Improved management of charcoal rot of strawberry (BS15005)
What’s it all about?
Beginning in mid-2017, this project is tasked with helping tackle charcoal rot, reducing its occurrence and related losses and costs for the Australian strawberry industry. It is responsible for investigating improved management approaches including chemical, biological and cultural options for the disease, which is caused by the fungus Macrophomina phaseolina and has symptoms including crown and root rot, plant wilting and yellowing of leaves (chlorosis).
The research team continues to evaluate the use of chemical fumigation, soil management and farm hygiene practices for strawberry crops with charcoal rot, confirming several key tactics that could be adopted by growers to add value to their operations.
The project team found that chemical fumigation reduces the incidence and severity of charcoal rot.
Trial results showed that broadacre fumigation (treating the whole paddock) is more effective than strip fumigation (treating the beds). In heavy soils with high infection levels, shank injection of the fumigant is better than application through irrigation tape.
Using films to cover the crop during fumigation was more effective than not doing so, due to improved targeting and less waste. The totally impermeable films (TIfs) retained fumigants in soils for longer and at greater concentrations and were significantly more effective than standard films made from low density polyethylene.
The effectiveness of fumigants when applied in combination will continue to be evaluated.
Careful soil management and good farm hygiene practices were found to be crucial. Charcoal rot can remain viable in soil for at least three months and buried infected strawberry crowns can infect newly planted strawberry runners.
Growers can reduce the spread of charcoal rot by using good farm hygiene practices that limit the movement of soil within and between strawberry farms.
Soil management research will continue in:
- The effectiveness of removing infected crop debris on the level of disease in a following crop.
- The effectiveness of crop termination as a strategy for controlling charcoal rot.
- Expanding knowledge of disease survival in a temperate environment.
The project team held a series of face-to-face meetings with growers and others in the supply chain, on ways that on-farm biosecurity can protect strawberry growers from charcoal rot and other pests and diseases. Presentations, survey days and a seminar were held in Queensland, Western Australia, South Australia and Victoria.
Farm biosecurity measures, such as biosecurity signs, paddock zoning, and vehicle and equipment wash downs, are a vital part of an integrated strategy for managing the disease, which can spread from farm to farm if precautions are not put in place.
The team reports that more strawberry fruit growers are adopting farm hygiene and biosecurity practices, including the use of footbaths to clean boots, cleaning equipment and clothing to minimize the spread of infested soil, and additional measures to inform visitors and staff about their biosecurity requirements. The project team anticipate that the adoption of these improved hygiene and biosecurity practices will reduce the spread of charcoal rot disease.
Since the team’s research has shown that new runners can be infected with charcoal rot when planted, they recommend removing infected crop debris from the paddock to significantly improve the control of charcoal rot.
- In case you missed them, read two articles in the July 2018 edition of the levy-funded Simply Red newsletter – one on the research showing that chopping infected crowns into soil reduces charcoal rot (on page 1) and one on the work on totally impermeable films (on page 3) and two articles in the December 2018 edition – one on improved practices for managing charcoal rot on page 3, and another on methyl bromide alternatives on page 8.
The research team report positive early findings from trials of new fumigants. While further work is required, they have so far found that new chemicals, when used in conjunction with existing chemical controls, can provide additional protection from the Macrophomina fungus in buried strawberry crowns and in soil.
Their research to date also shows that there are benefits in using totally impermeable films (TIFs) rather than standard plastic films (low density polyethylene) during production, with TIFs increasing the concentration of fumigants in soil, resulting in increased effectiveness.
The researchers have so far taken the findings to strawberry growers at eight locations in Victoria as part of a communication roadshow, and report that many growers have almost immediately begun adopting new recommendations.
Another study, looking at how charcoal rot is spread, has found that the presence of buried, infected strawberry plant material can lead to charcoal rot symptoms in runners up to four weeks after planting. This work was done in pots using a sterile medium, and now a field trial has been established to study the impact of crop debris removal and the effectiveness of an integrated package of best management practices from the project research, in controlling charcoal rot.
Guidelines for on-farm hygiene and biosecurity practices are under development.
To learn more, read two articles in the July 2018 edition of the levy-funded Simply Red newsletter – one on the research showing that chopping infected crowns into soil reduces charcoal rot (on page 1) and one on the work on totally impermeable films (on page 3).
The project team report that research results to date have driven the commercial trialling and adoption of ‘totally impermeable films’ (TIFs) for the first time in Australia, on 12 per cent of strawberry properties in Victoria. TIFs are laminated plastics that retain chemical fumigants for longer periods in soil than standard low-density polyethylene films.
Earlier in the project, a literature review identified the use of TIFs as a potential method to increase the effectiveness of currently registered soil fumigants against charcoal rot. Soil column and field trials confirmed their effectiveness in retaining fumigants in soil, leading to better control of charcoal rot. The researchers report that other potential benefits from the adoption of TIFs include lower emissions of fumigants to the environment, greater operator safety, and the opportunity to use lower rates of some fumigants, without compromising control of charcoal rot.
The project’s literature review also pointed towards new soil fumigants with potential to control charcoal rot and after importing the products from overseas, the researchers established the first trials in Australia to evaluate the chemicals. This has led to a label registration for ethanedinitrile (Draslovka’s EDN Fumigas). This year will be the first time Australian growers have the opportunity to use the product commercially – the label can be viewed by searching for product name ‘ethanedinitrile’ or product number ‘60096’ on the Australian Pesticides and Veterinary Medicines Authority website. Work related to new fumigants is ongoing, and includes the investigation of potential novel application techniques, such as application through irrigation tape and co-application with other fumigants.
Other work in the project has included a study of how long the Macrophomina fungus can survive in infected strawberry crowns. The researchers note that diseased strawberry plants and plants of alternative host species become a source of inoculum when they’re ploughed back into the soil, with the potential to infect new plants of the subsequent strawberry crop – and that current industry practice is to incorporate strawberry crop debris into the soil at the end of the season. In the disease survival study, viable Macrophomina was recovered from 30 per cent of infected strawberry crowns buried in the field for six months. “These initial results suggest the standard practice of incorporating infected strawberry plants at the end of the season will add to the level of inoculum in the soil, and potentially contribute to the level of charcoal rot developing in the subsequent strawberry crop,” the researchers note. Work in this area is continuing.
In conducting a review of information from Australia and across the world, the project team has identified better ways of applying soil fumigants to improve operator safety and increase effectiveness against charcoal rot. One technique identified is the use of plastic films with greater impermeability, and hence the potential to retain the fumigant.
The researchers have also set up soil column experiments to screen new and existing fumigants against charcoal rot, either alone or as mixtures. These experiments will be used to prioritise the most effective fumigant treatments for testing in field trials, which at the time of writing were due to begin around December.
Meanwhile, a study of how long the Macrophomina fungus will survive in infected strawberry crowns has been initiated. Infected crowns and part crowns buried in the field will be retrieved at fortnightly intervals and assessed for the presence of viable Macrophomina over the course of the six-month study, with the first retrievals now completed.
This project is a strategic levy investment in the Hort Innovation Strawberry Fund