World Journal of Environmental Biosciences
World Journal of Environmental Biosciences
2023 Volume 12 Issue 1

Integrated Management of Onion Thrips on Onion, Mecha District, Ethiopia

 

Etagegn Mulu1, Abaynew Jemal Jenber2*, AdaneTesfaye2, Besfat Belay2

 

1Department of Plant Sciences, Wollo University, Dessie, Ethiopia.

2Department of Plant Sciences, Bahir Dar University, Bahir Dar, Ethiopia.


Abstract

Insect pests like thrips attack onion crops and cause a yield loss of 30%—90% in the Mecha district. Hence, field research was conducted in Mecha District, Ethiopia, under irrigation conditions in 2019/2020 to develop management options for onion thrips. The treatment combinations were: two onion varieties: Adama red and Bombay red; two botanicals, namely, Datura stramonium and Azadirachta indica leaf powder, and the two synthetic insecticides, dimethoate (40%) and karate (5%). The study was set up in a randomized full-block design and repeated three times. Data were recorded and an analysis of variance was performed 3 times. The highest mortality percentage (65%) with the lowest population of thrips per plant (1.66) was shown from the Adama red variety treated with Datura stramonium. The lowest mortality (24.43%) with a high population of thrips per plant (4.0) was shown on Bombay red treated with Karate 5% EC. Bombay treated with Karate 5% EC gave the highest mortality percentage (53.3%), plant height (13.2 cm), marketable yield in kg ha-1 (8600, and total yield ha-1 (9441), subsequently Adama red treated with Datura stramonium. Partial budget analysis revealed that the application of Karate 5% EC ha-1 on the Bombay red variety yielded the highest net benefit with the lowest production cost that can be recommended for the study area.

Keywords: Botanicals, Insecticides, Onion varieties, Thrips infestation


INTRODUCTION 

 

Onion (Allium cepa L.), is a vital bulb crop and is associated with the Alliaceae family. Its regarded as the second most crucial horticultural crop, after tomatoes, with annual world production in 2017 of around 97 million tonnes (FAOSTAT, 2019). The bulbs are the fleshy structure that serves as a storage organ and vary in size, shape, color, and pungency, though warmer climates generally produce onions with a milder, sweeter flavor as compared to other climates. Physical protection is given by the dry outer papery scales, which form a close-fitting coat around the bulb.

Onions are one of the most commonly grown and commercialized vegetables are grown under irrigation in the Amhara region of Ethiopia. Currently, farmers in the most irrigable areas of the Amhara region produce large numbers of onion bulbs each year.  In Mecha District (study site), during 2016–2017, onions covered 931 hectares of land, and 10,719,100 kg was produced, of which 8,039,300 kg was supplied to the market (ATA, 2018).

 This may make green onions unmarketable and dry bulb onions less expensive. Onion thrips feeding can reduce bulb yields by 60% as well as transmit plant pathogens and exacerbate plant diseases (Leach et al., 2020). In Ethiopia, onion thrips are a major insect pest that destroys onion farms, especially during the dry season when rainfall is scarce. Yield loss in onion bulbs by onion thrips has been reported to range from 10 to 85% (Esheteu et al., 2015). 

Despite the immense merits of onions, their production has been constrained by a myriad of biotic and abiotic factors, as well as institutional ones. Yield losses of 26-57 % were reported due to onion thrips in Ethiopia. Eshetetu et al. (2015) also reported a yield loss of 10- 85% in the Upper Awash Agro-Industry Enterprise. These low yield results indicated the presence of a huge gap in using improved onion varieties and appropriate insecticides because of the absence of improved cultivars and limited attention and awareness of the benefits of botanical and synthetic insecticides. Therefore, this research was carried out to evaluate selected onion varieties, botanicals, and synthetic insecticides as management options for onion thrips in the study area.

MATERIALS AND METHODS

Description of the study site

This literature was done in Mecha District, Northwestern Ethiopia, under irrigation conditions during 2019/2020. Mecha District is geographically located at 11O 10′N to 11O 25′N latitude & 37O 02′E to 37O 17′E longitude with an elevation of 1960 m. a. s. l (Meters above sea level). Annual rainfall is 1395.23 mm. The mean maximum and minimum temperatures are 27 OC and 12.8 OC, respectively. The major crops produced in the area are Zea mays, Eleusinecoracana, Triticumaestivum, and Eragrostistef on the course of the main cropping season, and Triticum aestivum, Solanum tuberosum, Allium cepa, and Brassica oleracea during the irrigation season. The soil type of the area is characterized by 93% red soil, 3% black soil, and the remaining 4% gray soil.

Experimental materials and design

For each variety, seeds of the Bombay and Adama varieties were sown at the rate of 4 kg ha-1 (EIAR, 2007) on a 5 x 1 m well-prepared seedbed. The seedbeds were spaced 50 cm apart. After the seeds were sown, they were lightly covered with soil. All the necessary management practices were applied except for insecticides. Fifty days after sowing, the seedlings were transplanted into the experimental field. A Knapsack sprayer was used for spraying the insecticides. At the time of insecticide sprays, plastic sheets were used to prevent spray drift within plots.

There were ten treatment combinations of two onion varieties, i.e., Adama red and Bombay red, and four insecticides, i.e., two botanicals, jimson weed (Datura stramonium), neem (Azadirachta indica) leaf powder, and two synthetic insecticides, dimethoate (40%) and Karate (5%), applied to 10 experimental units. Experiments were designed with a factorial randomized complete block design (RCBD) with three replicates. Each plot is made up of ten rows two meters in length. The size of the gross plot was 2m x 2m (4 m2), and the total area was 232 m2. With spacing for improved onion production, 10 cm was spacing between plants, 20 cm between rows, and 40 cm was the size of the plant bed, including the irrigation water path used for irrigating the plants. The spaces between plots and replications were 1m and 1m wide, respectively. Diammonium phosphate (4.64 kg) and UREA (3.48 kg) fertilizers were applied and all agronomic practices were undertaken (EIAR, 2007).

Methods of botanicals collection and extraction

Neem (Azadirachta indica): The neem leaves were collected and dried in the laboratory for 3 days, and then ground using an electrical blender to make a coarse powder. 50 g of the powder was dissolved in one liter of water and extracted overnight. The next day, it was filtered with cheesecloth and diluted with one liter of neem leaf extract and nine liters of water. The solutions were ready to spray on onions infested with thrips. The application was made during evening watering. In Ethiopia, the economic threshold level for onion thrips was five to ten thrips per plant.

Jimson weed (Datura stramonium): Leaves were collected and dried in the laboratory for three days and ground using an electrical blender to make a coarse powder. The powder was mixed with water at a rate of 50 g/l and left overnight as described in (Keshav & Singh, 2013). The mixture was filtered the following day by the use of cheesecloth and then prepared for spraying when the threshold of five thrips per plant was exceeded (Alemnew, 2017).

Data collection

Vegetative data

The number of leaves per plant was obtained from 10 randomly selected plants. One week before harvest, measurements were taken on 10 randomly selected plants from each treatment plot in the central row.

Plant height (cm): was measured from the soil surface to the apex of the plant using a ruler at harvest.

Bulb yield and yield components

Biomass yield (kg): Biomass yields were recorded from ten randomly sampled plants after harvesting.

Marketable bulb yield (kg): determined after discarding unmarketable yields, which are damaged, small bulbs, splitters, thick-necked bulbs, doubles, rotten, off-color, and discolored bulbs. The weight of healthy bulbs and they are having locally acceptable marketable size were taken at harvest from each harvestable plot, excluding borders.

Unmarketable yield (kg): damaged, small bulbs, splitter, thick-necked, doubles, rotten, off-color, and discolor bulbs were taken at harvest from each harvestable plot, excluding border rows.

Total yield (kg): was calculated by adding marketable and unmarketable yield.

Number of thrips/plant

Data on thrips numbers were recorded at 15-day intervals, starting a week after transplanting and continuing until physiological maturity. The nymphs and adults were counted by inspecting the entire plant with a 10x hand lens. The thrips were counted during the wind-free time of the day, late afternoon.

The percent reduction in thrips/plants was calculated using the formula in Dutta et al. (2014) as in equation (1).

 

(1)

 

Onion thrips infestation

Infestation with thrips was determined by counting thrips from ten plants in each plot. Infestation started a week after transplanting and continued until the physiological maturity of the onion. The percentage of thrips was calculated as a ratio of infested to total sampled plants (Dutta et al., 2014), as in equation (2).

 

(2)

 

Thrips damage severity on onion per plant

The presence of silvery patches on onion leaves was used to determine the severity of thrip damage. About ten onion plants were randomly selected from each plot. Damage levels were rated a week after transplantation and continued until harvest. Leaves of each randomly tagged standing plant were examined based on (Smith et al., 1994) to assess severity on a scale of 1–5. Where 1 = no damage, 2 = up to 25%, 3 = 26–50%, 4 = 51–75%, and 5 = >75% damage.

Relative yield loss

The relative yield loss in yield components of each variety was determined as a percentage of the sprayed plots of the respective varieties. The losses were determined separately for each of the treatments with different levels of damage by using the formula given by (Shiberu & Negeri, 2014) as in equation (3).

 

(3)

Method of data analysis

The Data were subjected to two ways analysis of variance since they have an interaction effect using the PROC-GLM procedure of SAS version 9.1. The means were compared using Fisher’s LSD test at a 5% or 1 % level of significance. 

Economic analysis

The analysis of the economic data was conducted by abiding by CIMMYT (1988) and used to determine the income and expenses of every management employed in the study. The various costs of this study, including seeds, insecticides, and labor, have been considered. Pesticide costs were obtained from pesticide companies and local distributors. The purchase cost of seeds was 1300 and 1200 Kg/Birr for the Adama and Bombay red varieties, respectively. The cost of daily labor was 150 birr per day. The selling price of the marketable outcome at harvesting season on the local market was birr 43 per kg-1. The total cost of all treatments was calculated. Management was graded in ascending fashion of total variable cost and net profit was determined. Dominance analysis was used to eliminate treatments that were the most expensive but had a lower net benefit than the next lowest-cost treatment. To calculate gross income, Yields obtained from each treatment were used by ten percent and subjected to a partial budget analysis. The following formula was used to compute the partial budget analysis, as in equation (4).

 

(4)

For the calculation of the marginal rate of return, the following formula was applied as in equation (5).

MRR =DNIDIC

(5)

 

, DNI= difference in net income compared with the control, DIC= difference in input costs compared with the control.

RESULTS AND DISCUSSION

The population of onion thrips influenced by varieties and insecticides

In different treatments, the onion thrip population (both nymphs and adults) per plant varied from 4.33 to 5.66 a day before treatment application (Table 1). The analysis of variance revealed that varieties showed no significant effect on onion thrip numbers (p > 0.05). However, the major influence of insecticide application and the communication effect of varieties and insecticides consist of a very highly considerable (p < 0.001) effect on the number of onion thrips (Table 2). After one and two days of insecticide application, the number of onion thrips on untreated plots varied from seven on the Bombay diversity to eight on the Adama variety (Table 1). The lowest number of onion thrips and the highest mortality percentages of 3 and 30% were recorded from both varieties treated with A. indica, followed by Karate 5% EC with a mean population of four and a mortality percentage of 24.43%. In the control plot, however, the onion thrips population increased by 29.5% and 39.15 % for the Bombay and Adama varieties, respectively.

After 3 and 7 days, results found that the Adama red variety treated with D. stramonium showed the least thrips population/plant (3 and 1.66) and mortality percentages of 40% and 65.46%, respectively, followed by the Bombay red variety treated with A. indica with a mean population of 3 and 2, and a mortality percentage of 30 and 53.33, respectively. On the other hand, there was an increase of 40% and 79% in the thrips population in the control plot, respectively. Among the insecticide treatments used, botanicals had the lowest population of thrips and plants and the highest mortality percentage across all data recording intervals. The efficacy of synthetic insecticide treatments decreased with an increase in data collection intervals. In the case of botanicals, the efficacy of plant extracts increased with the increase in the data collection interval. Several researchers have reported that botanicals presented a considerable effect in decreasing the injury of onion thrips (Bradford et al., 2020; Begna, 2022; Shettima et al., 2022).

The overall mean population of thrips recorded on the onion crop ranged from 1.66 to 10 per plant. The number of onion thrips increased daily in the untreated control plot, which had 4.33–10 thrips per plant in each treatment. After seven days, plots treated with botanical and synthetic insecticides showed the maximum reduction in thrips populations. The maximum mortality rate was recorded for treatment with D. stramonium (65.46%), and the least was recorded for Karate (24.43%)-treated plots. The treatment of D. stramonium was the most efficient (65.46% mortality) in reducing the onion thrips population on onion crops, followed by A. indica (53.33%) and dimethoate 40% EC (50%). These results showed a greater reduction in insecticide-treated plots, and infestation increased in untreated plots. Thus, all treatments were significantly superior to untreated controls, causing 24.43-65% or more thrips mortality. Khaliq et al. (2014) reported that neem, Datura, and bitter apple caused significant reductions (45-70%) in onion thrips populations. Shettima et al. (2022) also showed that neem seed, neem oil, and fresh ginger are effective against onion thrips. Iglesias et al. (2021) concluded that biopesticides are an important component of an onion thrips management program. It has been also reported that carbosulfan, cypermethrin EC deltamethrin+ triazophos, bifenthrin, and dimethoate reduced the T. tabaci population for more than two weeks and the effect of imidacloprid was better than cyhalothrin (Ashghar et al., 2018).

 

 

Table 1. Effect of Varieties and Insecticides on Population and percentage mortality of onion thrips

Variety

Insecticides

Before Treatment

No of population After treatment

Mortality Percentage after Treatment

 

 

1day

1day

2 days

3 days

7days

1day

2 days

3 days

7 days

Adama

Non spray

5.66a

7.33a

7.66a

8a

10a

-29.5bac

-36.15b

- 40.93ba

-79.03

D. stramonium

5a

3.66b

3.66 b

3b

1.66c

26.16bac

26.66cb

39.26ab

65.46bac

A .indica

4.33a

3b

3 b

3b

2.33cb

30bac

30cb

30bc

46.66d

Karate

5.33a

4b

4 b

4b

3b

24.43bc

24.43c

24.43c

24.43

Dimethoate

4.33a

3b

3 b

3b

2cb

30bac

3ocb

30bc

50bdc

Bombay

Non spray

5.33a

7b

8a

8a

9a

-30.53ba

-50a

-50a

- 69.4ba

D. stramonium

5a

4b

3.66b

3b

2.33cb

20c

26.66cb

40ba

53.33bdc

A .indica

4.33a

3b

3b

3b

2cb

30bac

30cb

30bc

53.3bdc

Karate

5.33a

4b

4b

4b

3b

24.43bc

24.43c

24.43c

24.43

Dimethoate

4.66

3b

3.33b

3.33b

2.33cb

35a

28.33cb

28.33bc

50dc

LSD

 

1.35

1.33

1.32

1.38

1.09

10.06

9.7

13.37

16.67

CV

 

20.95

18.55

17.87

19.12

17.02

20.95

18.46

23.11

17.44

 

Onion thrips infestation as influenced by interaction of varieties and insecticides

A highly significant difference between the treatments was observed after insecticide application (Table 2). The analysis of variance showed that varieties had no significant effect on onion thrips infestations. However, the main effect of insecticide application and the interaction effects of varieties and insecticides had a very highly significant (p 0.001) effect on thrips infestation.

On the first days of treatment application (62 days), the maximum mean infestation (56.6%) was observed in the untreated plot of the Adama variety, and the minimum (30) onion thrips infestation was recorded in the Bombay variety treated with D. stramonium, and A. indica. After a week of treatment application (69 Days), the infestation was 70% at the Bombay variety, 73.3 at the Adama variety on untreated plots, 20 at the Bombay variety treated with D. stramonium, and 30 at the Adama variety treated with A. indica.

After the second week of treatment application (76 days), the infestation was 76.6% at the Adama variety,80 at the Bombay variety on untreated plots, and 30 at the Adama variety and the Bombay variety treated with A. indica. A substantial dissimilarity in thrips infestation was detected between the unsprayed plots (80) and A. indica. Treated plots represented 43.3% of all varieties after the third week of treatment application (83 days) and at the final week (90 days) of application of insecticides, 100% infestation was observed on untreated plots of the Adama red, and a minimum of 20% was recorded from the Bombay red treated with A. indica (Table 2). Thrips infestation was significantly higher in unprotected plots than in protected plots. Onions sprayed with neem oil had fewer T. tabaci and produced higher yields than onions unsprayed, regardless of the onion cultivar (Iglesias et al., 2021). Botanicals possessed considerable differences in mortality rate and the efficacy of botanical showed that neem seed powder was significantly superior in efficacy (Tesfaye et al., 2021). Controlling thrips populations with botanicals can increase onion production yield, even though botanicals are not equally effective as chemical insecticides in reducing thrips populations and reducing associated losses (Begna, 2022).

The difference in onion thrips infestation between sprayed and unsprayed plots might be due to insecticide effectiveness. The highest thrips infestation was recorded on untreated plots than on treated plots. Abdul et al. (2014) tested the effectiveness of three botanicals (Neem, Datura, and Bitter Apple) and three synthetic insecticides (Acephate, Spirotetramat, and Spinetoram) against onion thrips in an experimental field in Pakistan. He found that thrips populations were significantly reduced by all botanicals and chemical insecticides tested (45–70%), with botanicals controlling more than 60%.

 

 

Table 2. Effect of varieties and insecticides on onion thrips infestation on different days

                                   Treatments                                                                                           Percentage of infestation on different days

Variety

Insecticide

62

69

76

83

90

Adama

Non spray

56.6a

73.3a

76.6a

80a

100a

D. stramonium

33.3b

33.3b

36.6b

50b

23.3b

A. indica

30.0b

30.0b

30 b

43.3b

23.3b

Karate

36.6b

33.3b

33.3b

53.3b

26.6b

Dimethaote

30b

30b

30b

43.3b

20b

Bombay

Non spray

53.3a

70a

80a

80 a

90a

D. stramonium

30b

20b

30b

50 b

26.6b

A. indica

30b

30b

30 b

43.3b

20b

Karate

36.6b

36.6b

33.3b

53.3b

30b

Dimethaote

30b

33.3b

30  b

46.6b

23.3b

LSD

 

10.5

13.9

13.5

16.6

12.4

CV%

 

16.8

20.3

19.2

17.8

18.9

 

Onion thrips damage severity scale influenced by varieties and insecticides application

Extended leaf damage scores had significant differences between treatments.  The analysis of variance revealed that varieties had no significant effect on the thrips damage severity scale. However, the main effect of insecticide application and the interaction effect of varieties and insecticides had a very highly significant (p<0.001) effect on the damage severity scale.

At 62, 69, 76, and 83 days after treatment applications, the highest leaf damage (51–75%) was observed from the untreated plot of the Bombay red variety, while the least (26–50%) was recorded from the treated plots of both varieties. In the final week (90 days) of application of insecticides, the highest leaf damage (> 75%) and lowest leaf damage (51–75%) were shown on the unsprayed plots of the Adama, and Bombay varieties respectively. whereas Bombay red treated with Azandirachta indica and Adama variety treated with dimethoate showed the least leaf damage (up to 25%) (Table 3). All insecticides have control characteristics that can reduce onion thrips populations below threshold levels. Most growers are concerned about leaf damage, so insecticides are generally considered the most effective way to protect crops against insect damage. Biopesticides reduce onion thrips densities in onions. Reductions in thrips densities of 17.2% using Datura species extracts have been reported (Fitiwy et al., 2015).

 

 

Table 3. Effect of insecticides and varieties on onion thrips damage severity scale at various weeks

                                Treatment                                                                                                   Damage severity scale on different days

Variety

Insecticide

62

69

76

83

90

Adama

Non spray

3.2b

4.3a

4.3a

4.3 a

5a

D. stramonium

3c

3b

3b

3.3b

2.3cb

A. indica

3c

3b

3b

3 b

2.3cb

Karate

3c

3b

3b

3.3b

2.6cb

Dimethaote

3c

3b

3b

3 b

2c

Bombay

Non spray

4a

4.3a

4.6a

4.3a

4.66a

D. stramonium

3c

3b

3b

3 b

2.6cb

A. indica

3c

3b

3b

3 b

2c

Karate

3c

3b

3b

3.3b

3b

Dimethaote

3c

3b

3b

3 b

2.3cb

LSD

 

0.31

0.68

0.43

0.89

0.74

CV%

 

5.8

12.2

7.6

15.4

14.9

 

Effect of varieties and insecticides integration on relative yield losses

A maximum grain yield loss of 38.66% on the Bombay red variety during the study season was recorded. The Adama red variety showed a grain yield loss of 31.86% (Table 4). The level of infestation and the extent of yield losses due to thrips on onions were reported by various researchers differently. Damage levels could be higher on untreated onion crops. The current study was in line with Gebremedhn et al. (2018) reported significant differences within varieties for marketable bulb yield in onions. Apart from these, damage by thrips results in inferior quality at harvest, which in turn fetches low prices.

 

 

Table 4. Effect of Varieties and Insecticides on Relative yield losses, and Growth Parameters

Treatment

 

Marketable yield (kg/ha)

Relative yield loss (%)

Plant height in cm

Number of leaf/ plant

Adama

Non spray

6250dc

0

10.96dc

22.6dc

D. stramonium

7350bc

7.25

11.3dc

35.56b

A. indica

5400e

31.86

8.33f

17e

Karate

6950bc

12.3

12.66ba

24.23c

Dimethaote

7200bc

9.14

11.5bc

20.1de

Bombay

Non spray

5550de

35.46

9.7e

18.03e

D. stramonium

6525dc

24.12

13.2a

33.7b

A. indica

5825de

32.26

10.86dce

21.76dc

Karate

8600a

0

11.96bc

43.03a

Dimethoate

5275e

38.66

10.13de

20.26de

LSD

 

1.28

3.3

1.23

3.3

CV%

 

9.37

7.51

6.49

7.51

 

 

Effect of varieties and insecticides integration on growth parameters of onion

Plant height

The analysis of variance revealed that the main factor of variety was not significant. Though, the main effect of insecticide application and the interaction effect of varieties and insecticides had a very highly significant (p<0.001) effect on plant height. The tallest plants (13.2 cm) and (12.6cm) were observed in a variety of Bombay treated with Datura stramonium and the Adama variety treated with Karate 5% EC, respectively (Table 4). Shetimma et al. (2022) revealed that neem seed was recorded with the highest plant height followed by fresh ginger while the control was recorded with the least plant height followed by pepper seed.

Number of leaves

The current result revealed that the main effect of insecticide application had a significant (p<0.05) effect on leaf number per plant. However, the main effect of varieties was not significant. The interaction effect of varieties and insecticides had a highly significant (p<0.01) difference in leaf number per plant. The maximum number of leaves per plant (43.03) was recorded on the Bombay variety treated with Datura stramonium while the minimum number of leaves per plant was observed on the Adama variety treated with Azadirachta indica (Table 4). Shetimma et al. (2022) show that control appeared with the highest number of leaves affected followed by pepper seed while the least leaves damage was recorded under fresh ginger followed by neem Seed. However, there is no damage left recorded under the plot treated with neem seed.

Effects of insecticides and varieties integration on yield components of onion

The analysis of variance showed that a variety was not significant (p > 0.05) on marketable and total yield ha-1. But, the application of insecticide and the interaction effect of varieties and insecticides had a very highly significant (p < 0.001) effect on marketable, and total yield ha-1. The main effects of insecticide application, variety, and the interaction effect of varieties and insecticides had a very highly significant (p < 0.001) effect on biomass weight in kg ha-1. The highest biomass weight in kg/ha-1, 9166.6 kg/ha, was recorded in Bombay, treated with karate. Similarly, the highest marketable yield in kg ha-1 (8600), the total yield in kg ha-1 (9441.6), and the lowest unmarketable yield in kg ha-1 (833.3) were recorded on Bombay treated with karate, followed by Adama treated with D. stramonium biomass weight in kg ha-1 (8609), marketable yield in kg ha-1 (7350), total yield in kg ha-1 (9025), and unmarketable yield in kg ha-1 (966.6). Similarly, the smallest measurements of Biomass weight in kg ha-1(5833.3) on Bombay treated with A. indica, marketable yield, and the total yield in kg ha-1, 5400, and 6108, respectively was observed on Adama variety treated with A. indica (Table 5).

Yields of control plots were significantly lower than those of all other insecticides tested. Onion thrips damage can reduce onion yields by 9-25% compared to controls (Table 5). These results are consistent with those of Ibrahim et al. (2015) found significant differences in onion yield between dimethoate 40°, wood tobacco, karate 5°, Mexican marigold, and control groups. Plots treated with wood tobacco and karate 5 achieved tuber yields of > 30% compared to controls. Many studies have reported that higher bulb yields were obtained with insecticides that reduced thrip density (Negash et al., 2020). When onion thrips infestations remained above economic threshold levels, crop damage, and lower yields occurred. Therefore, in the present study, the control plot yielded a lower yield. When thrips population densities exceeded the economic threshold level, onion bulb yield was negatively correlated with the thrips population.

 

 

Table 5. Effect of varieties and insecticides on yield and yield components of onion

Treatment

Biomass yield(kg/ha)

Marketable yield (kg/ha)

unmarketable yield (kg/ha)

Total yield (kg/ha)

Variety

Insecticide

 

 

 

 

Adama

Non spray

7666.6cd

6250dc

966.6ba

8325bac

 

D. stramonium

8609.1cb

7350bc

1250a

9025ba

 

A. indica

6525ed

5400e

833.3b

6108e

 

Karate

83333.3cb

6950bc

966.6ba

7916bc

 

Dimethaote

8608cb

7200bc

966,6ba

7916.6bc

Bombay

Non spray

6666.6ed

5550de

833.3b

6383.3e

 

D. stramonium

7633.3cd

6525dc

1250a

7775dc

 

A. indica

5833.3e

5825de

1108.3ba

6666.6ed

 

Karate

9166.6b

8600a

833.3b

9441.6a

 

Dimethaote

6525ed

5275e

966.6ba

6383.3e

Least significance difference

 

1.72

1.28

0.36

1.36

coefficient of variation %

 

10.5

9.37

17.9

9.99

 

Economic analysis

The result of the economic analysis showed that the maximum net benefit (ETB 327,520 ha-1) with an acceptable marginal rate of return was obtained on the Bombay variety treated with Karate 5% EC insecticide (Table 6). This has resulted in a net benefit of 128,624 for the birr (the Ethiopian currency) over the least beneficial treatment (Bombay unsprayed), with a net benefit of 198,896. 5. The treatment combinations of the Adama variety with D. stramonium (278,945 ETB ha-1), Adama with dimethoate 40% EC (272,990 ETB ha-1), and Adama with Karate 5% EC (263,265 ETB ha-1) insecticide likewise possess the most net benefit close to the Bombay diversity treated with Karate 5% EC. So it was yielded in the net benefit of Birr 80049, 74094, and 6436 over the lowest benefit action (Bombay unsprayed), respectively (Table 7).

Nonetheless, other treatments were excluded by the superiority analysis because net benefits achieved decreased as costs increased (CIMMYT, 1988). Thus, the Bombay variety treated with Karate 5% EC insecticide is preferred in the study area due to the satisfactory marginal rate of reoccurrence and the huge net benefit seen between all the varieties and insecticides tested.

Based on CIMMYT (1988), all treatments with a net benefit less than or equal to the previous treatment are prioritized and excluded from future analysis.  Accordingly, a maximum net benefit of 327,520 Birr ha-1 with a production cost of 5300 Birr ha-1 was documented from a conduct combination of the Bombay diversity and Karate insecticide application. This was followed by the Bombay variety treated with Datura stramonium. Negash (2020) reported higher net returns from more effective insecticides imidacloprid against T. tabaci on onion. Abaynew et al., 2020) as well as Yechale et al., 2021) showed similar results and revealed the importance of partial budget analysis in economic inquiry.

 

Table 6. Partial budget analysis for the management of onion thrips on onion

Cost-benefit data

Adama*

Non spray

Adama*D. stramonium

Adama*A. indica

Adama

*Karate

Adama

*Dimethaote

Bombay

* Non spray

Bombay*D. stramonium

Bombay

*A. indica

Bombay

*Karate

Bombay

*Dimethaote

Adjusted Marketable yield (kg/ha)

5625

6615

4860

6255

6480

4995

5872.5

5242.5

7740

4747.5

Sale ETB ( kg-1)

43

43

43

43

43

43

43

43

43

43

Gross return

(ETBha-1)

241875

284445

208980

268965

278640

214785

252517

225427

332820

204146.5

Cost of Insecticide (ETB ha-1)

0

0

0

500

450

0

0

0

500

450

Cost of  Labor (ETBha-1)

0

300

260

0

0

0

300

260

0

0

Cost of seed

(ETB ha-1))

5200

5200

5200

5200

5200

4800

4800

4800

4800

4800

TVC (ETB ha-1)

5200

5500

5460

5700

5650

4800

5100

5060

5300

5250

Net benefit

 (ETB ha-1)

239375

27894

203520

263265

272990

209985

247417

220367.5

327520.5

198896.5

Cost benefit ratio

1:46

1:50.7

1:37.2

1:46.1

1:48.3

1:43.7

1:48.5

1:43.5

1:61.8

1:37.8

Table 7. Effect of Varieties and Insecticides on the dominance analysis of onion yield

Treatment combinations

Total variable cost

Net Benefit

Dominance

Bombay +un spray

Bombay + A. indica

Bombay + D. stramonium

Adama+ unspray

4800

5060

5100

5200

209985

220367.5

247417

239375

 

 

 

Dominated

Bombay + dimethoate

Bombay + Karate

Adama+ A. indica

Adama+ D. stramonium

5250

5300

5460

5500

198896.5

327520

203520

278945

Dominated

Dominated

 

Dominated

Adama + dimethoate

5650

272990

Dominated

Adama + Karate

5700

263265

Dominated

 

 

CONCLUSION

Evaluation of insecticides and onion varieties' reactions to onion thrips performed when treated with four insecticides Significant differences in yield and yield-related parameters of onions were recorded because of onion varieties and insecticide application; especially, the application of Karate 5% EC on Bombay gave high and comparable yields.  From this study, the Bombay variety was the best performer, which might be due to its ability to withstand the agroecology of the area. Nevertheless, the present results focus on the practical evaluation of insecticides and onion varieties for better yields of onions and suggest that the application of Karate (5%) EC to the Bombay variety was the most effective in the study area. Therefore, the selection of appropriate insecticides and varieties of onion is one of the issues to be considered in the future to maintain the yield of onions in the region.

ACKNOWLEDGMENTS: We would like to thank Koga Irrigation Scheme Site workers for their technical support in the fieldwork.

CONFLICT OF INTEREST: None

FINANCIAL SUPPORT: None

ETHICS STATEMENT: None

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