Ok Jae Won

A Survey of Weeds Occurrence on Paddy Fields in Chungnam Province in Korea

우리나라 농경지에 발생하는 잡초는 1972년 한국산잡초 목록(국립농업자재연구소)이 발간됨으로써 453종이 처음 으로 알려졌다(Lee et al., 2012). ‘논잡초 발생 양상에 관 한 연구’는 1971년에 처음으로 농촌진흥청 작물시험장 주 관으로 실시되었으며, 그 후 10년 주기로 현재까지 총 네 번의 조사가 이루어졌다(Kim, 1983; Park et al., 1995; Park et al., 2001; Park et al., 2002). 네 번에 걸친 논 잡초 발 생조사에서 우점 잡초의 순위에 많은 변화가 있었고, 경 지 이용형태의 변화, 토지 기반정비에 의한 입지조건의 변 화, 경종법, 재배관리, 특히 경운정지나 잡초 방제법의 변 화 등이 농경지에서 발생하는 잡초군락 천이의 주요 요인 으로 작용한 것으로 나타났다(Kim et al., 2012). 손제초에 의존하던 1970년대의 발생잡초의 비율을 보면 화본과 12%, 광엽잡초 50%, 방동사니과 19%, 기타 19% 등으로 나타났으며, 일년생과 다년생 잡초의 분포 비율이 7:3으로 일년생 잡초의 분포 비율이 높았고, 마디꽃, 쇠털 골, 물달개비, 알방동사니, 피, 밭뚝외풀, 가래, 사마귀풀, 올방개 순으로 우점하는 것으로 조사되었다. 뷰타클로르 입제와 같은 일년생 잡초 방제용 제초제의 사용이 증가된 1981년에는 화본과 7.4%, 광엽잡초 66.7%, 방동사니과 ABSTRACT. The survey of weed occurrence was conducted to identify problem weed species in the paddy field. The 320 sites of the 13 regions in Gyeongbuk Province were investigated from June to July, 2013. In the whole region, 51 weed species were identified including 34 annuals and 17 perennials. The highest importance value of annual weed and perennial was dominant 88.4 and 48.7%, in Gumi region, respectively. The most dominant weed species in paddy fields of Gyeongbuk Province were Monochoria vaginalis var. plantaginea (10.80%), followed by Lemna paucicostata (10.74%), Bidens tripartite (8.77%), Echinochloa oryzoides (7.17%), and Scirpus juncoides (6.20%). The similarity of paddy weeds in 13 regions observed through TWINSPAN analysis was distinguished by Ludwigia prostrata, Scirpus juncoides, Lindernia dubia, Polygonum aviculare, and Alopecurus aequalis var. amurensis. The weed species, Ludwigia prostrata, was divided into the four regions, Gyeongju, Gumi(direct seeding cultivation), Youngcheon and Euiseong and ten regions, Gumi, Bonghwa, Sanju, Goryung, Youngdeog, Pohang, Sanju, Andong, Yecheon, and Cheongdo.

Herbicidal Effects and Crop Selectivity of Sorgoleone, a Sorghum Root Exudate under Greenhouse and Field Conditions

Weeds are known to cause enormous losses due to their interference in agro ecosystems. Because of environmental and human health concerns, worldwide efforts are being made to reduce the heavy reliance on synthetic herbicides that are used to control weeds. In this regard phytotoxicity of allelochemical sorgoleone, which is a major component of the hydrophobic root exudates of Sorghum bicolor was evaluated in different weed species and also its crop selectivity in greenhouse and field conditions. Sorgoleone strongly inhibited the growth of different weeds by pre-emergence and post-emergence applications both in greenhouse and field conditions. Post-emergence application of sorgoleone on 21-day-old weed seedlings had a greater inhibitory effect than the pre-emergence application. Again, broadleaf weed species were more susceptible than grass species to the application of sorgoleone at both stages of growth. Growth of broadleaf weed species was suppressed by greater than 80% for most of the weed species except a few species and among them the species Rumex japonicus and Galium spurium were completely suppressed at 200㎍ mL -1 sorgoleone. Like greenhouse trial, sorgoleone was more effective for broadleaf weed species followed by sedge and grass weed species in the field condition. The growth inhibition of weeds was slightly lower in field condition compared to greenhouse condition. The crop species like rice, barley, wheat, corn, perilla, tomato, soybean and Chinese cabbage were tolerant to sorgoleone while lettuce and cucumber were slightly susceptible to sorgoleone. Consequently, sorgoleone may be applied to control weeds in organic farms without affecting the growth of crop.

Identification of Herbicide-Resistant Barnyardgrass (Echinochloa crus-galli var. crus-galli) Biotypes in Korea

The continuous use of acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors has led to the selection of herbicide resistant barnyardgrass populations in direct-seeded rice fields of Korea. This study was conducted to identify herbicide resistant barnyardgrass biotypes and to determine the cross- and multiple-resistance of them. 25% of the population collected from Taeahn was partially resistant to ACCase inhibitors and 22% collected from Kimjae were partially resistant to ALS inhibitors. However, 8.2% of the population from both sites was resistant to ALS and ACCase inhibitors. Resistance to sulfonylurea herbicide, flazasulfuron was identified from two barnyardgrass accessions collected from both Taeahn and Kimjae. One barnyardgrass accession from both sites was resistant to ACCase inhibitor, sethoxydim. The cross-resistance to ALS inhibitors was identified at one barnyardgrass accession from Taeahn and at two accessions from Kimjae. Further, crossresistance to ACCase inhibitors was also identified at barnyardgrass accessions from Taeahn and Kimjae. Multiple-resistance to flazasulfuron and sethoxydim was determined at four barnyardgrass accessions from Taeahn and at six accessions from Kimjae. Therefore, the herbicide mixture and sequences within a growing season or the herbicide rotation with different modes of actions across growing seasons are recommended to control herbicide-resistant barnyardgrass in infested fields.

Weed Flora and Management Practices in Peach Orchard Fields in Korea

In Korea, fruit represents one of the main categories of economic crops. The country’s fruit tree planted area was 155,000 ha in 2005, which is seven times larger than the acreage of orchards in 1955 (Ha and Chung, 2012). In particular, the area planted with peach trees has increased by around 3%, from 13,908 ha in 2011 to 14,210 ha in 2012. The yield of peaches ranked forefront in all fruits (Hong et al., 2012). In the face of the progressive increase in peach tree area, a series of problems have emerged in peach orchards, such as labor shortages, lagging product sales, and insufficient use of science-based management technologies. For these reasons, weed management methods are especially worthy of further study through surveys of weed flora. Weed flora is a common component of orchard ecosystems. On the one hand, an abundance of weed species can increase population diversity in orchards. A previous survey of weeds was carried out in the Chungnam region; its results showed that 75 weed species belonging to 26 families were identified in orchard fields and that Echinochloa crus-galli was the most dominant of the weed species with high densities (Choi et al., 2009a). Additionally, Park et al. (2005) reported that weed ranking in orchards according to dominance had changed compared to that reported a decade ago. On the other hand, weeds bring about some serious adverse effects for peach trees. These negative impacts are mainly divided into environmental and biotic effects. Environmental effects can mean competition for light, water, and nutrients between weeds and peach trees (MacRae et al., 2007). Peach tree yields, rootstock, and leaves are affected by weed competition (Tworkoski and Glenn, 2001). In contrast, the term ‘biotic effects’ can imply that weed species are known favorable hosts ABSTRACT. This study was carried out two surveys in 2015 to monitor weed occurrence and determine the most troublesome weeds in peach orchards of Korea. The first survey identified 56 taxa belonging to 23 families including 27 annuals, 11 biennials, and 18 perennials. Based on importance values, Conyza canadensis (5.12%), Plantago asiatica (4.17%), and Trifolium repens (3.86%) were the dominant weeds in the first survey (from April to June). Seventeen exotic weeds were identified in the first survey, including Conyza canadensis, Trifolium repens, and Chenopodium ficifolium. The second survey (from September to October) identified 42 weeds belonging to 19 families including 23 annuals, 5 biennials, and 14 perennials. According to importance values, Digitaria ciliaris (8.00%) was the most dominant weed, followed by Echinochloa utilis (6.61%) and Rorippa palustris (6.48%). There were 12 exotic weeds, including Taraxacum officinale, Rumex crispus, and Trifolium repens. Additionally, according to Braun-Blanquet’s scale showed that the dominance value was level 1 (41.98% and 46.43%, respectively) in two surveys. Currently, 40% of the total surveyed peach orchards applied herbicides for weed control. These results could provide basic data to assist orchardists in selecting the most suitable weed management methods; thereby, reducing labor inputs and effectively lowering costs while improving fruit yields in peach orchards of Korea.

Efficacy of glufosinate-ammonium to control annual and perennial weeds on the ridges of paddy fields

This study was conducted to evaluate the efficacy and phytotoxicity of glufosinate-ammonium in controlling annual and perennial weeds on paddy ridges. Glufosinate-ammonium SL (900 g a. i./ha) and glufosinate-ammonium ME (600 g a. i./ha) mixed with fluthiacet-methyl (10 g a. i./ha) were tested in the field experiments. Five annual weed species, Glycine soja, Erigeron canadensis, Disitaria ciliaris, Poa annua and Echinochloa utilis, and four perennial weed species Elymus tsukushensis, Taraxacum platycarpum, Equisetum arvense and Artemisia princeps were identified on the paddy ridges. The results of this experiment indicated that these annual and perennial weeds could be effectively controlled by both the herbicides. Application of these herbicides did not negatively affect the number of tillers and plant height of rice grown near the treated paddy ridges. Therefore, it can be concluded that the non-selective glufosinate-ammonium can provide an effective control of weeds on the paddy ridges if application is properly made.

Inhibition of weed germination by mixed microbial strains in pots under conditions similar to paddy soil

Inhibition of weed germination by mixed microbial strains was investigated in pots under conditions similar to paddy soil. Mixed microbial strains were comprised of four lactic acid bacteria and four saccharomycetes. Twenty seeds of Echinochloa crusgalli, Aeschynomene indica, Digitaria sanguinalis and Amaranthus retroflexus were, respectively, sown in petri dishes and each petri dish was treated with the microbial strain solution at six rates in order to assess its effect on germination. Results showed that the germination of these weeds was effectively inhibited by application of mixed microbial strains. To evaluate the weed control effect, 20 seeds of E. crus-galli, M. vaginalis, L. prostrata, S. juncoides and A. indica were successively sown in pots under conditions similar to paddy soil. Each pot contained 10 cm-deep paddy soil clean of surface weeds, and mixed microbial strains were applied to the pots two weeks after sowing. It was found that at 80 L/ha or higher rates mixed microbial strains could simultaneously and effectively control the above five weeds in pots under conditions similar to paddy soil. In conclusion, the present study results could serve as basic information for the development of new environmentally friendly microbial herbicides in paddy fields.

Herbicidal Efficacy of Benzobicyclon Up Granule Formulations in Infant Seeding Machine Transplanting of Rice

This study was conducted to investigate the herbicidal efficacy of up granule formula of benzobicyclon mixtures, benzobicyclon + azimsulfuron + oxaziclomefone up granule (BAO UG) and benzobicyclon + bensulfuron-methyl + fentrazamide up granule (BBF UG) to control annual and perennial weed species in a rice paddy field. Four annual weed species including Echinochloa crus-galli L. and three perennial weeds were dominated in the experimental field. Application of BAO UG and BBF UG was highly effective to control both annual and perennial weed species. No phytotoxic effect was observed in the rice based on the plant height, the number of tillers, and culm and panicle length. Finally, rice yield in the BAO UG and BBF UG treatment was as much as that in the hand weeding. This study indicates that self-dispersible floating formula of benzobicyclon mixtures can be applied to control both annual and perennial weed species in rice paddy fields and contribute to save labor costs.

Herbicidal Activities and Crop Injury of Hairy Vetch Residues

This study was conducted to evaluate the growth inhibition of weeds and selectivity of crop species by hairy vetch residues. The growth of all the weed species was suppressed greater than 90% at the ratio 60:40 of hairy vetch residues and no weeds were emerged at 90:10 mixture in the greenhouse. It was noticed that broadleaf weed species were more suppressed compared to grass weed species. Growth of weeds was significantly reduced and the inhibition percent was increased with increasing application depths of hairy vetch mixture both in vinylhouse and in field conditions. Among the different application depths of hairy vetch mixture, 0.75 cm depth of application tended to inhibit more, but statistically no significant difference was observed between 0.5 cm and 0.75 cm application depth. The growth of weed species such as Galium spurium, Chenopodium album, Plantago asiatica, and Rumex japonicus was greatly suppressed in the vinylhouse and the growth of G. spurium, R. japonicus and Amaranthus retroflexus was suppressed significantly in the field condition. The growth inhibition of all the above mentioned sensitive weed species was approximately 80% at the application depth of 0.5 cm. Crop growth was not hampered by using the residues of hairy vetch. This study demonstrated that rotation crop residues of hairy vetch contained high allelopathic potential to different weed species without hampering the growth of crop species.