2021 Cercospora Resistance Maps

Comments on Cercospora Leafspot (CLS) Maps from 2021 Growing Season

Note: Cercospora Leafspot (CLS) Resistance maps are presented as the average resistance level for the township based on individual samples collected and analyzed by Dr. Secor and Viviana Rivera-Varas at NDSU.

In 2021, due to supply chain issues in lab supplies, only half the number of locations were sampled as previous years.

Starting in 2019 for the DMI fungicides, (Eminent, Inspire, Proline & Provysol) Dr. Secor’s research lab provided measurements of resistance levels greater than 10ppm for EC50 values. Being able to have these observations provided greater resolution in the strength of resistance to the DMI fungicide populations. Prior to 2019 the map only showed EC50’s as greater than 10ppm was preserved but a new map was created to show the addition of the detailed data of greater than 10ppm measurements and this map will be referenced in the below comments. This map was segmented for all DMI’s by adding “Very High Level” categories of: 10.0001 - 25.0 ppm (VH1); 25.0001 – 50.0 ppm (VH2); >50.0 ppm (VH3). Creating these segments allows the use of the actual ppm measurements greater than 10ppm in creating the township averages.

To Note: The maps as well as the descriptions below are based on the average township severity rating based on all samples taken in that township. Individual samples may be below or above the average level of resistance for the township.

Map 1– Eminent/Minerva by township
Eminent/Minerva resistance levels remain mostly in the very high categories throughout the RRV. Map 1 shows that the Very High Level 2 resistant level (25.0001 – 50.0 ppm) is averaged in the majority of townships at 41.6% followed by Very High Level 3 (>50.0 ppm) at 32.6% of the townships. From 2020 to 2021 Very High 3 resistance levels increased from 17.5% to 32.6%. In 2021, 11.6% of the township are in the less than 10ppm average resistance level categories compared to 15.2% in 2020. Eminent/Minerva is strongly recommended to only be used as a tank mix partner with another non-Triazole fungicide. Not more than 50% of total applications per year should include triazoles. Contact your Agriculturist for information on a section by section basis.

Map 6 – Headline/Priaxor by township
Headline/Priaxor is reported in terms of % of sensitive/resistant isolates. The percent of isolates resistant to Headline/Priaxor are very high overall. 88% of townships averaged 100% resistance in 2021. In 2021, 11.1% of townships averaged some level of sensitivity to Headline/Priaxor. Ideal timing for this application remains to be the last week of August through the first week of September for sugarbeet root frost protection/recovery and plant health/storage benefits. Headline/Priaxor MUST be tank mixed with a full rate of each product in the tank mix, NEVER use these products without a tank mix partner. Contact your Agriculturist for information on a section by section basis.

Map 8 - Inspire by township
Inspire resistance levels are mostly in the Very High resistant level ranges. In 2021 the majority of township averaged in the Very High level 3 (>50ppm) range at 29% followed by Very High level 2 (25.0001 - 50 ppm) at 27.9%. For the Very High level 3 range this increased from 2020 levels which were at 17.1% of the townships. There was very little change in the percent of townships with less than 10ppm average resistance level which is at 32.7%. Inspire is strongly recommended to only be used as a tank mix partner with another non-Triazole fungicide. Not more than 50% of total applications per year should include triazoles. Contact your Agriculturist for information on a section by section basis.

Map 13 - Proline by township
Proline resistance levels remain mostly Very High throughout the RRV. In 2021, the Very High level 3 (>50 ppm) has the highest percentage of township averages at 79.5%, up from 2020 in which 54% of township had this resistance level. There was little change in the percent of townships at the less than 10 ppm average resistance level which is at 10%. Proline is strongly recommended to only be used as a tank mix partner with another non-Triazole fungicide. Not more than 50% of total applications per year should include triazoles. Contact your Agriculturist for information on a section by section basis.

Map 18 - Provysol by township
Provysol resistance levels remain mostly Very High. In 2021, Provysol resistance levels in the majority of townships averaged at the Very High Level 3 (>50 ppm) category at 55.3% which is up from 2020 which was at 28.5% of the townships. The percent of townships at the less than 10 ppm average resistance level is at 25.2.%. Provysol is strongly recommended to only be used as a tank mix partner with another non-Triazole fungicide. Not more than 50% of total applications per year should include triazoles. Contact your Agriculturist for information on a section by section basis.

Map 23 - TPTH (Tin) by township
Resistance continues to increase again for TPTH in 2021, which is again up from 2020. For the majority of the townships, 61.1%, averaged in the category of 51-75% of spores being resistance to 1 ppm of TPTH. This is up from 2020 where 20.5% of townships fell into this category. Tin should be utilized as a tank mix partner with other chemistries, at full rates of each tank mix partner. Contact your Agriculturist for information on a section by section basis.

Topsin by township – see 2019 Map 25
Samples were not run for Topsin resistance in 2021. Please refer to Map 25 – Topsin by Township from 2019. The 2019 Topsin map is reported in terms of % of sensitive/resistant isolates. The percent of isolates resistant to Topsin are very high overall, but Topsin remains quite effective as a tank-mix partner and helps to preserve other fungicides (reference TPTH). Topsin is NEVER recommended to be applied alone. Topsin with a suitable tank mix partner with TPTH in the 1st or 2nd fungicide application and remains to be a very good CLS management option. Remember Topsin PHI is 21 days, so plan harvest accordingly around your spray rotation.

General Comments
In 2021 the first cercospora spot were found the last week of June in the RRV. This is the same time frame as 2020, which was surprising considering the drought occurring in 2021. Cercospora remained under control for much of the growing season due to timely fungicide applications in which fungicides were tank-mixed and rotated. A late onset of cercospora infections occurred however in September with a favorable environment of precipitation and heat that spurred development but was as well favorable for beet growth. 2021 had an average of 3.4 CLS fungicide applications across our growing region, compared to 3.5 in 2020. The 3.4 fungicide applications is the second highest average in our data base dating back to 1980. With high cercospora inoculum present going into 2022, it is extremely important to have a well-timed initial fungicide application to keep cercospora from becoming established in fields. With current cercospora populations showing high levels resistance across all fungicides, continued diligent CLS management by tank-mixing and rotating fungicide modes of action is highly recommended to aid in reducing overall CLS infections and inoculum. Using 15-20 gallons per acre water at 80+ psi, starting spray program earlier and 12 day maximum spray intervals are all essential practices that need to implemented. Glyphosate applications must be separated from fungicide applications as water volumes vary by targeted pest.

For more information on CLS management, contact your Agriculturist. Another useful website is www.sbreb.org for the latest in North Dakota State University and University of Minnesota research information.