2019 Cercospora Resistance Maps

Comments on Cercospora Leafspot (CLS) Maps from 2019 Growing Season

Note: 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: 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 1.2– Eminent/Minerva by township
Eminent/Minerva resistance levels remain mostly high throughout the RRV. Comparing 2018 to 2019, more of the moderate levels were lost and replaced with high to very high levels of resistance levels. Very high resistance levels increased in each district. On map 1.2 (new map), shows that the Very High Level 2 resistant level of 25.0001 – 50.0 ppm is the majority of township measurements followed by Very High Level 3 in the >50.0 ppm range. 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 there is a noted reclamation of less resistance in the southern valley comparing 2019 to 2018. 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 8.2 - Inspire by township
Inspire resistance levels remain mostly high throughout the RRV. Comparing 2018 to 2019, more of the moderate levels were lost and replaced with high levels of resistance levels in each district. On map 8.2 (new map), it shows that the High Resistant level of 1.0001 - 10.0 ppm is the majority of township measurements followed by Very High Level 1 in the 10.0001 – 25.0 ppm range. Very High Level 2 & 3 are also present. 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 13.2 - Proline by township
Proline resistance levels remain mostly High to Very High throughout the RRV. Comparing 2018 to 2019, more of the moderate levels were lost and replaced with high levels of resistance levels in each district. On map 13.2 (new map), it shows that the Very High Resistant levels 2 & 3 (25.0001 - 50 ppm & >50ppm, respectively) are the highest percentage of township measurements. 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 18.2 - Provysol by township
Provysol resistance levels are mostly at the High Level throughout the RRV. Looking at map 18.2 (new map), it shows that the High Resistant of 1.0001 - 10.0 ppm is the majority of township measurements. The resistant levels of Very High 1,2 & 3 are present in somewhat equal distribution. Moderate levels to resistance are present in a lesser degree. 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
Continued good news in 2019 for TPTH effectiveness, overall reclaiming more sensitivity in townships when compared to 2018. The map indicates very low to slight TPTH resistance throughout the RRV. The only area that appeared this year with moderate resistance is west of Moorhead, with exception of a couple other scattered townships. Tin should be utilized as a tank mix partner with other chemistries, at full rates of each tank mix partner. The goal of the map was to show more details of resistance levels for continued BMP’s (Best Management Practices) of TPTH use. Contact your Agriculturist for information on a section by section basis.

Map 25 - Topsin by township
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 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 
2019 was a year that had good cercospora leaf spot control in the American Crystal Sugar growing area. Pressure was overall low at the beginning of the year and finished higher with wetter environmental conditions as the year progressed. 2019 had an average of 2.7 CLS fungicide applications across our growing region, compared to 2.9 in 2018. The tank-mix of TPTH + Topsin was applied on the most acres, as provided by Agriculturist in fungicide data collected. The reclamation of TPTH, according to the resistance testing process, shows the direct benefit of tank-mixing and rotating all fungicide modes of action in a cercospora leaf spot control program. Continued diligent CLS management by tank-mixing and rotating fungicide modes of action is highly recommended to aid in reducing overall CLS inoculum with current cercospora populations showing levels of high resistance. 15-20 gallons per acre water, 80+ psi, starting spray program earlier and 14 day maximum spray intervals are all needed practices with current CLS conditions. Glyphosate applications must be separated from fungicide applications as water volumes vary by targeted pest. 

Additional information is available from your Agriculturist. Another useful website is www.sbreb.org for the latest in North Dakota State University and University of Minnesota research information.