Kyushu Plant Protection Research

This paper deals with the results of the experiment to examine the inhibitory effects of three bacteriocides on lesion enlargement of rice plants inoculated with Xanthomonas oryzae.
The plants were grown in wooden frames (60×360×20cm) and were inoculated by spraying the bacterial suspension (about 5×10⁸/ml) at a rate of 80 ml per m² for five times during the period from the most active tillering stage to young-panicle formation stage.
Fentiazon wettable powder (3-benzylideneamino-4-phenyl-thiazoline-2-thione 50%) at a 1, 000 ppm, organic nickel wettable powder (nickel-dimethylthiocarbamate 65%) at a 1, 625 ppm and dihydro-streptomycin sulphate at a 500 ppm were effective by twice spraying 12, 17 days after inoculations. Spraying of the former two increased the yields by 23.0-28.7%, while the third one did not increase though lesion enlargement was inhibited.

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Degree of infection with citrus canker (Xanthomonas citri (Hasse) Dowson) varies according to the aging of leaf and fruit.
This experiment was carried out for determine the sensitive period of spring leaves and fruits. In the spring leaves, various ages of young leaves of some citrus species, Fukuhara, Natsudaidai and Satsuma oranges, were inoculated through stomata with bacterial suspension containning 10⁸ cells per ml. While the age distribution and its successional changes was investigated every 5 days during the growing period of spring leaves. And the period of stomatal infection was determined by the results of the stomatal inoculation test and the distribution of leaves ages.
In the fruits, using Satsuma orange fruits, stomatal and wound inoculation was made every weeks with bacterial inocula containing 10⁸ cells per ml from the beginning of June to the middle of September.
With stomatal inoculation, the spring leaves of all tested species, were sensitive while middle aged leaves were many, from 10 to 50 days (the most sensitive period, from 20 to 40 days) after the orange buds were out.
In the fruits of Satsuma orange, stomatal infection was caused from the beginning of June to the middle of August. The most sensitive period was July. Wound infection was caused during the middle of June to the end of August. The most sensitive period was during the middle of June to the middle of July.

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Adequate time of spraying of streptomycin for the control of citrus canker on fruits was studied.
Since the late of May to the biginning of September, the spray was carried out as shown in Table 1.
It was observed that the effective control was resulted by the spraying in June and July, especially, the spraying in July was most effective.

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In the factor affected to the residual effect of agricultural chemicals, the flowing down by rain is an important one. So, in this experiment, the authors examined the residual effect of some fungicide under the conditions of artifical or natural rain.
In the test of effect of inhibition to germination of spore of citrus melanose by rain drops containing fungicides, the rate of germination increased quickly in the plots of Dithane, but in the plots of Deran the rate of germination increased slowly.
The mist spray and common spray to residual effect were compared, mist spray that is lower dilution, showed the higher inhibition to germination than common spray, even the same active ingredient. This result were seen in both Deran and Difolatan.
The result of inoculation test at the natural rain, Deren and Dithane have shown similar te-ndencies in the case of a little rain. Therefore, rainfall and residual effect seemed to correlate closely. But in the case of a heavy rainfall or rain which falls immediately after spray, the residual effect with Deran and Dithane decreased remarkably, especially in Dithane.

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