Importance of Brassica soil amendments for managing soilborne disease in ornamentals and vegetables

View the project final report

• 2007 annual report

Commodities

• Agronomic: canola
• Vegetables: cucurbits
• Additional Plants: ornamentals

Practices

• Crop Production: cover crops
• Pest Management: biological control
• Soil Management: green manures
• Sustainable Communities: sustainability measures

Soilborne pathogens of ornamental and vegetable crops cause production losses every year. However, current disease control methods offer few options for control and chemical fumigation is increasingly limited and costly. Additionally, reliable and sustainable disease management methods appropriate for limited resource farmers should be further researched due to the lack of available effective sustainable management methods. Brassicas, including mustards and canolas, contain secondary metabolites, including glucosinolates, which decompose into biocidal and volatile isothiocyanates, as well as other chemicals, which are inhibitory to plant pathogens. Thus, Brassica amendments appear to be a viable alternative to chemical soil fumigation practices for managing pathogen populations, including fungi and nematodes, as part of a sustainable agricultural system in the southern United States. However, additional information is needed on effective Brassica spp. and rates of incorporation. Objectives in the study were to determine the importance of Brassica cover crop selection and biomass application rates for disease management of the root-knot nematode, Meloidogyne incognita, and Rhizoctonia solani AG4. For petunia and impatiens experiments over two years, Brassica amendments significantly reduce disease symptoms and recovery of Rhizoctonia solani from plants. Brassica crops were not significantly different from each other. Rate of Brassica application had the greatest impact on disease symptom reduction and reducing Rhizoctonia solani isolation, with a rate of 3000 g/square m being more effective than lower rates. There was no significant interaction between cover crop and amendment rate. No phytotoxic effects from the Brassica crops were observed at any rate of application. Results from Meloidogyne incognita experiments with cucumber were not conclusive because of problems with infestation methods allowing survival of nematode inoculum during the decomposition period of the green manure, while exposing the nematode to the effects of the Brassica amendment. However, galling from the root-knot nematode has been significantly reduced on cotton using Fumus to levels similar to the fumigant Telone II. This study indicates that Brassica selection has less effect than the amount of Brassica amendment incorporated. Thus, selection should be based on biomass production and not glucosinolate levels produced by a cultivar. This holds great promise, as growers can make selections based on adaptation of the Brassica species and cultivar. Also, this should reduce costs by allowing growers flexibility by purchasing the lowest priced cultivars. The study did document the suppression of the fungus Rhizoctonia solani on ornamentals and this should apply to vegetable crops where Rhizoctonia solani is an important pathogen. Effective management of soilborne pathogens for vegetable and ornamental crops using Brassica amendments in both limited-resource farming operations and home production appears promising.

Introduction

Soilborne pathogens of ornamental and vegetable crops cause production losses every year. However, current disease control methods offer few strategies for control and chemical fumigation options are increasingly limited and costly. Additionally, there is currently a lack of environmentally responsible and affordable disease management methods available for limited resource producers. Brassicas, including mustards and canolas, contain secondary metabolites, including glucosinolates, which decompose into biocidal and volatile isothiocyanates, as well as other chemicals, which are inhibitory to plant pathogens. Managing pathogen populations, including fungi and nematodes, with Brassica winter cover crops appears to be a viable alternative to chemical soil fumigation as part of a sustainable agricultural system in the climate of the mid-south. However, additional information is needed on effective Brassica spp. and rates of incorporation.

Various research has investigated several Brassica crops for effectiveness of disease suppression, though these studies typically only used a Brassica crop that was not designed for biofumigation purposes. Few studies have addressed the use of Brassicas specifically intended for biofumigation efforts, and those studies typically focused on row-crop production. These experiments will address appropriateness and effectiveness of three Brassica winter cover crops including one specifically bred for higher levels of glucosinolates, as well as rates of amendment. The purpose of this project is to determine the appropriate Brassica species and cultivar and amendment rate for management of nematodes and Rhizoctonia solani on vegetable and ornamental crops. The root-knot nematode and R. solani were selected for assessment because of the significance of these pathogens in all levels of vegetable and ornamental production, including limited resource farmers and organic producers. The Brassicas used included the Indian mustard (B. juncea cv. Fumus), the Indian mustard Bionute, and a canola (Brassica napas cv. Jetton).

Growing Brassica biomass in the location needing treatment also can assist in more efficient resource management when compared to strategies that use seed meal hauled into a location and perhaps also improving effects of the green manure crop due to the high volatility of the active compounds. This could allow many small operations to afford effective and environmentally responsible disease control, while improving yields and crop value. Additionally, this project could improve sustainable agriculture efforts through the reduction of chemical inputs in local ecological systems, reductions in fuel consumption, and improved availability of affordable, simple disease management methods to limited resource and home growers.

The anticipated impact of this project is to develop recommendations for the management of soilborne diseases in limited resource farming operations. This would allow for the integration of an improved sustainable method of disease management into the existing agricultural systems.

1. To determine the importance of Brassica cover crop selection and biomass application rates in relation to disease management of root-knot nematodes (Meloidogyne incognita) affecting cucumber.

2. To determine the importance of Brassica cover crop selection and biomass application rates in the disease management of Rhizoctonia solani AG4 on petunias and impatiens