Paddy Weeds Research Articles

Identification of phytotoxic substances from early growth of barnyard grass (Echinochloa crusgalli) root exudates.

Barnyard grass is a problematic weed worldwide. It competes with crops and causes reduction in crop yields. In this study, barnyard grass suppressed rice emergence, and the degree of rice inhibition was proportional to the density of barnyard grass. Root exudates of barnyard grass reduced germination and growth of lettuce, rice, and monochoria. Fifteen compounds potentially involved in the phytotoxic activities of barnyard grass were isolated and identified, including phenolics, long-chain fatty acids, lactones, diethyl phthalate, acenaphthene, and derivatives of phthalic acids, benzoic acid, and decane. Quantities of diethyl phthalate, decanoic acid, myristic acid, stearic acid, 7,8-dihydro-5,6-dehydrokavain, and 7,8-dihydrokavain were 2.7, 11.1, 19.6, 35.5, 10.3, and 15.5 microg/ml of barnyard grass root exudates, respectively. The two lactones exhibited the greatest inhibition, followed by the phenolics and the derivatives of phthalic acids. Fatty acids had stronger suppression than diethyl phthalate and ethyl ester-4-ethoxy-benzoic acid. The acenaphthene and decane derivatives were the least phytotoxic. The phytotoxins released by barnyard grass roots showed strong inhibition on growth of broadleaf indicator plants and paddy weeds, but were less effective on barnyard grass itself and rice. Our study revealed that in addition to competition, barnyard grass also interferes with rice and other plants in its surroundings by chemical means.

Current status of biological control of paddy weeds in Vietnam

Rice is a staple food in Vietnam and accounts for > 7.7 × 106 cultivated ha, which provide 35.5 × 106 t of rice, of which 4.2 × 106 t were exported in 2004. The enlargement of the cropping area and the enhancement of rice yield have rapidly increased the amount of agrochemicals, including herbicides, in crop production in Vietnam. From 1990–2003, the percentage of herbicides in total pesticides has increased ≈ 10‐fold to 30.2%. In addition, the improper use of herbicides caused environmental hazards, unsafe agricultural products, and human health problems. Biological management integrated with traditional weed control techniques might help to reduce the dependence on synthetic herbicides and build eco‐friendly, sustainable agricultural production in Vietnam. This paper reviews the efforts in establishing a strategy for biological management of weeds that was conducted in recent years by Vietnamese weed scientists. This has included cropping system management, water and soil management, integrated pest management, and utilization of plant allelopathy as major components of the strategy. Many plants with strong allelopathic potential can be a source for biological weed suppression and soil fertility improvement. The utilization of allelopathic properties in rice might also help to provide new rice cultivars with weed‐suppressing characteristics.

沈水性水田雑草のイネとのひ弱な競争能力 -スブタ, ミズオオバコ, コナギの評価から-

沈水性水田雑草のイネとのひ弱な競争能力 -スブタ, ミズオオバコ, コナギの評価から-

Seed germination responses of Monochoria korsakowii Regel et Maack, a threatened paddy weed, to temperature and soil moisture

AbstractTo better understand how to conserve Monochoria korsakowii Regel et Maack, a threatened plant species that was once a common annual paddy weed, the germination responses of M. korsakowii seeds to two ecological factors, temperature and soil moisture, were analyzed under laboratory conditions. Fully imbibed seeds that had been cold stratified were able to germinate over a wide temperature range with a required thermal temperature of 13–39°C. Germination was highly dependent on water table depth. Regeneration failure at the germination stage under the dry soil conditions of the fallow fields during the germination season of this species may be one of the reasons for the decline in M. korsakowii. Monochoria korsakowii had adapted to the traditional farming system, but does not persist under today’s farming systems, which include laying rice fields fallow and the use of herbicides. These are the main factors that have led to its decline over the years and to its status as a threatened plant.

Paddy weed control by medicinal and leguminous plants from Southeast Asia

Four common medicinal and two leguminous plant species from Southeast Asia were selected from a preliminary survey and examined for their potential use in paddy weed control. The screening indicated that all species exhibited strong allelopathic activities, the strongest of which was Nerium oleander. Allelopathic potentials of plant parts were ranked in the order: leaf>root>stem. The only exception was for Alocasia cucullata, where the stem displayed the highest potential. In a bioassay, N. oleander and Helianthus tuberosus showed the highest suppression of germination and growth of Echinochloa crus-galli (barnyardgrass) and Monochoria vaginalis (monochoria). Other than for Passiflora incarnata, the spontaneous growth of paddy weeds was significantly suppressed in a greenhouse at 1 t ha −1. At 1.5 t ha −1, all examined species markedly reduced weed plant growth and the dry weight of weeds by 60–100% and 70–100%, respectively. In paddy fields, weed biomass was reduced by 70–80%, and rice yield was increased by an average of 20% compared with the control. Stylosanthes guianensis, a leguminous plant widely used in Southeast Asia and Africa as a cattle feed, cover crop, mulch, and for soil improvement, gave the greatest increase in rice yield (25.8%). These plants might be useful as natural herbicides and might also contain numerous growth inhibitors that could be used for the development of biological pesticides.

Assessment of phytotoxic action of Ageratum conyzoides L. (billy goat weed) on weeds

Ageratum conyzoides L. (billy goat weed), showed strong inhibition on Raphanus sativus L. (radish) germination and growth in a bioassay. The leaves exhibited a greater suppression than the stem and root. The leaves of A. conyzoides applied at 2 t ha −1 reduced about 70% of the growth of Echinochloa crus-galli var. formosensis Ohwi. and completely inhibited emergence of Monochoria vaginalis (Burm.f. Persil var. plantaginea Solms.) and Aeschynomene indica L. in calcareous soil condition. Application of A. conyzoides leaves at 2 t ha −1 in a paddy field 2 d after transplanting caused about 75% paddy weed reduction and increased yield by 14% compared with a herbicide treatment. Three phenolic compounds were identified in the leaves, stem and root including gallic acid, coumalic acid, and protocatechuic acid, and catechin was found only in the stem. p-hydroxybenzoic acid was detected in both A. conyzoides leaves and stem. Three additional putative allelochemicals were found in the leaves consisting of p-coumaric acid, sinapic acid, and benzoic acid. The greater number of growth inhibitors found in the leaves might result in the stronger inhibitory activity than the stem and root. A. conyzoides might be a natural herbicide for weed control in paddy fields to reduce the dependence on synthetic herbicides.

Novel 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2] benzopyran derivatives: synthesis of chiral glycol benzyl ether herbicides.

Novel tricyclic 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran (TFB) derivatives were synthesized, and their herbicidal activities were elucidated. They were synthesized from D-glucose as a natural chiral source. The formation of the TFB skeleton was achieved by a Friedel-Crafts type intramolecular cyclization of methyl 5-deoxy-2,3-O-dibenzyl-5-C-methyl-D-xylofranosides. The intramolecular cyclization was dependent upon the electronic effects of the substituents at the C-2 benzyloxy group of methyl xylofranosides. Some TFBs exhibited a remarkable herbicidal activity to annual paddy weeds, such as Echinochloa sp, without injury to the rice.

Synthesis and Herbicidal Activity of Novel 3-Alkoxycarbonyl-3-aryl-2, 3-dihydro-2-oxo-1H-pyrrole Derivatives

In the course of efforts to find novel compounds with improved crop safety in transplanted rice by the modification of 1-[1-(3,5-dichlorophenyl)-1-methylethyl]-4-methyl-3-phenyl-3-pyrrolin-2-one (1a), which was reported to have excellent herbicidal activity against paddy weeds, 2,3-dihydro-2-oxo-1H-pyrrole derivatives with a quaternary carbon atom having an alkoxycarbonyl group at the α-position of the cyclic amide were synthesized and examined. Among these compounds, methyl 1-[1-(3,5-dichlorophenyl)-1-methylethyl]-2,3-dihydro-4-methyl-2-oxo-3-phenyl-1H-pyrrole-3-carboxylate (2a) was not only active against Echinochloa oryzicola and Scirpus juncoides but also compatible with transplanted rice even in harsh conditions. On the basis of preliminary experimental results, it was thought that 2a would generate the corresponding 2-oxo-3-pyrrolin (1a) through the metabolic degradation of the methoxycarbonyl moiety. © Pesticide Science Society of Japan

簡易な方法による休耕田シードバンクの把握

In this study, we designed simple method to evaluate of soil seed banks for vegetation management in fallow fields. Soil seed bank of eleven fallow paddy fields, which were various in period and management forms, in hilly and mountainous areas was sampled in summer, 2002. The paper provides effective method to predict succession stage of fallow period by referring to seed banks. We designed screening test system applied Washitani (1987) , which is method of gradually increasing temperature. We showed germination rate more than 80% of last germination rate mainly on paddy weed by this method. Therefore, this was confirmed that a convenient method was effective for grasp of seed bank. However, similarity was low between seed banks and vegetation, it needs that more improvement of the evaluation system made reflect succession stage.

水田雑草が生えにくい水稲根系の検討

水田雑草が生えにくい水稲根系の検討

山形県におけるスルホニルウレア系除草剤抵抗性雑草の発生

山形県におけるスルホニルウレア系除草剤抵抗性雑草の発生

Paddy weed control by higher plants from Southeast Asia

Ten higher plant species from Southeast Asia were selected as possessing the strongest allelopathic properties during a preliminary survey conducted in 2000–2002, and tested for biological weed control in paddy fields during spring and summer seasons 2002 in Viet Nam. All species studied promoted rice growth and yield and greatly reduced paddy weed growth at a dose of 2 tons ha −1. Two species including Bidens pilosa and Tephrosia candida were the most effective candidates attaining more than 80% weed control and increasing rice yield by 20%. They were suggested for use as potential natural herbicides. The other species including Blechnum orientale, Eupatorium canabium, Euphobia hirta, Lencaena glauca, and Morus alba might be useful as alternative materials for biological weed control and for the reduction of herbicides used in paddy field.

Kava root ( Piper methysticum L.) as a potential natural herbicide and fungicide

Experiments were conducted to examine the biological effects of Kava, a perennial pepper plant native to oceanic region on paddy weeds and fungi harmful to plants and crops. Kava showed a strong inhibition on growth of barnyardgrass ( Echinochloa crus-galli), monochoria ( Monochoria vaginalis), and knotgrass ( Paspalum distichum L.), which are among the most harmful paddy weeds. Kava completely controlled emergence of monochoria and barnyardgrass at a treated dose of 0.5 and 1.0 g, respectively. Application of Kava at 1 tonne ha −1 6 d after saturating paddy soil with water was an effective treatment. This caused around 80% reduction of natural paddy weed growth and increased tillering and root number of rice. In addition, Kava significantly inhibited growth of the five fungi: Fusarium solani, Pyricularia grisea, Rhizopus stolonifer, Taphrina deformans, and Thanatephorus cucumeris. The effect on R. stolonifer was the greatest and T. cucumeris and P. grisea were the second most affected. The inhibition of Kava on paddy weeds was species dependent, proportional to the treated doses and inversely proportional to the time after watering. Kava is a promising material, which might be used as natural herbicide and fungicide in the field to reduce the dependence on synthetic herbicide and fungicide in agricultural production.

Synthesis and Herbicidal Activity of 4-Thiazolone Derivatives and Their Effect on Plant Secretory Pathway

In the course of study to develop new herbicidal compounds, we found that some 4-thiazolone derivatives possessed herbicidal activity against several paddy weeds. As a result of a structure-activity relation study, 5-(2-chloroethyl)-5-methyl-2-(3-methyl-2,3-dihydro-1,4-benzoxazin-4-yl)-4-thiazolone (CMT) was selected as one of the potential herbicides for rice. CMT showed potent herbicidal activity against paddy weeds, especially barnyardgrass (Echinochloa oryzicola) and three-square grass (Scirpus juncoides). The herbicidal activity of CMT appeared to be caused by specific inhibition in the growing tissues. Electron microscopic observations of CMT-treated barnyardgrass revealed that exposure to 10 μM CMT for 4 hr caused swelling of the endoplasmic reticulum (ER) and Golgi apparatus, the separation of plasma membranes from cell walls, and an accumulation of small vesicles in the plasma membrane-cell wall interspace. These findings suggest that CMT acts primarily as an inhibitor of the secretory pathway, resulting in a dysfunction of cell wall biosynthesis.

2002年の黒竜江省の水稲冷害と水田の主要病・虫・雑草害

2002年の黒竜江省の水稲冷害と水田の主要病・虫・雑草害

SU剤抵抗性迅速検定法の改良と数種水田雑草への適用

SU剤抵抗性迅速検定法の改良と数種水田雑草への適用

水稲栽培における米ぬかペレットの抑草効果

水稲栽培における米ぬかペレットの抑草効果

田面水の撹拌が雑草の発生に及ぼす影響

田面水の撹拌が雑草の発生に及ぼす影響

千葉県鴨川市大山千枚田における畦畔とその主要雑草について

千葉県鴨川市大山千枚田における畦畔とその主要雑草について

近畿・中国・四国地域における植調適II試験からみた水田雑草の発生消長と気温との関係

近畿・中国・四国地域における植調適II試験からみた水田雑草の発生消長と気温との関係