Minimizing Crop Damage Through Understanding Relationships Between Pyrethrum Phenology and Ray Blight Disease...

Area of Science:

• Agricultural Science
• Plant Pathology
• Crop Protection

Background:

• Ray blight, caused by Stagonosporopsis tanaceti, is a major foliar disease affecting pyrethrum crops in Australia.
• Current fungicide application timing, based on stem height, may not be optimal for disease control.
• Economic losses due to ray blight can be substantial if disease management is not effectively timed.

Purpose of the Study:

• To develop a degree-day model to accurately predict pyrethrum stem emergence for optimizing fungicide application timing.
• To improve the initiation of prophylactic spring fungicide programs to minimize economic losses from ray blight.
• To quantify the relationship between fungicide timing and disease control efficacy.

Main Methods:

• Collected stem emergence data from 27 pyrethrum fields in Tasmania over three years (2009-2011).
• Developed a degree-day model using logistic growth functions and a nominal biofix date (austral winter solstice).
• Analyzed prediction errors using mixed-model analysis and quantified fungicide timing impact with split-line regression.

Main Results:

• A degree-day model accurately described temporal changes in stem elongation (R² ≥ 0.97).
• Optimal base temperature for the model was 0°C, with prediction errors varying by geographic region.
• The optimal timing for fungicide application was found to be significantly earlier than current recommendations, at 513.8 degree-days (10.7% stem elongation).

Conclusions:

• The developed degree-day model provides a more precise tool for initiating pyrethrum fungicide programs.
• Applying fungicides earlier in stem phenological development, guided by the model, enhances disease control and reduces crop losses.
• Regional correction factors are necessary for accurate degree-day predictions across different production areas.