I hung a couple of bag-a-bug (r) Japanese beetle traps yesterday. The scholarly literature suggests that these do more harm than good. I believe the opposite. So, every year, I hang two traps near my garden. I think they keep the Japanese beetle population down, if used correctly. Follow the instructions, hang them well away from and downwind of the space you are trying to protect. The idea being that as beetles fly upwind, lured by the scent of your delicious landscaping and garden plants, they will be diverted by the lures in these traps and DIE DIE DIE.
But this post isn’t about Japanese beetles per se. It’s about growing degree-days.
Growing degree-days and my pest calendar
Source: NC State University growing degree days explorer.
I used to think that various insect pests arrived on or about some fixed calendar date every year.
That’s not exactly correct. As it turns out, various species emerge, pretty much like clockwork, after a given amount of springtime warmth has occurred. That warmth is typically measured by growing degree-days with a 50 degree F reference point. In effect, it’s an estimate of the cumulative time and extent to which the air temperatures in an area exceed 50F.
Both the Japanese beetle and the squash vine borer show up right around the 1000 growing degree-days. Once you’re aware of that fact, you can pretty much set your calendar by their arrival. Last year, they were right on time (Post g22-023, Post g22-024).
Last year, my first Japanese beetle occurred on June 18. But this year is running a bit cooler than last. Which means a bit later than last year. Based on growing degree days, we’re about 100 degree-days behind where we were last year. Which, at current temperatures, should be about four days. That means I ought to see my first Japanese beetle on or about June 22 this year. And my first squash vine borer not long after that.
So I have my Japanese beetle traps up now. I can forget about them until it’s time to take them down and dispose of them.
