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1999 Report
Organic Raspberry Root Rot Control Study

Carol A. Miles, Ph.D., Tanya Cheeke, Rei Nakatani, Dawn Youmans, and Chuhe Chen, Washington State University Research and Extension Center, 1919 NE 78th St, Vancouver, WA 98665
Phone: (360) 576-6030  Fax: (360) 576-6032  Email: milesc@wsu.edu  URL:http://agsyst.wsu.edu

Funded by: Organic Farming Research Foundation & Washington State Commission for Pesticide Registration Funds Organic Research

Introduction

In 1999, Washington State University Extension began to study the efficacy of five organic treatments to control root rot (Phytopthora fragriae var. rubi) in red raspberries. Root rot is of primary concern to all raspberry growers in the region, but it is of particular concern to organic growers who have few options for controlling this disease. Our study was developed in cooperation with Jan Pigman, a certified organic commercial grower in Nisqually, Washington, who was searching for viable organic alternatives to reduce disease. Although this trial is focused on organic root rot control, all raspberry growers are impacted by this disease and will benefit from any new management strategies that are developed.

Our study builds upon research led by WSU Small Fruit Pathologist, Pete Bristow, from 1995 to 1998 that investigated the use of raised beds to control raspberry root rot in western Washington. Raised beds allow excess moisture to drain away from plant roots, thereby reducing the habitat for Phytopthora and other pathogens. However, these studies showed that raised beds alone were not adequate to control root rot or to ensure the long-term viability of the raspberry planting.

1995-96 raspberry field study – soil tensiometers to measure soil moisture in a raised bed.

In the spring of 1999, in cooperation with Jan Pigman at Pigman's Organic Produce Patch, and with the funding support of OFRF, we began to study six organic treatments in combination with raised and flat beds for the control of raspberry root rot. In the summer of 1999, we were able to match OFRF funds with funding from the Washington State Commission for Pesticide Registration (WSCPR). Matching funds were used to establish research plots at the WSU Vancouver Research and Extension Unit where raspberry diseases are a significant problem. WSU station plots include five organic treatments plus one chemical treatment and a control on raised beds only. It is our goal to use the WSU research station site to compare the effectiveness of organic disease control treatments to the standard chemical control treatment.

Establishing treatments in raspberry plots in Spring of 1999.

Procedures and Methods

Procedures and methods differ at the two research sites, Pigman's farm and the WSU Vancouver Research and Extension Unit.

Pigman's Farm – 1999

Research designis a split-plot where the main plot treatment is soil level (flat or raised) and sub-plot treatments and application rates were:

• Trichoderma – 4 g per subplot (2.4 lbs/acre)
• gypsum - 7.5 lb per subplot (1 ton/acre)
• composted chicken manure – 31 lbs per subplot (4 tons/acre)
• composted horse manure – 61 lbs per subplot (8 tons/acre)
• composted horse manure inoculated with Trichoderma – 61 lbs and 4 g, respectively, per subplot
• control (no application)

Composted chicken manure is typically used on the farm and was included in the study to evaluate how currently available resources may be effective for disease suppression. Horse manure was included in this study because it may be more conducive to disease suppression due to its high C:N ratio. Soil microbiologists who were consulted early on in this study also felt that composted horse manure may enhance the activity of Trichoderma.

Dr. Pete Bristow collecting plant samples for disease assessment in June 1999.

On April 20, 1999, soil and compost samples were collected and analyzed by William Matthews, Thurston County Conservation District (Table 1). All sub-plots, except those that received composted chicken manure, were fertilized with blood meal at the rate of 100 lbs N per acre. Composted chicken manure had a high nitrogen content and a good C:N ratio and was therefore left to be an adequate source of nitrogen.

The raspberry variety in this study is Chilliwack, and the study area includes 2 rows of newly established plants and 4 rows of 4-10 year old plants. Row length is 100 feet, and sub-plot length is 16 feet. One row of the newly established plants is raised and 1 row is flat. Two rows of the established plants are raised and 2 rows are flat. Figure 1 is an illustration of the study layout and the treatments.

On April 20, 1999, the two new rows of raspberries were planted and Trichoderma was applied in the root zone of the new plants. Also at that time, raised beds were created in the study area. On May 11, all other treatments were applied in four-foot wide bands, centered on the row. Trichoderma and gypsum were lightly incorporated; composted chicken manure, composted horse manure, and composted horse manure inoculated with Trichoderma were applied as mulch.

Plants were weeded three times throughout the growing season: April 28, June 30, and August 10, 1999. Raspberries were harvested from July 14 through August 10, and yield was measured. Yield was collected from the 5 feet of row in the center of each sub-plot. On June 30 and August 4, plants were rated for disease incidence. On September 2, whole-plant samples were collected for disease analysis from the area immediately adjacent to the yield-collection area. Disease analysis indicated that crown gall and Armillaria (shoe string) root rot were present in the field along with Phytophthora root rot.

Figure 1. Plot map of raspberry disease control study at Pigman's Organic Produce Patch, Nisqually, Washington and treatments applied in 1999 and 2000.

Results and Discussion -1999

The efficacy of the treatments to control raspberry disease differed between the raised beds and the flat beds (Table 2). On raised beds, plots that were treated with composted chicken manure produced the highest number of berries while on the flat beds, plots treated with composted horse manure produced the highest number of berries. Plots treated with Trichoderma produced the second highest number of berries on both raised and flat beds.

Table 2. Weight (grams) and number of marketable and unmarketable raspberry fruit harvested at Pigman's Organic Produce Patch in 1999.

Key:

Trichoderma appears to be having a beneficial effect in both the raised and flat bed rows, while chicken and horse manure compost seem to work well in one or the other, but not both. It is important to note these are preliminary results, and it is necessary to follow production trends for several years in order to determine if there is indeed a relationship between the applied treatment and disease control. Results from the 2000 research trials should give us a better idea of which treatments are working consistently to control raspberry disease.

Pigman's Farm – 2000

The same raspberry field area at the Pigman's farm was used for the study in 2000. Treatments were re-applied to the subplots:

• Trichoderma – 75g per subplot (20 lbs/acre)
• gypsum – 7.5 lbs per subplot (1 ton/acre)
• composted chicken manure – 57 lbs per subplot (8 tons/acre)
• composted horse manure – 57 lbs per subplot (8 tons/acre)
• composted horse manure inoculated with Trichoderma – 57 lbs and 75 g, respectively, per subplot
• control (no application)

On April 20, composted manure samples were collected for analysis. Chicken manure samples that were collected in April were mishandled in storage and samples were again collected on June 8. Unfortunately, neither manure sample had been analyzed by the time treatments were applied, so composted manure application rates in the study were based on estimated average nutrient contents. To ensure that plots receiving composted chicken manure were adequately fertilized, composted chicken manure was applied at the same rate as composted horse manure, 57 lbs per subplot, approximately equivalent to 8 tons acre. All other subplots were fertilized with blood meal at a rate of 100 lbs N per acre on May 4, 2000.

On April 20, all treatments were applied to the soil surface and were centered on the row. The amount of Trichoderma applied per subplot increased from 4 g (2.4 lbs/acre) in 1999 to 75g (20 lbs/acre) in 2000. This rate increase was based on manufacturer recommendations to increase the potential effectiveness of Trichoderma for Phytophthora control.

On June 8, 2000, primocanes were counted from 3-foot sections within each subplot. As primocanes were counted, the study areas were clearly marked with green flags. Primocane data has not yet been analyzed.

WSU Vancouver Research and Extension Center
In the fall of 1999, raspberry research plots were established at the WSU Vancouver Research station. The raspberry variety used in this study is Meeker and the planting is 4 years old. The study area is a randomized complete block design with 4 replications. Each row is 175 feet long and plot length is 25 feet. All raspberry rows in the study area are raised beds.

Treatments were applied November 29, 1999 and again on April 3, 2000. All treatments except gypsum were applied on both dates:

• Trichoderma – 117g per plot (20 lbs/acre)
• Gliocladium-41 – 117g per plot (20 lbs/acre)
• composted dairy manure – 24 lbs per plot (1.75 tons/acre)
• composted dairy manure plus Trichoderma – 24 lbs + 117g, respectively, per plot
• Ridomil – recommended conventional rate
• gypsum – 24 lbs per plot (1.75 tons/acre)
• control (no application)

Trichoderma, Gliocladium-41, Ridomil, and composted dairy manure were applied to plots by hand in four-foot wide bands, centered on the row. None of the treatments were incorporated into the soil. The Trichoderma and Gliocladium-41 granules were mixed with potting soil (to aid in spreading) and sprinkled on top of the raised beds. Ridomil was applied in liquid form using a backpack sprayer. Composted manure was applied as a mulch. For the plots that had composted manure inoculated with Trichoderma, the manure was applied first and the Trichoderma was sprinkled on top. The day following treatment application, it rained, so the treatments were able to quickly move into the soil. Gypsum was applied only in the fall as we felt that a fall application would be most effective.

On April 13, 2000 blood meal was mechanically banded near the root zones at a rate of 60 lbs N per acre (2.6 lbs per plot). On June 9, an additional 40 lbs N per acre was applied. Plants began to show nitrogen stress symptoms in early June, when hot temperatures caused rapid plant growth and nitrogen may not have been fully available in the soil.

On May 11, 2000, damage of root rot to primocanes was assessed. A three-foot area was randomly sampled and clearly labeled with colored flags and ribbon. The total number of primocanes was counted in the sample areas in May and will be counted again in July. In July, five primocanes will be randomly chosen within each of the sample areas, and measurements will be taken on cane heights and diameters. The damage to floricanes and fruit yield caused by Phytopthora will be evaluated during harvest using a visual disease rating scale and by comparing yield data. The berries in the sample area of each plot will be hand picked twice a week throughout the harvest season.

Outreach

Ø A brief article announcing funding for this project and an outline of the study appeared in the  Washington Tilth Journal, Summer 1999, Volume 7, Issue 3.

Ø A preliminary report was presented at the Washington State University Master Gardener conference in Seattle, October 1999.

Ø In November 1999, Anne Schwartz, Jan Pigman, Carol Miles, and Dawn Youmans, presented an overview of the study at the Washington State Tilth Producers Conference in Port Townsend.

Ø Our annual report and photos of the study are available on the WSU Agricultural Systems web site, http://vegetables.wsu.edu.

Ø An article discussing the study outline and preliminary results was submitted to the Western Fruit Grower in June 2000.