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Evaluation of Systemic Fungicides and Mineral Oil Adjuvants for the Control of Mal Secco Disease of Lemon Plants. Z. Solel, Division of Plant Pathology, The Volcani Institute of Agricultural Research, Bet Dagan, Israel; J. Pinkas(2), and G. Loebenstein(3). (2)(3)Division of Plant Pathology, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Phytopathology 62:1007-1013. Accepted for publication 13 March 1972. DOI: 10.1094/Phyto-62-1007.

The performance of systemic fungicides in controlling mal secco caused by Deuterophoma tracheiphila was evaluated in bioassays and in 1-year-old seedlings of Rough lemon, an extremely susceptible species. In bioassay tests, carboxin and cycloheximide were the most toxic compounds to D. tracheiphila, preventing germination at 2 µg/ml. Sprays applied before inoculation were superior to those applied afterward. Moreover, the efficacy of postinoculation sprays declined rapidly as application was delayed. Foliar sprays with aqueous benomyl suspension markedly decreased disease severity, whereas Thiabendazole (TBZ) and carboxin treatments were ineffective. Soil drenches with cycloheximide semicarbazone, benomyl, TBZ, and oxycarboxin prevented disease development in stems inoculated 1 month later. The first two compounds and carboxin inhibited infection in leaves inoculated soon after treatment. Certain mineral oils added to the aqueous leaf sprays of TBZ and carboxin greatly enhanced their performance, probably by increasing uptake. Carboxin suspended in undiluted mineral oil, applied to a band at the base of the stem, suppressed systemic development of the disease when stems were subsequently inoculated above the application band, and inhibited disease development in inoculated leaves. These results justify the evaluation of TBZ and carboxin with oils in mal secco-infected lemon groves, in a combined stem and foliar application.

Additional keywords: Citrus jambhiri.