followed by similar letter(s) do not differ significantly at 5% level

There was no significant difference among the treatments (Table 2).

Weed population (m^-2) after treatments: Hand weeding resulted in low population of weeds (3.56 m^-2) or application of Stamp at high dose (5 L ha^-1) also showed similar performance when compared to hand weeding. However, the population of weeds was maximum (64.83 m²) in plot where no weeding was done (Table 2).

Weed reduction (%): Weeds eradicated manually or application of Stamp-330 EC at 5 L ha^-1 proved equally efficient in reducing weed density (92.40 and 91.59%), whereas, low rate of Fusilade (4 L ha^-1) and Stamp-330 EC (5 L ha^-1) were found less effective in reducing weed density (Table 2).

Plant height (cm): The results revealed that all weed management treatments produced taller plants of cotton when compared to untreated check. Hand weeding and application of Stamp-330 EC at 5 L ha^-1 both produced equally maximum plant height (158.50 and 155.60 cm). The untreated plots resulted in poor plant height (126.00 cm).

Productive bolls plant^-1: Hand weeding and application of Stomp 330 EC at 5 L ha^-1 were non-significant treatments which exhibited equally maximum number of productive bolls (82.39 and 80.78 plant^-1). However, poor numbers of productive bolls (14.35 plant^-1) were recorded in case of untreated check (14.35 plant^-1).

Seed cotton yield (kg ha^-1): All weed control treatments improved yield as compared to untreated check. Comparatively hand weeding and application of Stomp-330 EC at 5 L ha^-1 recorded significantly maximum seed cotton yield (2121.75 and 1957 kg ha^-1, respectively) (Table 2).

DISCUSSION

Dependence on traditional agricultural and manual measures for crop weed control without herbicide application is most labor intensive and impractical in modern agricultural production. Elimination of weeds from crop fields by adopting various effective agricultural measures and maintaining favorable ecological conditions integrated with chemical weed control is the most effective measure (Zhang, 2003). In our country, interculturing is normal practice to eradicate the weeds but, this practice is not applicable during rainy season due to wet condition in the soil which do not permit the mechanical weeding, under such circumstances the chemical control measures are the alternate to control the weeds (Ansari et al., 2003).

The results of this research indicates that about 12 weed species appeared in the cotton field, among them Trianthema portulacastrum, Cyperus rotundus, Portulaea oleracea and Diugera arvensis were the major weeds. In Sindh, most of the cotton fields are severely predominated by the weeds and average population can go upto 65 m^-2. The application of post-emergence herbicides (Stomp 30 EC) and Fusilade 5 and 4 L ha^-1, respectively exhibited maximum reduction of weeds which was same when compared to hand weeding. These treatments in the study significantly enhanced better weed control results which in turn produced taller plants, more fruiting branches, higher number of productive bolls and seed cotton yield. Similar results had been reported by Nobrega et al. (1998). Rout and Satapathy (1998), Hiremath and Rao (2001), Panwar et al. (2001), Askew et al. (2002) and Ali et al. (2005) suggested the integrated use of various methods of weed control could enhance cotton productivity by controlling the weeds. Further, Duggan et al. (2004) also supported the findings of this study that application of Stomp-330 EC or Roundup against weeds produced more bolls and seed cotton yield. Bukun (2004) reported that herbicide (pre or post emergence) should be used to eliminate weeds from 1-2 weeks post crop emergence up to 11-12 weeks. Such an approach would keep yield loss level below 5%. Sivakumar and Subbian (2002) reported that different weed control treatments gave 40-60% more yield with 29-53% higher net monetary returns. Raskar and Bhoj (2002) observed that seed cotton yield increased by two hand weeding. However, Nadanassababady and Kandassamy (2002) reported that weed free treatments gave the highest N, P and K uptake in cotton.

CONCLUSION

All the herbicide treatments controlled the weeds. Hand weeding and application of Stomp-330 EC at 5 L ha^-1 were more effective in controlling the weeds which resulted better growth and seed cotton yield.