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- Author or Editor: Steven A. Hoying x
We are evaluating the severity of apple replant disease (ARD)-characterized by stunted tree growth in replanted orchards, attributed to root pathogens and/or edaphic conditions-and testing preplant soil treatments for control of this wide-spread problem. Soil samples were collected during 1996–98 at 17 orchards in New York's major fruit growing regions and plant-parasitic nematodes and nutrient availability were quantified. Apple seedlings and potted trees on M.9 rootstocks were grown in fumigated and non-fumigated soil samples as a diagnostic bioassay for ARD severity. Factorial combinations of metam sodium, consecutive cover crops of Brassica juncea `Forge' and Sorghum sudanense `Trudan 8', and fertilizer/lime amendments were applied as preplant treatments at each orchard, 9 to 12 months before trees were replanted. Diagnostic bioassays indicated severe ARD at more than half the sites, and nematodes were not a major factor. Responses to preplant soil treatments were highly variable across the 17 farms. The best tree growth and yields followed preplant metam sodium at some sites, Brassica juncea and Sorghum sudanense at others, or fertilizer amendments at a few others. Tree responses to combined preplant soil treatments were often additive, and greater at irrigated sites. Comparisons of preplant diagnostic bioassay results with subsequent tree responses to metam sodium at the 17 orchards indicated that diagnostic tests predicted from 7% to 75% of tree growth response to soil fumigation, varying substantially across years and sites. It appeared that ARD was variable and site specific in New York orchards, and could not be controlled effectively with a uniform preplant soil treatment across our major fruit-growing regions.