Sometime ago an article appeared regarding a fungus that was discovered to control dandelions in the lawns. At the time it was being tested for it's safety and effectiveness. The article stated it would hit the market in the near future. Well it is here now.
T he name of the product is "Serritor", the first biological weed killer.
When to apply is controlled by season and the weather quality in that season. It needs to be applied in moderate temperature weather, warm of course. Watering needs to be done within 24 hours of application.