FieldBindweed (Convolvulus arvensis) Control inTef (Eragrostis tef (Zucc.) Trotter) through Various Herbicide Combinations

Field bindweed is the major weed problem for tef producers across the central highlands of Ethiopia. Herbicide application alone or coupled with once or twice hand weeding for eld bindweed control is dicult due to its biological features, labor-intensive, and time-consuming. e eld trial was carried out at Debre Zeit from 2020 to 2021 cropping seasons to investigate dierent postemergence herbicides against the grass and broadleaf weeds, in general, and eld bindweed in particular, in tef farming, using a randomized complete block design with three replications. As a result, we could see that the herbicide combination had no visible eect on durum wheat’s overall performance, which makes us recommend it for the control of eld bindweed. In the sequential application, a wide spectrum of herbicides (Musket Power OD 460, Pallas 45 OD, and Sekator OD 375) were applied at tillering stage, and other selective herbicides (Derby 175 SC and 2,4-diamine salt 720 g/L 720 g/L) were applied at the heading stage, and the last nonselective herbicide (Roundup) was applied at physiological maturity of tef when the Convolvulus arvensis was regrowth naturally/latecomer weed. All postemergency herbicide treatments reduced signicantly both broadleaf and grass weeds, in general, and C. arvensis infestation, in particular, when compared to the weedy control. Of these, Musket Power OD 460 at tillering stage integrated with 2,4-diamine salt 720 g/L at the heading stage was more eective than other herbicides for eliminating all weeds andC. arvensis in particular throughout the crop life.is weedmanagement option resulted in considerably enhanced weed control eciency and weed killing potential, reduced weed dry biomass and yield loss, improved grain yield, and economic benet with an acceptable marginal rate of return for tef growers.


Introduction
Ethiopia is the source of many economically important crops, including tef Eragrostis tef (Zucc.) Trotter, which belongs to the grass or Poaceae family and the genus Eragrostis [1]. It is the only country in the world that uses tef as a cereal crop [2] and is mostly grown as an insurance or rescue crop to preserve the Ethiopian population [3]. Of the main cereal crops grown in the country, tef remains a crucial food crop with area coverage, production size, food, nutritional, and commercial value [4]. Tef grain is currently the most important staple grain for over 72% of Ethiopia's population, which is expected to reach 110 million people. is suggests that tef is an important and valuable crop for the country's agricultural system and food security. e cultivation of tef predates historical records by Ethiopian farmers, and it has a relative advantage over other cereals in both farming and utilization aspects [5]. Even though tef has versatile agro-ecological adaptations under diverse climatic, edaphic, and socioeconomic conditions, relative tolerance to both drought and ooding conditions and suitability for a variety of cropping systems and sustainable farming, tef productivity is still far below its potential, with an average grain yield of only 1.7 tons per hectare in Ethiopia, compared to maize (4 tons per hectare) and wheat (2.7 tons per hectare) [6]. Among the major yield-limiting biotic factors in tef production, annual and perennial grass and broadleaf weeds are the backbreaking, labor-intensive, and time-consuming operations in tef husbandry. Of these, the most important weeds of tef in Ethiopia have been identified by Fessehaie and Tadele [7] and Kassahun and Damte [8].
ey also listed other problematic weeds in tef including the parasitic witchweed (Striga hermonthica), the introduced alien invasive weed commonly known as congress weed (Parthenium hysterophorus), field bindweed, and other noxious weeds. Because of morphological features, especially its short and delicate stem, small leaves and shallow fibrous root system, and low seedling stand establishment, tef has a limited ability to compete with weeds. Consequently, both the yield and the quality of the grain and the straw are severely reduced/affected by the weed. Engstrom [9] found that weedy check plots produced 130 kg ha −1 grain yield compared to 2,460 kg ha −1 in weed-free plots, indicating that tef has a low competitive ability against weeds. Similarly, weed competition has been reported to cause a yield loss of 48 to 49% in the western Amhara Amhara region [7]. Likewise, Slotvisov et al. [10] revealed an 18% yield loss due to weeds, while Ketema [3] reported a 52% yield reduction without weed control.
Field bindweed was initially introduced to Ethiopia with lentil seed in the 1980s and has become a threat to tef producers in most tef-growing areas, particularly in the highland areas of Ethiopia [11]. is weed has a large mass of lush green foliage, may have grown to full maturity above crop height, and can smother crops causing difficulty for harvest, increasing the cost of harvesting and aggravating tef shattering, reducing harvesting material speed, reducing threshing efficiency, impeding cultural operations, and increasing separation losses and means; otherwise, dry grain will have higher harvested moisture content due to condensation transfer from green wet vegetation [12]. According to later studies, hand weeding has been used as the primary method of weed management for many years, even though labor shortages are becoming more of a constraint. Because of such shortcomings, a single application of postemergence selective herbicides (such as Starane M 64% B EC, Derby 175 SC, Mustang, and 2,4-diamine salt 720 g/L Amine Salt 72% S) about 25 to 30 days after crop emergence has proved effective in controlling the dominant broadleaf weeds in tef, thereby giving significant yield increase. However, for noxious weeds such as Convolvulus arvensis, due to its biological features, once or twice supplementary hand weeding in addition to the single postemergence application of herbicides may be needed depending on the weed flora infestation and effectiveness of the herbicides to maximize yields. However, this herbicide plus hand weeding cannot provide satisfactory control of the field bindweed because of labor-intensive and time-consuming operations in tef husbandry. On the other hand, due to the weed's regenerative ability and extensive root system, a single application of chemical field bindweed control is ineffective and challenging [13,14]. As a result, combining herbicides has many benefits over using a single active ingredient, including lower farming costs due to labor and time saving, reduced soil compaction due to fewer operations, and a delay in the emergence of herbicide-resistant weeds [15]. To overcome this problem, the application of economically visible herbicides more than once the application in different tef stages is an ideal means for controlling late comer weed, particularly C. arvensis. erefore, an investigation was planned to evaluate the sequential application of postemergence herbicides for field bindweed management in tef with the following objectives: to see how field bindweed and weed control efficiency in tef is affected by herbicide application in sequence; to examine the impact of sequential herbicide application on tef grain yield; and to work out the cost: benefit ratio of herbicides.

Description of the Study Areas.
e field trial was carried out at Debre Zeit Agricultural Research Center on-station under rain-fed conditions from 2020 to 2021. is location is one of the most important tef growing areas in Ethiopia, as well as the national center of tef breeding program excellence. Its geographical extent ranges from 08 o 45′ 15″ to 08 o 46′ 45″ N latitude and from 38 o 59′45″to 39°01′00″E longitude with an altitude of 1,900 ma. s. l. A first-class meteorological station within the DZARC measures different climatic elements. e records from 1972 to 2021 show that the mean annual rainfall is 815.7 mm. It has a unimodal rainfall pattern with an extended rainy season from June to September. However, July is the busiest month, followed by August (Figure 1). e mean annual maximum temperature is 26.3°C, and monthly values range between 24°C in July and 28.8°C in March. e mean annual minimum temperature is 10.7°C, and monthly values range between 7.5°C in December and 12.5°C in July and August. e major soil type of the trial fields is heavy black soil (Vertisol).

Experimental Treatments, Design, and Application
Procedure.
e experiment was carried out in three replications using a randomized complete block design. e plot size was 3 × 4 m with a harvestable area of 2.5 × 3.5 m and footpaths of 1 m between plots and 1.5 m between replications. ere were twelve treatments in the experiment, six postemergence herbicide treatments that were applied either integrated or sequentially, one weed-free check (hand weeding), one with a weedy check for C. arvensis, and one weedy check for all weeds ( Table 1). All postemergence herbicides were applied at recommended rates to three different tef growing stages when the weeds were at the early flowering stage. e first sprayed postemergence herbicides (Musket Power, Pallas, and Sekator) were broad-spectrum herbicides applied at the tillering crop stage. e other selective herbicides (Derby 175 SC and Agriherba) were used at the heading stage. e last nonselective herbicide (Roundup) was applied at 90% physiological maturity of tef when the C. arvensis regrew naturally. All naturally occurring field bindweed populations were selected during experimentation. Tef cultivar, namely, Dagim, was used as the test crop and sown at a recommended rate of 10 kg ha −1 in all plots by manual 20 cm row planting method. Fertilizers were used at the rate of 69 kg N ha −1 urea and 100 kg NPS ha −1 (19 N, 37 P 2 O 5 , and 7.6 S) as fertilizer sources. N 1/3 and NPS were entirety drilled in rows at the time of sowing, and the remaining 2/3 of N through urea was applied at the shoot elongation stage of the crop. Postemergence application of herbicides was sprayed uniformly on the weeds at the specified date per treatment using a manually pumped knapsack sprayer. e seedbed in both years was prepared using a moldboard plow followed by disking.

Data Collection and Procedures.
e weed population count was taken with the help of 0.5 m × 0.5 m quadrant, was thrown randomly at once in each plot before and after herbicide application, and was identified and converted into population density per m 2 . e biomass was harvested from each plot during crop harvest after the weed population was recorded. e harvested weeds were separated into paper bags and dried in a 65°C oven for 24 hours until they reached a constant weight, after which the dry weight was measured and converted to kg ha −1 .    e magnitude of weed reduction caused by the weed control treatment is denoted by weed control efficiency. e following formula was used to calculate the weed control efficiency: The dry weight of weeds in weedy check − Dry weight of weeds in treatment plots A dry weight of weeds in weedy check * 100.
(1) e weed index (WI) or relative yield loss is the percentage reduction in crop yield due to the presence of weeds when compared to weed-free plots. To put it another way, the weed index measures weed competition by a percentage reduction in yield due to its presence in the field: Yield from the weed − free plot − Yield from the other treatment plot Yield from the weed − free plot (kg) * 100.
Herbicide efficiency index (HEI) measures the herbicide treatment's weed-killing ability as well as the crop's phytotoxicity:

HEI �
Yield of treated plot − yield of contol(unweeded plot/yield of control (unweeded plot)) Weed dry weight in treated plot/Weed dry weight in control (unweeded) plot .
Aboveground dry biomass yield, grain yield, and harvesting index were recorded. e final product was measured and adjusted to 12.5% moisture content with the help of the following formula: Adjusted grain yield (kg ha −1 ) � Actual yield * 100 − M/100 − D, where M denotes the grain's measured moisture content and D denotes the designated moisture content.

Partial Budget Analysis.
e partial budget analysis was done to evaluate the cost involvement (fixed costs and variable costs as well) and benefits of herbicide treatment as described in the procedure of CIMMYT [16]. Yield from experimental plots was adjusted downward by 15%, that is, 10% for management difference and 5% for plot size differences. e number of laborers needed for manual weeding management (twice for tef' weed-free' treatment) and the herbicide application cost per hectare of land were 100 and 1, respectively. A person per day of labor cost was 200 ETB. e cost of herbicides was calculated based on the current local market price. Accordingly, the cost of Pyroxsulam was 3,000 ETB litre -1 ; the cost of 2,4-diamine salt 720 g/L was 400 ETB litre -1 ; the cost of flurasulam 75 g/L + flumetsulam 100 g/L was 600 ETB litre -1 ; the cost of 2,4-D-2-ethylhexyl ester + lodosulfuronmethyl-sodium sodium was 1,800 ETB litre -1 ; the cost of glyphosate was 450 ETB litre -1 ; and the cost of amidosulfuron + iodosulfuron-methyl sodium was 1,900 ETB litre -1 . Price of current tef grain (50 ETB kg -1 ) and price of straw (7.6 ETB kg -1 ) data were obtained from the Add'a district's Office of Trade and Transportation marketing case team.

Statistical
Analysis. All data were subjected to analysis of variance using PROC GLM procedure in SAS [17]. Analysis of variance (ANOVA) was carried out to examine the effects of postemergence herbicides on weed density, weed biomass, yield, and yield contributing characters of tef. Except "weed free" as a check treatment, weedy check for all weeds and weedy check for C. arvensis were used as a control treatment and compared to the other treatments. Similarly, in terms of yield, "weed free" was used as a control treatment and statistically compared to other treatments, as well as weedy check for all weeds and weedy check for C. arvensis. Mean separation of significant treatments was carried out using the least significant difference (LSD) test at a 5% level of probability.

Flora and Biomass of Weeds.
Tef was infested with broadleaf weeds, sedges, and grasses in both cropping seasons, with broadleaf weeds taking the lead. Before the application of the postemergence herbicide, the weed community consisted of 18 species representing eight different families (Table 2). e families Poaceae and Asteraceae predominated, the other families having more species.
e application of all herbicides significantly reduced the total dry biomass of all weeds (Table 3). Among these, Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage (34.3 kg ha −1 ) followed by Pallas heading stage (78.2 kg ha −1 ) offered the highest reduction in total dry weed biomass. e results showed that dual-purpose herbicide, Musket Power OD 460, controlled the weeds effectively during the early stages of crop growth, and in later stages, the regenerative ability weeds effectively was controlled by 2.4-D, which is a broadleaf control herbicide. However, the lowest weed dry biomass was observed in Musket Power OD 460 at tillering stage plus glyphosate at 90% physiological maturity of tef, which is statistically parity with Musket Power OD 460, Sekator OD 375, and Pallas 45 OD at tillering stage plus Derby 175 at the heading stage and Pallas 45 OD at tillering stage plus glyphosate 90% physiological maturity of tef. In general, the dry biomass difference among herbicides could be due to the herbicide killing potential and the weed tolerance to the tested herbicide. is finding is consistent with Sareta et al. [18], who found that postemergence herbicide application alone was not as effective as other agronomic practices.

Weed Control Efficiency and Weed Index.
e weed control efficiency results ( Figure 2) show that all nine herbicide treatments could reduce weed infestation in general and C. arvensis in particular in tef cultivation. Regardless of the weed-free check (hand weeding), the range of weed control efficiency of herbicide applications was 88.6-97.7% compared to the weed check for all weeds and 42.7-97.4% compared to the weedy check for C. arvensis. Among these herbicides, Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at heading stage followed by Pallas 45 OD at tillering stage plus 2,4-diamine salt 720 g/ L at heading stage recorded the maximum (97.7 and 94.7%) weed efficiency of all weed species compared to the weedy check for all weeds. While the lowest weed control efficiency was obtained from the application of Musket Power OD 460 at tillering stage plus glyphosate at 90% physiological maturity as postemergence treatment, which was statistically party with the application of Musket Power OD 460 at tillering stage plus Derby 175 SC at heading stage and Pallas 45 OD at tillering stage plus Derby 175 SC at heading stage. Results were also obtained in case of weedy check for C. arvensis, herbicide application of Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at heading stage followed by Pallas 45 OD at tillering stage plus 2,4diamine salt 720 g/L at heading stage offered the highest (97.4 and 70.8%) weed control efficiency, respectively. However, the lowest (42.7%) weed density reduction was achieved in plots treated by Musket Power OD 460 at tillering stage plus glyphosate at 90% physiological maturity as postemergence treatment.
e lower field bindweed reduction could be the regenerative ability of C. arvensis after   [20] also stated that C. arvensis had the highest susceptibility to herbicide combination iodosulfuron-methyl Na + amidosulfuron + safener mefenpyr-diethyl + fenoxapropp-ethyl, and triasulfuron + dicamba. Grain yield loss of tef was significantly different due to weed management practices, with the lowest yield loss (0.0%) recorded at weed-free check plot (hand weeding), followed by Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at heading stage offering the least (8.1%) yield loss of tef compared to the nine herbicide treatments combination (Figure 2). e lowermost loss of tef grain yield in weed-free treatment and sequential herbicide application (Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at heading stage) practices could be due to the absence/reduction of weed density, inhabit growth, and biomass accumulation of weeds. e crop that freely utilizes nutrients, sunlight, water, and better utilization of photosynthesis and improved yield attributes traits such as the number of effective tillers m −2 , panicle length, culm length, and thousand-grain weight cumulatively increased grain yield. However, the highest (42.4%) yield loss was recorded in a weedy check for all weeds followed by (39.3%) a weedy check for C. arvensis in Figure 2. is loss of tef grain yield both in weedy check for all and weed check for C. arvensis plots might be due to the presence of a greater density of weeds in the current study. ese findings are consistent with Amare et al. [21], who found that herbicide application combined with supplemented hand weeding reduces wheat yield loss more than uncontrolled weed treatment.

Herbicide Efficiency Index.
Comparing the weed management indices of postherbicides, significantly, the highest (27.4 and 14.8) weed killing potential for all weeds, in general, and C. arvensis, in particular, with less phytotoxicity at tef were obtained from herbicide combinations containing Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at heading stage of tef, respectively. However, the lowest (11.2 and 10.2) herbicide efficiency indices for all weeds and C. arvensis, in particular, were obtained from Pallas 45 OD at tillering stage plus Derby 175 at the heading stage of tef, respectively (Figure 3). is study found that applying herbicides in the sequence was more effective for controlling field bindweed (which has a regenerative ability, a large root system, and latecomer weeds) and was better than applying a single herbicide for annual weed control. However, understanding the possible interactions between herbicides and environmental factors such as precipitation may improve the effectiveness of this herbicide on field bindweed. Similar results were observed by [22].  International Journal of Agronomy

Grain Yield, and Total Aboveground Biomass of Tef.
Grain yield and harvest index of tef showed significant (P < 0.05) differences due to the sequential application of postemergence herbicides and the three weedy check treatments in the combined analysis (Table 3). e highest (1,933 kg ha −1 and 24.7) grain yield and harvest index were recorded in weed-free check, followed by Musket Power OD 460 (1,769 kg ha −1 ) at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage and Sekator OD 375 (21.4) at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage, respectively. However, the lowest (1,101 kg ha −1 and 15.8) grain yield and harvest index were recorded in the weedy check for all weeds, which was statistically partly with a weedy check for C. arvensis. Yield wise, both hand weeding and Musket Power OD 460 (1,769 kg ha −1 ) at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage outperformed the weedy check for all weeds by 43 and 38%, respectively. Both the above-mentioned treatment improves the grain yield by 40 and 34%, respectively. e improvement of tef grain productivity might be due to efficient control of weed growth, weed density, and efficient utilization of resources by crops, which lead to proper growth and development of crops that favour an increase in yield and yield attributes. e minimum grain yield was due to weed infestation, accumulation of high dry matter in weeds, and occurrence of different weed species in weedy plots. In line with this result, Brhane [23] reported that the highest grain yield of tef was obtained in weed-free treatment, while the lowest grain yield was obtained in the weedy check.
Similarly, Norberg Felix [24] reported that tef grain production was greater with herbicide application treatment compared to the weedy check treatment.
Total aboveground biomass yields as affected by weed management methods ranged from 7,037 to 9,152.8 kg ha −1 (Table 3). e highest biomass yield (9,152.8 kg ha −1 ) was recorded from sprayed of Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage, while the minimum biomass was recorded at weedy check for all weeds with the mean of 7,037 kg ha −1 . e increased biomass yield might be due to decreased weed population and dry weight caused by better utilization of growth resources and translocation of assimilates from source to seed since plants with better access to environmental resources had better photosynthate photosynthesis formation, and in turn, it is expressed on biomass. e reduced biomass yield in uncontrolled plots might be due to increased competition for resources; this increased competition between increased weed population and low weed control efficacy leads to thin and weak stems reduced tiller number and reduced total biomass yield. Similarly, Hanson [19] reported that the mixture of herbicides produced a higher biomass yield than weedy check plots.

Partial Budget Analysis.
A partial budget analysis was run to understand the efficiency and economics of input-output of tef production. According to the results, the highest net benefit was obtained from the application of Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage, followed by Sekator OD 375 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage and Musket Power OD 460 at tillering stage plus Derby 175 at heading stage and weed-free check (Table 4). However, due to dominance analysis, most of the treatments were dominated by the highest net benefit treatments. To identify treatments with maximum return on the  farmers' investment, marginal analysis was performed on nondominated treatments. us, based on the marginal rate of return (MRR), Musket Power OD 460 at tillering stage plus 2,4diamine salt 720 g/L at the heading stage was superior (4625.9%) rewarding treatment combination, and it was recorded above the acceptable minimum rate of return. is implies that for Birr 1.0 investment in tef production, the producer can get ETB 45.25. From this finding, it was observed Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage was crucial for the control of field bindweed in tef cultivation areas.

Conclusions
Grain yield of tef can be reduced up to 42.4 and 39.3% due to weed infestation in all weeds and C. arvensis in particular, respectively. Field bindweed and other weeds in general in tef cultivation could be managed effectively by the combined application of postemergence herbicides. Among different herbicide treatments, Musket Power OD 460 at tillering stage plus 2,4-diamine salt 720 g/L at the heading stage gave better results in terms of weed management index and a profitable alternative to the existing recommendation of weed control (twice hand weeding or herbicide application alone and/or plus other agronomic practices) for tef yield in Ethiopia. Generally, combining herbicides can reduce all weed species, including field bindweed, because of the weed's regenerative ability and extensive root system, as well as reduce farming costs by saving labor and time and delaying the appearance of herbicide-resistant weeds.
Data Availability e data used for the analysis of this research results are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest.