Evaluation of Pre - and Post-plant Treatments for Replanted Peach Orchards Roger A. Duncan *1 , Michael McKenry 2 , Kate Scow 3 , 1 University of California Cooperative Extension, 3800 Cornucopia Way #A, Modesto, CA 95358; 2 Department of Nematology, UC Riverside; 3 Department of Land, Air, and Water Quality, UC Davis As old peach and almond orchards are replaced, growers are faced with a poorly understood replant problem that involves pathogenic nematodes and soil-borne mycoflora. The most problematic nematodes in the North San Joaquin Valley are ring ( Mesocriconema xenoplax ), root lesion ( Pratylenchus vulnus) and rootknot ( Meloidogyne spp.). Ring nematode is associated with the bacterial canker complex, a disease that kills young trees in replanted orchards. Pre-plant soil disinfestation is a vital component when planting second or third generation orchards in sandy soils. Replanted orchards not fumigated prior to planting generally have poor vigor, do not grow uniformly and often succumb to bacterial canker disease within one to three years. Even after fumigation, second-generation orchards are often plagued with bacterial canker within 3-5 years. Growers often try post-plant treatments, including microbiological soil additives to maintain a “healthy” soil and prevent the rapid return of pathogenic nematodes. A trial was initiated in a commercial peach orchard to compare commercially available pre-plant fumigants for soil disinfestation and tree growth. Several post plant fertilizers, nematicides and microbiological amendments were applied for three years after planting in fumigated and non- fumigated areas. Trial Description. • A third generation peach orchard planted on Delhi Sand with a history of bacterial canker. • Fumigation treatments applied in October 2000. • Trees planted February 2, 2001 @ 919 trees per hectare. • Pre-plant fumigation treatments applied in October, 2000 across rows: 1) Untreated 2) 98% Methyl Bromide @ 439 kg per hectare - tarped 3) Vapam @ 250 ppm (701 l / ha) – “drench” application 4) Telone II @ 327 l / ha shank-applied to 1.25 hectares adjacent to trial. • Treatments applied at planting:  Composted green waste and steer manure @ 10,550 kg / ha each plus 4.5 kg of oyster shell flour per tree were applied to berms prior to planting and back-filled into planting holes. • Post-plant treatments: Below is a list of post-plant treatments that have been applied for three years to fumigated and non-fumigated areas through the drip irrigation system or as foliar sprays .