Climatic Factors and Synoptic Weather Charts Concerning the Initial Stage of Occurrence of Leaf Blast on Rice Plants in Paddy Fields
1971 Volume 1971 Issue 22 Pages 38-43
Details
1971 Volume 1971 Issue 22 Pages 38-43
The lesions of leaf blast caused by Pyricularia oryzae Cav. on leaves of rice plants wereinspected at the stage of primary infection in the paddy fields. All stands planted in 2.5-are field in 1961 to 1964, and plants grown in pots which were distributed at 24 spots in 4-hectare field in 1964 to 1967 and at 48 spots in 5-hectare field in 1968, and at 45 spots in another 50-hectare field in 1965 to 1968 were observed in Akita-ken.
When the lesions having grey centers with dark purple margins on the leaves of the same leaf-order appeared at first, it was designated as the initial stage of occurrence. Under the similar climatic conditions, inoculation tests were tried to evaluate the periods for developing such lesions. Based on the results, the date when infection occurred was estimated with twoday deviation.
After a period of more than 2 days at above 17°C, infection might be expected on a day without precipitation at night which followed to a period of more than 2 days with measurable rainfall. According to synoptic weather charts, there were low pressures in the eastward of the northern Japan and the south-westward of Kyushu, and the “Baiu front” moved to the southward by high pressure over Japan Sea.
