Organically acceptable practices to improve replant success of temperate tree-fruit crops

• Replanting into soil previously used to grow similar tree species usually results in poor early tree growth.
• The replant disease complex is caused by root lesion nematodes and several fungal genera, exacerbated by poor soil health.
• Organically acceptable strategies to improve replant growth include nematode antagonistic cover crops, organic soil amendments, green manure cover crops, and Brassica seed meals.
• Compost amendments show considerable promise for improving replant growth.

For most temperate perennial fruit crops, replanting into soil that was used previously to grow the same or a related crop species usually results in poor early growth, preventing new plantings from reaching potential levels of productivity and economic returns to growers. Increases in population densities of root pathogens along with deleterious changes in soil quality under the preceding crops are largely responsible for these replant disease complexes. Driven by the rise in organic fruit production and new restrictions on fumigants and fumigation practices in the conventional sector, considerable research has been aimed, over the past two decades, to the development of non-chemical and organically-acceptable means of managing replant disease complexes. As apple is the most widely grown temperate perennial fruit crop, the majority of this research has been directed at the apple replant disease complex. This review summarizes knowledge of the causes of replant disease complexes of temperate orchard crops, and recent applied research on organically-acceptable practices to reduce the impacts of these disease complexes. Brassica seed meal amendments and composts show considerable promise as pre-plant soil amendments to improve replanted tree establishment. Composts have the added benefit of contributing to improvements in overall soil health that may enhance productivity in the long-term. Additional research to understand better the mechanisms by which compost amendments enhance replanted tree establishment would lead to improvements in the effectiveness and reliability of their utilization to alleviate replant disease.