Location: Crops Pathology and Genetics Research
Project Number: 2032-22000-015-27
Start Date: Jun 20, 2013
End Date: Apr 29, 2016
Objective 1. The hypothesis is: that a peach seedling bioassay can be used to assess whether or not pre-plant soil fumigation is needed to control Prunus replant disease. In each of at least 20 orchard sites to be replanted with almond or peach, soil will be collected and used for a greenhouse bioassay to assess the potential of the soil to induce Prunus replant disease (PRD). The soil from each orchard location will be mixed with sterile sand to improve drainage and then subjected to three treatments: 1) a non-treated control, 2) soil pasteurization and 3) soil fumigation (chloropicrin (CP) or a 63:35 mixture of 1,3-dichloropropene (1,3-D): CP [i.e., Telone C35 formulation]). After dissipation of the fumigants, the soil samples will be distributed to replicate pots and planted with Nemaguard peach seedlings in a greenhouse. The seedlings will be grown for 8 weeks and then examined to assess severity of PRD symptoms (i.e., root cortex necrosis and growth suppression). The greater the severity of PRD symptoms in the control treatment as compared to the pasteurized and fumigated treatments, the greater will be considered the likely benefit from pre-plant soil fumigation in the sampled orchard. Objective 2. The hypothesis is: that growth responses to fumigation in an orchard will only occur in cases where the bioassay indicates potential for PRD. In at least 5 almond orchard locations in the Central Valley, replicate pre-plant fumigated and non-fumigated plots will be prepared and replanted to almond to assess the need for pre-plant soil fumigation. At least 2 of the sites will be in orchard soil where our bioassay indicated little potential for PRD, and 2 other sites will be in orchard soil where the bioassay indicated potential for severe PRD. Three treatments will be included, 1) a non-fumigated control, 2) a strip fumigation treatment with 1,3-D:CP (Telone C35, 540 lb/treated acre = ca. 270 lb/orchard acre) and 3) a spot fumigation treatment with the same fumigant (Telone C35, 540 lb/treated acre, ca. 54 to 75 lb/orchard acre). The need for fumigation will be assessed according to the annual measurements of steam diameter increases in each treatment, starting when the trees are planted. The magnitude of stem growth responses to fumigation (compared to the control) will be modeled to estimate yield effects and used to assess the value of fumigation. Objective 3. The hypothesis is:, spot fumigation will provide adequate PRD control and thereby facilitate large reductions in fumigant usage. The efficacy of spot fumigation treatments delivered as part of the orchard validations in Objective 2 will be evaluated and compared to the conventional strip fumigation treatments as described above (Objective 2). The hypothesis that spot fumigation will prove commercially adaptable, provide adequate PRD control, and thereby facilitate large reductions in fumigant usage will be evaluated by comparing efficacy and costs of the control, strip, and spot fumigation treatments.