EFFICACY OF HERBICIDES IN WHEAT (Triticum aestivum L.) AND ASSESSMENT OF THEIR PERSISTENCE THROUGH BIOASSAY TECHNIQUE
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Date
2006-01
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Abstract
A field experiment entitled “Efficacy of herbicides in wheat (Triticum aestivum L.) and assessment of their persistence through bioassay technique” was carried out at Instructional Farm, Junagadh Agricultural University, Junagadh on medium black clayey soils during rabi season of the year 2003-04 and 2004-05.
The experiment comprising 10 treatment was laid out in randomized block design with four replications. Treatments consisted of weed management viz., pendimethalin 1 kg ha-1 pre-em. + 1 HW (T1), isoproturon 0.75 kg ha-1 pre-em. + 1 HW (T2), isoproturon 0.75 kg ha-1 post-emergence at 30 DAS (T3), fluchloralin 0.45 kg ha-1 pre-em. + 1 HW (T4), metsulfuron 6 g ha-1 post-emergence at 30 DAS (T5), 2,4-D (S.S.) 0.96 kg ha-1 post-emergence at 30 DAS (T6), 2,4-D (E.E.) 0.75 kg ha-1 post-emergence at 30 DAS (T7), 2 hand weedings at 20 & 40 DAS (T8), weedfree (T9) and unweeded control (T10). Recently released wheat variety GW-322 was tested in the experiment.
The results of the experiment indicated that among different herbicides either applied as pre- or post-emergence in the trial was not found phytotoxic to the wheat crop as reflected in initial and final plant stand of the crop. Significantly the highest values of growth parameters
viz., plant height and leaf area index was observed under pendimethalin 1 kg ha-1 pre-em. + 1 HW and remained equivalent to weedfree. This treatment being equivalent to weedfree, also recorded significantly more number of total and productive tillers and spikelets per spike, higher test weight and grain weight per plant over unweeded control.
Significantly higher grain yield was produced under 2 hand weedings (3804 kg ha-1 ), pendimethalin 1 kg ha-1 pre-em. + 1 HW (3801 kg ha-1 ) and 2,4-D (S.S.) 0.96 kg ha-1 (3734 kg ha-1 ) post-emergence and they proved superior to rest of the treatments and remained equivalent to weedfree (4042 kg ha-1). The maximum straw yield was obtained under pendimethalin 1 kg ha-1 pre-em. + 1 HW (4366 kg ha-1), metsulfuron 6 g ha-1 post-emergence (4328 kg ha-1 ) and isoproturon 0.75 kg ha-1 pre-em. + 1 HW (4265 kg ha-1 ) and remained equivalent to weedfree (4590 kg ha-1).
Being equivalent effective to weedfree, among different treatments, pendimethalin 1 kg ha-1 pre-em. + 1 HW proved the most effective to reduce the weed population recorded at 20, 40 and 60 DAS as well as at harvest. This treatment also proved most effective to reduce dry weed weight which also reflected in higher weed control efficiency (92.02 %), higher herbicidal efficiency index (9.05 %) and lower weed index (5.93 % ).
Chemical analysis of weeds and crop plants indicated that the lowest loss of nutrients by weeds was under pendimethalin 1 kg ha-1 pre-em. + 1 HW and statistically similar to 2,4-D (S.S.) 0.96 kg ha-1 post-em. and metsulfuron 6 g ha-1 post-emergence and they remained equivalent to weedfree. Restriction in loss of nutrients favoured significantly higher nutrients uptake by the crop under these treatments.
Economical evaluation showed that the maximum gross returns was accrued under 2 hand weedings (32,750 Rs. ha-1 ) closely followed
by pendimethalin 1 kg ha-1 pre-em. + 1 HW (32,748 Rs. ha-1 ) and 2,4-D (S.S.) 0.96 kg ha-1 post-emergence (32,151 Rs. ha-1 ) and remained at par with weedfree. While significantly the highest net returns was obtained under 2,4-D (S.S.) 0.96 kg ha-1 post-em. (20,760 Rs. ha-1 ) and was found at par with pendimethalin 1 kg ha-1 pre-em. + 1 HW (18,464 Rs. ha-1 ). These two treatments, recorded additional net returns of 10593 and 8297 Rs. ha-1 over control, respectively.
The results of pot-bioassay revealed that the persistence effect of different herbicides applied in wheat crop was found non-significant on germination, plant height and dry matter production of mustard and cucumber at 30 as well as 60 DAS and significant on sorghum at 30 DAS.
Field-bioassay studies showed that different herbicides did not left their residual phytotoxic effect in the soil after harvesting wheat crop as it is proved through non-significant effect on germination, plant height and dry matter production of succeeding groundnut, greengram, cotton and pearlmillet.
Based on the pooled results of two yearsˆ experimentation, it is concluded that potential production and profit can be achieved by post-emergence application of 2,4-D (S.S.) @ 0.96 kg ha-1 at 30 DAS using spray volume of 500 liters. Pre-emergence application of pendimethalin 1 kg ha-1 supplemented by one hand weeding at 30 DAS also emerged out best treatments for minimizing weed problem in wheat. Both the herbicides were safe for standing crop as well as succeeding crops viz., groundnut, greengram, cotton and pearlmillet.
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HERBICIDES, BIOASSAY TECHNIQUE