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, 2006 and 2007 the efficacy of seven organic and/or biorational fungicides plus two cultural controls (in 2006 and 2007) were evaluated for managing gray mold on ‘Prelude’ and ‘Nova’ red raspberries. Treatments were determined based on input from a grower advisory panel. Most of treatments did not manage gray mold better than applying water to the plants (control 1). Applying Captan and Elevate in rotation (control 2) resulted in higher marketable yields and applying Oxidate and Milstop in a tank mixture resulted in lower marketable yields than spraying the plants with tap water.

Harvested raspberries were stored to determine the effect of the treatments on post harvest disease development. On most evaluation dates disease incidence was not different regardless of treatment. However, when differences were observed, spraying Captan and Elevate in rotation or Endorse resulted in the fewest diseased berries. All other treatments resulted in disease incidence not different than spraying water on the plants.

Two field days on bramble disease management attracting about 100 participants were co-hosted by the Pennsylvania State University, University of Massachusetts, Pennsylvania Association for Sustainable Agriculture, Pennsylvania Certified Organic or Nourse Farms. Additionally, a workshop on bramble disease management attracting about 85 participants was presented at the Farming for the Future Conference hosted by the Pennsylvania Association for Sustainable Agriculture. A field guide was developed and provided to participants of the field days and workshop. Additionally, the field guide along with instruction for its use was presented at the Vegetable, Berry and Greenhouse Growers’ Meeting in Mifflinburg, PA and at the Western Pennsylvania Vegetable and Berry Growers Seminar in Butler, PA reaching about 45 participants. Participants of these events indicated that their knowledge of bramble disease diagnosis and management increased as a result of the presentations. Additionally, numerous participants indicated they planned on adopting diagnosis and/or management strategies presented. A follow-up survey is currently being conducted to determine if planned changes were implemented.
.

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, 2006, and 2007 growing seasons, six organic/biorational materials, and an additional product in 2007, were evaluated along with two cultural treatments (one in 2006 and one in 2007). 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.

Gray mold treatments were applied to field plots consisting of ten foot long hedgerows and were arranged in a two (cultivars: ‘Nova’ and ‘Prelude’) X ten (eight treatments and two controls) factorial in a randomized complete block design with four replications. Spray treatments were applied in a volume of water equivalent to 50 gal/acre using a compressed carbon dioxide sprayer operated at 40 psi. The spray equipment was calibrated twice during the growing season. In accordance with current recommendations for conventional fungicides, spray treatments 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 following gray mold management treatments were evaluated. Milstop (BioWorks, Inc., Fairport, NY), approved for organic production, was applied at a rate of 3.75 pounds per acre. Endorse (Arvesta Corp., San Francisco, CA), was applied at a rate of 1.8 pounds per acre. Lime sulfur solution (Chemical and Fertilizer Corp., Hanover, PA), was applied at a spray volume of one percent. Phostrol (Nufarm Americas, Inc., Burr Ridge, IL), was applied at a rate of five pints per acre. Milstop + Oxidate (Biosafe Systems, Glastonbury, CT) tank mixture was used; Milstop was applied at a rate of 3.75 pounds per acre and Oxidate was applied at a spray volume of one percent for the first three applications, and then changed to one-third percent of spray solution volume. Oxidate can be used in organic production and falls into the restricted category, which allows its use when a need is documented. Oxidate + Vigor Cal Phos (Agro-K Corp., Minneapolis, MN) tank mixture was used. Oxidate was applied at a spray volume of one percent for the first three applications, and then changed to one-third percent of spray solution volume corresponding to labeled directions, and Vigor Cal Phos was applied at a rate of four quarts per acre. Vigor Cal Phos is labeled as a nutrient supplement. Shemer (AgroGreen Minrav., Ashdod, Israel) + Milstop as a tank mixture was used; Shemer was applied at a rate of 0.2 percent spray solution volume and Milstop was applied at a rate of 0.1 percent spray solution volume. The previous treatment was only evaluated in 2007. All chemical applications rates were based on 2005 manufacturer’s recommendations except for Shemer, which was based on 2007 recommendations.

A cultural treatment was evaluated during the 2006 fruiting season in which the specified plots were thinned to six canes per linear foot in August of 2005 and four to five canes per linear foot in March of 2006. The previous treatment was not evaluated during the 2007 growing season because it did not provide any disease control. A “V” trellis cultural control was initiated May 15, 2007 by tying floricanes to a horizontal trellis wire leaving primocanes unrestricted in the inner hedgerow.

Two experimental controls were used. These consisted of applying water at a rate of 50 gal/acre, and a standard fungicide rotation of Elevate 50 Water Dispersible Granules (Arvesta Corp., San Francisco, CA), applied at a rate of one and one-half pounds per acre and Captan 50 Wettable Powder (Arvesta Corp., San Francisco, CA), and applied at a rate of four pounds per acre.

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 in 2006 and 2007 after harvesting to determine the effect of the gray mold treatments on postharvest disease infection. During the 2005 growing season, insufficient yields prevented postharvest analysis. After each harvest, 13 ripe fruit (2006) and 16 ripe fruit (2007) from each treatment plot were placed in 28-celled plastic trays (Gardner’s Candies, Tyrone, PA). When less than 13 fruit (2006) and 16 ripe fruit (2007) were harvested from a treatment plot fruit from that plot was excluded from postharvest 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. All berries were infected by four days after postharvest evaluations but gray mold was not positively identified. 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 using SAS 9.1.3 (SAS Institute, Cary, N.C.). When differences were detected at P≤0.05, data were subjected to Duncan’s Multiple Range Test.

Yields
For all three years of the trial, there were no treatment by cultivar interactions for yield. Marketable yields, unmarketable yields and marketable berry weight were not different regardless of treatment or cultivar in 2005.

The planting was two years old in 2005. A mature raspberry planting with optimal yields is not seen until the third year after establishment. This might explain why differences were not seen between treatments and cultivars during this growing season.

Marketable and unmarketable yields and the percent berries infected with gray mold were not different by treatment in 2006. Using Captan/Elevate sprays (control 2) resulted in the largest berries at 2.6 grams. Water only sprays (control 1) resulted in berries that weighed 2.4 grams, which were similar in weight to berries sprayed with Oxidate + Vigor Cal Phos tank mixture, Lime Sulfur, Phostrol and Endorse or using “V” trellis and cane thinning cultural controls. Milstop applications resulted in berries smaller than those that received the water only sprays (control 1) at 2.2 grams, although berries were similar in size to plots receiving the “V” trellis cultural control. Oxidate + Milstop tank mixture sprays resulted in the smallest berries at 2.1 grams. ‘Nova’ plots had higher marketable and unmarketable yields and larger berries than ‘Prelude’. However, no differences were observed between cultivars for berries infected with gray mold.

In 2006, differences between treatments were only observed for marketable berry weight, in which plots sprayed with Captan/Elevate (control 2) were the largest. While not significant, plots sprayed with Captan/Elevate (control 2) had the highest yield and lowest percent unmarketable berries with gray mold, which might translate to significantly larger berries. Yields in 2006 were increased over 2005, with ‘Nova’ being more productive than ‘Prelude’.

Marketable berry weight and unmarketable yields were not different between treatments in 2007. Captan/Elevate sprays (control 2) resulted in the largest marketable yields at 5,220.6 grams. All remaining treatments except Oxidate + Milstop tank mixture resulted in marketable yields not different than the water only sprays (control 1) at 3,791.1 grams. Milstop + Oxidate tank mixture sprays resulted in marketable yields smaller than the water only sprays (control 2) at 2239.8 grams, although similar in weight to plots sprayed with Milstop, Lime Sulfur, and Shemer + Milstop. Differences were observed between treatments in regards to percent of berries infected with gray mold. Milstop and Lime Sulfur sprays resulted in a higher percentage of berries infected with gray mold than did the water only spray. The application of Endorse, Oxidate + Milstop, Oxidate + Vigor Cal Phos, Phostrol, Shemer + Milstop and the “V” trellis cultural control resulted in the percent of berries infected with gray mold similar to the water only spray (control 1). The Captan/Elevate (control 2) sprays resulted in a lower percentage of berries infected with gray mold than did the water only spray (control 1) although similar to plots sprayed with Endorse. ‘Nova’ plots had larger marketable yields than ‘Prelude’. ‘Prelude’ plots had a larger percentage of berries infected with gray mold than ‘Nova’. However, no differences were observed between cultivars for marketable berry weight and unmarketable yields.

In 2007, differences between treatments were observed for marketable yields, in which plots sprayed with Captan/Elevate (control 2) had the highest. Also, differences between treatments were observed for percent marketable berries with gray mold. The application of Captan/Elevate showed the best control of gray mold. This might be explained by the fact that Captan/Elevate (control 2) is a proven fungicide used by conventional growers. Once again ‘Nova’ was more productive than ‘Prelude’.

Postharvest Evaluation
Disease incidence four consecutive days after the June 30, 2006 harvest was not different regardless of gray mold treatment for ‘Prelude’. Upon final identification of pathogens, differences were not observed between treatments except for soft rot. For soft rot, Milstop sprays resulted in a higher disease incidence than did the water only spray (control 1). All other treatments resulted in soft rot disease incidence similar to the water only spray (control 1).

Disease incidence was not different regardless of treatment on ‘Nova’ berries one, two, three, and four days after the July 3, 2006 harvest. Final identifications on August 30 for gray mold, blue mold, and soft rot revealed no differences between treatments. For miscellaneous fungi, Phostrol sprays resulted in a lower disease incidence than all other treatments

Disease incidence was not different regardless of treatment for the four consecutive days after the June 25, 2007 harvest for ‘Nova’. Final identifications on August 7 for gray mold, blue mold, soft rot or miscellaneous fungi revealed no differences between treatments.

Disease incidence was not different regardless of treatment on ‘Prelude’ berries one, two, three and four days after the June 25, 2007 harvest. Final identifications on August 7 for gray mold, blue mold and miscellaneous fungi revealed no differences between treatments. Final observations on August 7 for soft rot showed Oxidate + Vigor Cal Phos sprays resulting in higher disease incidence than all other treatments.

There were few significant differences in postharvest evaluations and generally none of the treatments was more effective than the water only control. The predominant diseases observed in the postharvest evaluations were gray mold, blue mold (Penicillum expansum) and rhizopus soft rot (Rhizopus spp).

Extension Events
Conversations and e-mails with our advisory board led to the development of two field days, one workshop and presentations at two grower meetings on bramble disease management including the information we learned from the research trial.

The first field day took place in Rock Springs, PA and was attended by about 50 participants. It was co-hosted by the Pennsylvania State University, Pennsylvania Association for Sustainable Agriculture and Pennsylvania Certified Organic. The program included a plant pathologist, small fruit specialist, sustainable/organic specialist and Master’s student from the Pennsylvania State University and a certification specialist from Pennsylvania Certified Organic.

The second field day took place in South Deerfield, MA and was attended by about 50 participants. It was co-hosted by Nourse Farms, the Pennsylvania State University and the University of Massachusetts. The program included a plant pathologist from the USDA, Beltsville, MD, a small fruit specialist from the University of Massachusetts and small fruit specialist, sustainable/organic specialist and Master’s student from the Pennsylvania State University.

Additionally, a workshop on bramble disease management attracting about 85 participants was presented at the Farming for the Future Conference in State College, PA hosted by the Pennsylvania Association for Sustainable Agriculture. A 12-page field guide on diagnosing bramble disorders was developed and provided to participants of the field days and workshop.

Surveys administered to participants of these events indicated that their knowledge of bramble disease diagnosis and management increased as a result of the presentations (average of 3.33 before and 5.27 after the events; 7 point scale – 7 indicating excellent level of knowledge on bramble diseases and 1 indicating poor level of knowledge). The majority of participants indicated that they planned on using the field guide for diagnosing bramble disorders, a learned technique to identify diseases, the hand lens provided to identify diseases and other pests and a cultural strategy to manage diseases in the field.

The field guide along with instruction for its use was also presented at the Vegetable, Berry and Greenhouse Growers’ Meeting in Mifflinburg, PA and at the Western Pennsylvania Vegetable and Berry Growers Seminar in Butler, PA reaching about 45 participants.

A follow-up survey is currently being conducted to determine if planned changes were implemented.

Impacts and Contributions/Outcomes

Several materials with softer chemistries were evaluated for managing gray mold in a summer-bearing raspberry crop. None of the materials were found to be more effective than applying tap water (control). Growers can save the expense of purchasing these materials for managing gray mold on raspberries.

Several educational events were held in 2006 and 2007 to present information on diagnosing bramble diseases and managing those diseases using preventative tactics and spray options with softer chemistries. Two hundred thirty participants attended these events. The majority of participants indicated their knowledge of bramble diseases increased as a result of the events. The majority of participants also planned to adopt sustainable strategies for approaching disease management including using a field guide and learned techniques for diagnosing diseases and using a cultural strategy for managing gray mold. Forty percent of respondents to surveys planned to use an alternative fungicide to manage gray mold.

A follow-up survey is currently being conducted to determine how many participants adopted methods which were planned.

Collaborators: