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

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

Summary

Gray mold, caused by the fungus Botrytis cinerea, is an important disease impeding raspberry production. In 2005 and 2006, the efficacy of six organic and biorational fungicides plus one cultural control (in 2006 only) were evaluated for managing gray mold on ‘Prelude’ and ‘Nova’ red raspberries. Data collected included phytotoxicity, yields and postharvest disease incidence. Phytotoxicity was evaluated for the gray mold treatments on a weekly basis following each spray application. Fruit was harvested by hand every Monday, Wednesday and Friday from mid June to late July for both cultivars and were sorted into marketable and unmarketable categories. Fruit were subjected to postharvest evaluations to determine the effect of the treatments on postharvest disease infection of the raspberries. ‘Nova’ was more susceptible to phytotoxicity than ‘Prelude’ in both years. The application of Phostrol resulted in the highest percent phytotoxicity compared to all other gray mold treatments. Marketable and unmarketable yields were not affected by treatment in both years. In 2005 berry size was not affect by the gray mold treatments; however in 2006, using the Captan/Elevate rotation resulted in larger berries than all other gray mold treatments. In 2005 ‘Prelude’ and ‘Nova’ yielded similarly. However, in 2006, yields were higher and berries larger from ‘Nova’ than ‘Prelude’. The predominant diseases observed in the postharvest evaluations were gray mold, blue mold (Penicillum expansum) and rhizopus soft rot (Rhizopus spp.) and/or mucor mold (Mucor spp.).

Information generated through this study, as well as on bramble disease management and diagnosing bramble problems, was presented to 175 primarily grower participants through field day and workshop events.

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.

Accomplishments/Milestones

During the 2005 and 2006 growing seasons, six organic/biorational materials were applied to test plots along with one cultural treatment (in 2006 only; Table 1). An advisory panel consisting of six raspberry growers helped choose these treatments using criteria they considered important 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. Two controls, water-only and conventional fungicides, were also included comparison.

Gray mold treatments were applied to field plots consisting of 12 foot long hedgerows and were arranged in a 2 (cultivars: ‘Nova’ and ‘Prelude’) X 9 treatments factorial in a randomized complete block design with 4 replications. Spray treatments were applied in a volume of water equivalent to 50 gal/acre using a compressed CO2 sprayer operated at 40 psi. The spray equipment was calibrated twice during each growing season and was found to be stable and accurate. In accordance with current recommendations for conventional fungicides, treatments 1 – 8 were initiated at 10-15% bloom (early bloom), and then applied two more times at five to seven day intervals during bloom. Treatments were discontinued briefly, and then resumed when harvested berry counts reached 10-15% (early harvest) and continued on five to seven day intervals. These timings corresponded to early, mid and late bloom, and early, mid and late harvest.

The cultural control treatment (treatment 9 in Table 1) was not applied during the 2005 harvest season because the plants had not grown sufficiently. Canes were thinned to six per linear foot of hedgerow in August, 2005 to initiate the cane thinning treatment for the 2006 fruiting season. Plots receiving this treatment were then thinned to four to five canes in March of 2006.

Phytotoxicity was evaluated for the gray mold treatments on a weekly basis following each spray application. A visual rating scale of 0 to 100% using 10% increments was used. When less than 10% of leaf area or canes were affected a rating of 5% was assigned. The first symptoms of phytotoxicity appeared fourteen to fifteen days after the first spray application corresponding to an increase in daytime temperatures. Ratings were then taken weekly with the final observations taken within one week after the last spray.

Fruit was harvested by hand every Monday, Wednesday and Friday from mid June to late July. Berries were sorted by cultivar into marketable and unmarketable categories with those that were blemished considered unmarketable. Most blemishes were due to insect and mechanical damage. A lesser amount of diseased berries was also observed. Berries were weighed, counted and immediately subjected to post-harvest evaluation.

Fruit were evaluated after harvesting to determine the effect of the gray mold treatments on postharvest disease infection. After each harvest, 13 ripe fruit from each treatment were placed in 28-celled plastic trays (Gardner’s Candies, Tyrone, PA). When less than 13 fruit were harvested from a treatment plot fruit from that plot was excluded from post-harvest evaluation for that harvest. Trays were then placed in moist chambers. One gallon plastic slider bags (Wegmans private label, Wegmans Food Markets, Inc., State College, PA) lined with 2-layers of industrial hand towels (800 ft roll hand towels model no. 01000, Kimberly Clark, Neehan, WI) that were moistened with tap water were used as moist chambers. Moist chambers were then placed in storage for three days at room temperature followed by four days at 40 to 45ºF. Gray mold was not positively identified on any of the seven day post harvest studies; therefore, berries were maintained for analysis of morphological characteristics using a 3x Olympus dissecting microscope.

Numerical data were analyzed with General Linear Model analysis of variance. When differences were detected at P≤0.05, data were subjected to Duncan’s Multiple Range Test.

Differences in phytoxicity ratings were observed between the two cultivars and nine gray mold treatments (Table 2). ‘Nova’ was more susceptible to phytotoxicity than ‘Prelude’ in both years. The application of Phostrol resulted in the highest percent phytotoxicity when compared to all other gray mold treatments. Phytotoxicity ratings for ‘Prelude’ and ‘Nova’ in 2005 and ‘Nova’ in 2006 were negligible when treated with Control 1, Control 2, Endorse and Lime Sulfur treatments. Additionally, applying Milstop, Milstop + Oxidate and Oxidate + Vigor Cal Phos resulted in similar intermediate ratings. In 2006, phytotoxicity ratings for ‘Prelude’ were negligible when any other treatment besides Phostrol was used.

In general, the raspberry crop was small for 2005 and increased for 2006. In 2005, marketable and unmarketable yields and berry size did not differ by cultivar or gray mold treatment (Table 3). In 2006, marketable and unmarketable yields were statistically similar regardless of gray mold treatment. However, in 2006, ‘Nova’ plants had a significantly larger marketable and unmarketable yields and berry size than ‘Prelude’. Additionally, plants receiving the Captan/Elevate treatment produced larger berries; water, Endorse, Phostrol, Oxidate + Vigor Cal Phos and cane thinning treatments resulted in intermediate sized berries and Milstop and Oxidate + Milstop resulted in the smallest berries.

Predominant diseases observed in the postharvest evaluations were gray mold, blue mold (Penicillium expansum) and rhizopus soft rot (Rhizopus spp.) and/or mucor mold (Mucor spp.). Low yields in the 2005 growing season prevented adequate sample size for postharvest evaluations and therefore statistical analysis was not conducted on this data. Disease incidence for three consecutive days after harvest on July 3, 2006 was very high regardless of gray mold treatment for both cultivars. For berries harvested on July 17, 2006 disease incidence was similar one and three days after harvest. Two days after harvest, while some significant differences were calculated, none of the gray mold treatments resulted in disease incidence significantly better than the water treatment for ‘Prelude’ berries. ‘Nova’ berries had higher disease incidence when treated with Oxidate + Milstop. The other treatments resulted in similar berry disease incidence to the water treatment. When final observations were made to verify gray mold incidence, differences were not observed between treatments or cultivars in either year.

Table 1. Treatments used in this study.

Treatment
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 Cane thinning (as a cultural control to increase air circulation; 2006 only)
*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.

Impacts and Contributions/Outcomes

We have disseminated information on alternative approaches to disease management through targeted Extension events and publications. Forty participants attend a Bramble Disease Management field day, co-hosted by Pennsylvania State University, the Pennsylvania Association for Sustainable Agriculture and Pennsylvania Certified Organic, on August 8, 2004 in Pennsylvania. At the field day results from the raspberry trial, information on avoiding and managing bramble diseases and diagnostic tools for determining bramble problems were presented. Participants rated the field day highly and indicated that they would use diagnostic tools and cultural strategies and alternative fungicides for avoiding/managing diseases.

Fifty participants attended a second field day, co-hosted by Pennsylvania State University, Nourse farms and the University of Massachusetts, on August 24, 2006 in Massachusetts. A similar format to the August 8th field day was used and participants also toured Nourse farms. Participants rated the field day highly and also indicated that they would use diagnostic tools and cultural strategies and alternative fungicides for avoiding/managing diseases.

Eighty-five participants attended a workshop at the Pennsylvania Association for Sustainable Agriculture’s annual Farming for the Future Conference on February 2, 2007 in Pennsylvania. Bramble Establishment and Disease Monitoring was presented by a local organic bramble grower and Elsa Sánchez and Kathy Demchak represented Pennsylvania State University.

In the summer of 2007 participants of the two field days will be surveyed to determine adoption of diagnostic tools and cultural strategies and alternative fungicides for avoiding/managing bramble diseases. Additionally, the field trial will be repeated.

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