The Effects of Citrus Planting Design on Soil Properties and Phytophthora nicotianae Propagule Counts in Flood-irrigated Soil

The Lower Rio Grande Valley (LRGV) of South Texas is the citrus producing region of the state. Its subtropical semi-arid climate offers excellent growing conditions to produce oranges and sweet, deep red colored grapefruit. Foot rot and root rot, caused by Phytophthora nicotanae, are a big problem in the citrus groves of the LGRV. This oomycete infects the roots and trunk of the tree leading to tree decline and eventually it causes tree death. P. nicotanae infections to plant roots prosper in water saturated soils. Such conditions are readily found in the LRGV as citrus trees are typically flood irrigated in South Texas. We hypothesize trees planted on raised beds rather than flat ground will result in a lower count of P. nicotanae propagules in the soil as water will move laterally through the soil profile to irrigation roots without water touching the tree trunk. We compared the soil habitat of plastic mulch covered soil to bare uncovered soil on raised-beds vs. to flat-beds. We measured the soil gravimetric water content, bulk density, soil and ambient temperature under flat-covered, flat-uncovered, raised-covered, raised-uncovered beds, and quantified P. nicotianae propagules during the spring and summer trials. A comprehensive understanding of the soil environment under different planting methodologies will provide new opportunities to decrease disease incidence of P. nicotianae.