Biodesign Farm Disease Management System

eOrganic authors:

Helen Atthowe, Biodesign Farm

Alex Stone, Oregon State University

This article is part of the Biodesign Farm Organic System Description

Outcomes

Introduction

Biodesign Farm evolved management strategies that optimized soil organic matter and soil fertility while implementing good cultural practices to minimize the need for pesticides (Table 1). Practices included:

  • Organic soil amendments to improve soil and crop quality
  • Soil building to build high organic matter soils with diverse and healthy soil microbial communities
  • Maintenance and selective mowing of the between-row living mulch to build soil quality, maximize air flow, and provide habitat for aphid predators
  • Drip irrigation and irrigation management to maximize air flow and reduce foliar and fruit wetness
  • Three-year rotation of crops by crop family (Solanaceae, Brassicaceae, Fabaceae)
  • Cultural practices including raised beds and staking of tomatoes and peppers to maximize airflow and reduce leaf wetness and disease severity
  • Black plastic mulch on tomato, pepper, and eggplant crops to reduce splashing of pathogen spores by rain or irrigation water onto the stems/leaves/fruit, thus reducing disease severity

The semiarid climate of Biodesign Farm also contributed to low disease risk. Precipitation is only 13–16 inches and occurs mainly in winter, fall, and early spring.

Outcomes

Disease Incidence and Crop Quality

According to Helen, yield and quality losses to disease declined over 17 years, especially those resulting from tomato bacterial speck. This observation is supported by crop quality monitoring records (1994–2010).

  • Severity of tomato bacterial speck (Pseudomonas syringae pv. tomato) decreased over time and this disease did not occur from 2006–2010 in New field and from 1999–2005 in Old field. The dry climate and less intensive production in later years likely were contributing factors, although Biodesign's irrigation, black plastic, living mulch, and other practices may also have contributed to disease suppression.
  • Cucumber mosaic virus (Bromoviridae:Cucumovirus) was observed at very low levels on peppers in the early 2000s in Old field, but did not seem to affect crop yield. It was not observed from 2006–2010 in New field.

Pesticide Use

No pesticides were used to manage diseases at Biodesign Farm.

Key Practices

Rotation

Biodesign Farm's rotation developed around market opportunities and emphasized solanaceous crops. Table 2 and Table 3 show the rotation history. The main focus was a rotation of plant families and crop nutrient needs. The general 3-year rotation for each row was as follows:

  • Year 1: Solanaceous crops—tomatoes, peppers, eggplants
  • Year 2: Brassica crops—broccoli, cabbage, brussels sprouts
  • Year 3: Legume living mulch (Fabaceae) and/or other crops in the Cucurbitaceae, Allium, and lettuce families

Because the field was small, solanaceous crops often abutted and occasionally overlapped. The clover row middles rotated from year to year and also figured into the rotation, but not in a carefully planned manner.

Disease-Specific Practices

Biodesign also utilized practices targeted to specific crops and disease life cycles (Table 4):

  • Tomato bacterial speck: (Pseudomonas syringae pv. tomato) was a problem during long, cool, humid springs when tomatoes were covered with Reemay day and night to protect them from frost. As soon as nighttime temperatures rose, days got sunny and dry, and Reemay was removed, tomato plants seemed to grow out of the symptoms. Drip irrigation was used in the spring to avoid wetting foliage and developing fruit. Raised beds and staked tomatoes helped to maximize airflow and may have reduced disease severity. Black plastic mulch helped to reduce splashing of rain or irrigation water, which can carry spores of disease organisms up to the stems/leaves/fruit. Biodesign's soil building practices generated a soil with high microbial activity, which likely decomposed crop residues quickly. Disease residues are a primary source of bacterial speck inoculum, so the microbially active soil likely contributed to suppression of this disease.  Compost tea (made with Biodesign's on-farm-made sheep and/or cattle manure compost) was applied to tomato foliage in the spring (one to three applications) in the early 1990s, using a 3-gallon Solo backpack sprayer and an application rate of approximately 3 gal/300-ft row. This practice was abandoned by the late 1990s because it did not seem to have much effect and because disease problems had diminished over time.
  • Cucumber mosaic virus (CMV, Bromoviridae:Cucumovirus) was observed at low levels on peppers in the early 2000s but not thereafter. When possible, Biodesign grew CMV-resistant pepper varieties such as Revolution, Vanguard, and Socrates X3R. As CMV is transmitted by aphids, aphid parasitism (Insect Fig.2) likely contributed to CMV suppression. 

Soil building

Biodesign's soil-building system was designed to build high organic matter soils with a diverse and healthy soil microbial community. High-nitrogen (N) and lower carbon (C) soil amendments were applied in early years in Old field (1993–1996); higher C amendments were applied in later years. By 1999, manure-based compost rates had been reduced significantly, as mowed living mulch residues became more important (Table 2). In New field, Helen used higher C/lower N amendments from the start (Table 3).

Soil test records indicate a rise in soil organic matter (Soil Fig. 1) and, after 1996 in Old field, a decreasing trend in soil nitrate-N (Soil Fig. 3). Analysis of soil microbial population density in 1995 and 2007 showed relatively high levels of total microbial biomass and arbuscular mycorrhizal fungi. Some level of biological control may have been generated by the farm's soil amendments and soil-building practices, since damage from disease decreased over time.

Irrigation

In the beginning (Old field), drip irrigation was used almost exclusively to avoid wetting tomato foliage and minimize the environmental conditions that favor tomato bacterial speck. Some sprinkler irrigation was used to keep the living mulch row middles irrigated. By 2000, Biodesign was using both sprinkler and drip irrigation in Old field to irrigate all crops, including tomatoes. In New field (2005–2010), mostly sprinkler irrigation was used because the source was a gravity-flow, surface-water system (thereby eliminating energy costs). In New field, disease pressure was low, so disease avoidance was not the main priority when making irrigation decisions.

Analysis: Integrating Practice and Research

Disease may have been suppressed by Biodesign's design and soil/habitat-building practices, since in later years diseases occurred at relatively low levels. See the eOrganic video: Organic No-Till Living Mulch Disease: Weed Em and Reap.

Cucumber Mosaic Virus (Bromoviridae:Cucumovirus)

Biodesign's goal was to build high organic matter soils with a diverse and healthy soil microbial community. Analysis of microbial population density in Biodesign soils during on-farm experiments in 1996 and 2007 showed relatively high levels of total microbial biomass and arbuscular mycorrhizal fungi. There is some evidence to support Biodesign's hypothesis that microbes in healthy soil increase resistance to cucumber mosaic virus (Zehnder et al., 2000; Ryu et al., 2004; Elsharkawy et al., 2012). Aphid suppression may also have played a role. See Insect Management System.

This article was developed with support from USDA's National Institute of Food and Agriculture through the Western Sustainable Agriculture Research and Education program under grant number SW13-017.

 

References and Citations

Additional Resources

This article is part of the Biodesign Farm Organic Systems Description.

Table of Contents:


 

Published September 21, 2016

This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.

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