Abstract
Most citrus grove soils in Florida are infested with Phytophthora nicotianae, the causal agent of Phytophthora root rot which results in slow decline of tree condition and fruit production. The potential for composted municipal solid waste (CMW) as a soil amendment to provide long-lasting suppression of P. nicotianae and enhance root health and tree yield was evaluated. Composted municipal solid waste was applied to two groves of 25-yr-old Marsh grapefruit trees on sour orange rootstock and one grove of 6-yr-old Valencia orange trees on Carrizo citrange rootstock growing on marginal soils in a stage of decline in tree vigor. Two sources of CMW were applied as 5- to 10-cm-thick mulch layer under the tree canopy. Rhizosphere population densities of P. nicotianae were not reduced, but in some cases were increased by CMW. Root density response was site-dependent. Trees treated with CMW were more densely foliated probably due to improved soil moisture availability. Yields were not significantly greater at the second harvest after the application of CMW, but fruit size of Marsh grapefruit and Valencia orange was increased. The third year after application, CMW increased yield and size of grapefruit and size of orange. While CMW did not suppress P. nicotianae, the potential for CMW to improve citrus tree condition and productivity on certain marginal soils was demonstrated.
