In search of sustainable Botrytis management: An extension and research effort

In search of sustainable Botrytis management: An extension and research effort

Summary

Organic growers rely primarily on preventative tactics for pest management; however, for some pests, such as Botrytis diseases, preventative management strategies alone are not sufficient. For these pests, growers turn to alternative chemical options, the efficacy of which is often not established. This project contains a research and education component. For the research component we are evaluating six organic and biorational chemical options and two cultural strategies for Botrytis management in a raspberry field trial. Botrytis is the focus of the research project because it has a widespread negative impact on many crops. We selected raspberries to study because they are a high-value crop produced by a large number of growers in the NE US. Additionally, since raspberries are extremely susceptible to Botrytis, growers contend with it every year. Results can be transferable to other small fruit crops including strawberries. For the Extension component of the project, we are developing activities to increase awareness and use of preventative disease management options for small fruit crops, including those for Botrytis diseases.

Objectives/Performance Targets

Of the 100 growers attending Extension events, 80 will approach disease management on their farms in a more environmentally sustainable way and 50 will have adopted at least one recommended practice one year after Extension events. Surveys will be used to determine that milestones have been reached.

Accomplishments/Milestones

The first step in reaching milestone one was establishing an advisory panel to guide the research and Extension portions of this project.  Four raspberry growers from PA, and two from MA agreed to serve in this capacity.  They provided input on alternatives for Botrytis management based on criteria they use in selecting management tools.  These criteria included cost (in terms of both time and money), number or frequency of applications, safety to the environment and humans, compliance with the National Organic Standards, and broadness of expected spectrum of activity.

The alternatives identified in step one were used in step two.  In this step we completed the first year of a 2 year research trial to evaluate Botrytis management strategies.  The study is being conducted at the Russell E. Larson Agricultural Research Center at Rock Springs, PA.  Summer fruiting red raspberry cultivars ‘Nova’ and ‘Prelude’ were planted in May, 2004.  

Treatments were:
1.  Control 1 – No gray mold management. (Water only sprayed).
2.  Control 2 – Conventional fungicide program consisting of Elevate 50 WDG at 1.5 lb/acre (fenhexamid, Arvesta Corp., San Francisco, CA) and Captan 50 WP at 4.0 lb/acre, (captan, Arvesta Corp., San Francisco, CA) in rotation.  
3.  Milstop at 3.75 lb/acre,  (potassium bicarbonate, BioWorks, Inc., Fairport, NY)
4.  Endorse at 1.8 lb/acre (Polyoxin D zinc salt, Arvesta Corp., San Francisco, CA)
5.  Lime Sulfur Solution at 1% of spray solution volume (calcium polysulfide, Miller Chemical and Fertilizer Corp., Hanover, PA)  
6.  Phostrol at 5 pt/acre (mono- and dibasic sodium, potassium, and ammonium phosphates, Nufarm Americas, Inc., Burr Ridge, IL)
7.  Milstop at 3.75 lb/acre + Oxidate at 1% of spray solution volume* hydrogen dioxide, Biosafe Systems, Glastonbury, CT)
8.  Oxidate at 1% of spray solution volume* + Vigor Cal Phos at 4 qt/acre (nutrient supplement comprised of phosphorus salts of calcium and copper, Agro-K Corp., Minneapolis, MN)
9.  V-trellis (as a cultural control to improve sunlight penetration and drying of foliage)
10.  Cane thinning (as a cultural control to increase air circulation)
*Oxidate was applied at 1% of spray solution volume for the first 3 applications, and then changed to 0.33% of spray solution volume to align as closely as possible with label directions.

Treatments were arranged in a randomized complete block structured as a factorial with two cultivars and ten gray mold management strategies (including two controls).  Each treatment was replicated four times with plots consisting of 12 foot long hedgerows.  Data were collected from the center 10 feet of each plot.  Numerical data from 2005 were analyzed with General Linear Model (GLM) analysis of variance.  When differences were detected at P≤0.05, data were subjected to Fisher’s Multiple Comparison Test.

Treatments 1 – 8 (above) were initiated at 10-15% bloom (early bloom), and then applied two more times at five-day intervals during bloom.  Treatments were discontinued briefly, then resumed when harvested berry counts reached 10-15% (early harvest) and continued on five-day intervals.  These timings corresponded to early, mid and late bloom, and early, mid and late harvest.  

Data from the cultural treatments will be collected beginning in the 2006 growing season.  V-trellising is currently being constructed.  Canes were thinned to 5 to 6 per linear foot of hedgerow in August, 2005 to initiate the cane thinning treatment.  

We experienced drought conditions throughout much of the 2005 growing season.  As a result, very little gray mold was observed in the field until the end of the growing season.  Overhead irrigation was applied to promote disease development.

Phytotoxicity was evaluated for the fungicide treatments on a weekly basis following each fungicide application.  A visual rating scale of leaf area showing symptoms, from 0 to 100% using 10% increments, was used.  When less than 10% of leaf area was affected a value of 5% was assigned.

Differences were observed between the two cultivars and eight fungicide treatments regarding phytotoxicity.  ‘Nova’ was more susceptible to phytotoxicity than ‘Prelude’.  The application of Phostrol resulted in the highest percent phytotoxicity when compared to all other fungicide treatments.  The Control 1, Control 2, Endorse and Lime Sulfur treatments resulted in negligible phytotoxity ratings.  Applying Milstop, Milstop + Oxidate and Oxidate + Vigor Cal Phos resulted in similar intermediate ratings.

Fruit were harvested by hand every other day from each plot from June 27 to July 25, 2005 for ‘Prelude’ and from June 27 – August 2, 2005 for ‘Nova’.  Berries were sorted into marketable and unmarketable categories with those that were blemished considered unmarketable.  Berries were weighed and counted and immediately subjected to post-harvest evaluation.  

In general, the raspberry crop was small.  Differences in marketable yield were nonexistent for the two cultivars and eight fungicide applications.

Fruit were evaluated after harvesting to determine the effect of the fungicide treatments on shelf-life of the raspberries.  After each harvest, fruit from each treatment were placed in plastic trays (Sugarcraft Cake and Candy Supplies, Inc., Hamilton, OH).  The trays were then placed in moist chambers.  Various storage protocols were then evaluated before implementing a protocol of storage for three days at room temperature followed by four days at 40 to 45ºF.  Data collected are currently in the process of being statistically analyzed; however, the predominant diseases observed were gray mold, blue mold and rhizopus soft rot (Rhizopus spp.) and/or mucor mold (Mucor spp.).  

For the third step in reaching milestone one, we have been evaluating tools and techniques that will be part of the field day activities.  These tools and techniques will be presented to the grower advisory panel for their evaluation for usefulness prior to the field day.

Impacts and Contributions/Outcomes

Several products have been developed thus far, including several publications.  One such publication is an article that appeared in the Vegetable & Small Fruit Gazette and Pennsylvania Vegetable Growers Newsletter that was entitled In Search of Sustainable Botrytis Management (http://hortweb.cas.psu.edu/extension/vegcrops/vegetable_gazette/2005/june2005.htm#organic).

A presentation entitled Current Organic Efforts included a discussion of this study and was delivered to 22 participants of an advanced training organic workshop.  The study was also presented to 64 high school students as part of the Plant Scientist course for the Governor’s School of Excellence.  The Governor’s School of Excellence is a five-week-long competitive program held during the summer on the Penn State college campus where high school students attend classes designed for them.  A presentation entitled Botrytis Fruit Rot and Management was delivered to 50 participants at the 2005 Western Pennsylvania Vegetable and Berry Growers Meeting and to 150 participants at the 2005 New England Vegetable & Fruit Conference.  

A graduate student, Graham Sanders, is working on this project to partially fulfill the requirements of a Master’s degree.

Collaborators: