Preventative Root-Collar Excavation Reduces Peach Tree Mortality Caused By Armillaria Root Rot On Replant Sites.

Abstract

In the southeastern United States, Armillaria root rot (ARR) is caused by Desarmillaria tabescens and has become the primary cause of premature mortality in peach orchards. Most rootstocks used in commercial orchards are susceptible and management options are limited. A postinfection practice known as root-collar excavation (RCE), which involves permanent removal of the soil from the base of the trunk, has been shown to improve yields and prolong the productive life of symptomatic trees. However, symptomatic trees already have an advanced infection at the base of the trunk. This study evaluated the efficacy of preventative RCE on the progression of tree mortality in two orchards that were planted in infested replant sites. To provide convincing data for growers, the study was carried out in a commercial orchard and an experimental orchard for 8 years. Furthermore, representative enterprise budgets and net present value (NPV) analysis were utilized to compare the profitability of the two approaches. Trees were planted shallow on berms (45 by 90 cm) to facilitate RCE with hoes and AirSpade 2 years later. Tree mortality in the RCE treatment of the experimental orchard was first observed in year 6 and increased 8% on average per year thereafter. In contrast, tree mortality in the "Grower Standard" treatment was first observed in year 4 and increased 12.7% on average per year thereafter. At the commercial orchard, tree mortality in the RCE treatment was first observed in year 7 and increased 1.9% on average thereafter, while tree mortality in the Grower Standard treatment first appeared in year 5 and increased 4.3% on average thereafter. The delayed onset of ARR-associated tree mortality and the lower annual tree mortality rate in the RCE treatment led to higher NPVs in both locations. There were no negative effects on yield or fruit quality. However, the new planting system can create horticultural challenges, including the formation of a proper berm, uneven ground around the tree interfering with tree care and harvest, increased erosion due to channeling of rainwater, and increased rootstock suckering. The RCE is a valid option for southeastern growers needing to manage high ARR disease pressure on replant sites or on sites only recently cleared from ARR-infected forest land.