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Epidemiology and Control of Citrus Greasy Spot on Grapefruit in Texas. L. W. Timmer, Associate professor, University of Florida, Agricultural Research and Education Center, Lake Alfred 33850; R. J. Reeve(2), and R. M. Davis(3). (2)Formerly research associate, Texas A&I University Citrus Center, Weslaco 78596 (now technical representative, Zoecon Corporation, Weslaco, TX); (3)Assistant professor, Texas A&I University Citrus Center. Phytopathology 70:863-867. Accepted for publication 29 February 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-70-863.

Greasy spot and greasy spot rind blotch (GSRB) in Texas are caused by Mycosphaerella citri. In a 4-yr study to determine the effect of M. citri on red grapefruit in the semi-arid Texas citrus area, the maximum spray program (cupric hydroxide—spring, benomyl + oil—summer) sharply reduced foliar greasy spot and somewhat reduced GSRB. The minimum program (citrus spray oils in the summer) was less effective, but significantly reduced disease incidence compared to the no fungicide control. Neither program increased yield or fruit size, or reduced defoliation compared to the control. Applications of acaricides to control the citrus rust mite, Phyllocoptruta oleivora, significantly reduced foliar greasy spot symptoms in 2 of 3 years in orchard studies and in a test on container-grown trees. In 1978, ascospore production by M. citri was low during spring, but sharp peaks occurred following flood irrigations in late June and in late July. Most ascospores were trapped during abundant rainfall in late August and early September and infection apparently occurred primarily in late summer. Symptoms did not appear until early spring and the disease did not cause excessive premature defoliation. Benefits of fungicidal control of the disease in Texas are few.

Additional keywords: Citrus paradisi.