I have gotten good results with spraying with oil and dishwashing detergent here in Florida, I would think it would also work well in Wisconsin. I don't use the oil during our summer months. Three tablespoons of cooking oil per gallon of water, then 7-10 days later 2 oz of dishwashing detergent, I do this about every 2-3 months as a preventative measure and have not had any problems in several years.