Monday, August 1, 2011

Japanese beetle control in a Wisconsin home garden, part 1

(Part II is here)
Six summers years ago, Japanese beetles first made their appearance in my Madison WI garden.  Not knowing any better, I went and bought traps.  Literally tens of thousands of beetles were caught. The traps filled up so fast that by midday, some traps were so overflowing that there was no room for the beetles still being attracted to drop through the bottleneck of the bag and be caught, so that in the top of each bag, they swarmed over each other in seething masses trying to get to the trap-attractant.

A garden helper, A.H., was working on the flight path to one of the more popular traps, and he had to move his work station because unholy numbers of beetles kept flying straight into him, ten or a dozen strikes a minute by midday.   Other than colony-dwelling insects, such as ants or bees, I had never seen so many insects in one place at one time to that date. Their buzzing around the traps sounded like a bee-hive--a strong bee-hive of several supers.

Fortunately, I conceived of the idea of flaming the dead bugs before burying them. I have since read that their bodies contain eggs ready-to-go, so that burying dead beetles from traps simply places the eggs where they want to be--underground--despite the death of the beetle carrying the eggs.

The next year was a little better. I had read more about traps in the meanwhile, enough to know that the traps should be placed as far away from the garden as possible rather than in the garden itself, since only about 70-80% of all beetles attracted wind up in the traps.

This improved siting helped somewhat, yet, "better" is a relative term, and there were still no rose buds or hollyhocks that year from early July through mid-August, not a one.  Instead, there were swarms of beetles, sometimes in a mass as big as a grape, sometimes in a mass as big as a golf ball, around each unfortunate bud. It was enough to make me want to quit gardening.

BLENDERIZING THE BEETLES--short term vs. long term effects
One step taken was to buy a cheap blender and knock masses of beetles into it in the cool of the morning.  Once blended (ICK and DOUBLE ICK--it was a long time before I could bring myself to kill living things in a blender--even rose-eating Japanese beetles) I poured the beetle-juice all around. Also, the bags of dead beetles from the traps were lain under the most susceptible plants (mainly guaras). I believe the dead-beetle smell (they stank to high heaven) had a short-term effect because it helped somewhat to repel their friends from landing on those plants.  (By "somewhat" I mean that the day's guara blooms lasted until maybe 1 PM before the last was eaten up, rather than being gone by 11 AM.)

In retrospect, I believe the blenderizing had more of a long-term effect than a short-term one.  The short-term effect was to repel living beetles by the smell of their dead companions, and the effect was mild, at best. However,  the long-term effect was to speed up establishment in the soil of any diseases the beetles might be carrying.  For example, Milky Spore disease is a soil-borne disease which affects JB grubs, establishing chronic conditions which help keep JB numbers in check.  Milky Spore eventually becomes established in the soil as JB's move into an area. I believe (or hope, anyway!) that the blenderizing process, which spread JB bits into the soil faster than nature would have, sped up the establishment of any diseases the JB's might have been carrying, such as Milky Spore.

The next year, I grubbed up the most susceptible plants and either got rid of them or transplanted them into the shade.  Thus, the guaras were all pulled out and the rhubarb (a great beetle favorite) was moved into the shade of a tree.  (High shade, but shade nonetheless).  It has been my observation that beetles strongly prefer plants in full sun, passing over those planted in shade.

Several more years went by in this manner, with incremental improvements: fewer susceptible plants, better siting of plants and better siting of traps. In fact, eventually, I got rid of the traps altogether. The biggest improvement, however, came from there simply being fewer beetles. You see, I believe we were on the leading edge of an invasion into new territory. With no natural predators and no diseases, the numbers exploded. After having been established a few years, the diseases and predators caught up to the bugs, and nature has commenced to rebalance their numbers. (I have since attended a lecture by Phil Pelliterri--the entomologist who runs the Insect Diagnostic lab at UW-Madison--who agreed that this theory may be likely.)  However, although the plauge-like numbers went down, JB's are still present in sufficient numbers to threaten new plantings, especially of young trees.

All of which brings us to this 2014 post (Japanese Beetle control, part II) which discusses what additional steps have been taken, what nifty new tricks have been learned, and what has happened since these words were written in 2011.

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