My large flower garden has a a large population of white grubs this summer. I dug one hole and there were 13! My son in law put too fresh horse manure on my garden this spring and I think came from that. My flowers look fantastic however no damage yet, mostly dahlias, cosmos, zinnias, salvia etc. Will these grubs cause plant damage and what is the best and easiest way to rid my garden of grubs? I will use commercial products. THANKS! Michele