2015 BEETcast™ Advisory and Cercospora Leaf Spot Trials in Ontario

Rishi R. Burlakoti†, Sherri Tedford‡, and Cheryl Trueman‡
† Weather INnovations Consulting LP, ‡ Ridgetown Campus, University of Guelph

Weather INnovations has been delivering the BEETcast™ advisory in Ontario and Michigan for over a decade to help sugarbeet growers in managing Cercospora leaf spot (CLS). CLS is the most economically important disease in North America. The disease is favoured by warm temperature and longer duration of free moisture on the foliage due to rain shower, heavy dews, fogs, humidity etc. BEETcast™ helps growers for better fungicide timing to control CLS. The advisory recommends less numbers fungicide applications when environmental conditions are less favorable for disease development.

In recent years, Cercospora beticola, the fungus that causes CLS, has developed resistance to strobilurin fungicides, which were most commonly used to manage CLS in sugarbeet in North America. Fungicides from the Group 3 triazole group (i.e. Proline, Inspire) and contact copper and mancozeb products are recommended as alternative fungicides. To evaluate the new fungicide groups, BEETcast™ thresholds effective to registered products, and to better understand C. beticola spore activity in sugarbeet fields, a three-year (2013 to 2015) project is currently underway. The project is lead by Prof. Cheryl Trueman and graduate student Sherri Tedford, University of Guelph, Ridgetown Campus in collaboration with Dr. Rishi Burlakoti, Weather INnovations. Field trials are being conducted in Ridgetown and Pain Court. This project aims to improve the existing CLS advisory system by adding the pathogen component into the decision support tool. This article will provide a brief update on the 2015 field research related to spore counts and weather data.

This year, average temperatures in May were 2.5°C and 2.9°C higher than the 30-year normal in Ridgetown and Pain Court. The amount and frequency of rainfall was also high in both locations during the last week of May to the end of June (Fig. 4). The first spray threshold for BEETcast™ (50 DSV) was reached on June 21 in Ridgetown and on June 18 in Pain Court. The first spray threshold in Ridgetown was attained about 8 days earlier than in 2014. The sugarbeets reached canopy closure during the second and third week of June in both locations. CLS symptoms were first observed on July 9 in Ridgetown, which was about 3 weeks after the 50-DSV threshold reached. The first symptom appeared about a month after the 50-DSV reached in Pain Court. A similar trend was also observed in 2014. CLS symptoms appear on beets seven to 21 days post-infection.

Thus, in 2014 and 2015, it appears the BEETcast™ threshold effectively predicted the timing of the first fungicide application so that a fungicide could be applied prior to an infection period.

Fig.4. 2015 Weather pattern and BEETcast™-fungicide timing recommendations in Ridgetown and Pain Court, Ontario

Similar to the 2013 and 2014 spore count results, the numbers of Cercospora beticola spores were low during the early part of the growing season in 2015 (before mid July). Spore counts have increased since mid-July. CLS symptoms in control plots are progressing in both locations. The CLS severity is higher in Ridgetown than in Pain Court. Data collection is still underway and comprehensive analysis of three years of spore count (2013 to 2015) and their relationship with weather data and disease severity will be completed at the end of this year.

This project is funded in part through the Ontario Farm Innovation Program (OFIP). OFIP is funded through Growing Forward 2 (GF2), a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario.
Additional funding for the project from the Ontario Ministry of Agriculture & Food, the Ontario Sugarbeet Growers’ Association, and the Michigan Sugar Company is also appreciated.