Development of regional disease risk models for fungal diseases of pyrethrum (PY20000)

What was it all about?

This program investigated the environmental conditions that drive tan spot and ray blight outbreaks in pyrethrum.

Challenge

The diseases ray blight and tan spot, both caused by fungal pathogens, are the major diseases impacting pyrethrum production. Currently, a standard recommended spray program is deployed industry wide to manage these diseases. Managing these diseases represents significant financial and environmental costs to growers.

Anecdotal evidence from growers and results obtained from previous studies suggests that different growing regions and/or seasons are subject to different levels of disease pressure.

Response

Work undertaken in this project included a combination of field, greenhouse, and controlled environment studies. Field studies into the impact and the timing of that impact, of fungal diseases on pyrethrum yields were undertaken in collaboration with Botanical Resources Australia across four seasons from 2020 to 2023.

Field surveys were conducted on commercial properties across the 2021 and 2022 growing seasons with monitoring of fungal disease loads and environmental conditions. These surveys were supported with targeted greenhouse and controlled environment studies were conducted to supplement field observations.

Conducting all work in direct collaboration with Botanical Resources Australia and pyrethrum growers was to ensure visibility to, and feedback from, industry.

Benefit

The findings of this project highlighted the different times during the season that tan spot and ray blight reduce crop yields. Yield losses from tan spot were associated with that disease occurring in late winter and early spring. Disease carryover from previous seasons and spring rainfall were the major drivers of tan spot in pyrethrum. Identified thresholds for cropping density and spring rainfall provide tools to the industry for determining the frequency and timing of fungicide applications to sustainably manage this disease moving forward.

Ray blight in spring and early summer also resulted in significant yield losses. As a result of these findings, the industry has already changed management strategy with the removal of the pre-existing flowering fungicide program and supplementation of the spring program recommendations to improve control of ray blight in the late spring period. Mild temperatures, regular occurrence of days with rainfall and high humidity, in conjunction with proximity to neighbouring crops were the major drivers of ray blight outbreaks. The number and timing of fungicides in the late spring period can further be refined based on the predictive factors identified in this project.