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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Implementation of a Regional Fungicide Resistance Monitoring and Brown Rot Disease Management Program to Sustain Peach Production in the South

Project Directors (PDs): Guido Schnabel [1] Phillip M Brannen [2] Achour Amiri [3]

Lead State: SC Lead Organization: Clemson University

Cooperating State(s): Georgia

Extension Funding: $64,062

Research Funding: $93,576

Start Date: Jun-11-2008 End Date: Jun-10-2011

Pests Involved: brown rot disease

Site/Commodity: peaches

Summary: This is a joint research-extension project addressing the emergence of fungicide resistance in Monilinia fructicola, a serious threat to the sustainability of southern peach production and a key issue of the Pest Management Strategic Plan for Eastern Peaches. Preharvest fungicide applications are a critical component of integrated brown rot management, but resistance to benzimidazole and demethylation inhibitor fungicides have already caused control failures in commercial orchards. Consequently, usage of quinone outside inhibitors (QoIs) has increased; this fungicide class readily develops resistance, so the resistance risk is very great. If resistance to QoIs does develop, and we have strong evidence that it already has in some locations, growers will be left with no effective alternative for brown rot control. The goal of this project is to implement a region-wide and eventually self-sustaining resistance monitoring program that will enable growers to select the most effective pre-harvest fungicide program for their specific location. Our objectives are to (i) conduct training for county agents to assess fungicide resistance profiles of M. fructicola field populations; (ii) develop a regional monitoring program, where agents from southern states determine and report local resistance profiles; (iii) provide immediate prescription disease control recommendations based on resistance profiles; and (iv) update and improve current resistance management strategies by analyzing the effect of spray recommendations on resistance profiles and by conducting efficacy trials. We are requesting ~$100,000 for our research activities and ~$100,000 for our extension activities. This proposal addresses both future directions and focus areas of the IPM Road Map for the National IPM Program. Objectives: 1. (Extension) Technology transfer of the lipbalm method, to include on-site training for county agents and extension specialists in multiple states (AL, GA, NC, SC) 2. (Research) Develop a regional monitoring program, where agents and specialists from participating states GPSmark sample sites, collect samples, determine resistance profiles, and obtain spray records. 3. (Extension) Provide prescription disease control recommendations to agents and specialists based on resistance profiles 4. (Research) Improve existing resistance management strategies by analyzing the effect of actual sprays on resistance profiles and by conducting efficacy tests on DMI resistant populations across the three experimental years

Final Report:

Results From report submitted by the PI to USDA report system PROGRESS: 2008/06 TO 2011/06 OUTPUTS: The objective of this research/extension effort was to develop and implement a resistance monitoring program for sustained brown rot management in Southeastern peach production. We developed a fast and easy assay that can be used to determine location-specific fungicide resistance profiles. The assay used a standard laboratory sterile 24-well (6 x 4 wells) plate (12.5 x 8.5 x 2 cm). If held vertically, there are 4 wells per row allowing for 4 samples to be processed and 6 wells per column allowing for 6 treatments (one control and 5 fungicide treatments. Consequently, for a 10-fruit sample, three 24-well plates are required with the choice of leaving 2 columns empty or processing 12 instead of 10 fruit per location. Similar to the lipbalm tubes, the wells are prefilled with fungicide-amended or unamended PDA (1.5 ml per well) plus 100 mg/l streptomycin. When all the wells are filled with PDA, plates are sealed with removable plastic film for each column individually. A kit shipped to agents may contain 15 prefilled 24-well plates ready for inoculation, 5 data sheets, 1 user manual, 10 individually wrapped antimicrobial hand wipes, 60 toothpicks, and 60 individually wrapped cotton swabs; sufficient supplies to monitor 5 locations with 10-12 observations (fruit) per sample. Prior to inoculation, the seal from the first column is removed and spores are transferred to the center of the PDA-filled wells. Spores from the same fruit are transferred directly from the fruit or from the cotton swab into each well of a single column using a wooden toothpick. In our experience, the toothpicks do not need to be autoclaved for the assay when using antibiotics in the PDA. Furthermore, we have used the same toothpick to inoculate the 6-wells of a single column for a single fruit sample and then switch toothpicks when going to the next single-fruit sample (column) without noticing increased contamination problems. When all four columns are inoculated, the plastic lid is returned and the plate is labeled and incubated at room temperature (20-25oC) for exactly 72 h. Each batch of plates should undergo a standard quality control check prior to shipment to make sure the plates of the new batch perform as they should using DMI, MBC, and QoI fungicide sensitive and resistant isolates. Relevant Georgia and South Carolina county agents (11) and some specialists (3) were trained to use the Profile kit. Between 2008 and 2010 more than 120 kits were manufactured and shipped to participating agents. Data were collected at a total of 28 sites, 26 of them located in South Carolina. With one exception, all sites were commercial production areas. Agents were able to use the kit for demethylation inhibitor (DMI), benzimidazole (BZI), and quinone outside inhibitor (QoI) fungicide resistance monitoring. The data was analyzed and timely recommendations were provided to agents and growers. The service was featured at educational sessions, in trade journals and we published in peer reviewed journals and book chapters. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period. IMPACT: 2008/06 TO 2011/06 Resistance to DMI, QoI and MBC fungicides has been detected in the Upstate and Midlands of South Carolina as well as the Midlands of Georgia. The only area in the Southeast that has not yet been impacted by resistance is South Georgia, where limited disease pressure allows producers to use conventional, less expensive fungicides. Because MBC fungicides have been used since the early 1980s and because MBC resistance is known to persist for years in peach production areas, pre-harvest brown rot spray programs have primarily relied upon rotations of QoI and DMI fungicides in recent years. So far, we have not encountered populations with dual resistance, despite laboratory evidence that selection for DMI resistance may increase selection for QoI resistance. This finding is of critical importance because it allows producers to select efficacious fungicides for brown rot control in the presence of resistance to another chemical class. The data indicate that preharvest spray programs consisting of DMI fungicides or DMI fungicides alternated with QoI fungicides selected significantly more for DMI resistance. Likewise, spray programs based on QoI fungicides or QoIs applied in combination with DMI fungicides selected significantly more for QoI resistance. The data also indicate that frequent applications of the same members of a specific chemical class will select for resistance more rapidly, which is consistent with our general understanding of how fungicide resistance develops in the field (Wade 1988). The more unexpected result was that the rotation of DMI and QoI fungicides, which has been recommended as a general anti-resistance management strategy, did not appear to reduce the number of resistant isolates in the 10-fruit samples compared to programs using either fungicide exclusively. However, outbreaks of brown rot were not observed, indicating that the QoI fungicides likely controlled the DMI-resistant portion of the population and the DMI fungicides likely controlled the QoI-resistant portion of the population. To date, we have not observed a population or even a single isolate with resistance to both chemical classes. We believe that the implementation of this monitoring program in South Carolina and Georgia and the resulting recommendations for resistance management have prevented disease epidemics in 2009, a year that was conducive for a disease epidemic. We estimate that losses due to pre- and postharvest brown rot would have been 10-15 % in each state, which translates into $4 to 8 million in revenue for each state, if key growers had not made adjustments to their spray programs. This first prototype of a kit-supported resistance monitoring program was developed specifically for the brown rot disease of peach due to documented cases of field resistance to multiple chemical classes of fungicides in M. fructicola. However, the Profile kit can be developed for other pathogens with high potential of resistance development including Botrytis spp. causing gray mold of fruits and vegetables; Penicillium spp. causing rots in citrus and pome fruits; and Alternaria spp. causing disease on multiple crops.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system Resistance to DMI, QoI and MBC fungicides has been detected in the Upstate and Midlands of South Carolina as well as the Midlands of Georgia. The only area in the Southeast that has not yet been impacted by resistance is South Georgia, where limited disease pressure allows producers to use conventional, less expensive fungicides. Because MBC fungicides have been used since the early 1980s and because MBC resistance is known to persist for years in peach production areas, pre-harvest brown rot spray programs have primarily relied upon rotations of QoI and DMI fungicides in recent years. So far, we have not encountered populations with dual resistance, despite laboratory evidence that selection for DMI resistance may increase selection for QoI resistance. This finding is of critical importance because it allows producers to select efficacious fungicides for brown rot control in the presence of resistance to another chemical class. The data indicate that preharvest spray programs consisting of DMI fungicides or DMI fungicides alternated with QoI fungicides selected significantly more for DMI resistance. Likewise, spray programs based on QoI fungicides or QoIs applied in combination with DMI fungicides selected significantly more for QoI resistance. The data also indicate that frequent applications of the same members of a specific chemical class will select for resistance more rapidly, which is consistent with our general understanding of how fungicide resistance develops in the field (Wade 1988). The more unexpected result was that the rotation of DMI and QoI fungicides, which has been recommended as a general anti-resistance management strategy, did not appear to reduce the number of resistant isolates in the 10-fruit samples compared to programs using either fungicide exclusively. However, outbreaks of brown rot were not observed, indicating that the QoI fungicides likely controlled the DMI-resistant portion of the population and the DMI fungicides likely controlled the QoI-resistant portion of the population. To date, we have not observed a population or even a single isolate with resistance to both chemical classes. We believe that the implementation of this monitoring program in South Carolina and Georgia and the resulting recommendations for resistance management have prevented disease epidemics in 2009, a year that was conducive for a disease epidemic. We estimate that losses due to pre- and postharvest brown rot would have been 10-15 % in each state, which translates into $4 to 8 million in revenue for each state, if key growers had not made adjustments to their spray programs. This first prototype of a kit-supported resistance monitoring program was developed specifically for the brown rot disease of peach due to documented cases of field resistance to multiple chemical classes of fungicides in M. fructicola. However, the Profile kit can be developed for other pathogens with high potential of resistance development including Botrytis spp. causing gray mold of fruits and vegetables; Penicillium spp. causing rots in citrus and pome fruits; and Alternaria spp. causing disease on multiple crops.

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