In the last few days, I also noted that a Master Consulting Rosarian in the Minnesota Rose Society said on Facebook that he is spraying JBs with carbaryl (Sevin), apparently unconcerned (or unaware ) that Sevin kills bees, lady beetles, predatory wasps, syrphid flies, lace wings and virtually every other beneficial insect in the garden. I also noted that the Minnesota Rose Society posted the same advice on their website.
In my mind, spraying JBs with an insecticide like Sevin is the classic "fool's errand" because what you spray today affects the JBs (and pollinators) in your garden for a day or so and has no effect on the thousands of JBs arriving in your garden from somewhere within a five-mile radius of your garden for the next six or eight weeks. This is also true of the pyrethroids, which linger longer in the garden. The implication is that, ultimately, one would have to spray again and again, creating, for all intents and purposes, a toxic waste site, devoid of all life except roses. (Confession: I know this so well because I sprayed insecticides, especially the pyrethroids, to control JBs, until I became aware of the damage I was doing. It has taken several years for the beneficial insects to return and, happily, they are back in force.)
The irony in all of this is that organic control of JBs is extremely easy and totally non-disruptive to the eco-system of your garden.
Know Your Enemy
To control JBs organically, you must know your enemy. First, understand that most of the JBs invading your garden come from amazing distances, up to five miles away, where they pupate in the rich turf of golf courses, cemeteries, parks, pretty neighborhood lawns etc. In other words, the vast majority of JBs you see during the four or five weeks they invade your garden do not originate in your garden or lawn. So, you can spray them with insecticides but you can’t stop them from coming; and you can treat your lawn with a neonicotonoid grub control, like imidicloprid, or a biological control like the milky spore bacteria to control the JB grubs for next year, but unless everyone within a five-mile radius does the same thing, you can’t stop them from coming and coming and coming.
Here's an article I wrote one year ago: "Attacking Japanese Beetles -- Know Your Enemy":
The first annual step in organic JB control is pretty simple: once in the morning and once in the evening, knock them or pick them off the buds and leaves of your roses into a can or bucket of soapy water. Skin-tight surgical or milking gloves help, if you’re squeamish about touching the JBs. You’ll soon realize that JBs have a dropping instinct, which makes them easy to drown. They’re harder to catch in the hot sun of mid-day, when they quickly fly away. You’ll find that JBs are very docile and don’t sting or bite, leaving only a little stain in your hand of what we’ll call “beetle juice”, so I seldom wear gloves when working on them. Using a few drops of dish-washing detergent in the water creates surface tension and impedes them from making an emergency takeoff. Here's what that looks like:
The second step (actually it should be the first overall step) is to redesign and prepare your garden for organic JB control. I call it varying and mitigating the JB target so they don't land solely on the roses. Having a variety of perennials, annuals and herbs, like oregano and cilantro, among your roses gives the JBs somewhere else to land and the damage is not nearly as noticeable as it is on the roses. I have beds of zinnias where the JBs gather and I now drown as many JBs on the zinnias as on the roses; lots of chewed leaves but they’re very fast-growing and keep ahead of the JBs. Here's a recent picture (just before that JB went into the soapy water, between my thumb and forefinger):
I also plant patches of oregano in each rose bed to attract beneficial insects, particularly predatory wasps, into the garden. The JBs like that too, which makes it doubly effective, and they certainly can't hurt the oregano! Here's how that looks right now (and that JB bit the dust too, after posing for me):
Step three is to aggressively dead-head your roses while attacking the JBs. One of the things I have noticed is how JBs tend to cluster on spent blooms that are losing their petals. I don't know why that may be but it's a very good reason to get all of those spent blooms off the plants. And, while you're doing that, you're setting up your roses for the next flush of bloom, when the JBs are finished. Here's what I mean by spent bloom clustering. If you look carefully, you can see the sexual activity resulting from the JB female pheromone:
If you don't panic, there's a bit of sport in this too. JBs are amazingly canny critters and it's useful to observe what they do, especially in the heat of mid-day, as they approach your garden. When a JB arrives in the garden, it hovers, like a helicopter, looking for a suitable place to land. And, almost always, it will land on a flower or leaf that has one or more JBs already on it, or on a flower or leaf that has been previously chewed by other JBs; obviously attracted to the sexual pheromone of other JBs. (I've actually gotten pretty good at grabbing them in mid-air as they look for a sexy place to land, and that's fun.) So, it's important to get rid of tainted leaves and flowers, whenever possible. It’s really hard to dead-head a brand-new bud that has a JB embedded in it but it's necessary, in order to stop it from attracting incoming beetles. Using the old-fashioned, thumb and forefinger method of dead-heading, while drowning JBs, is very effective in encouraging rapid growth on roses, which is indicative of the positive multiplier-effect that organic gardening always has. There will be more new buds!
This is important: Don’t be tempted to squish JBs! When you squish a female JB, her sex- pheromone is spewed out and brings in every male in the neighborhood! This is also why JB traps are not a good idea, at least in your own garden. Here’s a quote from the University of Minnesota on JB traps:
“Pheromone traps contain the sex pheromone of the JB female. The pheromone is very powerful and will call in beetles from a few thousand feet. Research demonstrated that more beetles fly toward traps than are caught, resulting in surplus beetles that feed on your plants. Think twice before purchasing and installing a pheromone trap.”
For more information on this, please take a look at my article from last year: "Attacking Japanese Beetles -- Organically":
Also, please take a look at my most important blog post of all "The Pesticide-Free Rose Garden":
And finally, please remember that the key element in organic gardening is PATIENCE!
Don't panic; JBs only last about four weeks and, if you work hard to deter them organically, they ultimately go away, leaving you with lots of beneficials and pollinators, as well as fully dead-headed rose gardens, ready for the rest of the growing season. And remember that every JB you drown is a monster-bug that can't breed more monster-bugs next year. It’s particularly enjoyable taking them down when they’re atop one another, stopping the breeding cycle.