Preventing Cercospora leaf spot fungicide resistance in sugarbeets
Rotating fungicide classes or tank-mixing products with different modes of action are effective fungicide resistance management strategies for sugarbeets.
Michigan growers are fortunate to have several very effective fungicides for control of Cercospora leaf spot. In order to maintain effectiveness of products, it is recommended to always rotate fungicides and fungicide classes. The best resistance strategy is to use each fungicide class only once in your leaf spot spray program.
Both systemic and contact fungicides options are available to control Cercospora leaf spot in sugar beets. Systemic compounds give longer control compared to contact fungicides. Contact (protectant) compounds must be applied more often and tend to be less costly per application.
The systemic products that are most effective are: Inspire XT (triazole), Eminent (triazole), Headline (strobilurin), Proline (triazole) and Gem SC (strobilurin). These fungicides will penetrate the leaves and move a small distance. Fungicides such as Super Tin (tin), Dithane, Penncozeb, Manzate (EDBCs) and Kocide (copper) are contact fungicides and must be applied before disease development.
Contact fungicides can be tanked mixed with systemic compounds as a resistant management strategy. This is generally utilized if a systemic fungicide class is to be used more than once in a season. Remember the same chemical family should never be applied consecutively and always rotated to an unrelated chemistry.
If Quadris (strobilurin) has been used as a foliar Rhizoctonia spray at the 4 leaf stage or later, then a Triazole fungicide should be used as the first leaf spot spray. Be aware, timely applications are also critical to prevent leaf spot resistance. Allowing the disease to develop and increase inoculum will only increase the chances of fungicide resistance developing. Michigan growers should follow the BEETcast model appropriately for their area for improved timing of applications. Contact your local sugarbeet agriculturist or MSU Extension for further information.