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Questions when Managing Cercospora Leaf Spot (CLS) of Sugarbeet (07/06/17)

Can I mix different fungicides? Can adjuvants/stickers help improve efficacy of fungicides? When should I start fungicide application? How much water should I use and at what and pressure? At what temperature does Cercospora become less damaging?

Questions when Managing Cercospora Leaf Spot (CLS) of Sugarbeet

Can I mix different fungicides – Yes. When mixing different fungicide products, follow the directions on the labels or the A.P.P.L.E.S. method. To a tank partially filled with water, Agitate and then add in the following order - Powders (dry), Powders (soluble), Liquid flowables and suspensions, Emulsifiable concentrates, and Solutions - making sure that each product is uniformly mixed before adding the next product.

Can adjuvants/stickers help improve efficacy of fungicides? Yes – but observed only under high disease pressure. Very limited testing has been done mainly with products with experimental numbers and only using individual fungicides such as Headline and Inspire XT. MasterLock adjuvant has improved efficacy of Inspire XT. Test mixtures for compatibility with adjuvants before using on entire field. More testing is ongoing with adjuvants and fungicides.

When should I start fungicide application? It is best to start after row closure since inoculum pressure was high in 2016.

How much water should I use and at what and pressure? For ground application, apply fungicides in 15 to 20 gallons of water per acre at 75-100 psi pressure; aerial applicators should use 3 to 5 gallons of water per acre for best results.

At what temperature does Cercospora become less damaging? The pathogen becomes less active and damaging when night temperatures fall below 60 F and when day temperatures go beyond 95 F.

Correction: Please note that one application of Minerva Duo (16 fl oz) has 4 oz of TPTH (WP formulation) which is equivalent to 80% of the labeled rate of TPTH when used alone. Use mixtures of effective fungicides for control of CLS in 2017.

Mohamed Khan

Extension Sugarbeet Specialist

NDSU & U of MN

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