Over the past couple of years I've written about the Japanese beetle life cycle, their destruction to landscape plants in the Denver area (including lists of plants they like and mostly avoid) and some of the false information that is out there roaming the local internet community bulletin boards. This is one pest insect that garners lots of discussion most of the summer season, right up there with Emerald Ash Borers, which are plaguing Boulder County (they haven't been detected in Denver...yet).Click HERE for the spring larvae control blog. We're beyond killing their spring larvae at this point. Instead, we need to focus on emerging adults and their next generation as females lay eggs in to September. In the spring blog there are links to earlier writings with more information about Japanese beetles and research-based control options (for larvae and adults).
Japanese beetle adults have emerged around me, I haven't locked onto one yet, but that will happen any minute. My friend Peggy spotted six beetles on Father's Day. In a couple of weeks, the number will rise to seventy, or seven hundred or more, depending on how long they've been visiting your garden and the meals you're serving, or shall I say growing. They've been in my garden for a good six years so they know my street address.
Very recently I learned from a PhD professor in ornamental pathology at the University of Tennessee (Knoxville) that JBs eat in groups, not because a crowd of beetles attract more numbers to the plant, but because once a plant is chewed, volatile oils are released and beetles are strongly attracted to the scent of the plant oils from leaves and flowers.
That opens up some defensive possibilities for gardeners - how about spraying your plants before beetles arrive in the garden? Maybe early action will reduce numbers, maybe it might deter them so they go to the Virginia creeper next door. Maybe it won't be hot on the fourth of July? That's a a whole lot of maybes, but what Dr. Windham said makes sense. Keep them from chewing and releasing plant oils in the first place and just maybe....
He also stressed the importance of consistent, daily hand removal by flicking or tapping adults into soapy water. He has graduate students at the University of Tennessee who tap beetles off the research roses twice a day. We don't have that kind of help, but try to work in some flick time early in the morning or late evening when the beetles are more sluggish and taking a break from their constant chewing, scr_ _ _ _ _ and egg laying routine.
I try to avoid any spray contact with bees and other pollinators in my garden, so I spray well after the sun has set - while it is still barely light outside. I don't spray in the morning because pollinators are often active before first light.
Time to retreat to the basement or pack the car and head to the mountains or anywhere where it's cooler - it was 99 degrees today, the first day of summer. Unlike me, Japanese beetles love hot weather.
