Combating apple replant disease in Australia (AP00003)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Apple replant disease (ARD) was reported wherever apples were grown, and generally had a biological cause. It posed an acute dilemma for orchardists with the phasing out of the most effective treatment, methyl bromide (MeB), by 2005 under the Montreal Protocol because of its ozone-depleting properties. Hort Innovation (then Horticulture Australia Limited) had provided funding to a group of Tasmanian researchers to assess alternatives.

The key components of this project comprised of a comprehensive review of the literature, followed by glasshouse and field trials of a range of potential alternative treatments to MeB for apple-replant disease. Glasshouse trials using MeB as the standard indicated that monoammonium phosphate (MAP), Basamid®, Perlka® and various biological agents gave good protection against the disease. The beneficial effects of the first two agents supported previous reports for these agents while Perlka® had not been previously recorded for this purpose. However since it was reported as a broad-spectrum biocide its efficacy in controlling apple replant disease was easily explicable. The benefits recorded for compost amendment were attributed to a nutrient effect on growth rather than inhibition of the disease.

A field trial undertaken at the Grove Research Centre included agents found to be effective in the glasshouse trials plus others being reported as promising alternatives. Telone C-35® was shown in the field trial to be at least as effective as methyl bromide, with Perlka® + MAP, Basamid® and compost additions resulting in only slight improvements in plant growth over the replant-disease controls. Other treatments including MAP, Trichopel®, Perlka®, and various biocontrol agents were ineffective in combating the disease in the field. It should be noted however that the poor result found in the field trial for Basamid® and MAP contrasted with previous results obtained by other workers and were possibly the result of particular field conditions or method of application. In a second field trial, adding MAP or fresh soil to the planting hole were both found to substantially reduce the effects of ARD, in line with previously published results.

Recommendations:

This study confirmed Telone C-35® as a viable alternative to MeB for treating apple replant disease in replant orchards. Converting to Telone C-35® treatment had the advantage of growers being able to use the same equipment and similar field management methods as for MeB. For low impact (non-fumigant) control of ARD, continued use of MAP was recommended and for control without synthetic chemicals, addition of fresh (non-ARD) soil in the planting hole substantially reduced the impact on tree growth.