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Title: EVALUATION OF ROOTSTOCKS AND FUMIGANTS FOR CONTROL OF ALMOND REPLANT DISEASE

Author
item Browne, Greg
item CONNELL, J. - UC DAVIS PLANT PATH
item Becherer, Harold
item MCLAUGHLIN, S. - UC DAVIS PLANT PATH
item SCHNEIDER, S. - UC DAVIS PLANT PATH
item LEE, R. - UC DAVIS PLANT PATH
item HOSODA, E. - UC DAVIS PLANT PATH

Submitted to: Proceedings of Methyl Bromide Alternatives Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2003
Publication Date: 6/1/2003
Citation: Browne, G.T., Connell, J., Becherer, H.E., Mclaughlin, S., Schneider, S., Lee, R., Hosoda, E. 2003. Evaluation of rootstocks and fumigants for control of almond replant disease. Proceedings of Methyl Bromide Alternatives Conference.

Interpretive Summary: A severe replant disease (RD) has affected many first-year almond orchards in the upper Sacramento Valley. The disease is characterized by a failure to grow and death of almond trees that are planted at cleared field sites with a recent long-term history of almond culture.We conducted multiple orchard replant experiments to evaluate the efficacy of the pre-plant fumigation and rootstock treatments for management of the RD. At commercial sites previously affected by severe RD, we replanted almond trees after different combinations of pre-plant fumigation and rootstocks treatments. All of the experimental trees grew satisfactorily until May 2003. By July 2003, most trees planted in non-fumigated sites stopped growth and exhibited moderate to severe RD symptoms (Figs. 1, 2; Orchard 1 and Orchard 2). Lovell, Nemaguard, and Marianna 2624 rootstocks all were affected, although symptoms were most pronounced on the latter (Fig. 1). In the first experiment at both orchards, pre-plant fumigation with either methyl bromide:chloropicrin (75:25, 1 lb per tree site) or chloropicrin (1 lb per site) generally prevented RD. In the second experiment at each orchard, several fumigant alternatives were equal to or better than MB for preventing RD (Fig. 2). In Orchard 2, chloropicrin effectively prevented RD when used at 0.25, 0.5, 1.0, or 2.0 lb per tree site (Fig. 3). This research demonstrated practical and effective fumigant alternatives to methyl bromide for management of the RD.

Technical Abstract: A severe replant disease (RD) has affected many first-year almond orchards in the upper Sacramento Valley. The disease is characterized by a failure to grow and death of almond trees that are planted at cleared field sites with a recent long-term history of almond culture.We conducted multiple orchard replant experiments to evaluate the efficacy of the pre-plant fumigation and rootstock treatments for management of the RD. At commercial sites previously affected by severe RD, we replanted almond trees after different combinations of pre-plant fumigation and rootstocks treatments. All of the experimental trees grew satisfactorily until May 2003. By July 2003, most trees planted in non-fumigated sites stopped growth and exhibited moderate to severe RD symptoms (Figs. 1, 2; Orchard 1 and Orchard 2). Lovell, Nemaguard, and Marianna 2624 rootstocks all were affected, although symptoms were most pronounced on the latter (Fig. 1). In the first experiment at both orchards, pre-plant fumigation with either methyl bromide:chloropicrin (75:25, 1 lb per tree site) or chloropicrin (1 lb per site) generally prevented RD. In the second experiment at each orchard, several fumigant alternatives were equal to or better than MB for preventing RD (Fig. 2). In Orchard 2, chloropicrin effectively prevented RD when used at 0.25, 0.5, 1.0, or 2.0 lb per tree site (Fig. 3). This research demonstrated practical and effective fumigant alternatives to methyl bromide for management of the RD.