In conservation biological control programs, cultivation of flowering plants around/in agricultural fields is considered to be an effective approach to enhance predatory activity of natural enemies by providing their foods, refuges and oviposition sites. The minute pirate bug, Orius strigicollis, is an omnivorous predator and is used as an important biological control agent against thrips pests in Japan. However, little is known about the insectary plants available for O. strigicollis. Here, we investigated the longevity of O. strigicollis adults maintained on flowers and leaves of 10 plant species. In all tested plants except for French marigold, the predators fed on flowers survived longer than those fed on leaves of the same plants. In particular, flowers of buckwheat, coriander, dill, fairy-fan flower, holly basil, sweet alyssum and vervain increased longevity of O. strigicollis by four fold or more than the corresponding leaves. However, survival rate of O. strigicollis nymphs and the number of eggs deposited by female adults on buckwheat flowers was lower than those fed on Mediterranean flour moth eggs. Based on these results, we discussed possibilities of flowering plants serving as food resources for O. strigicollis in the field.
A few Olpidium species are recognized as fungal vectors of plant viruses. For the control of viral diseases caused by Olpidium species, it is important to quantitatively detect the presence of such fungi in field soil. We developed a quantitative detection system for Olpidium bornovanus being able to transmit Melon necrotic spot virus. We constructed a direct direction assay that detected fungal-specific bands from DNA isolated from soil using PCR analysis, and an indirect detection assay that combined fungal propagation in the root of the host plant and detection of specific bands from root DNA by PCR analysis. The results of these detection assays indicated that detectable sensitivity of the indirect detection assay was higher than that of the direct detection assay. We believe that the indirect detection assay is practical and useful for the quantitative detection of the pathogenic fungus.
The wintering density of Liriomyza chinensis (Kato) pupae was estimated as 154.7 individuals/m2 on green onion fields in Nara prefecture. The wintering pupae of L. chinensis were considered to be living in the soil from late September until late March.
Soil fumigation with 30 kg/10 a dazomet was highly effective in controlling L. chinensis pupa without covering the ground with film. Application of 10 kg or 20 kg/10 a dazomet and then covering the ground with film was highly effective. As a result, dazomet was considered highly effective for control of the overwintering pupa of L. chinensis under the low-temperature condition.
Successional changes in powdery mildews prevailing in greenhouse tomatoes were examined during the rotated cultivation of susceptible and resistant hosts. The pathogens, forming eight-conidial pseudochains, were separated from pathogens forming four-conidial pseudochains and dominated throughout the planting of resistant wild tomato plants. These pathogens were identified as KTP-03 and -04 of Oidium neolycopersici.
We evaluated the effects of agrochemical application on the density of Amblyseius swirskii released on greenhouse melon plants to control Thrips palmi. Seven to fourteen days after release of A. swirskii, 14 types of insecticides, 6 types of acaricides, and 7 types of fungicides were sprayed on melon plants in each plot. At 3–4, 6–8, 13–14, and 20–21 days after application, the density of A. swirskii and T. palmi larvae were examined by visual counting. It was found that 7 insecticides [Pyridalyl, Dinotefuran, Cyromazine, Pymetorozine, Flonicamid, and BT (Bacilex and Delphin)] did not affect the density of A. swirskii. However, only Pyridalyl, when used in combination with A. swirskii, was useful in controlling T. palmi larvae. Three acaricides (Cyenopyrafen, Acequinocyl, and Cyflumetofen) and 4 fungicides (Wettable sulfur, TPN, Kresoxim-methyl, and Triflumizol) did not affect the density of A. swirskii. The use of these 14 agrochemicals should be recommended in integrated pest management (IPM) programs combined with A. swirskii to control pests on greenhouse melon.
Experiments were carried out by using four small glass houses. A predatory mite, Phytoseiulus persimilis Athias-Henriot had been observed to control the population of the two-spotted spider mite, Tetranychus urticae Koch successfully on egg-plants since the ratio of the number of P. persimilis female adults per plant to that of T. urticae was more than 0.1. Spraying of propylene glycol monolaurate, which killed T. urticae selectively with minimal effects on P. persimilis,increased the ratio of the predators drastically, which had been released once and increased on egg-plants before spraying the acaricide. Some plants, where the ratio of the predators was less than 0.1, remained although the average ratio of the predators was more than 0.1. However, thenumber of plants, where the ratio of the predators was less than 0.1, tended to decrease gradually with the passing of the days. Positive correlations between the densities of the both species were observed after the ratio of the predators had been more than 0.1 for two weeks. These results suggested that P. persimilis tended to disperse depending on their own density and density of T. urticae when the ratio continued being more than 0.1.
We examined the effect of lime applications with serial earthing-ups on welsh onion white rot disease in an infested field. By 4-serial lime applications from October until December, the rate of vendible welsh onions was raised from 3.3% to 24.0%. To define the effect of maintaining high soil pH in cold season, we carried out the inoculation test using a combination of leaf sheath disks and sclerotia at different pH values and temperatures. The disease incidence in leaf sheath disks with the initial pH 7.0 or 7.5 was significantly fewer than that with pH 6.5 or lower at 10 or 5°C. From these results, we suggest the benefit of the maintaining high soil pH in cold season to alleviate welsh onion white rot disease.
To isolate Pseudomonas syringae pv. japonica (Psj) from wheat seeds, we surface-sterilized seeds in 1.5% sodium hypochlorite for 3 min and inserted them in selective medium to be cultured for 7 days at 25°C. Psj cells were detected despite the surface sterilization. However, surface sterilization reduced the detection rate in barley. In the membrane filter method, Psj was detectable even in trace amounts after immersion of 100 g of wheat seed (2500 grains) for 4 days at 10°C in sterile distilled water, collecting the bacterial suspension on the membrane filter and applying it to selective medium. The method made it possible to detect Psj when only 0.08% of wheat seeds were contaminated.
A nonpathogenic strain of Xanthomonas sp. 11-100-01 was tested for its ability to control bacterial canker of citrus. The nonpathogenic bacterium survived on wounded citrus leaves for up to 2 weeks. The strain 11-100-01 sprayed at 108 cfu/ml officially reduced the leaf symptoms on potted citrus plants ‘Harumi’ inoculated by X. citri subsp. citri. In a field test, the application of the strain 11-100-01 in combination with copper formula effectively reduced the canker disease on leaves and fruits. This bacterial strain was considered as a practical alternative for copper formula which usually causes phytotoxicity in summer time.
We examined the potential for biological control of broccoli black rot, caused by Xanthomonas campestris pv. campestris, using a stock solution of a nonpathogenic strain, Xanthomonas sp. 11-100-01. The results are based on four times of field experiment. Our results suggest effective disease control was achieved, but at levels inferior to those obtained using a basic copper sulfate wettable powder. However, control was equal to that obtained using the Pseudomonas fluorescens wettable powder and was significantly higher than in the non-treated plants. In addition, the basic copper sulfate wettable powder induced phytotoxicity symptoms such as black spots on the leaves, whereas the 11-100-01 stock solution produced no symptoms. This is the first report of the biological control of broccoli black rot using a nonpathogenic Xanthomonas strain.
We developed a simple method to test the Quinone outside inhibitors (QoI) sensitivity of Pestalotiopsis longiseta, the causal fungus of tea gray blight. Diseased tea leaves were incubated under humid conditions for 2-4 days to form conidia. Healthy mature tea leaves were boiled in water for 5-10 minutes, immersed briefly in a 200-fold dilution of azoxystrobin 20% flowable, and placed on wet facial tissues in an air-tight container. Conidia on lesions were transferred to wet absorbent cotton and inoculated onto the boiled tea leaves. After 3 days incubation at room temperature, QoI-resistant isolates grew equally well on both fungicide-treated and non-treated leaves. In contrast, QoI-sensitive isolates did not grow on the fungicide-treated leaves. Both highly and moderately resistant isolates were identified as resistant in this test. Pestalotiopsis longiseta was distinguishable from unwanted fungi based on the formation of black conidial masses after 7-10 days incubation under diffused daylight.
Citrus melanose caused by Diaporthe citri reduces the commercial value of mandarin fruit. It is time-consuming for growers to control this disease in Wakayama Prefecture because it is necessary to treat the trees with fungicides four or five times. In this study, Ditianon 42% wettable powder was sprayed twice by late-June and Mancozeb 80% wettable powder was sprayed in August. According to a meta-analysis of ratio of severely diseased fruits in five experiments, the risk of this system is somewhat lower than that of the conventional system (fungicide Mancozeb was sprayed four times). This result suggests that it is possible that the frequency of spraying to control melanose can be decreased to three or four times.
Since 2002, the cabbage looper Trichoplusia ni (Hubner), a serious lepidopterous insect pest of cruciferous vegetables in other parts of the world, has often occurred in Aichi Prefecture. Therefore, in the present study, the susceptibility of T. ni to 22 insecticides was evaluated by the leaf dipping method. T. ni showed low susceptibility to organophosphorus insecticides but high susceptibility to other insecticides such as carbamates, pyrethroids, nereistoxins and Bt. However, it showed high susceptibility to lufenuron, flubendiamide, and indoxacarb. In addition, the susceptibility of T. ni to various insecticides was comparable to that of the common cutworm Spodoptera litura (Fabricius), which is the most serious lepidopterous insect pest of crciferous vegetablesin Japan.
Although T. ni showed lower susceptibility to PAP, acephate, and pyridalyl than S. litura, its susceptibility to other insecticides was as high as that of S. litura. These results indicate that T. ni can be easily controlled using insecticides that are effective against the common cutworm except for organophosphorus insecticides.
We developed a microbial pesticide “Hasumon killer®”, which included Spodoptera litura nucleopolyhedrovirus (SpltNPV) as the effective ingredient. It is known that this insect virus is rapidly inactivated by sunlight; however, the persistence of the formulated SpltNPV under field condition was not clear. To quantify the effect of the virus on soybean foliage, leaves from different positions of the plant were examined for insecticidal activity. The bioassay showed that loss of activity was rapid on the upper leaf. At 7 hr post spraying, the upper leaves retained about one-fourth of their initial activity, and most activity was lost by 48 h post spraying. The retention of the virus on the leaf surface was investigated by qt-PCR analysis. Approximately one-half of the initial virus amount was lost from the surface of upper leaves at 7 hr post spraving. After 72 hr the virus adhered to leaf was reduced to 20% or less of the initial virus amount on the whole foliage. These result indicate that exfoliation of the virus from the leaf surface was the major factor responsible for the loss of activity.
The toxicity of fourteen insecticides on melon thrips, Thripspalmi Karny, collected from cucumber or eggplant in four regions of Osaka Prefecture was examined using a broad bean leaf dipping method. The corrected mortality rate was high with emamectin benzoate and medium or low with the other insecticides. The results indicate that only emamectin benzoate is highly effective in controlling the four regional populations.