Sequential application of different pre and post emergence herbicides for weed management in Bt cotton

Introduction

Cotton crop is sensitive to weed competition during initial growth stages due to slow growth and wider spacing. Weeds compete for nutrients, water, light and thus reduce cotton yield substantially. Being heavily fertilized/manured and often irrigated are also among the factors responsible for heavy weed infestation. In case of heavy rains, providing timely weed control becomes difficult as soil becomes sticky and wet leading to poor workability while in dry soil, the surface becomes hard making inter-row cultivation difficult. Also, non-availability of human labour for weeding makes timely weed control tedious and uneconomic. So, the use of effective and broad-spectrum pre-emergence and post-emergence herbicides in cotton for weed management is considered necessary. Chemical weed control became more important and attractive to farmers. In the absence of interculture and with regular monsoon rains, weeds germinate in different spells and compete with crop plants and finally reduce the seed cotton yield. Hence, there is a need to go for application of pre-emergence herbicides to manage the weeds in the early stage of crop growth and some selective and non-selective post-emergence herbicides to manage the weeds to eliminate weed competition throughout the critical period and in later stages of crop growth for getting higher cotton yield.

Materials and Methods

The experiment was conducted at Research farm of Cotton Research Unit, Dr.PDKV, Akola. Eight treatments were tested in randomized block design replicated thrice. The application of herbicide was done as per the treatments with manually operated knapsack sprayer attached with a flood jet nozzle. After calibrating the sprayer, water volume used was 700 lit. per ha. for PE and 500 lit. per ha. for PoE.

T8

Weedy check *Pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% w/w ZC649.25 g ha -1 is a new pre emergence broad spectrum label claim herbicide in cotton.

Weed study: For weed population study and weed dry weight was recorded by using a quadrate of 1 m x 1 m from a random spot in the plot where weed infestation was representative of the treatment. Then weeds were grouped as monocot species and dicot species. Weed control efficiency and weed index were computed as below-Dry matter of weeds in untreated plot-Dry matter of weeds in treated plot WCE (%) =

x 100 Dry matter of weeds in untreated Yield from weed free plot-Yield from treated plot WI (%) =

x 100 Yield from weed free plot

Results and Discussion

Weed studies

At all the growth stages of cotton T 7 (Farmers practice-3 hoeing + 3 Hand weeding) recorded lowest weed count and weed dry matter due to continuous intercultural and hand weeding operations in this treatment. At 30, 60, 90 DAS and at harvest, weedy check observed maximum weed population and weed dry weight due to uncontrolled growth of weeds in this treatment. Diuron 80% WP @ 1.5 kg ha -1 as a pre-emergence spray was found very effective in controlling all the monocots and dicots weeds upto 60 DAS as compared to other pre-emergence ready mix herbicide Pyrithiobac Sodium 3.1% w/w + pendimethalin 34.0% w/w ZC 649.25 g ha -1 as pre-emergence spray. Other post emergence herbicides viz. pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 and glufocinate ammonium non selective herbicides controlled the weeds in the later growth stages of cotton. Similar results of glufocinate ammonium were also reported by Young et al. (2001) [12] and Bharathi et al. (2011) [1] . However at 90 DAS and at harvest, T 5 treatment i.e. Pyrithiobac Sodium 3.1% w/w + pendimethalin 34.0% (Ready mix) w/w ZC 649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS recorded minimum weed population followed by T 2 i.e. Diuron 1.5 kg ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS which was found significantly at par with each other and significantly superior over other treatments except farmers practice where lowest population was recorded. Hanumanth, (2017) [5] earlier reported that diuron (PE) followed by either mechanical weeding or post emergence application of pyrithiobac sodium + quizalofop ethyl was able to control weeds. Varsha et al (2018) [11] also reported that mechanical weeding thrice at 20, 40 and 60 DAS reduced the weed growth in both red and black soils. Among the herbicides, diuron at 1.0 kg per hectare fb pyrithiobac sodium + quizalofop ethyl in red soil and both diuron at 1.0 kg ha -¹ and 0.75 kg ha -¹ along with sequential application of herbicides reduced the weed count.

Weed control efficiency and weed control

At all the growth stages of cotton i.e. at 30, 60, 90 DAS and at harvest, the highest weed control efficiency of 97.69%, 94.84%, 94.21% and 91.41% was recorded under farmers practice i.e. T 7 (3 Hoieng +3 Hand Weeding) as indicated in Table 3. This may be due to better control of weeds due to cultural practice. The weed control treatments (T 1 , T 2 and T 3 ) where diuron 80% wp was sprayed as a pre-emergence also showed maximum weed control efficiency at 30 and at 60 DAS and found statistically at par with each other. Similar results were reported by Tiwara and Brar (1990) [10] and Chethan (2013) [2] . At 90 DAS and at harvest T 5 and T 2 treatments showed highest weed control efficiency than other herbicide treatments. Sequential herbicide application combined with cultural practice performered better in controlling weeds and ultimetely increased WCE. While lowest weed index was noticed in (T 5 ) i.e. Pyrithiobac Sodium 3.1% w/w + pendimethalin 34.0% (Ready mix) w/w ZC649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS. This might be due to integrated weed management approach and effective weed control in treated plot which resulted increase in yield.

Highest weed index of 56.12 was recorded in weedy check treatments might be due to weed competition with crop and reduced the seed cotton yield. Similar results were also reported by Singh et al. (2016) [8] and Rathod et al, (2023) [6] .

Growth and yield attributes of cotton

All the growth characters viz; plant height, number of leaves, number of sympodial branches and plant dry matter were noticed highest in farmers practice of 3 hoeing and 3 hand weedings. Cultural practice of 3H + 3HW was found comparable with T 5 treatments i.e. Pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% (Ready mix) w/w ZC 649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS and T 2 i.e. Diuron 1.5 kg ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS and in respect of plant height and number of sympodial branches per plant. Similar results were also reported by Rathod et al, (2023) [6] . Weed control practices caused significant variation on seed cotton yield and number of picked bolls per plant. The highest seed cotton yield (2785 Kg ha -1 ) was registered with 3H+3HW which was found at par with T 5 treatment (2625 Kg ha -1 ) i.e. Pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% (Ready mix) w/w ZC 649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS followed by T 2 treatment (2593 kg ha -1 ) where diuron @ 1.5 kg ha -1 as a pre-emergence fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS was done. In case of boll weight maximum weight was observed in farmers practice i.e.4.72 g, however different herbicidal treatments recorded more or less similar values of boll weight and found non-significant results. Lowest boll weight (4.28) was recorded in weedy check. Similar results were recorded by Rathod et al, (2023) [6] and Reddy et al, (2023) [7] . Deshpande et al. (2006) [3] also found same results that the highest seed-cotton yield was recorded by 3 hand-weedings + 3 hoeings.

Economics

Cost of cultivation varied under different weed control treatments. The minimum cost of cultivation (46056 ₹ ha -1 ) was registered under weedy check plot. However, it was recorded maximum (75597 ₹ ha -1 ) under farmers practice of 3H + 3HW followed by 63892 ₹ ha -1 in T 2 treatment (Diuron 1.5 kg ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS). The cost of cultivation under different herbicide treatments varied from 46056 ₹ ha -1 to 75597 ₹ ha -1 . Maximum GMR of 184389 ₹ ha -1 was registered in 3H + 3HW as a cultural practice followed by 173753 ₹ ha -1 in T 5 treatment (Pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% (Ready mix) w/w ZC649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha-1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS) closely followed by 171635 ₹ ha - 1 .in T 2 i.e. Diuron 1.5 kg ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS. However significantly highest NMR of 111180 ₹ ha -1 was noticed in T 5 as against 108792 ₹ ha -1 in T 7 . Closely followed by T 2 treatment. Similar results are found by Sreena et al., (2019) [9] . Also, the maximum B:C ratio was recorded in T 5 (2.78) followed by in T 2 (2.68) and least B:C ratio in weedy check treatment (1.76). The less B:C ratio in 3H+3HW was observed due to more labour charges needed for hoeing and hand weeding than the herbicide cost required. 4. Conclusions 1. In cotton, for effective weed management 3 Hoeing and 3 hand weeding proved better in controlling weeds, lesser weed dry matter accumulation, higher weed control efficiency, minimum weed index and higher seed cotton yield highest gross monetary returns among all the weed management practices. 2. Among the herbicides, sequential application of either Diuron 1.5 kg ha -1 (PE) or Pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% (Ready mix) w/w ZC 649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS was found comaprable in controlling weeds, maximum weed control efficiency, lowest weed index and comparable yield as obtained in cultural practice of 3H+3HW. 3. Sequential application of pyrithiobac Sodium 3.1% w/w + Pendimethalin 34.0% (Ready mix) w/w ZC 649.25 g ha -1 (PE) fb pyrithiobac sodium 6% EC + quizalofop ethyl 4% EC w/w MEC 125 g ha -1 (PoE, 25-30 DAS) fb hand weeding at 50-55 DAS found most renumerative integrated approach for manageing the weeds in cotton. 4. Therefore, under scanty of labour it is advisable to follow the sequential application of pre and post emergence selective herbicides in combination with hand weeding in later growth stages of cotton for effective and economical weed management.

References

1. Bharathi S, Pavani M, Narayana E. Response of Bt. cotton to post-emergence herbicides in vertisols of Krishna zone. International Journal of Applied Biology and Pharmaceutical Technology. 2011;2(1):1-7.
2. Chethan KS. Sequential application of pre and post-emergent herbicide for weed control in Bt cotton. [MSc Thesis]. Dharwad: University of Agricultural Sciences; 2013.
3. Deshpande RM, Pawar WS, Mankar PS, Bobde PN, Chimote AN. Integrated weed management in rainfed cotton (Gossypium hirsutum L.). Indian Journal of Agronomy. 2006;51(1):68-69.
4. Gardner AP, York AC, Jordan DL, Monks DW. Management of annual grasses and Amaranthus spp. in glufosinate-resistant cotton. The Journal of Cotton Science. 2006;10:328-338.
5. Hanumanth M. Productivity, profitability and environmental impact of different weed management options in high-density cotton (Gossypium hirsutum L.). [MSc Thesis]. Hyderabad: Professor Jayashankar Telangana State Agricultural University; 2017.
6. Rathod NS, Khargakharate VK, Deshmane AB, Bhosale BB. Impact of pre-and post-emergence herbicides on growth, weed indices and yield attributes of Bt. cotton hybrids under high-density planting in the Maharashtra region. The Pharma Innovation Journal. 2023;12(2):651-655.
7. Reddy V, Kulkarni S, Chavan M, Ajayakumar MY, Rudramurthy. Effects of integrated weed management practices on weed parameters and yield of Bt cotton (Gossypium hirsutum L.). International Journal of Environment and Climate Change. 2023;13(11):324331.
8. Singh K, Singh HP, Singh K. Weed management in cotton with pre-and post-emergent herbicides. Indian Journal of Weed Science. 2016;48(3):348-350.
9. Sreena KS, Yadahalli GS, Chittapur BM, Ajayakumar MY, Bhat SN, Naik N. Economic attributes of Bt cotton (Gossypium hirsutum) using sequential application of herbicides under TBP Command Area. International Journal of Current Microbiology and Applied Science. 2019;8(9):1958-1964.
10. Tiwana US, Brar LS. Effect of herbicides on weed control efficiency and production potential of American cotton. Indian Journal of Weed Science. 1990;22:6-10.
11. Varsha N, Madhavi M, Ramprakash T, Suneetha Devi KB. Efficacy of diuron along with sequential application of herbicides for weed control in cotton. International Journal of Current Microbiology and Applied Sciences. 2018;7(6):3423-3436.
12. Young BG, Young JM, Gonzini LC, Hart SE, Wax LM, Kaputsa G. Weed management in narrow and wide-row glyphosate-resistant soybean (Glycine max). Weed Technology. 2001;15:112-121.