Paddy fields, herbicides

The E, value for R is used in Eq. 35, since the value for such highly congested groups as R CHBr is difficult to estimate accurately. From these informations and considering a certain, but not significant, collinearity between E and values for compounds included in Eq. 35 as well as the easiness of preparation, S-47 (18 R = t-Bu) where rc(R) = 2.2 and E (R ) — —2.5, was selected as a promising novel paddy field herbicide and forwarded to extensive field trials. 

Development of paddy field rice herbicide Thenylchlor, A-(2,6-dimethyl-phenyl)-A-(3-methoxy-2-thenyl)chloroacetamide 98YGK221. 

The concentration of chlornitrofen in river water released from flooded paddy fields 30-60days after application was detected in the range 0.039-1.25 agL . Eurther, it was reported that the DTso of diphenyl ether herbicides in groundwater, river water and seawater were 17-84, 14-140 and 10-88 days for chlornitrofen, and 18-131,4-206 and 6-23 days forbifenox, respectively. Diphenyl ether herbicides in... 

Only a few models applicable to paddy field conditions have been developed. RICEWQ by Williams, PADDY by Inao and Kitamura," and PCPF-1 by Watanabe and Takagi are useful for paddy fields. EXAMS2 by the United States Environmental Protection Agency (USEPA), a surface water model, can also be used to simulate paddy fields with an appropriate model scenario and has been used for the prediction of sulfonylurea herbicide behavior in paddy fields. The prediction accuracy of PADDY and PCPF-1 is high, although these models require less parameter... 

Chen, Y-L., Chen, J-S. (1979) Degradation and dissipation of herbicide butachlor in paddy fields. J. Pest. Sci. 4, 431. 

Du Pont started relatively late in the triketone field, and directed their efforts toward novel fused bicyclic acids. As a result of their work in this area, they discovered the broad leaf weed cereal herbicide ketospiridox [58] (62, proposed common name. Fig. 4.3.10). Ishihara, inspired by earlier work of Hokko [59], identified some new benzoyl analogues with cyclic acetal meta-substituents (63 and 64, Fig. 4.3.11) that they claim have good pre-emergent activity in flooded rice paddy fields without damaging the rice seedlings [60]. 

The herbicide with the trade name Sanbird is able to control both annual and perennial weeds in paddy fields [5] with application rates of 3-4 kg ha . As a very selective herbicide in rice it was a good innovation for the Japanese rice market. This product reached peak sales in Japan in 1986 with 650000 ha (28.6% market share) [6]. This declined with the introduction of sulfonylurea herbicides such as bensulfuron-methyl in the year 1987. In 2005 Sanbird was only used on 101 200 ha (5.9% market share) in Japan [7]. 

These result in a different environmental behavior and different herbicidal activity [14, 18]. The half-lives in paddy field soil rose from 4 to 15 days for pyrazoxyfen and to 38 days for benzofenap. The application rate of 3 kg ha is as high as for both the other rice herbicides but benzofenap allows a longer weed control of up to 50 days compared with 21-35 days with pyrazoxyfen. Importantly, benzofenap is a more crop selective herbicide. Another advantage of benzofenap over pyrazoxyfen is that it is not temperature-dependent. Even at higher temperatures no phytotoxicity is observed. 

The first compound of the heteroaryloxyacetamide class (simplified as oxyacetamides) launched in 1986 was mefenacet (FOE 1976 Fig. 8.1), as a paddy rice herbicide. Whereas FOE 1976 was synthesized at Bayer (now Bayer CropScience), its good performance was investigated by biologists of Nihon Tokushu Nouyaku Seizou K.K. (now Bayer CropScience K.K.) through primary, secondary and field trial tests. 

Concentrations of Herbicides Used in Rice Paddy Fields in River Water and Impact on Algal Production... 

In Japan, more than half of agricultural land is paddy fields. The rice herbicides are easy to run off especially because those are applied directly to the surface water of the paddy field. Thus, some rice herbicides are detected frequently in river water of Japan at die low ppb levels for some mondis after the rice-planting period (2-6). Alterations of a phytoplankton community as a result of toxic stress may affect the structure and ftmctioning of the whole ecosystem (7). However, there have been few reports on the influence of the rice herbicides to phytoplankton (8-11). Therefore it is inqiortant to assess the effects of these herbicides on primary production in riverine, lake and marine ecosystems. 

Acylanilides (abbreviated as anilides in this article) are generally used as selective pre- and/or post-emergence herbicides in paddy rice fields. The herbicidal activity of the anilides is similar to those exhibited by the auxin-like plant growth regulators. 

It has been proposed to use hemoglobin adducts in biomonitoring, as a dosimeter for the biologically active dose of arylamines/arylacetamides. This may also provide information about the individual susceptibility to the toxic and carcinogenic effects of these chemicals30,31. Field workers exposed to Propanil (38), a major herbicide in rice paddies,... 

One case-control study in Italy has reported an increased risk of STS for women who worked in rice fields (55.). While it has been suggested that this study provides evidence implicating phenoxy herbicides, at best the evidence is very weak, since the association was based on 3 women who worked in the rice fields during the 1950s. There is no suggestion that they had any direct contact with phenoxy herbicides, although it was postulated that they may have had indirect exposure in the rice paddies from previously-applied herbicides. 

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