Abstract: The study on weed control in lentil was conducted at the National Agricultural Research Centre, Islamabad during Rabi, 1987 and 1988. The performance of selected Pre-emergence herbicides; Oxadiazon, Pendimethalin, Isoproturon and Methabenzthiazuron and Post-emergence herbicides; Fomesafen, Fluazifopbutyl and Methabenzthiazuron alone and in combinations were evaluated to know their broad spectrum performance, if any; against a lentil variety Precoz. Hand weeded and weedy plots were kept for comparison of yield and economic gains. Most of the herbicides applied and hand weeded plots controlled the weeds density per unit area by 19 and 100% and significantly increased grain yield by 9 to 113% (440 kg/ha to 936 kg/ha). Among the pre-emergence weedicides, Oxadiazon gave the highest grain yield of 764 kg/ha and earned net return/per rupee investment of Rs. 1:2.15, while post-emergence treatment hand-free check (twice) gave the highest yield of 936 kg/ha or 113% increase over control (440 kg/ha) and earned net return of Rs. 1:2.86, whereas mixture of Fluzifopbuty+ Fomesafen at given rates of 0.50+0.13 a.i/ha and 0.75+0.13 a.i/ha produced 635 and 849 kg/ha respectively by controlling grasses and broad-leaved weeds to the extent of 69/100 and 75/94% and earned net returns of Rs. 1:2.14 and 1: 3.22 respectively.
Introduction
In Pakistan, 11.3% of the total crop losses are due to weeds as compared to world loses of 9.5% (Crammer, 1967). Tahira and Khan (1987) reported that annual losses caused by weeds alone may be of Rs. One billion in Pakistan. Ozair (1987) and Riaz (1991) observed that the magnitude of yield losses due to weed pest in kharif pulses range from 75-84%. Nabi and Ansari (1977) reported weeds not only compete with crop for water, light and nutrient but also impart physiological disorder to man and livestock and economic resources. Malik (1983) reported that hand weeding did not increase the seed of chickpea, while application of 1.5 kg/ha Maloran (Chlorbromuron), 2.5 kg Tribunil (Methabenzthiazuron) or 4 kg Igran (Terbutray)/ha increased yields from 0.82 to 0.95, 0.91 and 1.41 t/ha respectively. Pastua and Sinsky (1986) observed that pre-sowing herbicides viz Adabex, Dual and Eradicane gave good weed control and after sowing Bladex, Dual and Maloran were effective. Alhawat et al. (1981) investigated that clean weeding increased the yield of Bengal gram (Cicer arietinum) , lentil (Lens culinaris Medik), pea (Pisum sativum), cowpea (Vigna unguculata) and mung (Vigna radiata) by 107, 150, 90, 85 and 90% respectively. Weeding only once increased yields by 72, 113, 57, 40 and 2%. Mahoney (1981) found that net returns were relatively higher with chemical weed control and resulted in seed yields of 1.87 t/ha compared with 1.34 t/ha without weed control. Ali et al. (1988), Bernal (1981), Basler (1981), Panday (1981), Elliott (1981), Mittal and Singh (1983), Singhte et al. (1984), Talasava (1987), Khatiwada et al. (1988) and Kumar (1989) reported that the application of weedicides help in controlling weeds population, increase in grain yields and net return. Binswinger and Shethy (1977) found once hand-weeded plots of sorghum, pearl millet , groundnut, paddy, chilies, pigeonpea and chickpea increased yield by 48, 40, 81, 73, 91, 40, 48 and 60% respectively. Cultural and mechanical methods of weedings are prevalent in our country, although experimental results revealed that chemical operations have been very effective and economical (Nabi and Ansari, 1977). Singhte et al. (1984) investigated that incessant rains during the early crop season normally limit the weeding operations, therefore, chemical weeding under such circumstances become indispensable and can be the only mean excellent alternative. The present study was, therefore, conducted to evaluate the effectiveness and economics of weedicides for lentil, which can be acceptable to the growers of this crop.
Materials and Methods
The experiment was planted on 10th November, 1987 and 13th November, 1988 during rabi season at National Agricultural Research Centre, Islamabad. Lentil variety Precoz was drilled manually within rows at the rate of 25 kg/ha at 30 cm inter-row spacing. Plants were thinned four weeks after sowing to maintain optimum plant population. Fertilizer was applied at 20:50:00 NPK at the time of land preparation. Crop management practices included two pre-plant ploughings and levellings with land planker. There were no rains till 3-4 weeks after planting, therefore, flood irrigation was done. Chemical, commercial, common names, formulation, herbicide dose (kg.a.i/ha) and mode of application are given in Table 1. Pre-emergence herbicides namely Methabenzthiazuron, Pendimethalin, Oxadiazon and Isoproturon were applied at 1.25, 1.25, 3.00 and 1.50 kg a.i./ha respectively, whereas post-emergence herbicides Fluazifopbutyl and Fomesafen were applied alone and in combinations at 0.50, 0.75, 0.13, 0.50+0.13, 0.75+0.13 and 1.25 a.i. kg/ha. Hand weeding and weedy checks treatments were kept for comparison purposes. Weedicides were applied with a manually operated knapsack sprayer mounted with a hollow-cone type brass nozzle. Pre-emergence herbicides were applied three days after sowing, while post-emergence were applied when weeds attained 4-5 leaf growth stages. Weed population was low due to low natural precipitation and drought. Hence, data were also recorded on visual observations for the weed control and lentil phytotoxic herbicides (Table 2), whereas data on weed re-emergence of grass and broadleaf (Total No. and % control), fresh weed bio-mass, germination, plant height, grain yield ( weight/ kg and grain loss/%) are reflected in Table 3.Harvesting was done from three randomly selected 1 m2 spot in each treated plot. Three samples of chickpea were pooled and threshed. Yield data were averaged and analyzed. Economic analysis was done using the Partial Budget Method, as suggested by the Agricultural Price Commission (APCOM), (Anonymous, 1999). Cost benefit ratios were calculated by dividing extra benefits attained from the enhanced yield by the incurred for each treatment.
| Table 1: | Commercial, Common and Chemical names of herbicides, Formulation and doses used in the study |
| Table 2: | Visual observations for weed control and lentil Phytotoxicity by pre.and post-emergence herbicides |
| Table 3: | Weed control in lentil by pre. and post-emergence herbicides |
Measured by 1-m2 quadrate when crop started senescence to assess the longitivity of herbicidal effects. Fumaria indica, Anagalis arvensis, Convolvulus arvensis Sorghum halepense, Eachinochloa colona, Cynodon dectylon. Note = The values are average of two years. | |
Cost includes labor charges at Rs. 30/man day for 25 man days for first weeding and 20 man days for second weeding, herbicides prices, labor charges for herbicides application and equipment charges Rs. 300/- in extra costs each case and threshing at Rs. 10/40 kg of lentil (Table 4).
| Table 4: | Economics of weed control methods in lentil |
Results and Discussion
Pre-emergence herbcides, Methabenzthiazuron, Pendimethalin, Oxadiazon and Isoproturon were applied at of 1.25 to 3.0 kg a.i./ha and controlled grasses and broad leaf weeds by 100 and 96% respectively. However, initially crop germination suffered from toxic effects of the herbicides at seedling stage in case of Oxadiazon, which was recovered during vegetative growth stage. Other pre-emergence herbicides suppressed the crop growth in general. On an average weed control was obtained by these herbicides (Table 3).
Longitivity of pre-emergence herbicides observed through weed quadratic analysis which reveals that Methabenzthiazuron gave good prolonged grass check and medium broad leaf weed control whereas Pendimethalin and Oxadiazon checked 90-96% broadleaf weeds until the end of the crop season. The higher number of weed per quadrate and the subsequent higher fresh weed biomass in Isoproturon treated plots indicate the least persistence throughout the crop season. Pendimathalin though gave a medium broad spectrum weed control and hence least weed biomass and significant crop phytotoxicity reduced yield significantly. Butler and Alexander (1987) and Stringi et al. (1988) found that L. culinaris tolerated Bladex, Sincor, Stomp, Actazine and Gardoprim at 1,5, 0.35, 1.0, 0.75 and 1.0 kg/ha. After the hand weeded (check), the highest grain yield was to the tune of 74% in case of Oxadiazon, followed by Methabenzthiazuron , which corresponds to medium weed control accumulating the lowest weed biomass. These results are in conformity with Singh et al. (1985) that Fluchoralin and Methabenzthiazuron at 1.5 kg/ha pre-em. Increased yield by 79 and 66% respectively. Schultz et al. (1984) found that pre-em. application of herbicides alone and in combination controlled weeds by 66-100% and 96-98% in peas and lentil. Aretit applied as post-em. against broadleaved weeds was practically phytotoxic to lentil crop.
Fluazifop-butyl at both the rates of 0.50 and 0.75 kg a.i./ha and in combination with Flex at 0.13 kg a.i./ha controlled 100% grasses. Fomesafen alone or with Fluaziifop-butyl caused slight phytotoxicity to lentil which however, was recovered at the advanced growth stages. Methabenzthiazuron remained very effective as pre. and post-emergence herbicide. It had no check on grasses but effectively controlled broad-leaf weeds.
Post-emergence Methabenzthiazuron although significantly reduced the weed biomass and subsequently increased the grain yield by 9 to 113% over control. Its performance as post-emergence application was not very appreciable as more grasses were prevalent after the mid season of the crop (Table 2, 3). Mixture of Fluzifopbutyl at 0.75+0.13 kg a.i/ha gave the highest broad-spectrum weed kill and the lowest weed biomass, consequently yielded 849 kg/ha grain yield which was the highest increase over weedy check and next after the weed free check. Similarly 75 and 94% control of grass and broad leaf by the same mixture accumulated 175 grams weed biomass at the end of the season which was again highly non-significant and, therefore, grain yield increase was 48% over the weedy check. Each of these herbicides while used alone, gave an appreciable control of either group of weeds which gave significantly higher grain yield, but lower than when mixed together (Table 3). Kukula et al. (1985) found that post-emergence herbiicides are not recommended due to possible phytotoxic effects, however, 1 kg a.i./ha of Fusilade (Fluziifop-butyl) proved selective control of grass weeds, if applied when grasses were 10-15 cm high. Similar results were also reported by Gill and Brar (1977), Jalis et al. (1977), Misra and Tosh (1978), Gill et al. (1978) and Majeed et al. (1983). Yadav and Singh (1988) reported that Tribunil at 0.75 and 1.50 kg/ha provided the highest yields from chemical control (2.2 t and 2.09 t resp.) followed by Basalin at 0.5 and 1.0 kg. Fusilade was the least effective herbicide and some phytotoxicity was noted from Ronstar (Oxadiazon) which was tested at 0.75-1.50 kg.
All the herbcides, except nitrofen gave more than 100% higher grain yield of green gram than the unweeded control, but Trifuluralin and Chloramben proved more promising in clusterbean, giving yield equal to that of hand-weeded treatment (Daulay and Singh, 1982). Hand weeding controlled grasses and broadeaf weeds by 37 and 75% respectively in both the years because of labor intensive strategy, which is even beyond the resource poor farmer. Haqqani et al. (1989), Bhardwaj (1978), Misra and Tosh (1978) and Majeed et al. (1983) also confirmed these results that hand weeding (generally 2 hoeings and one hand weeding) are as better or at least comparable with chemical herbicides.
Economic analysis: The economic analysis revealed that application of weedicides seems to be economical in all treatments over hand-weeding and more specially over control in enhancing yield level by 9% to 113% (Table 3). Relatively high to low level per Rs. spent was calculated at the tune of Rs. 3.22, 2.86, 2.15, 2.14, 1.78 and 1.04 in case of Fluzifop-butyl+Fomesafen, hand-weeding, Isoproturon, Fluziifop-butyl (alone), Fluzifopbutyl+Fomesafen and Fomesafen (Table 4). Oxadiazon proved its worth in controlling weeds as a pre-emergence herbicide while others responded negative returns. Similar results were reported by Bhardwaj (1978). Majeed and Hussain (1983) and Tahira and Khan (1987) reported that amongst the herbicides and cultural practices, Dicuron M.A. 60 W.P. not only controlled the maximum weeds (96.87) but also yielded the highest return of 3.30/per rupee invested, registering an increase of 37% over control. Riaz (1991) found that application of Pendimathaliin at 1 kg. a.i./ha and hand weediing at 14 and 28 days after emergence (DAE) increased yield of mungbean by 83% and earned highest cost: benefit ratio of 1:4.95. It is concluded that Dicuron M.A. 60 W.P. at of 2.5 kg/ha, Buctril M at 1.75 l/ha, hand weeding and bar harrowing gave higher grain yield of 55.7, 39.8, 34.9 and 11.0% respectively. Zafar (1988) and Hawkins et al. (1971) concluded that the profitability of herbicide use was very high, ranging from US $ 3.30 to $ 4.89/$. The results are also in agreement that net return/ha given by hand weeding and weed-free are $ 213 and $ 146-426 respectively. On the basis of present findings, Oxadiazon, Fluzifopbutyl alone and in combination with Fomesafen and Fomesafen alone are recommended as pre. and post-emergence herbicides to benefit the farming community as a whole.