Studies on the control of citrus fruits decay in storage. (IV)

Control of decay by o-Phenyl Phenol aerosol. (1)

Abstract

Recent tests have shown that dipping or spraying with a solution of sodium o-Phenyl Phenol (Dowi-cide A) gives good control of rot in Satsuma orange fruits during storage. From the practical point of view, however, dry method of application is desirable. Therefore, a study on the formula-tion and applying method of OPP for aerosol (smo-ke) has been made. The test material of OPP was packed in a “Citsin smoke candle, ” and released in the air of a closed fumigation chamber, having a space of 4 cubic meters, to sink upon the orange fruits or glass slides. It was shown that a rate of 2gm OPP per cub. m., added with 1gm hexamine and 1gm NH₄Cl, is effective and safe. When OPP was smoked at this rate on glass slides, it supp-ressed completely the germination of spores of common green mould (Penicillium digitatum), and the effectiveness lasted for 90days. Treatment of the fruits before storage in December, caused no visible injury to the fruits till the following April and gave control of rots as good as the spraying with Dowicide A. Use of 6gm of OPP alone per cub. m. induced burning, which was avoidable by adding 3gm hexamine to OPP.
A preparation, from which NH₄Cl was omitted, showed'a tendency to increase the fungicidal effec-tiveness, but it produced an undesirable effect, forming powdery crystals upon the surface of the fruits. When each of OPP and hexamine was packed in separate candles and fumigated together, it was found that effectiveness lowered a little at a rate of 0.4gm of OPP, per cub. m. and powdery cristals blemished the fruit, at a rate of 0.5gm. An addition of hexamine to 0.3gm of OPP per cub. m. did not caused a reduction of the effective-ness. The amount of OPP deposit on the surface of fruits decreased with time; for example, it reduced to quarter after 30 days. This suggests the volatility of OPP. It was confirmed by the fact that OPP deposit on the surface of cover glass inhibited the germination of spores of common green mould on glass slide at distance of about 5 cm in closed chamber.
Tests on a practical scale were made in the store houses of the Experiment Station and a commercial grower. Aerosol application of OPP at a rate of 2gm per cub. m. showed good control of rot espe-cially common green mould, almost equal to the spray treatment with Dowicide A. A slight varia-tion of the effecitiveness due to the position of the materials in the store house may be seen.