Numerous Unsuccessful attempts have been made to replant sites in citrus groves where trees have been infected with Armillaria mellea. The original rootstock, sweet orange, is susceptible. Some sour orange rootstocks are resistant to the disease, but cannot be recommended because of susceptibility to tristeza (quick decline). Troyer citrange and trifoliate orange are most commonly replanted now, but both are extremely susceptible to Armillaria mellea. An Ichang hybrid has shown resistance in greenhouse tests and is now being field tested.

This cooperative Armillaria research effort was under project leaders Donald E. Munnecke and Martin J. Kolbezen, Plant Pathology Department; Lewis H. Stolzy, Irrigation Department; and Albert O. Paulus, Extension Plant Pathologist, University of California, Riverside. The Hinckley Orange Grove Company in Bryn Mawr cooperated by providing the site where the experiment was conducted; Dow Chemical Company provided the methyl bromide; Neil Maclean Company applied the fumigant; and Dr. Thomas M. Little, Extension Statistician, made the statistical analysis of the data.