The photolysis rate (conversion per unit energy) of naproanilide (2-(2-naphthoxy)-propionanilide) in water was related with sunlight energy (below 340nm). This relation was expressed by the following equation under seasonal sunlight conditions in an FRA-greenhouse. P=P′×exp (-K×E′), where P is the concentration of remaining naproanilide, P′ is an initial concentration of naproanilide, K is a photolysis constant and E′ is the energy (cal/cm²) of sunlight (below 340nm). The energy required to photodecompose the 50% of the starting material (PL₅₀; cal/cm²) was expressed by the following equation. PL₅₀=0.693/K. The PL₅₀ value of naproanilide was 10.3mcal/cm² (below 340nm) and reproducible in the FRA-greenhouse. Since the half-life period of naproanilide by photolysis depends on experimental conditions, such as weather and solar altitude, it would be better to use the PL₅₀ value rather than the half-life period to express the reliable photostability of naproanilide. The photolysis rate of naproanilide was pH-independent in water, and slower in O₂-free water than in natural water. Sunlight energy (below 340nm) was measured with a UV radio meter UVR-254 (Tokyo Kagaku Kikai Co., Ltd.) in the FRA-greenhouse at Chigasaki City (139°30′ east, 35°29′ north). These data are useful to estimate the photostability of naproanilide in water under natural sunlight conditions.

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Effects of Polyoxin D on cell wall regeneration and its biosynthesis of Pyricularia oryzae were investigated using the protoplasts originated from mycelia of both Polyoxin D-sensitive and Polyoxin D-resistant isolates. Regeneration and reversion of protoplasts from the sensitive isolates were strongly inhibited by Polyoxin D as compared with protoplasts from the resistant mutant. Sensitivity to Polyoxin D increased in protoplasts more than in intact spores and mycelia. Concanavalin A and succinated-Wheat Germ Agglutinin were bound to the surfaces of regenerating protoplasts, but succinated-Wheat Germ Agglutinin was scarcely bound to the reversional hyphae from protoplasts treated with Polyoxin D. Incorporation of ³H-N-acetylglucosamine into cell wall fraction strongly inhibited in protoplasts from both the sensitive and the resistant at 5μg/ml and 10μg/ml of Polyoxin D, respectively. These results support the postulated mechanism of action of Polyoxin D that this fungicide interferes with fungal chitin biosynthesis, and also suggest some utility of protoplasts in such pesticide studies.

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We studied the acid moieties of the following imidoyl imidazole derivatives; alkyl, alkoxyl, alkoxyalkyl, substituted phenyl and aryl compounds with hetero atoms of sulfur or nitrogen in order to determine their fungicidal activities. Phenyl compounds that have ortho-substituents such as 2-trifluoromethyl were highly fungicidal. Moreover, N-substituted-2-pyridyl compounds, such as N-5-chloro-3-methyl-2-pyridyl, with amine moieties showed higher antifungal activity than N-phenyl compounds. Some of these compounds have excellent preventive, curative and systemic effects on various crop diseases. Certain N-2-pyridyl benzimidoyl imidazoles showed excellent fungicidal activity against powdery mildew and gray mold on cucumber and against blast on rice plants. 1-[N-(5-Chloro-3-methyl-2-pyridyl)-2-trifluoromethylbenzimidoyl] imidazole (48), a representative compound, had the following effects at the concentrations shown; preventive of powdery mildew at 0.54ppm and gray mold at 7.7ppm, and curative of rice blast at 16.8ppm (EC₅₀). In addition, its antifungal spectrum was very broad, and it was especially efficacious against Basidiomycetes and Ascomycetes. At 1ppm in the nutrient medium, it strongly inhibited sporidial multiplication and ergosterol biosynthesis on Ustilago maydis. These results indicate that the mode of action of N-2-pyridyl benzimidoyl imidazoles is the inhibition of ergosterol biosynthesis.

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The behavior of the herbicide Sethoxydim, (±)-2-(1-ethoxyiminobutyl)-5-[2-(ethylthio)-propyl]-3-hydroxycyclohex-2-enone, in sugar beets (Beta vulgaris) was investigated by leaf treatment of the [4-¹⁴C]-labeled compound. The ¹⁴C in treated leaves gradually decreased to 37% 7 days after application. Much of it was translocated to untreated leaves and a little to the root. The amount reached a maximum of 15.9% (9.7ppm as the parent compound) and 4.2% (13.4ppm), respectively, on day 3 after treatment, and then decreased to 0.02ppm or less at the final sampling on day 90. Sethoxydim was rapidly converted to its sulfoxide and sulfone, and their oxo-tetrahydrobenzoxazole and desethoxyl derivatives, and further to the conjugates of these compounds.

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The development of insecticide resistance in rice brown planthoppers and its mechanism were studied. The susceptibility of malathion- and MTMC-selected strains to malathion decreased to 1/39 and 1/25 of the initial level after 45 selections, respectively, while that to MTMC decreased to 1/2.5 and 1/4.2. These selected strains were more susceptible to synthetic pyrethroids than the parent strain. K1 and K2 showed high synergism to the selected strains, and also inhibited the decomposition of malaoxon. Malathion resistance in the malathionor MTMC-selected strains was suggested to be caused by high degradative activity to malathion and malaoxon. The mechanism of MTMC resistance in the MTMC-selected strain was presumed to be caused by low sensitivity of acetylcholinesterase.

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Residues of the herbicide molinate (S-ethyl perhydroazepine 1-carbothioate) and its degradation products in soil and rice plants were quantitatively and qualitatively determined after the application of azepine-ring-labeled ¹⁴C-molinate under glasshouse conditions. At the harvest, 21% of the total radioactivity applied was detected in the soil and 1.6% in the rice plants. Molinate was distributed uniformly throughout the soil layers at approximately 0.06ppm. In addition to molinate, 2-oxo-molinate, 4-oxo-molinate, molinate-acid and hexamethyleneimine were detected. Radioactivity of each compound was less than 1% of the total applied, equivalent to 0.02ppm in soil. In the rice plants, about 96% of the radioactivity was in straws and 4% in grains. In the rice plants, 4-OH-molinate, 2-oxo-molinate, 4-oxo-molinate, CMET (S-ethyl N-carboxymethylthiocarbamate), molinate-acid and molinatealcohol were detected in free or conjugated forms. The concentration of each compound was less than 3ppb in the grains and less than 15ppb in the straws. Molinate was presumed to be metabolized partially to plant constituents.

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The percentage of airborne spray droplets in three oil-based aerosol formulations giving different spray-droplet sizes (19.4, 35.8 and 71.4μm on the average according to Rosin-Rammler's equation) was measured in the Peet Grady Chamber. The percentage of airborne droplets decreased with the lapse of time, and the larger the droplets, the faster the decrease. The comparison of the settling period of each droplet calculated by Stokes's law with regard to the percentage of airborne droplets revealed that the droplet size decreased in a short period due to the evaporation loss of a solvent which made up the droplets.

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The adsorption-desorption of DTP [4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole], a hydrolysate and herbicidal entity of pyrazolate, was studied with various types of soil. The adsorption isotherms of DTP fitted the empirical Freundlich equation. Although distribution coefficients (Kd) of DTP significantly varied among the test soils, the soils had a great adsorptive capacity for DTP. Most of DTP adsorbed by the soils was gradually and steadily desorbed into water. In paddy fields where a granular formulation of 10% pyrazolate was applied, both pyrazolate and DTP, forming a treatment layer at the soil surface, were hardly mobile by leaching and gradually dissipated through biodegradation.

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Effects of the selective postemergence herbicide quizalofop-ethyl on lipid biosynthesis were studied in excised stem-base segments from corn seedlings grown in a greenhouse after foliarapplication. Incorporation of ¹⁴C-acetate into total lipid of the segments was inhibited by the (R)-(+)-enantiomer, while the (S)-(-)-enantiomer was inactive. TLC analysis of the lipid extract showed quantitative alteration especially in fatty acid and phospholipid. Comparison of HPLC profiles of phenacyl esters of the fatty acid fraction and their ¹⁴C-determination with those of the control revealed a reduction in palmitic acid and linoleic acid content. The results indicated that fatty acid biosynthesis is a possible primary site of action of quizalofopethyl.

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Thirty-nine O-aryl O-ethyl N-sec-butylphosphoramidothioates were synthesized and tested for their antifungal activity against Pseudopernospora cubensis. Structure-activity relationship of various aryl substituents were examined. A 5-methoxy group on the 2-nitrophenyl moiety possessed an optimum van der Waals volume. A 4, 5-methylenedioxy substituent on the 2-nitrophenyl group was comparable to the most effective 5-methoxy group. A strong electron-withdrawing group on the 2-position, for instance a nitro group, was an important molecular requirement. Compounds with only a 3, 4-methylenedioxyphenyl or a 3, 5-dimethoxyphenyl group were also effective.

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An arrestant to keep A. kariyai in the host habitat was synthesized by Wittig reaction followed by hydrogenation from a furan compound. Using this synthetic arrestant, its effect on the parasitization rate of A. kariyai to P. separata was examined in laboratory and green-house conditions. In both conditions, treatment of the host habitat with the arrestant increased the parasitization.

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d-Limonene (p-mentha-1, 8-diene) is a monocyclic monoterpenoid found in citrus oils. The spectrum of insecticidal activity of d-limonene was examined by using the German cockroach, Blattella germanica (L.), house fly, Musca domestica L., rice weevil, Sitophilus oryzae (L.), and western corn rootworm, Diabrotica virgifera virgifera LECONTE. Bioassays were performed to determine topical, fumigant, oral, repellent, residual, ovicidal, and larvicidal activities. The material was slightly toxic topically to German cockroaches and house flies and was synergized with piperonyl butoxide. High concentrations of vapors caused mortality in German cockroaches and rice weevils. Oral administration did not result in mortality to either adult or nymphal cockroaches but accelerated growth in nymphs. Repellent activity against German cockroaches was noted at high concentrations. No residual activity was observed on any of four surface types exposed to adult German cockroaches. d-Limonene inhibited western corn rootworm egg hatch at high concentrations and showed moderate toxicity in soil against third-instar western corn rootworm larvae. These findings indicate that the insecticidal properties of d-limonene are limited.

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[in Japanese]

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The mode of action of phosphoramidothioates was examined with reference to their anti-AChE activity. N-Isopropylphosphoramidothioate, isofenphos, was the most toxic to the adzuki bean weevil among N-alkyl substituted compounds. LD₅₀ values for the insects were not correlated with the in vitro anti-AChE activity of these oxons. It was demonstrated that phosphoramidothioates and these oxons became potent inhibitors of AChE by the incubation with the rat liver microsomal NADPH system and the chemical treatment with peracid. The inhibition of AChE activity was reduced by the addition of SKF 525-A to the microsomal system. The stereospecificity of isofenphos and its oxon on biological activity was obvious. The (+)-isomers of both the compounds were more toxic to insects than the (-)-isomers. Chiral isomers and racemate of isofenphos-oxon were activated with the microsomal NADPH system and the I⁵⁰ values became 1.47×10^-7M, and 6.19×10^-5M for the (+)- and (-)-oxon, respectively. The data suggested that the (+)-isomer was easily bioactivated and the I⁵⁰ values of chiral isomers after the bioactivation were sufficient to explain their insecticidal activity. ¹⁴C-Isofenphos metabolism was different between animals and plants. In mammals and insects, isofenphos was rapidly transformed into the water soluble metabolites, and in plant isofenphos and isofenphos-oxon were very persistent. Isofenphos was metabolized by (1) oxidative desulfuration, (2) desphenylation, (3) desN-alkylation and (4) N-desalkylation, and the formation of water soluble metabolites through isofenphos-oxon was proposed to be the main metabolic pathway. In all experiments, the conversion to water soluble metabolites was dominant in the cleavage of P-O-C (aryl) bond and only desphenyl compounds were found in plants. The effect of chirality was seemingly small in the metabolism of isofenphos based on the examination in the rat liver microsomal system and in the housefly. The amount of isofenphos-oxon metabolized from the (-)-isofenphos was always larger than that from the (+)-isomer, but quantitative differences of other metabolites between both the chiral isofenphos was obscure.

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Now that many biocidal types of herbicides are being phased out in the field of newer herbicides designs, because of phytotoxicological selectivity or environmental considerations, the photosynthesis inhibiting herbicides, which make up the group which we call inhibitors in photosynthetic electron transport, light-activated herbicides and so on, have come to dominate the herbicide molecular design. Cyclic imide herbicides belong to this diverse group of compounds and have a number of interesting features. For instance, both potency and phytotoxic selectivity vary over great extremes, all the way from the total herbicides to highly selective compounds which are almost safe to many useful plants. It is not at all difficult to synthesize an entirely new photosynthesis inhibitor, because there is a great deal of diversity of permitted attachments to the basic structure. The problem is to design compounds which are of modest price, excellent potency and appropriate safty to useful plants and the environment. To find out a solution to this problem in the molecular design of cyclic imide herbicides, the author has applied so-called biorational approaches in which we can systematically make use of information obtained from studies on phytotoxic actions, metabolism, absorption and translocation, mechanism of action, structure-activity relationships, agricultural application and others. The discovery of phytotoxic properties of N-aryl-3, 4, 5, 6-tetrahydrophthalimides (Ia) gave a new impetus to the subsequent research for the related imide types of herbicides (Ib, IIa-b & IIIa-d) which have been found as pre-emergence or early post-emergence herbicides. These herbicides shows phytotoxicity at low rate against many grassy and broadleaf weeds and are exceptionally phytotoxic to hairly galinsoga, common purslane and toothcup. Further biological and biochemical studies using higher plants, e. g. sawa millet, tobacco plants, pigment mutants of rice plants and mung bean, and unicellular green microalgae, Scenedesmus acutus, have revealed that these cyclic imide class of herbicides commonly indicate an apoplastic pattern of translocation in plants, a light-dependent bleaching action and a severe decrease of photosynthetic pigments caused by inhibition of the light-dependent 5-aminolevulinate formation step in chlorophyll biosynthesis and photooxidative destruction of plant pigments already formed. A closer look at the structure of the compounds (Ia-b, IIa-b & IIIa-d) shows a number of interesting features; namely, alkylene ring (Moiety A), electron-donating moiety (Moiety B), imide structure (Moiety C) and aryl ring (Moiety D), all of which could be responsible for their herbicidal activity. Having such structural consideration in mind, all series of compounds were analyzed on the basis biological and biochemical data in order to obtain some ideas why these imide types of compounds exhibit so potent phytotoxic activity, and also to find out whether variation in their structures would be possible. In the context of the molecular design of cyclic imide herbicides, principle information has been obtained on the structural characteristics required for herbicidal activity and it suggests that a large number of cyclic imide types of compounds can be herbicidal. The incidence of this activity is extremely high amongst compounds whose structure conform to the following rule; (1) C₁ and C₂ carbon atoms in the alkylene ring should form part of planer in Moieties A and B, (2) Moieties B and C should form a planer

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Pyrazolate [4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-pyrazolyl p-toluenesulfonate] is a wide spectrum herbicide with excellent selectivity in paddy rice. It has proved successful in controlling both annual and perennial weeds including the problem species of Cyperus, Echinochloa and Sagittaria. The Laboratories set up a research project for perennial weeds control in 1971 and started to screen compounds for several weed species. In 1973, a leading compound was found, which was then optimized through extensive derivatization and evaluation of herbicidal spectrum, selectivity to rice plants, toxicity and environmental safety, cost-performance, etc. The compound thus selected, 4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole, was so soluble in water that its direct application into paddy fields gave some unfavorable results in biological performance. Accordingly, the compound was derivatizedto mask the hydroxy group aiming at chemical slow release of the herbicidal entity into paddy water. Among a lot of derivatives, pyrazolate was finally selected for its cost-performance, low toxicity to non-target organisms, low impact to the environment. Pyrazolate, with its extremely low solubility along with high hydrolyzability in water, continuously releases the herbicidal entity into paddy water. Its release rate was further optimized to attain maximum herbicidal effect by means of formulation technology such as micronizations of the crystal particles and granular formulations with which the dispersion of ultrafine particles is suppressed to a certain extent. Since the launch of the single active ingredient preparation (Sanbirde^®) in 1980, combination products with many other herbicides manifesting either synergistic or complementary effects have been developed.

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Pencycuron (1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea) is a new fungicide specifically active against Rhizoctonia solani causing a number of important plant diseases such as sheath blight of rice, black scurf of potato and seedlings damping-off of various crops. In the course of screening trials of benzylurea derivatives originally intended to search for herbicidal candidates, some compounds turned out to be fungicidal to rice sheath blight, and this fact led us to study further on the structure-activity relationships. In the general formula of Xn_??_-CH₂(R)NC(Y)N(R¹)R², a para substitution of the benzyl moiety was indispensable to a potent activity, and halogens especially the chlorine substitution provided the highest activity. The alkyl moiety should be bulky with 3 to 6 carbons in total and branched at the first carbon having not more than two carbon chains. sec-Butyl and cyclopentyl group were most active. R¹ should be a non-substituted phenyl group. Any substituents either electron-withdrawing or electron-donating on benzene ring acted only against the activity. R² should be hydrogen and any other substituents could not contribute to an elevation of the activity. Although urea (Y=O) was more active than thiourea (Y=S) in general, the same tendency in the activity relations was shown with both types. The activity of pencycuron was extremely selective even among the group of R. solani. Most of the important groups as crop pathogen were highly sensitive but some others were tolerant. Pencycuron is essentially a contact fungicide and non-systemic. The majority of the applied substance in plant was localized at the treated zone and was mostly retained as the parent form. The GLC profiles of metabolites derived from both isolates of R. solani sensitive and non-sensitive to pencycuron were not much different and no metabolite exceeding the amount of pencycuron could be found. The characteristic of pencycuron in disease control should be due to an excellent prevention against infection with a remarkable long-lasting efficacy. The highly selective activity to R. solani with very low potential to non-target organisms may serve for a high degree of safety to users, less hazard to the enviroment and favourable compatibility with many kinds of crop.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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