Implementing an Effective Strategy for Management of Internal Discoloration of Horseradish Roots
Horseradish is grown for its white flesh and pungent roots. Approximately half of the total commercial horseradish in the United States is produced in Illinois. Over the past years, the horseradish growers in Illinois, and other horseradish producing areas in North America, have experienced internal discoloration in horseradish roots, causing up to 100% yield losses and threatening horseradish industry.
We propose a comprehensive research/education effort to meet the pressing need for management of internal discoloration of horseradish root by thermo-therapy of planting root stocks (sets) to eradicate set-borne inoculum of the pathogens and set treatment with biofungicides to protect the plants during the growing season in the fields against soil-borne inoculum of the pathogens that cause the internal root discoloration. The proposed approach can be implemented in both traditional and organic horseradish productions.
The apparently asymptomatic, horseradish sets saved by growers to plant in the following season are a major source of root infection (set-borne inoculum). Also, the causal agents (Fusarium and Verticillium species) of the internal discoloration of horseradish roots survive in soil (soil-borne inoculum. The symptoms of internal discoloration of horseradish roots become visible after about 12 weeks from the time of contact of the pathogen with the root. Horseradish sets are usually planted in May and harvested during September-November.
Application of either the biofungicide (SoilGard 12 G or Serenade MAX) onto pathogen-free horseradish sets (either generated by tissue culturing or cleaned up by thermo-therapy) protected the roots in the field for about 12 weeks (from May until the end of July or mid-August). As a result, the remaining period of the growing season (August-September), even with conducive conditions for development of the disease, is not long enough for expression of the discoloration to make the roots unmarketable. After October, the environmental conditions are usually not conducive for development of the discoloration.
The cost for eradication of set-borne inoculum by thermo-therapy and set-treatment with biofungicides for one acre is about $80. Both of the biofungicides are registered for use in organic production too. Thus, this is a novel integrated strategy for managing a complex plant disease, which is a serious threat to the production of a high-value crop, with no hazard to the environment or human health, no license-requirement for application, and a very cost/effective approach. It takes ≥ 12 weeks for soil-borne inoculum of the pathogens to cause observable internal discoloration of horseradish root.
The results of this project will be rapidly implemented because of the following reasons. First, there is no other effective method for controlling the most destructive disease of horseradish. Second, the developed strategy can be implemented in both traditional and organic horseradish production. Third, all materials used in implementing this IPM-approach are commercially available. Fourth, it is a very cost/effective method - total costs for implementing this disease management practices are going to be less than 3% of farm-gate value and less than 1.5% of product value of horseradish crops. Fifth, conducting trials in commercial fields at Collinsville, IL, the largest horseradish growing area in the world, will provide the opportunities for most of the horseradish growers to observe the effectiveness of the strategy. Sixth, the strong outreach component of the project will ensure that growers gain the knowledge they need. Seventh, by practicing the new IPM strategy, 100% of fungicides used for intended control of internal discoloration of horseradish roots will be eliminated.
The developed IPM approach will be widely used and it will ensure that horseradish industry will continue to be a significant component of agricultural industry.
Project goals and objectives
Project objectives include: 1) to demonstrate importance of set-borne inoculum and its eradication by thermo-therapy; 2) to demonstrate the effectiveness of two newly registered biofungicides for control of internal discoloration of horseradish roots; 3) to demonstrate benefits of using an IPM approach to solve the complex internal discoloration disease of horseradish root; and 4) to help establish a sustainable horseradish production system.
Targets are that: 1) >90% of the growers (45 growers) have increased their understanding of the new IPM strategy, 2) >70% of the growers (35 growers) willing to try the new strategy, and 3) >50% of the growers (25 growers) have begun using the IPM strategy in two year.