Recipient Organization
AUBURN UNIVERSITY
108 M. WHITE SMITH HALL
AUBURN,AL 36849
Performing Department
Horticulture
Non Technical Summary
Acreage dedicated to tree fruit production has declined largely because of soil environment stresses. A fungus, which causes a disease known as Armillaria Root Rot (ARR - also known as oak root rot) lives in the soil and affects peach as well as other crops. Armillaria root rot has been known to infect the roots of peach trees since the 1850's. Today ARR poses a significant threat and has been identified by industry stakeholders as a key tree pest particularly injurious to the peach industry with no good means of control (Horton et al., 2004). Armillaria root rot along with another soil-borne disease, peach tree short life (PTSL), are two of the leading causes of tree mortality in southeastern peach production and has cost the industry $10 million in lifetime production losses. The Armillaria fungus will colonize the root of a peach tree ultimately spreading to the root crown at the base of the tree resulting in tree death. Above ground, symptoms include presence of small leaves, branch dieback, dieback of whole scaffolds, and eventually all branches. Below ground, the white fungal mass of ARR can be found under the bark beneath the soil line. Typically, the fungus does not advance above the soil line. Peach trees infected with ARR generally live 3-5 years after planting. Increasingly, trees are succumbing to the disease between 1 and 3 years well before a profit can be realized. Worse is the fact the fungus remains viable in the soil for many decades in colonized root pieces remaining from previously infected trees. This reduces land area on which peaches can be planted. Options for management in ARR are few and are not without their limitations. Researchers are currently developing technologies to manage ARR in peach orchards. These technologies are root collar excavation (RCE) and use of the ARR-resistant rootstock 'MP-29'. Root collar excavation takes advantage of the soil-limited nature of ARR fungus and is a process by which soil is removed from the root crown of the tree using an implement such as an air spade. Root collar evacuation, therefore, creates a physical barrier that delays ARR colonization of the root crown leading to increased tree longevity. In ARR-resistant rootstock technology. A peach x plum interspecific hybrid, 'MP-29', has demonstrated resistance to ARR. Not considering the production challenges this rootstock presents to nursery operations such as slow grow resulting in a longer production period, the adaptability of the rootstock to the environments of the Alabama soils is not fully known. The objectives of the project are to develop a protocol for the control of Armillaria root rot in peach to reduce orchard replant diseases. To accomplish this research will be conducted at the Alabama Agricultural Experiment station and at on-farm locations that will investigate the use of RCE and ARR resistant MP-29 rootstock. Trees subjected to these systems will be evaluated for plant vigor, time of flowering, trunk cross sectional area, harvest date, fruit quality, and tree survivability. The compilation of the data gathered from this portion of the project will provide materials for the second objective, which is to provide research-based information to growers, industry leaders, Extension personnel, and researchers on Best Management Practices for ARR in peach orchards. This work will be an asset to these groups and will be available for underserved communities such as veterans and will include the socially, economically, and educationally disadvantaged.
Animal Health Component
50%
Research Effort Categories
Basic
10%
Applied
50%
Developmental
40%
Goals / Objectives
Goal oneDevelop a protocol for the control of Armillaria root rot in peach to reduce orchard replant diseasesThis study will be conducted in collaboration with researchers at the University of Georgia (UGA), Clemson University (CU), and the Alabama Cooperative Extension System (ACES). Researchers at CU have well established trials that have been conducted for at least a decade. Trials were established at two farm locations in SC. In these trials, it was noted that RCE trees on 'Guardian' rootstock showed significantly greater survivability than non-RCE 'Guardian' trees 5 years after planting. The study includes the long-term longevity of excavated trees and the impact of unexcavated trees on berms. We will also assess productivity of excavated trees with trees planted according to grower standard. Currently, it is unknown whether there are differences in yield between RCE and non-RCE. Collaborators at CU will continue to collect data from these studies.Similar to CU, replicated field trials at experiment stations and field demonstrations at on-farm locations (OFL) will be established to determine the effects on tree phenology/physiology, crop yield, fruit quality and acceptance of RCE and 'MP-29' technologies in peach orchards. Additionally, an economic analysis will be conducted to determine the feasibility of incorporating these novel strategies to control ARR using yield data and observations collected at OFLs. Yield data will be collected from demonstration plots at the convenience of the grower cooperator. Data gathered from these studies will be used to develop protocol for the management of ARR in southeastern peach orchards as well as other Extension and scientific journal articles.GoaltwoProvide research-based information to growers, industry leaders, Extension personnel, and researchers on Best Management Practices for ARR in peach orchards.Though these two technologies have yielded promising results in other experiments, there remain barriers of perception and impracticality to overcome. First, growers question the expense of time and money of installing berms, but more so, they question expenses surrounding air spade removal of soil from the crown of the trees. Secondly, many growers have learned from nursery owners that 'MP-29' grows slowly and it is a difficult stock upon which to graft. Unlike other more vigorous rootstocks such as 'Guardian'™, 'MP-29' requires two seasons of growth before they are ready for the market. Growers are aware that currently, in order to produce'MP-29' nurseries would have to modify their operations in a way that would accommodate a biennial production cycle.To allay these concerns, field demonstrations will be conducted at on-farm orchards known to have high ARR pressure to show the effectiveness of these crop management strategies to industry leaders. Three peach orchards located in Chilton, County, AL were selected: Orchard 1(32 45'47 33''N 86° 47' 30.71''W); Orchard 2 (32 44'16.51 33''N 86° 37' 09.03''W); and Orchard 3 (32° 54'02.15''N 86° 40' 27.26''W). Additionally, cost analyses pertaining to each strategy will be developed. Information from these demonstrations as well as from replicated trials will be disseminated through Extension meetings, conferences, field days, webinars, blog articles, and fact sheets. Surveys will be conducted to gauge growers' opinions and attitudes towards root collar excavation and 'MP-29 before and after demonstrations.
Project Methods
Objective one. Develop a protocol for the control of Armillaria root rot in peach to reduce orchard replant diseases.Year 1. In Alabama, a field trial will be installed at the Chilton Research and Extension Center in Clanton (CREC). The field will be prepared and rows formed during the winter of year one. The study will follow a randomized complete block split-plot design. Two to three main treatments will be established on single rows and will consist of a berm row, berm row that will receive RCE, or a non-berm row. Experimental sub-plot treatments will consist of 'Julyprince' grafted onto 'MP-29' (JP/MP) or 'Guardian' (JP/GN) rootstocks. 'Guardian' rootstock will be obtained from a reputable commercial nursery. To determine growth response of the various treatments trunk cross sectional area will be calculated from trunk diameter measurements in the fall taken 30 cm above the graft union. The following equation was used: where and r = radius (1/2 diameter). In all main plots, temperature probes will be installed at a depth of 15 cm in the center of each replication to measure soil moisture and temperature near soil surface.Demonstration plots will be installed at two OFL sites with a history of ARR and will consist of rows approximately 33 m in length spaced 5.5 m apart.In March of each year, nematode populations will be assessed as a diagnostic of PTSLSoil sample will be submitted to the Soils Laboratory at Auburn University. Year 2. Young peach trees will continue to be fertilized according to recommendations (Lockwood et al., 2005). Trunk diameter will be measured in the fall 30 cm above the graft union of each tree of each subplot (rootstock cultivar). At the end of year two, RCE will be applied to berm RCE treatments. Soil at a depth of approximately 10 cm will removed from the base of trees using an air spade with a compressor setting of 100 psi.Year 3. In year three, trees will be monitored for signs of decline. Each incident of tree mortality will be evaluated for cause of death. Root crowns will be inspected for the presence of well-developed, distinctive mycelial fans beneath the root bark, which is diagnostic of ARR (Beckman et al., 1998).Secondly, trees dead or in decline will be assessed to determine if PTSL is the cause of decline. A sudden collapse of the tree in early spring after flowering, dead scaffold branches, and increased sucker a the base of the tree are diagnostic of PTSL.Finally, whole trees including roots will be removed occasionally and sent to the Plant Diagnostics Laboratory at Auburn University for further evaluation when a cause of death cannot be determined in the field. Other causes of tree mortality could be insect damage, crown gall, or mismanagement (Beckman et al., 1998).Phenological parameters will be measured consisting of trunk diameter measurements in the fall, date of percent 30 % bloom, and date of 100 % bloom. Photosynthesis will be measured once each month on a clear day between 1100 and 1430 HR on three most recently mature leaves from the central tree in each sub-plot (Wilkins et al., 2002). Leaf surface are and foliar nutrition will be determined yearly during August. To determine leaf surface area, 100 healthy most recently mature leaves from the central tree in each sub-plot will be collected and analyzed using a leaf surface area analyzer. These leaves will then be sent to the Soils Laboratory at Auburn University of foliar nutrient analyses. Each month from April through October, number of suckers generated both at the base and beyond the base of the tree will be counted. Characteristic of MP-29 rootstock and RCE is the production of profuse suckering (Schnabel et al., 2012; T.G. Beckman personal communication).Consistent yield of high quality fruit is an indicator of overall profitability of peach orchards. Therefore, in year three, treatment trees will be allowed to produce a crop, which is standard practice in commercial orchard. Fruit will be harvested and yield per tree determined from the central tree of each sub-plot when the fruit external background color is turns yellow. Fruit of 'Julyprince' has a dark blush color which covers 80% of the fruit surface, and a yellow background color when ready for harvest. Data collection will include number of thinned fruit per tree, total yield per tree, fruit size, firmness, percent brix (sweetness), and average fruit weight.Extension specialists or Regional Extension Agents (REA) will coordinate harvests with grower cooperators to collect yield data. Each year during the second harvest, 20 fruit from each sub-plot will be used to measure organoleptic quality. Firmness will be measured using a penetrometer using a 0.8-cm plunger. Juice will be hand squeezed from each fruit and analyzed using a handheld, temperature compensating digital refractometer.Years 4 and 5. Data collected in years 1-3 will continue in years 4 and 5. Tree vigor, fruit yield and quality, and mortality rate will continue to be measured. Data will be analyzed in order to determine the effectiveness of these treatments in developing a protocol on best management practices for Armillaria root rot in each.Objective twoProvide research-based information to growers, industry leaders, Extension personnel, and researchers on Best Management Practices for ARR in peach orchards.Though these two technologies have yielded promising results in other experiments, there remain barriers of perception and impracticality to overcome. First, growers question the expense of time and money of installing berms, but more so, they question expenses surrounding air spade removal of soil from the crown of the trees. Secondly, many growers have learned from nursery owners that 'MP-29' grows slowly and it is a difficult stock upon which to graft. Unlike other more vigorous rootstocks such as 'Guardian'™, 'MP-29' requires two seasons of growth before they are ready for the market. Growers are aware that currently, in order to produce'MP-29' nurseries would have to modify their operations in a way that would accommodate a biennial production cycle.To allay these concerns, field demonstrations will be conducted at on-farm orchards known to have high ARR pressure to show the effectiveness of these crop management strategies to industry leaders. Three peach orchards located in Chilton, County, AL were selected: Orchard 1(32 45'47 33''N 86° 47' 30.71''W); Orchard 2 (32 44'16.51 33''N 86° 37' 09.03''W); and Orchard 3 (32° 54'02.15''N 86° 40' 27.26''W). Additionally, cost analyses pertaining to each strategy will be developed. Information from these demonstrations as well as from replicated trials will be disseminated through Extension meetings, conferences, field days, webinars, blog articles, and fact sheets. Surveys will be conducted to gauge growers' opinions and attitudes towards root collar excavation and 'MP-29 before and after demonstrations.