Integrated disease management in pyrethrum (PY16000)
What’s it all about?
With an increasing number of foliar and flower diseases placing constraints on pyrethrum production – reducing yields and the lifespan of crops – and fungicide resistance a rising cost and risk, this investment will aid pyrethrum growers in minimising these issues. Beginning during 2017 and set to run for three years, it involves research into the key pathogens that affect pyrethrum production, the timing of their influence, and their susceptibility to fungicides.
This information will be used to help growers optimise the number and timing of fungicide applications, and the research team will look at combining this with efforts to increase host resistance and reduce pathogen carryover between seasons.
Ultimately, the project will help the industry decrease its reliance on fungicides – reducing economic and environmental costs of production – while increasing pyrethrin yields.
The researchers report that the project is on track with results now coming in from trials. Trial results include…
- Thirty commercial fields distributed across the pyrethrum growing regions of Tasmania were surveyed again in December 2018. Data from this season and 2017/18 were combined to identify key fungal pathogens. Flower pathogens Botrytis cinerea and Sclerotinia were not found to be major pathogens of pyrethrum flowers, contrary to previous beliefs. The dominant floral pathogen across both seasons was Stagonosporopsis tanaceti which was found in 93 per cent of fields over both years, with an average flower incidence of 45 per cent. Itersonilia perplexans was also found in less than 10 per cent of sampled flowers.
- Replicated field trials evaluating the application of fungicides in the autumn following harvest for disease management were run in two commercial fields in 2018/19. Autumn applications of fluopyram were associated with reductions in the diseases ray blight and tan spot in winter 2018, and increased crop canopy development. This effect continued into spring for ray blight, but not tan spot. Final crop yield effects varied at sites, with one having an 80 per cent yield increase, but a second site showing minimal increase. The difference may be down to the incidence of ray blight at the sites.
- Two replicated field trials to assess potential fungicides for the control of spring dieback were initiated in July 2018 and concluded in January 2019. These trials continued from work conducted in 2017/18 and supported previous observations that fungicide products containing the active ingredient fluopyram give significant disease control in winter. At one of two trial sites in 2018/19 disease pressure was very low and the fungicide treatments provided little yield benefit. However, at the second site disease levels were more typical of spring disease pressure and pyrethrins yield was much higher than controls. Applications of pydiflumetofen and azoxystrobin were also associated with significant yield increases and improved disease management.
- A replicated field trial was established within a commercial first harvest field in November 2018. The cumulative benefit of each successive fungicide application, from 0 to 4 sprays, was evaluated. Pathogen incidence was low, and no yield benefit was found.
In February 2019, a new field trial was established at the Vegetable Research Facility at Forthside to look at the effects of irrigation, fungicide applications and manual crop residue removal of post-harvest disease. Disease incidence and plant growth data is currently being collected from this trial which is expected to finish in January 2020.
Once the trials are finished, results will be compiled and recommendations for growers will be produced.
All facets of the project are progressing well…
The research team completed a review of fungicide efficacy, finding that there is little scientific evidence on the effects of several key fungicides, especially tebuconazole, prothioconazole and fluazinam. As a result, the team has begun testing the first two for effectiveness against two common foliar pathogens, and fluazinam will be tested next.
Two field spring fungicide field trials were initiated in July 2018, repeating the 2017 trials to provide more certainty of findings. Fungal incidence and disease severity assessments have been already made and yield assessments will be made in December 2018.
Surveys of foliar disease pathogens were conducted in 30 commercial fields distributed across the pyrethrum growing regions of Tasmania in October 2018. Fungal identifications have been made from these samples, the data have been collated and the same areas will be surveyed later in the season to assess the incidence of floral pathogens.
A greenhouse study on the effect of timing of infection by pathogens is currently ongoing. Pyrethrum plants will be inoculated at various stages of flower maturity and disease incidence measured.
As reported in the last edition of Hortlink, field trials were established in August 2017 in commercial fields in northern Tasmania. Examining the efficacy of a selection of fungicide products for the control of spring foliar disease, there were two sites established to look at currently available products when incorporated as the second spray in spring fungicide programs.
There was also a third field trial established for trialling possible new fungicides in the control of foliar diseases. Some potential products have been singled out and represent avenues for further investigation.
Other areas of investigation for the project include the management of flower diseases, with an initial trial running from November 2017 to January 2018 to look at the cumulative benefit of each successful fungicide application, from zero to four sprays. Conditions were reported as abnormally dry, and disease pressure subsequently low, so further work in this space is required. However the experiment “did demonstrate to industry the potential for reducing the current flowering fungicide program without yield penalty, especially under low disease pressure conditions.” More work in this space is to come.
In addition, the project team has been undertaking surveys for foliar disease pathogens across 30 commercial fields across Tasmanian pyrethrum growing regions. From set areas within the fields, leaf samples were collected in October 2017 and flower samples in December. From this work, the researchers report…
- Didymella tanaceti (responsible for tan spot) was the dominant leaf pathogen, though was detected in less than 10 per cent of flower samples.
- While Stagonosporopsis tanaceti (responsible for ray blight) was detected in 90 per cent of the fields in October, it was found in only nine per cent of the leaf samples taken at the time – however it was present in all fields at the time of flower collection and found in around a third of flowers sampled.
- Fungal pathogens that have previously been dominant in flowers were only detected at very low incidences (Botrytis cinereal, which causes botrytis flower blight) or not detected (Sclerotinia spp, responsible for Sclerotinia flower blight).
Field trials were established in August 2017, in commercial fields in northern Tasmania, to examine the efficacy of a selection of fungicide products for the control of spring foliar disease. There are two sites looking at currently available products, and a third trialling possible new fungicides.
The project team report that these trials have initially demonstrated “considerable visual differences in field observations, suggesting products that may have improved efficacy relative to the current standards”. At the time of writing, however, yield data from the trials was still to be evaluated and, when combined with the observations during the season, will provide a fuller picture. Look for updates in future editions of Hortlink.
The project team has also been undertaking surveys for foliar disease pathogens across 30 commercial fields across Tasmanian pyrethrum growing regions. In October 2017 they collected leaf samples from each site to make fungal identifications, and in December the same plot areas were assessed for the incidence of floral pathogens. Again, look for updates in future editions of Hortlink as results are collated and the research progresses.
This project is a strategic voluntary levy investment in the Hort Innovation Pyrethrum Fund