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Michelle M. Leinfelder and Ian A. Merwin

Apple replant disease (ARD) is a common problem typified by stunted growth and reduced yields in successive plantings of apple (Malus ×domestica Borkh.) in old orchard sites. ARD is attributed to biotic and abiotic factors; it is highly variable by sites, making it difficult to diagnose and overcome. In this experiment, we tested several methods of controlling ARD in a site previously planted to apple for >80 years. Our objective was to evaluate practical methods for ARD management. We compared three different experimental factors: four preplant soil treatments (PPSTs) (compost amendments, fumigation with Telone C-17, compost plus fumigation, and untreated soil); two replanting positions (in the old tree rows vs. old grass lanes); and five clonal rootstocks (`M.26', `M.7', `G.16', `CG.6210', and `G.30') during 4 years after replanting. The PPSTs had little effect on tree growth or yields during 4 years. Tree growth was affected by planting position, with trees planted in old grass lanes performing better than those in the old tree rows. Rootstocks were the most important factor in overcoming ARD; trees on `CG.6210' and `CG.30' grew better and yielded more than those on other rootstocks. Rootstock selection and row repositioning were more beneficial than soil fumigation or compost amendments in controlling ARD at this orchard.

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Michelle M. Leinfelder, Ian A. Merwin, Gennaro Fazio, and Terence Robinson*

We are testing control tactics for apple replant disease (ARD) complex, a worldwide problem for fruit growers that is attributed to various biotic and abiotic soil factors. In Nov. 2001, “Empire” apple trees on five rootstocks (M.26, M.7, G.16, CG.6210, and G.30) were planted into four preplant soil treatments—commercial compost at 492 kg/ha soil-incorporated and 492 kg·ha-1 surface-applied), soil fumigation with Telone C-17 (400 L·ha-1 of 1,3-dichloropropene + chloropicrin injected at 30 cm depth five weeks prior to replanting), compost plus fumigant combination, and untreated controls—at an old orchard site in Ithaca, N.Y. Trees were replanted in rows perpendicular to, and either in or out of, previous orchard rows. Irrigation was applied as needed, and N-P-K fertilizer was applied in 2001 to all non-compost treatments to compensate for nutrients in the compost treatment. After two growing seasons, the rootstock factor has contributed most to tree-growth differences. CG.6210 rootstock supported greater growth in trunk diameter, central leader height, and lateral shoot growth (P < 0.05), regardless of preplant soil treatments and replant position. Trees on M.26 grew least over a two year period. Replant growth was greater in old grass lanes than in old tree rows, despite higher root-lesion nematode populations in previous grass lanes. Growth responses to preplant soil fumigation were negligible. Preplant compost did not increase tree growth during year one, but did increase lateral branch growth in year two. Results thus far suggest that replanting apple trees out of the old tree-row locations, and using ARD tolerant rootstocks such as CG.6210, may be more effective than soil fumigation for control of ARD in some old orchard sites.