Integrated weed management in sunflower

Introduction

One of the most significant oilseed crops in the world, the sunflower (Helianthu annuus L.), is a member of the Asteraceae family. The production of edible oil is the primary goal of sunflower cultivation. It includes oleic acid (42-57%) and linolenic acid (33-48%), which lowers lowdensity lipoprotein cholesterol, making it a good source of unsaturated fatty acids and lessens the risk of heart disease. Currently sunflower is grown in India on an area of 0.228 million ha with a production of 0.212 million tones and productivity of 0.93 t ha -1 (Indiastatagri, 2020) [2] . Weeds compete with sunflower for nutrients, moisture, light and space, thus reducing yields and decreasing the effectiveness of other inputs (Suresh and Reddy, 2010). Weeds can also act as hosts for harmful pathogens and pests. A dry-land crop like sunflower may have a yield loss of 60-90% due to intense competition. This costs growers money through decreased crop yields. Weeds that were not controlled reduce the sunflower yields by up to 62% (Sumathi et al. 2009) [7] . According to Raut et al. (2015) [6] , the type of weed, its density, the timing of its emergence, the crop, as well as soil conditions, all affect yield. Herbicides are therefore, a very efficient and cost-effective method of controlling weeds. Pre-emergence and post-emergence herbicides can be used to manage weeds at crucial times of crop growth. Due to continuous application of herbicides, herbicide resistance is also causing problem now-a-days. The conventional method of weed control is laborious, insufficient and costly hence, neither herbicide nor cultivation practices are adequate for consistent and acceptable weed control. Therefore integrated weed management is the best for higher productivity, using pre and post emergent herbicides in combination with hand weeding or inter cultivation. Integrated Weed Management (IWM) is a sustainable approach to the management of weeds by combining all available weed control techniques, including preventative measures, monitoring, crop rotations, tillage, crop competition, mechanical and physical control, herbicide rotation, herbicide mixtures, biological control, nutrition, irrigation, flaming, etc. in a way that minimizes economic, health and environmental risks (Swanton et al., 2008) [9] .

Materials and Methods

The field experiment was conducted during spring 2022-23 at Odisha University of Agriculture and Technology, Bhubaneswar, Odisha. The experimental site is located 64 kilometers from the Bay of Bengal at 20°27' North Latitude and 85°79' East Longitude, at an elevation of 25.9 m above mean sea level (MSL). It belongs to the East and South Eastern Coastal Plain Agroclimatic Zone of Odisha. The soil was sandy loam in texture, acidic in reaction (pH-5.9), having medium organic carbon (0.62%), medium available nitrogen (295.13 kg/ha), low available phosphorus (2.59 kg/ha) and medium available potassium status (262.29 kg/ha). The experiment was laid out in randomized block design with eight treatments and replicated thrice. The treatments were, T1-Pendimethalin @1.0 kg/ha as PE fb One intercultivation at 30 DAS, T2-Pendimethalin @1.0 kg/ha as PE fb Quizalofop Ethyl 10 EC @37.5g/ha as PoE at 20 DAS, T3 -Oxyflurofen @0.025 kg/ha as PE fb One intercultivation at 30 DAS, T4-Oxyflurofen @0.025 kg/ha as PE fb Quizalofop Ethyl 10 EC @37.5 g/ha as PoE at 20 DAS, T5-Two intercultivation at 20 & 40 DAS, T6-One intercultivation at 20 DAS fb one hand weeding at 30 DAS, T7-Weed free (three hand weeding at 15,30 and 45 DAS), T8-Unweeded control. The test hybrid DRSH-1 was sown on 06.01.2023 and harvested from 08.04.2023 to 10.04.2023. The crop was fertilized at the rate of 60 kg N, 80 kg P2O5 and 60 kg K2O/ha in all the treatments. Half of nitrogen and full dose of P2O5 and K2O were applied as single basal dose in the form of Urea, Single super phosphate (SSP) and Muriate of potash (MOP), respectively. Remaining half dose of nitrogen applied in two equal split at the time of earthing up and at the time of bud initiation stage. The seeds of DRSH-1 cultivar of sunflower were sown with a spacing of 60 cm × 30 cm. Weed density and weed dry weight at 30, 60 and 90 days after sowing were recorded from pre marked quadrants of 1m 2 area. The weed data were subjected to square root transformation (√x+1) to normalize the distribution. Weed growth attributes viz.,weed density (No/ m 2 ) and weed dry weight (g/ m 2 ), weed control efficiency (%) and weed index(%) were computed. Individual species wise weed counts were grouped into grasses, sedges and broad-leaved weeds and expressed as number/m 2 . For the estimation of weed dry biomass the weed samples were uprooted, washed in tap water; sun dried and further dried at 70 0 C in oven till constant weight. Thereafter, the dry weight of weeds was recorded in g/m 2 . Weed control efficiency (%) and weed index (%) were calculated by using the formula: W.C.E (%) = (Wc-Wt/Wc) ×100, where, Wc = Dry matter of weeds in weedy check (control). Wt = Dry matter of weeds in weed control treatments and WI (%) =X-Y/X, where X=seed yield from minimum weed competition plot, Y= seed yield from treatment for which weed index is to be worked out. Seed yield were determined from the net plot area and were weighed in kg or gram and converted into kg/ha. Economics of different treatments was calculated by taking into account the prevailing market price of inputs and produce of the experimental year. Gross returns were worked out for each treatment based on quality and market prices of the produce. The net return was also worked out by deducting the cost incurred from the gross returns of the particular treatment. Benefit cost (B: C) ratio was calculated by dividing the gross return with cost of cultivation. The data were analyzed as per the analysis of variance (ANOVA) for randomized block design at 0.05 probability.

Results and Discussion

Weed flora

In the experimental field, 11 types of weeds belonging to 5 different families were present(table 1). The important narrow leaved weeds during spring 2023 in the experimental site were Cynodon dactylon, Digitaria ciliaris, Digitaria sanguinalis, Sorghum halepense, Cyperus rotundus, Cyperus iria, Fimbristylis miliacea and broad-leaved weeds were Heliotropium indicum, Alternanthera philoxeroides, Spilanthes acmella and Amaranthus viridis. Similar observations were found by Bharati et al. (2020) [1] .

Effect of different management practices on weed control

Weed population, weed dry weight, weed control efficiency and weed index were significantly influenced by different weed management practices (Table 2). At all the stages (30 DAS, 60 DAS and harvest), the highest weed population and weed dry weight was recorded under unweeded check as compared to other treatments. While weed free treatment attained significantly lower weed population which is followed by One intercultivation at 20 DAS fb One hand weeding at 30 DAS. This may be due to the effectiveness of intercultural operations and hand weeding, which both reduce weed populations. The similar results were observed by Nagamani et al. (2011) [5] . The weed free (three-hand weeding at 15, 30 and 45 DAS) treatment had the lowest weed dry weight at harvest which remained at par with one intercultivation at 20 DAS fb one hand weeding at 30 DAS. Similar findings were found by Kalaiyarasan and Vaiyapuri (2018) [3] . Weed control efficiency (WCE) was computed by taking into account total weed dry weight, which includes a range of weed species in different proportions, in order to prevent emphasising the effects of specific weed species. The weed free treatment in the current study indicated higher WCE (80.50%), because weeds were effectively controlled in a timely manner. The next best treatment was One intercultivation at 20 DAS fb One hand weeding at 30 DAS (75.72%) followed by Two intercultivations at 20 and 40 DAS (68.03%) followed by Pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS(66.13%). This was attributed to lower weed population, which resulted in reduction of total dry weight of weeds in these treatments due to better control of weeds by cultural methods and imposition of herbicides. Similar findings were recorded by Mahapatra et al. (2024) [4] . The extent of yield reduction due to weed competition as assessed through weed index (WI) has evidently indicated the suppressing effect of weed free check which had minimum weed competition and maximum seed yield. After weed free treatment, the lowest weed index was recorded in One intercultivation at 20 DAS fb one hand weeding at 30 DAS(6.77) followed by Two intercultivations at 20 and 40DAS (9.19) followed by Pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS(10.05). The lower value of weed index was due to lower weed infestation resulting in lower weed biomass production. Similar results were found by Bharati et al.

Effect on crop growth and yield

The maximum plant height (190 cm.) was recorded in weed free (three hand weeding at 15, 30 and 45 DAS) at harvest which remained at par with one intercultivation at 20DAS fb one hand weeding at 30DAS and Two IC at 20 and 40 DAS. The largest head diameter (17.4 cm) was observed in weed free (three hand weeding at 15,30 and 45 DAS). The smallest head diameter (10.5 cm) was recorded with control. The impact of integrated weed control on 100 seed weight was determined to be nonsignificant. The highest 100 seed weight (5.53g) was recorded in Weed free (three hand weeding at 15, 30 and 45 DAS) treatment followed by One intercultivation at 20 DAS fb one hand weeding at 30 DAS (5.38 g), Two intercultivation at 20 & 40 DAS (5.36 g) and Pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS (5.23 g). The lowest 100 seed weight (4.72g) was recorded with Unweeded control. The seed yield varied significantly as a result of different integrated weed management practices. The highest seed yield (1980 kg/ha) was observed in Weed free (three hand weeding at 15, 30 and 45 DAS) which is at par with One intercultivation at 20 DAS fb one hand weeding at 30 DAS (1846 kg/ha), Two intercultivation at 20 & 40 DAS (1798 kg/ha) and Pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS (1781 kg/ha). The lowest seed yield (1002 kg/ha) was recorded with control because of highest removal of nutrients and moisture by weed and severe crop weed competition resulting in poor source-sink relationship with poor yield components. Similar type of results were also reported by Sumathi et al. (2009) [7] . [10] observed similar findings of highest oil yield with the weed free treatment.

Effect on economics

Weed free (three hand weedings at 15, 30 and 45 DAS) resulted in highest gross return (Rs.133878/ha) and net return (Rs.57311/ha) and unweeded control produced the lowest net return (Rs.7793/ha). Pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS resulted in highest BC ratio (1.81). Similar results were reported by Tadavi et al. (2017) [10] .

Conclusion

Weed free (Three hand weeding at 15, 30 and 45 DAS) treatment recorded the highest weed control efficiency, seed yield, gross and net returns, but the B:C ratio is highest in pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS. Hence, the treatment, pendimethalin @1.0 kg/ha as PE fb one intercultivation at 30 DAS can be regarded as the efficient and economical integrated weed management practice for increasing sunflower yield.

References

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