Abstract

A field trial is underway in Ithaca, New York, to examine the ability of an alternative fumigant to methyl bromide, the use of compost, tolerant rootstock genotypes and cultural control to reduce the impact of apple replant disease in this replanted orchard site.

Issue

ARD is a disease complex that often affects young apple trees in replanted orchards. Up to 70 percent of replanted orchard sites in New York are affected by ARD. ARD results commonly in reduced fruit production, especially during the early years of orchard growth. Thus, apple growers who took on loans to replant their orchards get into serious financial trouble in replaying them. The most common remedy, soil fumigation with methyl bromide, is not available for much longer, as the methyl bromide is scheduled to be phased out this year. Moreover, soil fumigation proved helpful only in about 50 percent of tested New York State orchard sites.

Response

In 2001, a 20-year old orchard in Ithaca, New York, was replanted. The old trees were removed and preplant soil treatments of fumigation with Telone C-17, compost application or a combination of the two were applied. Five dwarfing or semi-dwarfing rootstocks were planted into two different positions: the old tree row (OR) or the grass lane (GL) of the previous orchard. Replant tree growth in the OR was reduced compared that in the previous GL. DNA fingerprinting revealed significant differences in the bacterial community composition between OR and GL. However, there were no significant differences in the community composition of Oomycetes. This 'old row effect' was detrimental to trees on the rootstocks M7, M26 and CG16, while the growth of trees on CG30 and CG6210 rootstocks, chosen for their ARD tolerance, was similar in both positions. Three projects are running currently: 1) A comparison of the performance and the microbial rhizosphere community composition of five different rootstocks in a replanted orchard site, starting one year after replanting through the first harvest; 2) A comparison of the performance and the microbial rhizosphere community composition of fourteen different rootstocks in replant soils collected in three major apple growing regions in New York; 3) An evaluation of a possible connection between ARD severity and ground-cover management strategies in the previous orchard using seedling biotests.

Impact

The results of our research will help apple growers choose tolerant rootstock genotypes when replanting their orchards. Our work will also yield a better understanding of the mechanisms behind ARD and yield improved disease management strategies for growers.

Funding Sources

• Other USDA (e.g., Water Quality, Special Grants, NRI)

Key Personnel

• Ian Merwin, Cornell University
• Janice Thies, Cornell University
• Eric Nelson, Cornell University
• Angelika Rumberger, Cornell University
• Shengrui Yao, Cornell University
• Michelle Leinfelder, Cornell University