Objective. 3 – Implement Short- and Long-Term Approaches to Manage ARR

Summary of Objective 3

Newly discovered and/or developed rootstocks will be evaluated for desirable horticultural traits on replant sites. Cultural practices have the potential to reduce the financial burden of ARR to producers by extending the long-term productivity of Prunus orchards until ARR resistant compatible rootstocks are developed.

Obj. 3a. Identify resistant germplasm that also has optimal horticultural characteristics

Team Lead: G. Reighard

Team Members: D. Chavez, P. Brannen, J. Cook, SG nursery

Obj. 3b. Evaluate binary sectoral rootstocks as a strategy to increase longevity on ARR sites

Team Lead: T. Gradziel

Team Members: K. Gasic, G. Reighard

Almond is mechanically harvested so orchard floor needs to be even to allow for easier collection of the fruit. Therefore for a medium term solution we are testing sectoral rootstocks to extend longevity on the ARR sites.

Obj. 3c. Evaluate the efficacy of root-collar excavation (RCE) for ARR on peach and cherry

Team Lead: Guido Schnabel

Team Members: B. Koc, A. Iezzoni, D. Chavez

 A short-term solution to ARR diseases is Above Ground Root Collar Excavation (AGRCE), a horticultural practice that promises significantly longer tree survival on ARR-infested replant sites. In this practice, soil is removed from around the lower trunk of the tree (root collar) thereby exposing the primary roots. Following root collar excavation, the fungus retreats from already colonized roots due to drying and long term exposure to heat. Although this increases tree longevity, methods need to be refined to maintain the excavated area from continuously filling in with soil. The Schnabel lab (Clemson University) more recently developed and examined a new approach, resulting in peach trees with above-ground excavated root collars and eliminating many of the challenges of the earlier methods of root collar excavation. Pilot studies have demonstrated the potential of AGRCE for ARR management, but the larger scale commercial viability of this new planting technique must be investigated. Furthermore, the current method to excavate soil from the root collar is a difficult, labor and time intensive operation. Thus, the development of an alternate strategy to accomplish root collar excavation is critical for commercial production.

 

 

 

 

A component of Objective 3 is to address the need to determine and demonstrate the commercial viability of AGRCE, along with the development of a new mechanical root collar excavation system. Field trials were established throughout South Carolina in 2011 on ARR-infested replant sites. Overall tree health and performance are currently being assessed to determine the viability of the new system for commercial production. Currently, an air spade is used to excavate the soil from around the root collar (pictured left). A new mechanical system is also being evaluated to excavate the root systems in an efficient manner.

Grower demonstrations have been organized throughout the Southeast to educate growers on berm preparation and tree maintenance. Here, the levee plow is utilized to create the raised beds.

Equipment Utilized

A Weedbadger Model 2030 was acquired and modified for root collar excavation. The equipment was mounted on a tractor with the three point hitch mechanism. It has a hydraulic system with a PTO driven hydraulic pump. We fixed and confirmed the operations of the pump, valves, hydraulic actuators (cylinder and motor), and hydraulic lines. Next, we designed two paddle wheels in different sizes. The first paddle wheel had 19.5 in diameter and 4 in tall paddles. After initial testing in field conditions, we increased the diameter of the paddle to 22.5 in with 6 in tall paddles. The larger diameter and height of the paddle wheel ensured excavating the berms between the trees successfully. We are currently testing attachment of chains to increase the width of the excavation and to create a uniform spread of the excavated soil between the tree rows.

During this project term, we fine tuned the paddle wheel mechanism and integrated a safety guard. Different brush mechanisms to excavate the soil near the tree trunks for finer soil excavation with minimal disturbance to the tree roots will be tested.

The levee plow was presented to around 20 peach growers (SC and GA) and around 700 new acres in SC and 1,295 new acres in GA were established using the AGRCE planting system since the start of this project.

Significantly lower tree death was observed on Above Ground Root Collar Excavation planting compared to grower standard. In the AGRCE orchards, tree mortality was delayed, both in an experimental and in a commercial orchard, and lower percent mortality over time was observed. No difference in disease incidence, yield, and fruit quality between grower standard and established AGRCE field trials was observed.