Integrated Management of Corn Marigold ( Glebionis segetum) in Tef Field at Western and Southwestern Shewa Zones in Ethiopia [version 2; peer review: awaiting peer review]

Background: Corn marigold (Glebionis segetum (L.) Frourr. ) is a serious weed species of agricultural crops in many parts of Ethiopia. However, there is a lack of information on its management in tef fields in the country. Therefore, the current work was designed with the objectives of evaluating integrated management of the weed and determining the most economical integrated weed management options in tef fields. Methods: The field experiments were conducted in naturally corn marigold infested fields of Cheliya and Woliso districts of West and Southwest Shewa Zones in Ethiopia, respectively, during 2020 to 2021 cropping seasons. Results: Different corn marigold management practices exhibited different responses to different parameters of the target weed and the test crop differently. Application of Pyroxsulam 45g L -1 at a rate of 0.40 l ha -1 supplemented with once-hand weeding and Halauxifen-methyl 100g kg -1 + Florasulam 100g kg -1 sprayed at a rate of 50 g ha -1 supplemented with once-hand weeding increased grain yield by about 70 and 50%, respectively, over the weedy check. The marginal revenue and benefit-cost ratio obtained from the marketing of goods for the application of Pyroxsulam 45g L -1 with one supplementary hand weeding of corn marigold increased by110 89%, respectively, as compared to the weedy check. Conclusions: The present study revealed the role of


Introduction
Tef (Eragrostis tef ) is the most important staple grain for over 60-72% of Ethiopia's population (Gizaw et al., 2018). Its cultivation predates historical records by Ethiopian farmers, and it has a comparative advantage over other cereals in terms of farming and utilization (Minten et al., 2018). It is one of the most widely cultivated and economically important cereal crops in Ethiopia, but one of the lowest in production. Because of its weak root system and short stem with narrow leaves, it is vulnerable to weed competition (Tessema, 2002). Tef-weed competition is a big threat to the crop production and productivity, causing great yield loss.
Particularly, corn marigold (Glebionis segetum (L.) Fourr.) is considered as one of the most difficult weed species in many countries of the world in general (Karamaouna et al., 2019) and in Ethiopia particularly (Asres & Das, 2011;Shashitu, 2019). They are specifically harmful in the high land part of Ethiopia and can significantly reduce crops yield (Asres & Das, 2011;Shashitu, 2019). Corn marigold has been reported to cause 56% yield losses in wheat in Ethiopia if appropriate management measures are not implemented (Shashitu et al., 2018).
Similar to other weeds, corn marigold competes with agricultural crops for water, nutrients, minerals, space and light. Its competitive advantage is enhanced by its extreme fast growth rate, fast spreading ability, rapid multiplication via seeds, and strong competitiveness with crop (Shashitu, 2019). It is a noxious weed which highly adapted to a wide range of nutrient and environmental conditions. Its complicated root system, large number of branches that are difficult to uproot, and cutting worsen its infestation (Shashitu, 2019) Figure 1.
Corn marigold is observed spreading fast and invading grazing and crop lands at an alarming rate at Dabat (Assefa, 2019), Debark districts (Asres & Das, 2011) in Amhara regional state and Cheliya and Woliso districts (Shashitu, 2019) in Oromia regional state in Ethiopia. It is becoming a noxious weed to crop production and causes yield and seed quality reduction in crops at highland parts of the country. As evidenced from Figure 2A-F, it infests grazing land, faba bean, tef, wheat, and linseed fields at Cheliya and Woliso areas in Oromia regional state in Ethiopia.
Hand weeding is the most often utilized weed management approach in tef fields to reduce the detrimental impact of corn marigold. Due to overlapping operations with other crops, farmers' family labor is insufficient during the main cropping season for timely and adequate control of corn marigold in tef fields (Nagassa et al., 2022). Hand-weeding tef fields takes time and is typically done late in the season, after the weed have reduced crop growth and development. It's especially tough because of the constant rain during the primary cropping season, which inhibits people from getting out into the field and conducting field activities.
Though the threat of corn marigold in tef production is increasing spatially and temporally in Ethiopia, few studies have been conducted on its management and feasibility of the management option in the country. Therefore, this study was

REVISED Amendments from Version 1
There are minor modifications between the previous version and this version. Language improvement, use of the chemical names of the herbicides other than their common name, including some computed parameters, discussion, and interpretation of the results are the major ones. Data corrections on very few parameters were also done in the revised version of this manuscript.
Any further responses from the reviewers can be found at the end of the article conducted with the objectives of developing effective integrated management of corn marigold, determining the grain yield benefit and yield losses derived from the use of integrated management of the weed, and determining the most economical integrated weed management options tested in tef production in the selected sites of the western and southwestern zones of Ethiopia.

Study area
The study was conducted at Cheliya and Woliso districts in Oromia regional state in farmers' fields during the main cropping season of 2020 to 2021 (Figure 3). A naturally corn marigold infested field per district was selected (Table 1 and Figure 3).

Treatments, experimental design and crop husbandry
The experiment consisted of six treatments arranged in randomized complete block design with three replications on the plot size of 4 m Â 5 m. Spacing 1.5 m between blocks and 1m between plots were used. Tef seed rate of 10 kg ha -1 of "Kuncho" variety was drilled in rows 20 cm apart. NPS and urea fertilizers were applied at rates of 150 and 200 kg ha -1 , respectively. NPS was applied at sowing time, whereas urea was applied in two split half amounts at sowing time and the remaining amount at the tillering stage of the crop. The herbicide amount required for the treatment was calculated and measured using a sensitive digital balance and measuring cylinder and applied 30 days after sowing (DAS) Table 2. For all herbicide treatments, a uniform spray volume of 200 l ha -1 was used. Moreover, all experimental plots management activities were executed to the standard level.

Data collected
Both corn marigold weed and tef crop data were recorded. The weed parameters such as the number of corn marigold before and after treatment, biomass and visual scoring scale were recorded using appropriate materials and procedures. The weed control efficacy percentage was calculated using the appropriate formula. Tef parameters plant height, biomass, and grain yield were recorded, and a harvest index was calculated.  Number of corn marigold: was counted at 30 th and 60 th days after sowing using 1 m * 1 m quadrat.
Visual scoring: was undertaken using 1-5 scale scoring system at 15 th and 30 th , days after herbicide application (Taye et al., 2007).
Biomass of corn marigold (kg/plot): the weed shoot biomass at crop physiological maturity from the net plot area was recorded and weed control efficacy was calculated using the following formula: Where, WDC and WDT are weed dry weight in control and any particular treatment, respectively.
Plant height: was measured from the ground level to the tip of ten randomly selected plants from harvestable rows at physiological maturity.
Grain yield (kg ha -1 ) was measured by harvesting the crop from the net plot area.
Shoot biomass yield: At physiological maturity, the shoot biomass of ten plants selected randomly from the destructive rows was measured after oven drying the harvested produce till a constant weight.
Harvest index: The plants harvested for shoot biomass yield at physiological maturity was used to calculate the harvest index by dividing grain yield by the total shoot dry biomass yield.
Harvest index % ð Þ¼ Seed yield Shoot dry biomass * 100 Relative tef yield loss due to weed was calculated as follows: Relative yield loss % ð Þ¼ MY À YT MY * 100 Where, MY = maximum yield from a treatment, YT = yield from particular treatment Actual yield loss due to corn marigold ¼ CFy À FPy ð Þ CFy * 100 Potential yield loss due to corn marigold ¼ CFy À CCy ð Þ CFy * 100 Where, CFy = crop yield in corn marigold free plots, FPy = crop yield in farmers' practice, and CCy = crop yield in corn marigold un-weeded check plot.
Data on inputs and their costs were collected for each evaluated weed control option/treatment, including the costs of procuring herbicides and planting materials, labor expenses for land preparation, tillage and herbicide application, hand weeding, and tef harvesting.
The costs of Pyroxsulam 45g L -1 (2974-birr L -1 ), Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 (10913-birr kg -1 ), and Flurasulam 75 g L -1 + Flumetsulam 100 g L -1 175 SC (8400-birr kg -1 ) were obtained from the prevailing local market (53.37 Ethiopian Birr = $1 United State during merchandising). The shopping unit value of the knapsack sprayer was 1200 birr as information gathered from Addis Ababa (central market), Ethiopia. Around West and Southwest Shewa zones, the labor cost man -1 day -1 was ranges from 50-150 birr. In addition, data on the market price of tef per kilogram were collected at each site. The current market price (as of January 2023) was taken from farmers who sell tef in local markets and district extension workers to compute benefit cost ratio.

Data analysis
The collected data were subjected to analysis of variance using SAS computer software version 9.4. However, Means were separated using LSD procedure at the 95% confidence level, when they found statistically significantly different.

Cost-benefit analysis
The cost-benefit analysis for the proposed management practices, which included herbicidal and cultural (manual weeding) strategies, was determined using the (Program et al., 1988) process. During the cost-benefit analysis, the total input cost of production, gross revenue, marginal revenue and benefit-cost ratio were all taken into account. The total input cost (additional expenses for weed and trial management) was calculated by adding all costs (variable + fixed input costs) incurred during the study. Tillage and fertilizer costs, as well as planting and harvesting wages, were considered fixed production costs. While the knapsack sprayer, herbicides, and manpower for pesticide spraying and manual weeding were considered variable production costs.
The gross revenue was concluded by multiplying of commercialized price and grain yield (Daramola et al., 2019).
The marginal revenue was computed as subtracting the total variable costs from the gross revenue (Daramola et al., 2019) In addition, the benefit cost ratio was computed as the proportion of marginal revenue (numerator) and total variable cost (denominator) (Daramola et al., 2019).

Analysis of variance
The variance analysis revealed statistically significant differences in the evaluated weed management strategies on both the corn marigold and tef characteristics (Tables 3 and 4). Different corn marigold management approaches produced different results in weed parameters including weed biomass and weed control efficiency, as well as crop factors like plant height, biomass yield, grain yield, and harvest index.

Weeds dry weight
There was statistically significant difference in corn marigold dry weight among management strategies (Table 3). In the weed-free plots, there was no weed dry weight recorded. Following the weed free plots, the application of Pyroxsulam 45 g L -1 supplemented with once-hand weeding significantly decreased the weed dry weight by about 33-fold, followed by the application of Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 supplemented with once-hand weeding, which decreased the weed dry weight by 30-fold as compared to the weedy check. However, farmers' family labor is insufficient for timely and adequate management of corn marigold in tef field, as it needs continuous removal of the weed as it emerges. Hand-weeding tef fields is time-consuming and usually done late in the season, after the weeds have reduced crop plant growth. It is especially difficult because of the heavy rain during the main cropping season.

Weed control efficiency
The effects of weed management strategies on weed control efficiency were significantly different (Table 3). Continuous hand weeding of corn marigold as it appeared in the field resulted in complete eradication, whereas Pyroxsulam 45 g L -1 supplemented with once hand weeding followed by Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 supplemented with once hand weeding resulted in effective corn marigold destruction. However, frequent hand-weeding of the weed in   tef field is one of the most difficult tasks faced by farmers, especially during the main cropping season. It requires 3-4 rounds of continued weed removal per season to make the field weed-free. Uprooting the weed is difficult due to its complex root system, and cutting it worsens its infestation. Additionally, tef seedlings are also uprooted and the crop population reduced during frequent hand weeding.

Yield and yields attributes
The effect of weed management practices on plant height, biomass yield, grain yield, and harvest index were significantly different whereas there was a statistically insignificant difference among all management practices on the crop harvest index (Table 4). However, in tef crop yield, there was a statistically insignificant difference among weed free plots, Pyroxsulam 45 g L -1 spray supplemented with once hand weeding, and Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 spray supplemented with once hand weeding (Table 4). The application of Pyroxsulam 45 g L -1 supplemented with once hand weeding increased the tef yield by about 70%, followed by Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 sprayed with once supplementary hand weeding with the crop yield increment of 50%. Overall, the results showed a good agreement in the trends of all yield related parameters.

Effect of corn marigold weed on yield loss in tef
The highest yield was obtained from weed free plots, followed by the application of Pyroxsulam 45 g L -1 at 0.40 l ha -1 with supplementary hand weeding. The minimal relative yield loss (0.44%) due to corn marigold was obtained from application of Pyroxsulam 45 g L -1 at 0.40 l ha -1 with supplementary hand weeding, followed by application of Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 at 50 g ha -1 with one supplementary hand weeding with intermediate relative yield loss (12.10%) ( Table 5).
Based on corn marigold density per area, the potential tef yield loss by the weed ranged from 23.75 to 62.93%, whereas the actual tef yield loss was 13.67 to 47.09% (Table 6). Both actual and potential yield losses due to the weed were highest at West Shewa Zone (Cheliya District), whereas yield losses due to the weed were lowest at Southwest Shewa Zone (Woliso District). This might be due to the fact that the weed density in Cheliya District was higher than that in Woliso District.

Cost-benefit analysis
For the integrated use of herbicide application and supplementary hand weeding for corn marigold management, the marginal revenue (MR) and benefit-cost ratio (BCR) were computed for treatment combinations. The cost-benefit analysis showed that significant variation in MR and BCR was observed among the evaluated experimental treatments (Table 7). Comparing the management practices, the most prominent MR 72459-and 71210-birr ha -1 ) and BCR (2.86 and 2.63) were calculated from application of Pyroxsulam 45 g L -1 supplemented with hand weeding and weed free plots, respectively. Conversely, the lowest MR (34633-and 46571-birr ha -1 ) and BCR (1.51 and 1.97) were computed from weedy check and application of Flurasulam 75 g L -1 + Flumetsulam 100 g L -1 supplemented with hand weeding, respectively, whereas the intermediate MR and BCR were obtained from the application of Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 with supplementary hand weeding. The MR and BCR obtained from the marketing of goods for application of Pyroxsulam 45 g L -1 supplemented with hand weeding of corn marigold increased by 110 and 89% as compared to corn marigold weedy check (control plot) (Table 7). Cost-benefit analysis indicated that integration of Pyroxsulam 45 g L -1 with supplementary hand weeding exhibited the topmost MR 72459 Birr ha -1 ) and BCR (2.86), followed by the weed free plots correspondingly with the MR of 71210-birr ha -1 and BCR of 2.63. Overall, integrated use of broad leaf killer herbicides with supplementary hand weeding provides a better MR and BCR than single weed management practices (Table 7).

Summary and conclusion
Corn marigold is one of the aliens weed species that has seriously infested cereal and pulse crops in many parts of Ethiopia since its introduction. It is a noxious weed that is difficult to manage due to its: prolific seed production, fastest growth and spread, adaptation to a wide range of environmental conditions, and strong competitiveness with crops. Integrated effects of herbicide application and hand weeding significantly lowered the weed infestation in the study locations. The current study revealed that application of Pyroxsulam 45 g L -1 at a rate of 0.40 l ha -1 supplemented with once-hand weeding and Halauxifen-methyl 100 g kg -1 + Florasulam 100 g kg -1 at a rate of 50 g ha -1 supplemented with once-hand weeding effectively manage the weed and increased tef grain yield. The marginal revenue and benefit cost ratio obtained from the marketing of goods for application of Pyroxsulam 45 g L -1 at a rate of 0.40 l ha -1 supplemented with hand weeding of corn marigold increased by about 110 and 89% as compared to a weedy check. In conclusion integrated management of corn marigold by integrating broad spectrum and/or broad-leaf killer herbicides with hand weeding practices played a crucial role in improving tef production and productivity by contesting the weed. Forthcoming studies should focus on scaling up and popularizing these technologies in corn marigold weed-infested tef fields in Ethiopia.

Data availability
All data supporting the results are included in the article, and no extra source data are necessary.