What was it all about?

Starting in 2017, this three-year research project undertaken by the Department of Agriculture and Fisheries (DAF) and the Victorian Strawberry Industry Certification Authority (VSICA) developed new practices for improved control of charcoal rot for strawberry growers.

Charcoal rot is a major disease of strawberry, capable of causing devastating plant deaths with substantial financial impact through lost income. A soil borne disease caused by the fungus Macrophomina phaseolina it has been found throughout Australia, although not in all strawberry production districts. Symptoms include crown and root rot, plant wilting and yellowed leaves (chlorosis).

The new practices and key findings from the research included:

• The use of totally impermeable film (TIF) with fumigants reduces plant deaths due to charcoal rot by 91 per cent. TIF retains chemical fumigants in the soil at higher concentrations (up to 32 per cent) for longer periods than the industry-standard low-density polyethylene (LDPE) plastic mulch. Income from additional fruit harvested exceeded the additional TIF cost.
• The pathogen that causes charcoal rot survives in buried strawberry crowns from one season to the next. Standard industry practice has been to return infected strawberry crowns to the soil at the end of the fruiting season. Surviving phaseolina in infected crowns transferred to new strawberry plants within weeks, with up to 50 per cent of plants dead after eight weeks.
• Field research results contributed to the registration (2018) of EDN Fumigas™ for use in strawberry. Chemical fumigants not yet registered in Australia were also evaluated to identify possible future control options.
• Chemical fumigants Tri-Form® 80 and EDN Fumigas™ reduced charcoal rot plant deaths by 83 per cent and 95 per cent respectively, compared with untreated soil.
• Fumigant application techniques were shown to improve charcoal rot control results. Direct injection into the soil by shank fumigation reduced plant deaths by up to 37 per cent compared with drip applied fumigation. Field experiments showed that broadacre fumigation under LDPE of the entire paddock reduced charcoal rot deaths by 66 per cent compared to strip fumigation of the raised beds under LDPE.
• Destroying an old strawberry crop with metham sodium followed by pre-plant fumigation was shown to increase fruit yields by 30 per cent and revenue by $1.29/plant the following season, compared with pre-plant fumigation alone.

Strawberry growers across Australia were regularly informed of the benefits of farm biosecurity practices through many communications events. Project team members delivered presentations at 41 events in five states, along with 14 articles in industry publications.

Increased awareness led to adoption of these improved farm practices by Australian strawberry growers, resulting in a 5 per cent reduction in charcoal rot on Victorian strawberry farms from 2017 to 2020, for example. This amounts to an estimated $5M additional revenue in 2020 from improved management of charcoal rot in the Victorian industry alone.

The project team also identified aspects of managing charcoal rot that require future research, including biofumigants and other non-chemical controls, and the evaluation of diagnostic tests to support growers in the selection and use of the most cost-effective treatments.

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Read these articles published in the Simply Red industry magazine:

• The fungus causing charcoal rot can survive between crops in infected crowns, July 2018, No 50, pp1-2
• Totally impermeable films increase fumigant concentrations in soil, July 2018, No 50, pp3-5
• New practices for improving control of charcoal rot, January 2019, No 52, p4
• The use of totally impermeable films (TIFs) with soil fumigants is a cost-effective treatment for management of charcoal rot, June 2019, No 54, pp12-13
• Highlights from the international research conference on methyl bromide alternatives and emissions reductions, December 2017, No 48, p8
• Developing improved practices for managing charcoal rot in strawberry, December 2017, No 48, p3
• Retaining infected crop debris leads to charcoal rot, June 2019, No 54, p7

And these from various editions of the Australian Berry Journal:

• Charcoal rot – A disease of strawberry and blueberry, Summer 2019, pp43-45
• New practices for Improved control of charcoal rot, Winter 2020, pp57-59
• Black TIF mulch reduces charcoal rot of strawberry more effectively than silver TIF, Winter 2020, pp61-63
• Combination treatment reduces charcoal rot and increases fruit yields of strawberry, Spring 2020, 70-72.