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White patches on beetsWhite patches on beets usually means some form of mildew, a fungal disease: http://www.ipm.ucdavis.edu/PMG/r735100611.html  There are numerous fungicides to prevent the spread of mildew. Speak to your local garden center about what's available in your state.  

2015 Special Edition Garden GuideCooking Fresh with The Old Farmer's AlmanacThe Almanac Monthly Digital MagazineWhat the heck is a Garden Hod?