2020 Cercospora Resistance Maps

Comments on Cercospora Leafspot (CLS) Maps from 2020 Growing Season

Note: Cercospora Leafspot (CLS) Resistance maps are presented as the average resistance level for the township based on individual samples collected. 

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.  The historical map only showing 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. 

Map 1– Eminent/Minerva by township
Eminent/Minerva resistance levels remain mostly in the very high categories throughout the RRV.  Comparing 2019 to 2020, Very High resistance levels increased in each district.  Map 1 shows that the Very High Level 2 resistant level (25.0001 – 50.0 ppm) is the majority of township measurements followed by Very High Level 3 (>50.0 ppm).   However, 11 Moderate level (0.1 – 1.0 ppm) townships were gained over the previous year.  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.  Mostly this has leveled off, but in 2019 it was noted there was reclamation of less resistance in the southern valley, however in 2020 it looks to have retreated to slightly higher resistance.  It is strongly recommended Headline/Priaxor applications be preceded by fungicides with other modes of action to reduce concern from fields where resistance has been documented.  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 increased throughout the RRV.  More townships increased in 2020 to Very High-level categories with VH level 2 (25 - 50 ppm) becoming the majority at that average.  This is up from the High level (1.0 – 10ppm) rating having the majority of townships in 2019.  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 2020, the Very High level 3 (>50 ppm) has the highest number of townships averaging that rating.  This has increased in comparison to what was seen in 2019.  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 in the majority of townships averaged at the Very High Level 2 (25 – 50 ppm) throughout the RRV this is up from 2019 when the majority was in the High Level (1 – 10 ppm). 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
Unfortunate news for TPTH from 2020 samples.  There is increased resistance in 2020 samples being fairly evenly distributed amongst townships in the categories from Sensitive to High Resistant.  This is in stark contrast to 2019 where a strong majority of townships averaged at the Sensitive level.  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 2020.  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 1^st or 2^nd 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
2020 was a year with very high infections of cercospora leaf spot in the American Crystal Sugar growing area.  The hot, humid weather provided a favorable environment for early cercospora development and CLS pressure was high throughout the growing season.  2020 had an average of 3.5 CLS fungicide applications across our growing region, compared to 2.7 in 2019.  3.5 fungicide applications is the highest average in our data base dating back to 1980.  With high cercospora inoculum present going into 2021, 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.