Japanese beetle control in a Wisconsin garden, part II

Much delayed, here is a post on the continuing saga of Japanese beetles in my Wisconsin garden (part 1, written in 2011, is here).

SURROUND WP

In 2011, I had just planted some apple trees--very young, very tender, very expensive. The best Japanese Beetle control I found for these valuable plants was an item called Surround WP.  The WP stands for "wettable powder," and Surround is the brand name for a type of kaolin clay which has been specially treated to make it apply-able to growing plants.  Kaolin clay is simply a natural type of soil--a clay soil--which is composed of very fine particles (as are all clays) and is white in color.  The Surround is mixed with water in the instructed amounts, and then the milk-like result is applied --either by spray or by dipping--on whatever you want to protect.  In my case,  the young apple trees were being murdered by the Japanese beetles.  I've hunted through my photos, but can't seem to find the ones I took of the trees when treated, so here's a link to a photo found on the web--other than being much smaller, my trees looked identical once treated--dusty and gray, yet unquestionably alive and un-eaten.

Surround evidently clogs up the JB's pores (or something like that) in a purely mechanical (not chemical) manner.  It worked well, but has some drawbacks.

• It has to be re-applied after a rain--any rain. 
• As the tree grows and puts out new leaves, these have to be protected, so even with no rain, you have to spray regularly. 
• It would only really work on quite small trees--the challenge of covering a full-gown birch or elm (JB favorites) with a powdery coating on every leaf would be impossible to meet. 
• If you miss, the beetles will find that spot. 
• You have to have the correct kind of sprayer.  

My first sprayer, not rated for wettable powders, clogged easily, then wore out. Even with a sprayer rated for wettable powders (as my second sprayer was) the Surround and water mix has to be kept agitated.  Commercial operations evidently get around this by using additives to keep the powder suspended but I had no access to such things, and had to keep stopping and shaking up the tank.  Also along these lines, you absolutely HAVE to clean out the entire mechanism with plain water (and spray, and spray, and spray until the water comes out clean) or the Surround will clump up and ruin the sprayer.

Bottom line: the Surround WP did protect my apple trees, even in the face of massive JB pressure, when nothing else on the face of the earth seemed to do the trick, but you have to keep it up. Without the Surround, the little apple trees would surely have died in their first season.

 TINCTURE OF TIME

This summer (2014) the beetles have not been much of a problem (not yet, anyhow).  I believe this is for several reasons. The other day, I saw a flock of starlings working over some rose bushes, tearing at the petals.  I've never seen that behavior before in birds.  I finally figured out that the birds, now with enough years of exposure, have learned to eat JB's. Further, the very harsh winter we just had (polar vortexes and all that) have perhaps put a dent in the JB numbers. And, I think that once Wisconsin was no longer on the leading edge of the invasion, the numbers of beetles settled down.  The original invasion was very like a biblical plague, but the numbers now are much more manageable.  In other words, just wait, and the passage of time tends to smooth out most problems. (Although, if you have found this post because you are suddenly overwhelmed with JB's for the first time, the sad thing is that we are talking years, not weeks or months, until the situation simmers down.)

TRAP CROPS--Fine-line buckthorn bushes

The roses are staying: that's non-negotiable.  Yet, I've grubbed out pretty nearly every other major JB attractant (like guara--which was pathetically attacked) and relocated to the shade most other JB faves (such as rhubarb).

In the full-sun perennial beds live three fine-line buckthorns,* which are also a major attractant.  I didn't grub them out because I thought of trying a systemic insecticide.  Now, I don't much believe in chemical fixes, but my thinking was that my buckthorn don't flower (or at least, haven't yet) and the only way that a systemic insecticide would get loose into the ecosystem was if something was actually eating the plants.  In that case, I rationalized, the destructive creatures would get what they deserve (actually, rationality didn't much enter into it: "die, beetles, die!" was a lot closer to my exact thought).

However, daydreaming about this solution was one thing, and reality another: I never could bring myself to actually apply such a chemical in the garden here.  So, the buckthorns just got eaten to a tatter every year.

This year it finally occurred to me that the buckthorns are acting as a trap-crop.  The poor bushes get set back so far that they will never grow to full height, and they look awful: mangy and bitten.  Yet, being all-green (no flowers) even with a heavy load of JB's, they look less mangy than did a flowering attractant, such as the guara.  And the thing is, although the buckthorn are loaded with JB's, other plants growing nearby, even roses, have a much lesser load. See for yourself: these two photos, taken one minute apart, are of plants located quite near one another.

Buckthorn as a trap crop: Japanese Beetles on buckthorn

The buckthorn is acting as a trap crop, so there is little 
Japanese Beetle pressure
on roses growing nearby

Putting two and two together (for, as Gandalf said about Butterbur,  even slow thinkers will see through a brick wall in time) I've finally determined to stop fantasizing about rubbing out the JB's on the buckthorn via poisonous insecticides, while also accepting that the buckthorns must not be grubbed out, but are to remain: a trap crop sacrificed to protect other, more valuable, flowering plants.

YMMV: a different trap crop might work better in your area. The penny-drop is not that buckthorn is a good trap crop for roses (although that combo is working here in this garden) but that a plant much-infested with JB's might be seen as a good thing, if it is reducing pressure on other plants. 

--TK

* Although buckthorn is said to be invasive in certain areas, the "fine-line" variety I planted is said to be non-invasive (click linky above for description).