Rapid apple decline has researchers stumped.

Abstract

Young apple trees have been inexplicably dying across the United States and Canada. Growers are eager to understand whether this syndrome—called rapid or sudden apple decline—poses a serious new threat to the valuable fruit industry, and how it might be fought. Drought and severe cold could be underlying causes, but they don9t appear to be the whole story. Scientists are examining other factors, including pests and pathogens. Some researchers wonder whether certain types of rootstock or exposure to herbicides might make young trees more susceptible to disease or stress. The nature of modern apple farming could be a factor. Rapid decline is most common in densely planted orchards, which are proliferating because they are more efficient to manage. Tightly packed trees have shallow roots and must compete for nutrition and moisture, which can make them more vulnerable to drought.