Distribution, Severity Status, Farmers Knowledge and Management Practices of Wild Radish (Raphanus raphanistrum L.) in Horro Guduru Wollega Zone, Western Ethiopia

The objective of the study was to study the distribution, severity status, farmers’ knowledge, impacts and management practices of Wild Radish (Raphanus raphanistrum L.) in Horro Guduru Wollega Zone, Western Ethiopia. The collected data were analyzed by using descriptive statistics. The Shannon Diversity Index (SDI), the evenness, species richness and Jaccards Similarity Index (JSI) was calculated from the recorded weed samples. Correlation of vegetation variables among and between sampled Administrative Kebeles’ was analyzed b y SPSSv20 software. The result of the study indicates that out of the sampled 160 respondents 92 (57.5%) of them heard about wild radish plant as a weed and the rest of 68 (42.5%) of the respondents did not know this plant as a weed. Among the respondents 88 (55%) of them identify R.raphanistrum plant as a weed. There was high negative correlation between mean R. raphanistrium density and Shannon diversity index with R 2 = 0.642, p<0.001. This study showed that high infestation level of R . raphanistrum was observed in Horro district followed by Abayi Chomen, Amuru and Jima Rare districts. The highest and lowest mean population (±SD) of R. raphanistrum per quadrate was recorded at Horo (249.82 ± 34.67) and Jima Rare (13.72 ± 14.16), respectively. The biodiversity impact of R. raphanistrium at highly infested areas were more visible than the moderately infested areas. Horro and Abayi Chomen districts showed the lowest Shannon Diversity Index value of 1.78 and 2.12, respectively, due to the fact that, their species diversity was highly affected by the high population density of R. raphanistrium. Moreover, the standing herbaceous vegetation from the sampled sites of Horo district (Doyo Bariso and Gudina Abuna administrative kebeles) showed higher Jaccards Similarity coefficient (0.84), where there was high R.raphanistrium infestation level. The study proved that R. raphanistrum was emerged as invasive weed and have been disseminated into neighbor districts’ and zones. Therefore, further research should be conducted to quantify the distribution, increases in species abundance as well as its impact on biodiversity and socio-economic aspects, which may support to contain R. raphanistrum distribution and planning on its prevention and management.

Wild radish seeds commonly remain dormant (up to 70%) and viable in the soil for 6 to 15 years at depth in undisturbed soil (Madafiglio 2002;Newman 2003). It has the potential to be introduced accidentally in agricultural produce from many different sources as a contaminant of grain seed (Woolcock & Cousens 2000). Once established, this species invades disturbed habitats such as agricultural land, abandoned fields and roadsides (McGeoch et al. 2009). Moreover, it competes successfully with agricultural crops, has a long-lived seed bank and a rapid life cycle (Warwick & Francis 2005). R. raphanistrum life cycle ranged from 43.5 to 230.5 days. Plants emerged in the fall (seasons between summer and winter) had greater biomass production and seed production compared to once emerged in summer months (Singh 2009).
Wild radish produces up to 45,000 seeds m -2 . One plant in a wheat crop can produce 292 seeds and 52 plants m -2 can produce 17,275 seeds (Cheam & Code 1998). Singh (2009) reported that an average of 1,470 seeds plant -1 was produced when emergence occurred in July compared with an average of 10,170 seeds plant -1 when emergence occurred in November. Later emerging plants have a lower chance of setting viable seed and produce less seeds. It is also a prolific seed producer and can cause yield losses if not controlled in a timely manner (Singh 2009). Yield losses depend on wild radish density and time of emergence in relation to the crop. Densities as low as 10 wild radish plants m -2 reduced wheat yields by up to 20% (Reeves et al. 1981;Warwick & Francis 2005), with up to 50% reduction at densities of 80 wild radish plants m -2 (Hashem et al. 2001a). R. raphanistrum that emerges with the crop can cause more than 90% yield loss whereas populations that emerge more than 7 weeks later cause less than 20% yield loss (Blackshaw 2001). The allelopathic potential produced by this plant suppress the nearby growing cereal crop plants by emitting the allelochemical. Holm et al. (1997) also reported that ingestion of R. raphanistrum by sheep and cattle may taint milk and become health hazard (toxic substances due to erucic acid and glucosinolates content) and if bread wheat becomes contaminated with large quantities of R. raphanistrum seed, 'bread poisoning may result. Holm et al. (1997) reported that R. raphanistrum has been as weed of 45 crops in 65 countries. Holm et al. (1991) on the Book of "World Weeds: Natural Histories and Distributions" mentioned the presence of R. raphanistrum at 'Say Ager at 9°N 39.5°E in Ethiopia. This book presents comprehensive and upto-date information on over 100 weed, including those species responsible for a high proportion of the world's crop losses. At this time R. raphanistrum ('gommanee' in Afaan Oromoo) infested Horro Guduru Administrative zone of Oromia Regional State infested. Dechasa (2003) reported that R. raphanistrum was first detected in Horro district of Horro Guduru Wollega zone. Ravi et al. (2014) also stated that R. raphanistrum is one of the most widespread, damaging and difficult weeds to control but little studied weed in Ethiopia, particularly in Horo Guduro Wollega zone of Oromia Regional State, where it is common in cultivated crops. Information's obtained from Zone Agriculture Office reviled that the problem of R. raphanistrum last from 20 to 25 years and now its severity increases from year to year. The farmers experience some cultural practices such as hand weeding and slashing and herbicide spraying to reduce the damage caused by R. raphanistrum. However, neither of these practices is effective so far for the management of R. raphanistrum especially in cereal crops. Even though the farmers of the study area experienced some cultural practices and herbicide application, its distribution and severity status increases from year to year. Thus, the goal of this study was to investigate the distribution, colonization history and severity status of R. raphanistrum in Horro Guduru Wollega zone of Oromia Regional State. [1012 words; 13811 ÷ 1012 = 13.6%]

MATERIALS AND METHODS 2.1. Description of the Study Area
The study was conducted in Horro Guduru Wollega Administrative zone (HGWz) of Oromia Regional State ( Figure 1). The zone town, Shambu, is located at 314 km west of Addis Ababa (Belay et al. 2015). The zone has a total population of 570,040 of whom 285,515 male and 284,525 were female (CSA 2007). From the zonal population 505,301 were rural dwellers, of which 252,474 and 252,827 were male and female, respectively. Among the rural people, 121,136 were households with an average of 4.71 family sizes. From the total population of the zone 64,739 or 11.36% are urban inhabitants. The two largest ethnic groups reported live in HGWz were the Oromo (86.12%) and the Amhara (13.34%), while other ethnic groups made 0.54% of the zone population. 'Afaann Oromoo' and 'Amharic' languages are spoken by 85.95% and 13.59%, respectively, while the remaining 0.46% of them spikes other languages as primary language. The majority of the inhabitants were Protestants, with 42.99% while 38.47% of the population professed Ethiopian Orthodox Christianity, 8.91% observed traditional beliefs (Wakefata) and 8.61% of the population were Muslim.
The study area is stratified into three agro ecological zones based on agro-climatic conditions namely; low land 7.86% (1000-1500 m), mid land 37.89% (1500-2300 m), and high land 54.75% (2301-2835m), with an average altitude of 2296 m.a.sl (Mekonnen et al. 2012). The zone town, Shambu, lies with geographical coordinates of 09º29´N and 37º26´E. The zone has one long rainy season characterized by unimodal distribution and extends from March to mid October with an average rainfall that ranges between 1000-2400 mm (Olana 2006). The monthly mean temperature varies from 14.9°C to 27°C. The area is favorable for multi disciplinary agricultural of R. raphanistrium, weed infestation level, damage status, management practices and possible ways of weed dissemination mechanisms were collected from the respondents through interview questionnaire. Additionally at kebele level, focus group discussions having 10-15 members were implemented for brain storming and testing of farmers' knowledge on R. raphanistrium.
Based on the agro ecology of the study area, from each administrative kebele's three sites and 36 quadrates from each site were selected purposively and the degree of infestation of R. raphanistrium and other herbaceous weeds stand were record. Following Phil et al. (2004) procedure, GPS was used to locate the the coordinates of study area. Arc View GIS 3.2 software was used to map the study sites and the infestation area. Secondary data was collected from zone and district agricultural offices for additional information.

Data collection 2.3.1
Respondents knowledge on Wild Radish, R. raphanistrum Information related to peoples" perception about the impact of R. raphanistrum in rural areas (both arable and non-arable lands) was collected from sampled study areas. A preliminary survey was conducted before the actual research work to test the actual distribution of the wild radish, R. raphanistrum. The survey was undertaken to observe the presence of different weed species, R. raphanistrium presence or not, the possible dispersal mechanisms, its invasiveness, its impact on crop yield, animal and human health. For interview questioner and semi-structured interview, 160 respondents (farmers) at the age range of 30 to 75 year were included. Equal number of respondents from each administrative kebeles' were identified and selected through purposive sampling procedure. The selection of the respondents was based on the awareness on the aggressive colonization of R. raphanistrium on arable land and non-arable land (roadsides) its impact on crop production, livestock and plant biodiversity. Furthermore, for additional information field observations, interview and focus group discussions were made with development agents and district agricultural experts.

2.3.2
Sampling method and sample size determination of R. raphanistrium and herbaceous weeds stand data Wild Radish, R. raphanistrium and herbaceous vegetation samples were collected from 24 farmhouse holds. Field crops considered for data collection were cereals, pluses, and oil crops. Field crop types used for herbaceous weed sample collection were 'teff'', wheat and maize for cereal crops; field pea and broad bean for pulse crops and noug for oil crops. Wittenberg et al. (2004) transect survey method was employed and a quadrate was laid at a distance of 50 m. For each sample plot of field crops, four sample quadrates were taken by laying a quadrate (1m x 1m) at a distance of ten meters and marked out (Kombiok et al. 2003). Weed vegetation stand data including R. raphanistrium were collected from 864 quadrates of 144 sample sites from six field crops of eight sampled administrative kebeles.
The majority of the plant species collected from the quadrates were identified in the field and recorded. The nomenclature of the rest of plant species were identified by using the Flora of Ethiopia and Eritrea (Hedberg & Edwards 1995) and by weed identification hand book of Naidu (2012). All herbaceous plants that are within the quadrate were identified in the field and counted. Subsequently, at every time of data collection the sample quadrates of crops in the two districts were weeded, the number of weeds per quadrate was counted, and the average was determined per quadrate.
In order to investigate the relative abundance and composition of the herbaceous vegetation as impacted by wild radish, R. raphanistrium, the proportion of individual species (cover and abundance of the plant species) encountered in each of the quadrates was recorded using the procedure documented by Wittenberg et al. (2004). This method involves a total estimate based on abundance and cover of the species where invasion is spatially patchy. The total estimate scale (abundance plus coverage) can be shown as follows. None of any plant species covers an area =0, plant species covers ≤ 5% area = 1, plant species covers 6 to 25% area = 2, plant species covers 26 to 50% area = 3, plant species covers 51 to 75% area = 4 and plant species covers 76 to 100% area = 5. Following the methods suggested by Chellamuthu et al. (2005), the sample sites were categorized into different groups based on percent area coverage of wild radish infestation levels: No wild radish infestation = 0%, very low level of infestation = ≤ 10%, low level of infestation = 11 to 25%, moderate level of infestation = 26 to 50% high level of level of infestation = 51 to 75% and very high level of infestation = 76 to 100%.
Diversity of the species for the vegetation data from the sample sites in the study areas were compared using Shannon Diversity Index. This index accounts both for the abundance and the evenness of the species in natural environment as shown by the equation below (Shannon and Wiener, 1949). It is also used to assess the impact of R. raphanistrium on the diversity of herbaceous plant species. The higher value of index of diversity indicates the variability in the type of species and heterogeneity in the community where as the lesser values point to the homogeneity in the community.
H= -∑ (1) Where H" = Shannon diversity index; P i = the importance value of the i th species; S = total number of species in the sample quadrate. The evenness of species 'E' was calculated as proposed by (Hill, 1973): This index explains how equally abundant each species would be in the plant community and high evenness is a sign of ecosystem health. This is because it does not have a single species dominating the ecosystem. The evenness or equitability assumes a value '0' and '1' with '1' being complete evenness and '0' a single species dominating the area. The similarity of the standing vegetation (herbaceous vegetation layer) among the sample sites in this study area was compared using Jaccard's coefficient of similarity (JCS) as shown by the equation below. This coefficient of similarity has been recognized robust and unbiased compared with other similarity indices, even with small sample size (Ludwing & Reyonlds 1988). ( Where, JSC = Jaccard"s Coefficient of Similarity; a = species common to quadrate 1,2,3,4,5 and 6; b = species present in quadrant 1 but absent in quadrate 2,3,4,5 & 6; c = species present in quadrate 1 but absent in 3,4,5 & 6; d = species present in quadrate 1 but absent in quadrate 2, 4, 5 & 6; e = species present in quadrate 1 but absent in quadrate 1, 2, 3, 4 & 6; f = species present in quadrate 1 but absent in quadrant 1, 2, 3, 4 & 6 and = species present in quadrate 6 but absent in quadrate 1, 2, 3, 4 & 5. The coefficient has a value from '0' to '1', where '1' reveals complete similarity and '0' complete dissimilarity.

Data Management and Analysis
Collected data were entered into MS Excel spreadsheet (Excel 2007) for clearance of data. Descriptive statistics and percentage were analyzed using Excel spread sheet and Statististical Program for Social Sciences (SPSS) Version-20 software. Chi-square was used to identify the level of significances between dependent and independent variables. Mean and standard deviation were used to analysis the wild radish and other weed species structure and distribution performance of the mentioned weed species. In all cases, the 95% confidence interval and the 5% level of significances can be used to declare the significant difference. The correlation of vegetation variables such as species composition, species richness, average R. raphanistrium density/sample, and average number of flower head/plant among sample sites were done to check if there is any association among and between sample sites.

Household Characteristics and demography
The householders' education level, Age and sex, family size and household characteristics are indicated in Table  1. The householders' education level, Age and sex, family size and household characteristics are indicated in table 1. It depicted 78.2% of the respondents had formal education; out of which 48% attended elementary education (1-4), 19.4% attended Junior Secondary School (5-8), 7.5% attended high school (9-12) and 2.5% were TVET graduates. In the current study, 95.63% of the family leaders were male while 4.37% household heads were females. This study also indicated the mean family size was found 6.46 person/households. Even though the households in the study area were mainly male headed, women play a significant role in weed management than their men counterparts. Very small numbers of young male households (< 40 years age) participate in weed management, which might be because, as socio-cultural norms of the rural community weed management is the farm activity expected from females and farming with an oxen or plougishing is the activity assigned for young men households. Farm households whose age above 70 years are on retirement from major agricultural activities except participating on supervision of farming activities and rendering guidance for the family members. Data obtained from the survey reviled that among 160 respondents 156 (97.5%) were married and four (2.5%) were widowed/divorced. Crop production only 0 0 Crop and Animal production (mixed) 160 100

Crop production and weed management practices in the study area
In the study area farmers' practices hand weeding, slashing and herbicide application for weed management. During field survey, some of crop fields were infested with different weed species (broad leaved and grassy weed species). The infested crop fields were crops of those elder people and poor families, which were in shortage of labor and resources. Most of the young peoples' that are at the active stage of production were migrated to nearby towns for search of high-level education and jobs. Due to these shortage of man power, older men and women including under aged children's were responsible for managing cultivated crops and live stock herding. Among 160 sampled respondents 123 (76.87%) of them used chemical herbicides for weed control.

Wild Radish Introduction to Horro Guduru Wollega zone (HGWz) and its Distribution
For the emergence of wild radish, the elders in the study area and the zone Agriculture and Natural Resource Office senior experts told two ideas. Information obtained from HGWz Agriculture and Natural Resource Office senior experts indicates that the introduction of wild radish for the first time observed in Horro district at Doyo Bariso kebele on experimental plot lands of Agricultural Research Station (1.25ha) which was owned by Bako Agricultural Research Center (BARC) since 1979. During farmers' field day, farmers who visit the field experiments on the station observe R. raphanistrum as ornamental plant and interested with the colors of the plant (yellow and white color) and they took the seed and seedlings to their home garden as an ornamental plant. After a few years, these peoples recognized it as this plant is dangerous weed plant rather than ornamental one. Another idea we come over for the introduction of R. raphanistrum was that this weed plant was introduced with infested cereal grains used for seed purposes. Interviewed two elder farmers who are residents of Doyo Bariso kebele mentioned that "the introduction of R. raphanistrum in to the locality was through cereal grain seeds introduced from other places (personal communication with Ato Shumbash Tesgera and Bayana Gabawa). The two elder men introduced wild radish unknowingly since 1986 with cereal grain seeds from their relatives. According to these two elders, suspicion for the introduction of this plant was by the owner of the research station, BARC, who brought different cereal grain seeds for experimental purposes during its stay at Doyo Bariso. The second idea for the introduction of R. raphanistrum was food aid grains introduction to their area during the 1990 drought and starvation, which was the case for the death of thousands and hunger for millions of the people in Ethiopia including HGWz the zone. Even though these two ideas were raised from different corners, there was no tangible information and responsible bodies for the introduction of wild radish, R. raphanistrum into the study area including the year of introduction.

Farmers knowledge on emergence and distribution of Wild Radish (R. raphanistrum)
Respondents' knowledge on emergence and distribution of wild radish (R. raphanistrum) in the study areas is depicted in (Table 2). According to the information obtained from the respondents, prior to 1979, the study area was free from R. raphanistrum infestation. Data obtained from the survey shows that most of field crops grown in the study area were infested by different common weed species including R. raphanistrum. The knowledge of the respondents on R. raphanistrum infestation on their farmland and homestead was tested whether their farmland and homestead is infested or not by this invasive weed. Data obtained from respondents' shows that out of the sampled 160 farmers 88 (55%) of them know R. raphanistrum as a weed on their farmland and homestead. The rest of 72 (45%) of respondents did not know this plant as a weed in their area and administrative kebeles'. Only respondents nearby Horro district and the near-by infested kebeles' have some information about the emergence of this invasive weed. From the sampled respondents 92 (57.5%) of them gave their idea as they know when did the R. raphanistrum infest their locality and 68 (42.5%) respondents do not know when did R. raphanistrum infest their locality.

Extent of wild radish (R. raphanistrum) distribution, dispersal mechanisms, impacts and management methods employed
The extent of wild radish (R. raphanistrum) distribution, dispersal mechanisms, impacts and management methods employed by the sampled respondents are indicated in Table 3. According the results of data collected 50% of the respondents who are aware gave their idea, the wild radish extent of distribution in their area was high. The respondents declare grain seeds, food aid, animas, floods, farm implements and vehicles are mechanisms of weed seed dispersal in which grain seed in the form of seed accounts 51.87%. They recognize the impact of R. raphanistrum on crop stand, soil fertility and biodiversity but they were not aware of its allelopathic effects on the crops. Only 8.75% of the respondents aware about the allelochemical produced by wild radish that has a phytotoxic effect, which suppress the growth of the neighbor plants. This idea goes in line with the idea of (Singh 2009). Among the respondents, 84.4% of them were not aware of the wild radish impact causing the milk bitter. The result of this study indicates that the issue is an urgent task to draw attention of responsible bodies and communities in general for managing and preventing further dissemination of this weed within the zone as well as in the country. The high infestation level and distribution of Wild radish, R. raphanistrum in HGWz of sampled areas are shown in Figure 2, 3, 4 and 5.

Common weed species ranked first by respondents
The results of ranking common weed species and farmers' perception is depicted in Table 6. Among the respondents 89 (55.6%) of them ranked R. raphanistrum as a first dangerous weed because of its high spread and fast invasion in the field crops, along roadsides and along the margin of farmland. Digitaria sp ('serdo' or 'ye engicha sar') a common grassy weed in the study area ranked first by 25 (15.6%), Bidense pachyloma (Adey abeba) ranked as first by 11(6.9%) of the respondents, Bidense pilosa (Chegogit or ye seytan merfee) ranked as first by 10 (6.3%), Guizotia sp ranked as first by 9(5.6%) and Cyperus sp ranked as first by 16 (10%) of the respondents because it is well known distributed weeds in their surroundings with negative effects on native plants and crop yield. Those respondents who did not know R. raphanistrum weed and ranked the other weed species as first were mainly from Administrative kebeles of Jima Rare and Amuru district which were lately infested by R. raphanistrum. Moreover, the farmers from Jima Rare and Amuru emphasized mainly on Bidense pachyloma and Cyprus sp, which is problematic weed in their field crop and home garden. The respondents who were unaware of R. raphanistrum (44.4% of the respondents) also explained that the R. raphanistrum weed has neither an impact nor negative effect on the growth and development of field crops and different plant species that have either economical or medicinal values (Table 6). In the open field these weed species have various economical values as feed for animals. The respondents explained that the diversity and population stand of these weed plant species were impacted by R. raphanistrum have been decreasing from time to time in the previous infested area.
According to the farmers and agricultural experts" observation, the plant species in their surrounding that outcompete R. raphanistrium for long period of time are mainly Bidense sp, Cyprus sp, Guizotia sp, Argemone Mexicana, Euphorbia pulcherima and Bidense pilosa were some of the mentioned weed species. According to the majority of the respondents, the parasitic weed Cuscuta campestris (Yenug anbessa) is one of the most important weed considered as a 'silent killer' that reduces the annual production of Noug/Niger seed in the study area.

Vegetation data associated with wild radish and land use type
The vegetation data associated with R. raphanistrum with different invasion levels and the respective land-use type in 144 different sample sites are presented in Table 7. As it can be seen from the table that 18 (12.5%) samples sites were taken from each Administrative kebele of Horro, Abayi Chomen, Jima Rare and Amuru districts. The status of R. raphanistrum infestation were very high in Gudina Abuna & Doyo Bariso kebeles of Horro district and high in Homi & Jare kebeles of Abayi Chomen district. The infestation of R. raphanistrum in Gudina Abuna, Doyo Bariso, Homi, and Jare Administrative kebeles were observed in arable land, grazing land, roadsides and wasteland while in the rest of the four kebeles of Jima Rare and Amuru districts the R. raphanistrium infestation were only observed in arable land specially in the fields of cereal crops. J/Rare = Jima Rare; S/Gamachisa = Sochosa Gamachis; I/Ilamu = Ibsa Ilamu; W/Bera = Wara Bera '*' Level of infestation based on R. raphanistrium infestation: Low (10-25%); Moderate (26-50%); High (51-75%); Very high (>75%) of the total percent of area coverage by R. raphanistrium

Cumulative and mean number of native and wild radish by vegetation type
Mean wild radish per quadrate is high in field pea field followed by wheat, which was 38.4 and 36.5 quadrate -1 ( Table 8). The list mean per plot was in the fields of 'teff' which accounts 30.6 quadrate -1 . 'Teff' filed is prepared to make smooth which make favorable condition for 'teff' seed for easy germination. This shallow, smooth and ramped seedbed suppresses the germination of wild radish found under the depth soil but weed seed found on top of the soil can germinate easily.
Among the common few weed species recorded during the survey were: R. raphanistrum, Bidense pachyloma (Adey abeba), Bidense pilosa (Chegogit seytan merfee), Andropogon abyssinicus ( The biodiversity impact of R. raphanistrium weed on highly infested areas was more visible than the moderate and low infested areas. The sampled sites in Horro district starting from Doyo Bariso to Gudinna Abuna (Sakala and Dimbe area) have lower diversity index (H) (highly infested area) as compared to other sites where the calculated Shannon Diversity Index is high (where invasion was low) (Table 9). Horro and Abayi Chomen showed the lowest Shannon Diversity Index value of 1.78 and 2.12 respectively due to the fact that, their species diversity was highly affected by the high infestation of R. raphanistrium. Comparatively, the Sochosa Gamachisa, Ibsa Ilamu, Makano and Wara Bera administrative kebeles have a diversity Index of greater than 4.0 showing low R. raphanistrium infestation in the area and the its impact on species diversity is low. This is because of the early infestation of the two sample districts of the study area.
Similarly, the evenness index was found to be higher in un infested areas which indicated that the species are evenly distributed. This is true in this present study sites such as Sochosa Gamachisa, Ibsa Ilamu, Makano and Wara Bera administrative kebeles, where the evenness index were above 4.12 which shows the sampled area were less infested by R. raphanistrium. In contrast, the fact that it was lesser in the R. raphanistrium infestation, the area indicated patchiness in distribution, which shows a few species dominate the area. This study showed that in the study areas of R. raphanistrium infested sites the numbers of desirable weed plant species were highly declined. Such a reduction could be attributed to the increasing abundance of the R. raphanistrium in the sites. The result of this study goes in line with the study of Kohli et al. (2004) and Sakai et al. (2001) where invasive plants are known to exert significant impact on the natural communities as they cause their displacement and hence bear imbalance in the natural and agricultural ecosystem. This imbalance causes the formation of large monoculture of invasive plants in the alien environment. The weed affects not only the species diversity of the native areas, but also their ecological integrity. Moreover, environmental degradation and disturbance favors the invader species such as R. raphanistrium weed. Under such circumstances, the weeds easily establish themselves in the sites and start interfering with other native species by suppressing their potential growth and biomass production. R. raphanistrium was known to suppress the associated species through the release of allelochemicals from decomposing biomass and root exudates into the soil environment (Norsworthy 2003;Malik 2009).
There is a high negative correlation between mean R. raphanistrium density and Shannon diversity index with R 2 = 0.642, p<0.001. The equation for the regression line is y = 38.53-1.959 (Figure 6). High negative correlation means that as the mean R. raphanistrium density increases, the Shannon Diversity Index decreases. This in turn shows the R. raphanistrium effect on the biodiversity of plants.

Jaccards Similarity Coefficients (JSC) of Herbaceous Vegetation
The Jaccards Similarity Coefficients of standing herbaceous vegetation associated with R. raphanistrium at 8 sampled Administrative kebeles' of 144 sites and 864 quadrates is depicted in Table 10. This coefficient of similarity has values from '0 to 1', where '1' reveals complete similarity and '0' complete dissimilarity. Thus, the standing herbaceous vegetation from the sampled sites of the Doyo Bariso and Gudina Abuna administrative kebeles showed higher Jaccards Similarity coefficient (greater or equal to 0.84), where there was high R. raphanistrium infestation level. This was due to the complete dominance of R. raphanistrium weed over other herbaceous plant species of the study area.
The high similarity value between R. raphanistrium invaded areas of Doyo Bariso and Gudina Abuna administrative kebeles indicated that there is no radical change on species composition within the area. In contrast, other kebeles from Jima Rare (Sochosa Gamachisa and Ibsa Ilamu kebeles') and Amuru (Makano and Wara Bera kebeles') districts showed relatively lower similarity coefficient than administrative kebeles from Doyo Bariso and Gudina Abuna revealing low impact of the wild radish weed in the area.

Comparison and correlation of mean R. raphanistrium density
The study of R. raphanistrium mean density and species richness in eight PAs, is shown in Table 10. Jare has the first highest mean R. raphanistrium density, which accounts 62.7 m -2 but with relatively low species richness. Gudina Abuna and Doyo Bariso accounts the second highest mean R. raphanistrium density, which is 60.9 and 60.7 m-2 with the species richness value of 34 and Homi, accounts the fourth highest with its mean 54.7 m -2 R. raphanistrium density comprising species richness of 35. In general, the result from the table shows that there was a trend of decrease of species richness as the mean R. raphanistrium density is increasing in the study sites. This is particularly true in Horro (Doyo Bariso and Gudina Abuna kebeles) and Abayi Choman district (Homi and Jare kebeles), and in areas where the distribution of R. raphanistrium weed is highest, respectively, as compared to other study sites. In contrast, species richness increases as mean R. raphanistrium density decreases as in the case of sample sites such as Wara Bera, Makano, Ibsa Ilamu and Sochosa Gamachisa kebeles'. This definitely shows the impact of R. raphanistrium weed on species diversity and hence in species richness of the study area.

Mean of Wild Radish height, branches and flower head mean number per plant
The mean of R. raphanistrium height, number of branches and number of flower heads counted in three different times (at the beginning of June, July, September and October) in eight Administrative kebeles'under 144 sample sites are shown in Table 13. From the table, the highest mean height (0.96m) of Raphanus was recorded in Jare kebele. The specific localities where this height recorded were along the way to Fincha town. The average number of branches counted in the same localities was 44 followed by Doyo Bariso where number of branches per plant was 42 with an average height of 0.88m. Generally, the findings of this research shows a decreasing trend of mean height, number of branches, and flower head plant -1 from Jare to Mekano kebele (that is, from sample sites along the way from Abayi Chomen, Horo, Jima Rare to Amuru district). The mean number of wild radish flower head counted per plant showed a considerable increase from June, July to October particularly in highly infested areas, especially Shambu town surrounding W.U. Shambu campus, Doyo Bariso and Gudina Abuna sites of Horo district and Homi and Jare site of Abay Chomen district. The increased number of flower head/plant counted in September may be because of optimum rain that the area has got during the time of data collection. From this study, it was found that the average number of flower heads plant -1 counted in September and October was greater than that of the remaining two rounds for all the sites in the Doyo Bariso and Gudina Abuna sites, where the level of infestation was higher. In comparison, Jare kebele has the highest average number of flower heads counted plant -1 was 1234 in two rounds followed by Doyo Bariso, which was counted 1216 flower heads plant -1 (Table 13). The average numbers of flower heads counted for the sample sites of Ibsa Ilamu and Sochosa Gamachisa of Jima Rare district and Makano of Amuru districts are very low as its level of infestation was lower due to its late emergence of this weed into these localities. 3.14. The competitive ability of plant species Even though the experiment on the competitive ability of plants was not done in this present study, it is feasible to list down plant species that frequently occurred in the sampled sites of infested areas tolerating the ill effects of R. raphanistrium. Thus, the plant species that can tolerate the effect of R. raphanistrium weed have the highest relative frequency indicating its frequent occurrence in both highly infested and low infested areas (Table 14). Even though their abundance varies, the occurrence of R. raphanistrium weed was 456 (79.2%) out of 576 sampled quadrates. Accordingly, Cyprus sp was the second frequently occurred plant species with the relative frequency of 70.8% in the mentioned study area and thirdly Digitaria sp which occurred in 70.3% out of sampled sites. 2 This is so because R. raphanistrium, Ageratum conyzoides and also Euphorbia sp. are tropical in origin and they possess similar growth strategies. They grow fast, deep rooted that help the plant to extract minerals and water in the sub soil and they have greater reproductive potential, competitive ability, and allelopathy that make them successful invaders of non native habitat (Grice, 2006). Due to its high growth rate, R. raphanistrium becomes competitive and develops the ability to exclude the growth of other species (Table 15). 19.09 60.37 N.B. '*'Weed sample collection and population density counting was done in 2016 in the months of July, August, September, October, November and December and '+' September, October, November and December.

Severity status of R. raphanistrum in common field crops host plants
In all the study area cereals, legumes and horticultural crops were observed as major host plants for R. raphanistrum (Table 16). It occurs in most of field crops and horticultural crops within geographical range of the study sites. This study is in line with the study of Holm et al. (1997) which stated that R. raphanistrum is a major weed of cereals, especially wheat, particularly winter-sown wheat. It is also common in a number of field crops like maize, tef, barley, , legumes crops, horticultural crops, pastures and fodder crops. It is likely to occur in any crop within its geographical range.

Wild Radish Management Practices exercised by growers' indigenous knowledge
Not only for R. raphanistrum, for all weed management 87% of the respondents responds practicing of winter soil cultivation starting from the month of February until seed sowing. The rest 9% practice mechanical destruction and 4% practice hand weeding. After crop emergence growers uses different measures of weed management including R. raphanistrum. Among them chemical control, hand weeding and slashing (mechanical destruction) is the commonly practiced methods. Among the respondents 47% of them responded the application of herbicide (2, 4-D), 42% responded hand weeding and 11% responded slashing. As long as the management is concerned, hundred percent of the respondents who knew the weed before this study only mentioned hand hoeing/hand pulling/uprooting and burning of wild radish weed in its early period before it sets flowers.

Associations of Biological Control Agents (Pathogen and Insect) with Raphanus raphanistrum
During field surveys un identified potentially pathogenic fungi was found from naturally infected R. raphanistrum in field conditions from the seedling stage up to plant maturity in the districts Horo (Doyo Bariso kebele) and Abayi Chomen (Homi kebele) (Figure 7). It was the first pathogen to produce disease symptoms on R. raphanistrum, occurred in winter. During field survey, it was not observed on neighboring edible brassicaceae plants, which in the future invites for in-depth study. White pustules of sporangia of this oomycete were generally located on the leaves and stems and occasionally on the inflorescences and pods of R. raphanistrum. Erysiphe cruciferarum and other pathogenic fungi caused severe infections on the vegetative and reproductive parts of wild radish plants (Naceur et al., 2009;Ravi et al., 2014). Symptoms first appeared as circular to irregular white patches on both sides of the leaves, and on stems and pods, often thinly covering the whole surface.

Insects as Biological Control Agents
Aphid species (white aphids) and ladybird beetles (green ladybird beetles) make associations with R. raphanistrum. Wild radish plant fed by this aphid was stunted in growth and physiological stand and leaf development was seen reduced. Its secretion of honeydew causes white sooty mildew to grow on the plant, thus further reducing the photosynthetic area of the host plant. Even though wild radish is affected by aphid and powdery mildew the host spasticity of these two agents needs further research whether they are host specific or not.

Discussion
The study showed that heavy and widespread infestation of R. raphanistrum, mostly on farmlands, field crop borders, roadsides, grazing and fallow lands of Horo and Abayi Chomen districts of Horo Guguru Wollega zone (HGWz). R. raphanistrum grows and develops very well in fallow lands of farm fields. During field travel of the survey R. raphanistrum has been observed in the field crops of Guduru, Jima Geneti and Jardega Jarte districts of HGWz, along the roadsides and near dwelling sites. The R. raphanistrum infestation was also observed on some fields and road sides of west Showa zone of Chelia District in the farm fields of wheat, barley and ''teff'' and around Gedo town. This report is in agreement with the finding of Holm et al. (1991) who reported the initial occurrence of R. raphanistrum in Ethiopia at 'Say Ager' area. The result of this study indicated that the exchange of grain seeds within administrative kebeles' and districts, and the foothold weed seeds by animals' and human activities aided the weed dispersal extensively into adjacent agricultural lands and neighbor districts.
From the result of the study it was found that 89(55.6%) of the interviewed farmers rank R. raphanistrum as the first and most serious weed in rangelands and croplands. Similarly, from the respondents of this present study R. raphanistrum has a great impact on crop plant species as mentioned previously in the result. Very little or sometimes no other vegetation were seen in R. raphanistrum dominated areas of Doyo bariso, Gudina and Abuna of Horo district, and Achane and Jare of Abayi Chomen district. Warwick and Francis (2005) who reported that, because of its efficient biological activity and adaptability to varying soils and microenvironments, evidence this, R. raphanistrum weed has a tendency to replace the dominant flora in wide range of habitats cutting across zonal boundaries and agro-climatic conditions. The field observation during our survey shows that wherever it invades, it forms a territory of its own by replacing the indigenous natural flora including pasture grasses. The study conducted by Norsworthy (2003), Malik (2009) and Singh (209) indicated that the R. raphanistrum allelopathic properties through the release of allelochemicals, which cause inhibition of germination and suppression of natural vegetation and associated plant species including the cereal crops and medicinal herbs, pose a strong threat to biodiversity. Respondents of the study area explained their idea as they did not recognize the impact posed by wild radish but heard about the impact of the R. raphanistrum on crop and grazing land, seed grain market, milk quality and biodiversity.
This present study revealed that there was a sharp decline of herbaceous plant diversity index as the density of R. raphanistrum increased. This reality can be observed from ' Figure 2 and 3', which shows the existing field reality, how the local herbaceous species are being replaced by wild radish, R. raphanistrum. The result of this study is similar with Burns et al. (2013) and Lesley et al. (2014) findings where the Shannon index shows greater plant diversity in un infested area, whereas the index was reduced by 36 to 51% in the R. raphanistrum infested areas. Therefore, the higher value of the diversity index indicates the variation in the type of species and the heterogeneity in the community, whereas the lesser value points indicates the homogeneity in the community. In areas of high R. raphanistrum infestation, there was also a high mean R. raphanistrum density per m 2 as described in Figure 5. This is probably due to high viability of the R. raphanistrum seed banks in soil. Thus R. raphanistrum density per m 2 is often increasing in every generation, unless intervention is taken to control its distribution and invading un infested areas. This is because R. raphanistrum is capable of emerging and producing seeds during most of the year (Singh 2009).
This present study identified that the mean number of native weed plants and R. raphanistrum by vegetation type in the sampled filed crop quadrate -1 were 41.3 and 26.3, respectively. The minimum and maximum-recorded mean number of native weed plants and R. raphanistrum was 20.9 -61.8 and 19.2 -53.7, respectively. This finding shows that how the newly emerging weed plant, R. raphanistrum hardly replacing the native weed species. This a b study goes in line with the finding reported by Cheam & Code (1998). The number of flower head capitula -1 for this present study is much higher where a single plant producing an average of 1056.6 flower heads. This might be because of the fact that the season for data collection was more suitable for R. raphanistrum growth and development. In this present study, germination usually occurs after the 1 st rain of March, but continuous new flushes occur throughout the year after rain. Roberts and Boddrell (1983) reported that in Australia germination usually occurs after autumn rains, but "flushes" of germination occur throughout the year after rain. In the UK the peak period of germination is in March and April, but seedlings continue to appear until late autumn. R. raphanistrum flowering occurs from late July (4-12 weeks after emergence) and can continue for 12-42 weeks (Lee & Snow 1998;Malik, 2009). Moreover, the above data showed certain similarity with the study done in South Carolina by (Singh, 2009). He described that the inflorescence bearing flowers started appearing in late July or early August. The flowering stage in some plants lasted until November and then seed setting started. In the present study, the rainy season (July, August and September), some new seedlings emerged and they flowered in September and lasts up to November. In October, the seed setting was observed in most of the plants. The seeds fully ripened in the month of November and December or it completed its life cycle by that time.
The plant species that were identified from this present study which have R. raphanistrum competitive ability for long period are mainly Bidense sp, Cyprus sp, Guizotia sp, Argemone Mexicana, Euphorbia pulcherima and Bidense pilosa were some of the mentioned weed species. Due to its high growth rate and its adaptability, R. raphanistrum becomes competitive species and it develops the ability to colonize and exclude the growth of other species affecting the biodiversity of the study area. R. raphanistrium endanger the native biodiversity by choking and deliberate takeover of the native plants in Horo and Abayi Chomen districts, which goes in line with the finding of Holm et al. (1997), Warwick and Francis (2005), Wilson et al. (2009) and Barnaud et al. (2013). Majority of the respondents were not aware of about the allelopathic chemical produced by R. raphanistrum that has a phytotoxic effect on neighboring plants, which suppress the growth of the neighbor plants. The inhibitory allelopathic effect of R. raphanistrum associated with the production of glucosinolates (GSLs) on the germination and seedling development of plants was previously studied by (Norsworthy 2003;Singh 2009).
Moreover, during data collection un identified naturally occurring fungi pathogenic found attacking both the vegetative and the reproductive parts of the wild radish, R. raphanistrum. This finding goes in line with the result stated by Ravi, et al. (2014) who reported that in Ethiopia at Horo Guduru Wollega zone of Oromia Regional state R. raphanistrum was found infected by naturally occurring fungi pathogenic Erysiphe cruciferarum, which was for the first report in Ethiopia. The same study by Naceur et al. (2009) mentioned that in Tunisia fungus isolation from the foliar tissues exhibiting disease symptoms showed that R. raphanistrum was infected with the fungi Erysiphe cruciferarum, Albugo candida, Alternaria spp. including A. brassicicola, and A. raphani, Stemphylium herbarum, Peronospora parasitica and Phoma lingam. Ascochyta spp., Cercospora armoraciae, Cladosporium cladosporioides and Colletotrichum higginsianum are here reported from R. raphanistrum for the first time. In addition to this un identified green Coleoptera was found attacking R. raphanistrum in the study areas of Horo district that warrant assessment for use in classical biological control. Foliar pathogenic fungi and insect biological control have a potential in the integrated weed management of R. raphanistrum, these two role merits further investigations Naceur et al. (2009).
For restricting the entrance of R. raphanistrum seed into a non-infested area, avoiding buying grain seeds from infested area and sowing clean seeds, avoiding exchange of hay and crop straw from R. raphanistrum infested areas and quarantining stock that have recently been in infested areas are vital for reducing R. raphanistrum spread. In R. raphanistrum infested areas to minimize the population of the latter emerging weed seedlings, shallow cultivation following early coming rains will increase seedling emergence. Cultural control practices including uprooting of the weed before flowering and seed setting must normally be combined with chemical treatments to ensure effective control of this weed. R. raphanistrum is capable of emerging and producing seeds during most of the year, and season-long control measures should be adopted to prevent seed production and replenishment of the R. raphanistrum soil seed bank.
For restricting the entrance of R. raphanistrum seed into a non-infested area, avoiding buying grain seeds from infested area and sowing clean seeds, avoiding exchange of hay and crop straw from R. raphanistrum infested areas and quarantining stock that have recently been in infested areas are vital for reducing R. raphanistrum spread. In R. raphanistrum infested areas to minimize the population of the latter emerging weed seedlings, shallow cultivation following early coming rains will increase seedling emergence. Cultural control practices including uprooting of the weed before flowering and seed setting must normally be combined with chemical treatments to ensure effective control of this weed. R. raphanistrum is capable of emerging and producing seeds during most of the year, and season-long control measures should be adopted to prevent seed production and replenishment of the R. raphanistrum soil seed bank.

Conclusions
In conclusion, the prevalence and rapid colonization potential of R. raphanistrum over long distances facilitate its rapid spread within the zone and neighbor zone. An important consideration would be thus; since this species is already widely distributed throughout Horo Guduru Wollega zone, locally occurring in high densities our understanding of the colonization dynamics of R. raphanistrum invasions can have a direct impact on crop yield and biodiversity of the study area as well as impact on the region and the nation. It is also a prolific seed producer and can cause yield losses if not controlled in a timely manner. Furthermore, our study demonstrated the influence of R. raphanistrum colonization and pathway of this weed invasion. Indeed, until now the biological and anthropogenic invasions have received far less attention compared to ecological processes. Large numbers of the respondents were not aware of the nature and impacts of this invasive weed on the biodiversity and microenvironment. Our knowledge on R. raphanistrum invasion nature can greatly benefited from the recent study in developing and advising management strategies of this invasive weed for the communities and concerned government institutions based on geographical and environmental features at both the population and individual level.
Given the opportunity to address problems of invasive alien plant species (IAPS), the priority must be to create public awareness and action through disseminating the information on risky species. As concern and awareness of IAPS problems, including R. raphanistrum, grows in the study area, the initial action often taken should be containing R. raphanistrum to prevent its dissemination in to un infested area. The survey should include checking the presence and severity of other invasive weed species problems. In infested areas, an accurate assessment of the target weed plant (R. raphanistrum) infestation will help to contain and preserve the neighboring un infested land and enhances the success of future large-scale control programs. Preventing encroachment into the land that is not infested, detecting, and eradicating new weed introductions, containing large-scale infestations using an integrated approach will help in managing this newly emerging invasive weed.
Weed control should focus only not on croplands, but focus on fallow lands, roadsides, rangelands and waste sites with an understory of residual weed plants. Suppressed weeds have the greatest chance of reestablishing dominance on these sites. These areas must be spot treated each year to ensure control and minimize reinvasion of the emerging invasive weed species. In these cases, some of the weed management unit will require control measures that are repeatedly applied until the weed seed bank and root reserves are exhausted. Control methods used must be based on the biology of the weed. When doing so, the next control efforts should focus on the sites adjacent to those initially treated to minimize reintroduction of the weeds.