Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2005
Publication Date: 11/1/2005
Citation: Mazzola, M., Mullinix, K. 2005. Comparative field efficacy of management strategies containing brassica napus seed meal or green manure for the management of apple replant disease. Plant Disease. v. 89. p. 1207-1213.
Interpretive Summary: Control of soil borne pathogens and parasites is crucial to the successful establishment of new orchards on old orchard sites. Although soil fumigation can effectively achieve this goal, there is a desire to develop environmentally sustainable measures that are compatible with current orchard management systems and achieve effective disease control. A wheat cover crop and rape (Brassica napus) green manure crops each provided a degree of disease control and increased growth and yield of apple. However, the response observed was inferior to that attained through soil fumigation and was not likely to provide growers the returns necessary to sustain economic vitality. The use of rape seed meal, a bio-product of soil extraction from seed, when used in conjunction with the fungicide mefenoxam was as effective as soil fumigation for the control of replant disease at certain sites. This alternative treatment was less effective on sites where the lesion nematode contributed to disease development. This plant parasitic nematode rapidly recolonized orchard soils and within one year had attained populations equivalent to or greater than that present before soils were treated. Modification of this system to ensure that the seed meal is incorporated into soils to greater depth may provide more effective control of the lesion nematode and ensure efficacy across apple orchard ecosystems.
Technical Abstract: Alternative measures to the use of pre-plant soil fumigation for the control of apple replant disease, were evaluated in the orchard. A one-year wheat cover crop consisting of three short-term cropping periods with removal of plant material after each sequence and a three-year B. napus green manure significantly enhanced growth and yield of Gala/M26. However, in each instance the resulting disease control and growth response were inferior to that achieved through pre-plant soil fumigation. A three-year bare fallow and one- or two-year B. napus green manure neither suppressed disease development nor enhanced tree growth. Pre-plant RSM amendment in conjunction with post-plant mefenoxam soil drench provided effective disease control and the resulting tree growth and yield were comparable to that attained in fumigated soil at Columbia View orchard. At the WVC orchard, the growth response attained with the alternative treatment was inferior to pre-plant soil fumigation, which was associated with an apparent re-infestation of RSM-treated soils and tree roots by Pratylenchus spp. Application of RSM after wheat cropping or in conjunction with soil solarization provided an intermediate level of disease control and corresponding reduction in growth and yield of apple relative to pre-plant fumigation at both sites. Manipulation of the RSM application method to ensure incorporation to greater soil depths should enhance disease control reliability and provide further support for the adoption of this alternative replant disease management strategy.