Rust Disease on Lemongrass in California

Lemongrass (Cymbopogon citratus) is a minor crop grown for its edible stem and oil. The plant is grown both commercially, by specialty producers, and noncommercially, particularly by homeowners of various Asian communities. For several years, a rust disease has affected the lemongrass plantings in coastal and inland California. Symptoms consist of elongated, stripelike, dark brown lesions that develop on both sides of leaf surfaces. Only lesions on abaxial leaf surfaces erupt and develop dark cinnamon brown uredinial pustules. Lesion development can be substantial, and coalescing lesions result in significant foliage death. Ellipsoidal urediniospores measured 22 to 28 μm by 22 to 25 μm and contained 3 to 4 germ pores in an equatorial configuration. Uredinia contained clavate paraphyses. Teliospores were not observed. Based on the morphology of the uredinia and urediniospores, the rust was identified as Puccinia nakanishikii (1). Rust on lemongrass has been observed during various seasons, but this is the first report identifying the causal pathogen in California. A Darluca mycoparasite species was often observed in uredinia of infected lemongrass from the coastal counties. In the United States, P. nakanishikii has also been reported on lemongrass in Hawaii (2). References: (1) G. B. Cummins. 1971. The Rust Fungi of Cereals, Grasses, and Bamboos, Springer-Verlag, New York. (2) D. E. Gardner. Plant Dis. 69:1100, 1985.