The yield of wheat is low as compared to other wheat growing countries of the world. The reason for low yield are many, but one of the most serious but less noticeable cause is presence of weeds which exhibits serious negative effect in crop production. The major loss in wheat yield are due to weed infestation, which is 1.25 to 2.5, million tones per year (Ahmed, 1984). Weeds decrease yield from 15 to 50% or in serious cases it may lead to complete failure of crop (Gill and Walid, 1979). Weed compete with crop plants for nutrients, soil moisture and sunlight and thus, reduction in crop yields has direct correlation with weed competition. However, an increase in one kilogram of weed growth corresponding to reduction in one kilogram of crop growth (Rao, 1988). Blair et al. (1999) suggested that there is the need to adopt weed control practices more precisely, both for economic and environmental reasons. Froud and Williams (1999) in order to predict the consequences of failure to control weeds in any single season, it is proposed that knowledge of the population dynamics of the species concerned is essential. While a wealth of literature is available, but the number of areas require further investigation with regard to reproductive output Considering the losses caused by weeds and their impact on crop growth, this study was conduct in the field on post emergence weed control in wheat.
Materials and Methods
The study was carried out at Students Experimental Farm, Sindh Agriculture University Tandojam, Pakistan to determine the post emergence weed control in wheat, during Rabi Season 2002-2003. The experiment was laid out in Randomized Complete Block Design, with four replications. The treatments were various levels of herbicides (Topik 240 WP @ 250 g ha-1, Topik 240 WP @ 200 g ha-1, Topik 240 WP @ 300 g ha-1, Arelon 50 dispersion @ 0.75 l ha-1, Arelon 50 dispersion @ 1.0 l ha-1, Arelon 50 dispersion @ 1.5 l ha-1, hand weed control and weedy check full season were applied during weed post emergence.
Irrigation and fertilizer application
The first irrigation was applied at the crown root initiation stage or after
21 days after sowing. The subsequent irrigations were applied according to critical
stage of the crop.
The fertilizer was applied at the rate of 120 N and 75 P kg ha-1, in the form of Urea and DAP. The full dose of phosphorus and half of nitrogen was applied at the time of seedbed preparation. The remaining half of nitrogen was split applied at second and fourth irrigations.
Herbicide treatments were applied as post-emergence level after first irrigation,
when the crop was at 2-3 leaf stages through knapsack hand sprayer. The weeds
were counted two times during study period i.e. before and after the application
of each herbicide application. In hand weeding treatment, two weeding were done
i.e. after the first and second irrigations. Weeds were counted on per m2
basis, from each treatment at random. The weed density (m2) was measured
and intensity of weeds was also calculated as percentage. The list of weed flora
recorded in the experiment is present in Table 1.
Weed spectrum (species)
Different weed species infesting the experimental area were recorded 48
h before the herbicide application.
Weed density (m2)
Weed population were recorded 48 h before herbicide application, again weed
population were recorded 15 days after herbicide applications. Weed density
was counted in a quadrate of 1 m2 from each treatment at random.
The data was statistically analyzed according to the experimental design
and the test of significance were made where it was necessary, following the
procedure out lined by Gomez and Gomez (1984).
Results and Discussion
Weed density (m2) and intensity (%)
The results of the experiment revealed that with the application of herbicides
though the number of weeds of all species decreased in all species, but in most
of the cases their intensity increased which exhibits that weeds even with the
application of herbicides and hand weeding continued their growth.
|| Weed density/intensity (%) in wheat before and after application
|Weed intensity = Number of one weed species/Total number of
all weed species
|| Plant height, tillers, spikelets and grains per head as affected
by post emergence weed control
||Weight of grains, seed index and grain yield of wheat as affected
by post emergence weed control
It was also observed that in case of Billi Boti, Wild Oats and the Meno weed
intensity increased. This shows that these weeds are very difficult to control
Wheat parameters as affected by post emergence weed control
The maximum plant height of 90.10 cm was obtained with the application of
Arelon-50 dispersion at the rate of 0.750 l ha-1(an increase of 4.71%
over weedy check), followed by Topik-240 WP at 250 g ha-1 and Topik-240
WP at 300 g ha-1 where plant height was obtained as 88.85 with an
increase of 3.25% over weedy check. The minimum plant height (84.90 cm) was
obtained where Arelon-50 dispersion at the rate of 1.0 l ha-1 was
applied (Table 2).
The results further showed that more number of tillers, spikelet count, maximum grains per ear head, heavy and bold grains, seed index and final seed yield per hectare were superior with the application of Topik-240 WP at 250 g ha-1, followed by Arelon-50 dispersion at the rate of 0.750 l ha-1 over weedy check. The minimum number of these recorded crop parameters were recorded in the plots where no herbicide or any weed control practice was adopted (Table 2 and 3). This shows that application of herbicides not only control the weeds but also helps in enhancement of grain yield. This may be due to certain characteristics of herbicides which are helpful for development and growth and various yield components which increased and supported the grain yield of the crop. The results are in agreement with Jain et al. (1998), who reported that the application of herbicides in the wheat crop exhibited satisfactory and maximum grain yield. It may therefore be concluded that herbicide applications at proper rate may not only control weeds but also helps an increase in grain yield.