Japanese beetle courtesy of Shutterstock
To trap or not to trap? That is the million roses question, isnt it? Conventional wisdom holds that the use of Japanese beetle-specific traps will increase beetle damageon plants adjacent to the trap sites. Youcan find that wisdom repeated everywhereon extension articles, Internet blogs, over and over, accepted and final.
Well, friends, ProfessorRoush had a mentor who once said to me If I wrotethat the sky is green in a book chapter of an authoritative text, in 10 years the entire world would be repeating that the sky is green. Phrases like conventional wisdom just raise my hackles, because if weve learned anything from the past millennium, its that if we followed conventional wisdom,we would still believe thesun revolved around the earth,the New World wouldnever have been discovered by Europeans, and I wouldnt be trying to garden in the hell-hole of Kansas.
In the throes of anguish after Japanese beetles finally reached Manhattan, Kansas,I set out to look at some of theactual research behind the no-trap recommendation, and I can already tell you that the question is far from settled. Most of thestatements that Japanese beetle-specific traps increase plantdamage and dont affect beetle numbers are referenced back to two papers in the Journal of Economic Entomology, 1985 and 1986, authored by F. Carter Gorden and Daniel A. Potter from the University of Kentucky. The papersindeed reach the referenced conclusions, but if you examine thematerials and methods of their researchyoull discover the interesting fact that theyplaced their traps at 1.2 meters above the ground in both studies.I already knew that a more recent study, by Alm in 1996,found that a height of 13 cm above the ground was the most efficient trap height, whichjust happens to also be the averageheight thatJapanesebeetles fly around a garden.The1985 and 1986papers, for those metrically-disadvantaged, had their traps at 120 cm, so, in essence, they were expecting these lumbering insectoid rocks to find the traps approximately 10 times farther off the ground than they normallyfly. Thus science advances gardening.
I also reviewed a 1998 Journal of Arboriculture paperby Wawrzynski and Ascerno that found that mass trapping over15 acre areacaused a 97% reduction in Japanese beetleswithin 4 years. Consequently,I really wonder if gardeners havent been kept from using the best tools for this particular job.Commercial traps that use both floral attractants and pheromone lures aredemonstrablyeffectivea popular bag-a-bug trap performed pretty well in a 2003 report by Alm and Dawson
What does that mean for ProfessorRoushs garden? It means that Im going to buck the conventional wisdom and trap thebodacious beetlesout of my garden for a couple of years to see if I can slow down the invasion. Based on the research available, I will place my traps as close as possible to the recommended13 cm height and I will place them at least 30 feet away from the nearestimportant plant so as not to attract beetles right onto my roses. I will empty the traps regularly so the dead beetle stench doesnt drive others away and I will make surethe lures stay attached. Ill let you know how it goes.
Ive already caught threehard-shelled fiends that wont be breeding little beetlesfor next year. Ihope thatit is simple logic. Less breeding, less beetles, more roses.