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United States Department of Agriculture

Agricultural Research Service

Title: Examination of Symptoms and Control Measures for Replant Disease of Almond and Peach in California

Authors
item BROWNE, GREG
item Connell, Joseph - UCCE
item SCHNEIDER, SALLY

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 22, 2005
Publication Date: N/A

Interpretive Summary: Trials were conducted in orchards near Chico, CA and microplots near Parlier, CA to examine symptoms and control measures for a replant disease (RD) on almond. In the orchard trials, areas with a recent history of severe RD were cleared, given soil fumigation treatments in the fall, and replanted with almond trees on various rootstocks the following winter. The replants in non-fumigated soil developed severe RD (stunting, wilting, chlorosis, defoliation) by the following summer, while those in most fumigated treatments remained healthy. Trees in non-fumigated soil developed smaller trunk diameters and fewer healthy roots < 1mm diameter, compared to the healthy trees. Almond developed RD on all rootstocks evaluated (Marianna 2624, Lovell, and Nemaguard), but Marianna 2624 was the most severely affected. Pre-plant tree-site (spot) fumigation treatments with methyl bromide (MB), chloropicrin, 1,3-dichloropropene (1,3-D), 1,3-D + chloropicrin, iodomethane, and iodomethane + chloropicrin all prevented severe RD. Broadcast soil fumigation with chloropicrin also was effective, but broadcast MB and 1,3-D were ineffective. In microplots of RD-conducive soil, chloropicrin was more potent than MB for prevention of RD on Nemaguard peach. There was no association between nematodes and RD in orchard or microplot trials. The RD apparently was mediated by biological agent(s) other than nematodes and can be prevented with appropriate preplant tree-site spot fumigation treatments with chloropicrin or other MB alternatives. The effectiveness of the spot treatments indicates that RD can be prevented with relatively small amounts of fumigant per treated hectare.

Technical Abstract: Trials were conducted in orchards near Chico, CA and microplots near Parlier, CA to examine symptoms and control measures for a replant disease (RD) on almond. In the orchard trials, areas with a recent history of severe RD were cleared, given soil fumigation treatments in the fall, and replanted with almond trees on various rootstocks the following winter. The replants in non-fumigated soil developed severe RD (stunting, wilting, chlorosis, defoliation) by the following summer, while those in most fumigated treatments remained healthy. Trees in non-fumigated soil developed smaller trunk diameters and fewer healthy roots < 1mm diameter, compared to the healthy trees. Almond developed RD on all rootstocks evaluated (Marianna 2624, Lovell, and Nemaguard), but Marianna 2624 was the most severely affected. Pre-plant tree-site (spot) fumigation treatments with methyl bromide (MB), chloropicrin, 1,3-dichloropropene (1,3-D), 1,3-D + chloropicrin, iodomethane, and iodomethane + chloropicrin all prevented severe RD. Broadcast soil fumigation with chloropicrin also was effective, but broadcast MB and 1,3-D were ineffective. In microplots of RD-conducive soil, chloropicrin was more potent than MB for prevention of RD on Nemaguard peach. There was no association between nematodes and RD in orchard or microplot trials. The RD apparently was mediated by biological agent(s) other than nematodes and can be prevented by appropriate fumigation with chloropicrin or other MB alternatives.

Last Modified: 9/10/2014
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