Annual Report of The Kansai Plant Protection Society

Effect of the predatory mite, Amblyseius swirskii Athias-Henriot on the population of thrips and whitefly was investigated on greenhouse cucumber. In the released plot, 25 A. swirskii per square meter were released for control of the melon thrips, Thrips palmi Karny and the sweetpotato whitefly, Bemisia tabaci (Gennadius) on 20 and 27 September and 4 October 2007, respectively. A. swirskii colonized on leaves and the population densities of 2 pest species became lower in the released plot than in the control plot 3 weeks after first releasing. The temperature condition during the investigation (average: 16-33 °C, max: 19-48 °C, min: 6-23 °C) did not affect the colonizing success of A. swirskii on greenhouse cucumber.

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The movement of five leaf vegetable insect pests, Athalia rosae ruficornis, Phyllotreta striolata, Plutella xylostella, Chromatomyia horticola and Thrips tabaci were examined with an ultraviolet (UV)-transmitting plastic film and four UV-absorbing films, which blocked wavelengths below 340 nm, 360 nm, 370 nm or 380 nm. The insects were placed in an experimental box covered with the UV-transmitting film and the UV-absorbing film; their choice behaviors were observed. The numbers of A. rosae, P. striolata and T. tabaci distributing in the area under all the UV-absorbing films tested were smaller than those under the UV-transmitting films. Movement of P. exlostella and C. horticola into areas under films blocking UV wavelengths below 360 nm,370 nm and 380 nm was suppressed compared to that with the UV-transmitting films. From these findings, we would expect the five insect pests tested to avoid light conditions that do not contain UV wavelengths of 360 nm and less.

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Broccoli in markets frequently suffers from black spot disease and rapidly turns yellow, thus losing commercial value. To clarify the causal pathogen, we isolated micro-organisms from infected broccoli and examined them for their pathogenicity using an inoculation assay. The pathogenic isolates obtained were further examined and identified using morphological and molecular characteristics. For molecular analyses, the nucleotide sequences of ribosomal DNA internal transcribed spacer regions were determined, and specific gene sequences were amplified using PCR. The highly pathogenic isolate obtained was identified as Alternaria brassicicola HLYB-4. Vegetative hyphae of the isolate slowly elongate and produce spores, even during cold storage (5 °C). Optimal hyphal growth was observed at 25 °C. Both ethylene production and chlorophyll degradation of diseased broccoli increased after infection with this isolate, promoting senescence of florets. However, higher temperatures (35 °C) severely restricted growth of the pathogen.

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The conditions inducing the peak dispersion of conidia of Botryosphaeria berengeriana were investigated using data collected during eight periods of continuous rainfall between 1991 and 1992. These rainfall events varied from 800 to 1540 minutes in duration. Conidia were collected about every two hours onto 2 glass microscope slides coated with glycerol jelly using a spore trap. The spore trap was set up in the midst of some naturally infected pear prunings about 20 cm in length at the height of 1 m from the groundside. This monitoring clearly showed that at least three hours from the beginning of a rainfall episode was needed before a large number of conidia of Botryosphaeria berengeriana dispersed under continuous rainfall. Moreover, it was shown that 60% or more of the total number of conidia produced by a rainfall event were released in the total period of 4-6 hours before and after the peak. Clarifying the rainfall conditions that induce maximal dispersion of conidia will help in understanding and so preventing disease outbreaks.

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