Three-year comprehensive experiments were conducted to compare the dissipation patterns of a total of 16 pesticides, including 3 metabolites, as granular formulations applied in lysimeters and paddy fields with two soil types. Analytical concentrations of the target pesticides in paddy water were analyzed using a granular kinetic model consisting of the following parameters: release rate, decrease rate, and dissolved concentration. Results of parameter grouping analyses of the kinetic models showed that 56% of data reproducibility (entire grouping) was obtained between replicates for the lysimeters. In comparisons between the lysimeters and paddy fields, 48% of decrease rates and 34% of release rates were grouped, although significant differences were observed with a nearly 90% difference for dissolved concentrations. These differences might be attributed to the hydrological components such as water management and meteorological covariates in paddy fields, the daily percolation in lysimeters and the adsorption-desorption kinetics between paddy water and soil.
Comparative experiments investigating the dissipation of four nursery-box-applied pesticides and three foliar-applied pesticides were conducted using lysimeters and in actual paddy fields. In the lysimeter experiments, there were test plots for submerged application for both application types. Analytical concentrations of the pesticides in paddy water were evaluated using appropriate kinetic models. The detection levels of pesticides in the paddy water for the nursery-box and foliar applications were 10–77% and 42–79% of the submerged application, respectively. The times required for 50% dissipation (DT50s) in case of the nursery-box and foliar applications were 0.8–10.4 days and 0.5–2.7 days, respectively. Although overall dissipations were affected by the physicochemical properties of the pesticide and the experimental design in the test plots, the initial detection levels in the lysimeters, governed by the runoff at transplanting and the deposition at spraying, were comparable with those in the actual paddy fields.
Ipfencarbazone exhibits excellent herbicidal activity against Echinochloa spp. and is safe for rice. The effects of ipfencarbazone on very long chain fatty acid (VLCFA) elongation in rice and late watergrass and its inhibitory mechanism were investigated in this study. Although ipfencarbazone inhibited VLCFA elongation in the microsomes prepared from late watergrass and rice at low concentrations, the inhibitory effect was higher in late watergrass than in rice. These results suggested that the primary site of action of ipfencarbazone is VLCFA elongase (VLCFAE) and ipfencarbazone has a differential affinity between the VLCFAEs of the plants. The inhibitory activity of ipfencarbazone became higher in proportion to pre-incubation period with the VLCFAE. The degree of inhibition did not decrease by dilution of the VLCFAE–ipfencarbazone complex. These results suggested that ipfencarbazone binds to the VLCFAE irreversibly.
Ultrasound, which refers to frequencies above the audible limit of human hearing, is a candidate for inducing resistance to pathogens in plants. We revealed that aerial ultrasound of 40.5 kHz could induce disease resistance in tomatoes and rice when the plants were irradiated with ultrasound of ca. 100 dB for 2 weeks during nursery season and reduced the incidence of Fusarium wilt and blast diseases, respectively, when plants were inoculated with pathogen 0 or 1 week after terminating irradiation. Disease control efficacy was also observed with ultrasound at frequencies of 19.8 and 28.9 kHz. However, cabbage yellows and powdery mildew on lettuce were not suppressed by ultrasound irradiation. No significant positive or negative effect on growth was observed in tomato and rice plants. RT-qPCR showed that the expression of PR1a involved in the salicylic acid (SA) signaling pathway was upregulated in the ultrasound-irradiated tomato.
Phytophagous insects utilize visual, olfactory and gustatory cues to find food. The brown marmorated stink bug, Halyomorpha halys (Stål), quickly approaches fresh peanut seeds newly introduced into the rearing cage in the laboratory but shows less interest in stale peanut seed previously infested by conspecifics. This observation suggests that H. halys can perceive the quality of food by detecting the volatile(s) from fresh peanut seeds. A bioassay revealed that H. halys adults could more quickly find fresh peanut seeds than three-day-infested peanut seeds, which is consistent with laboratory observations. Hexanal was found to be the major volatile component of fresh peanut seeds but not of previously infested ones. In the two-choice assays, the adult bugs that did respond were significantly attracted to fresh peanut volatiles and hexanal. Hexanal also induced proboscis-protruding behavior in adult H. halys, which suggested that this compound is a key stimulant of foraging behavior of laboratory-reared H. halys adults.
The ethyl acetate extract of the culture filtrate of Phlebia tremellosa promoted elongation of the lateral roots of lettuce seedlings at 250 µg/mL. We purified two compounds that promote root elongation by using activity-guided chromatographic fractionation. On the basis of spectroscopic analyses, these compounds were identified to be isolactarane sesquiterpenes derived from the dehydrogenation of merulactone, which was previously isolated from the same species. We named the purified compounds phlelactones A and B. Phlelactones A and B promoted primary root elongation at 100–300 and 10–30 µg/mL and the elongation and formation of lateral roots at 300–1000 and 30–100 µg/mL, respectively.
The relationships between plant growth stage and pesticide-uptake ability were investigated via cultivation of Brassica rapa L. var. perviridis in soil to which was added four pesticides of relatively high log KOW: fenobucarb, procymidone, flutolanil, and tolclofos-methyl. The root concentrations of pesticides were low in very young seedlings with undeveloped root systems, highest in seedlings with developed root systems, and tended to decrease until the usual harvesting stage. Additionally, the shoot concentrations of tested pesticides showed the same trends as the roots. The pesticide-uptake abilities of roots were lowest in very young seedlings and then constant for seedlings until the harvesting stage. In contrast, the pesticide-translocation abilities from root to shoot were constant regardless of growth stage. The results indicated that changes in shoot concentrations with growth stage were affected by the development of the root system and pesticide-uptake ability of roots.