Japanese Beetles are the scourge of Twin Cities rose gardens, as well as virtually everywhere south of Minnesota. From my perch in Edina, Minnesota they are, without a doubt, my biggest problem as a rose grower. The reason is that there are so many of them – thousands and thousands -- and there is so little I can do about stopping them. There is nothing more frustrating than admiring a perfect new rose bud and finding a couple of ugly Japanese Beetles (JBs) burrowing deeply inside the bud, eating it from the inside out… sickening.
I hate these bugs! Here's how they looked in two of my beds this afternoon. Normally I would have been on JB patrol in my gardens sooner but I was busy with other things and this was the result by late afternoon:
And here's how they looked after they joined their predecessors of today, in my can of soapy water, which I carry wherever I go on JB patrol in the garden during July and August. This is kind of time consuming, but absolutely the right way to deal with JBs, at least in a home or small public garden. Much more on that later.
It's interesting that there seems to be a north/south line of demarcation in the Twin Cities for JBs. We live in the southwestern part of the metro area and have been seeing JBs for just the last six or seven years, peaking in 2012, as our winters have become less severe, statistically moving us into the range of USDA zone 5. Most gardeners in the northern suburbs, roughly 10 miles from us, as well as gardeners in St. Cloud, northwest of us, have never seen JBs. That would indicate that JBs are harbingers of climate change, as are many other insect species. Since 2012, we have had lighter infestations, until this year, which is quite heavy, approaching the levels of 2012, at least here in Edina.
To understand what we can and can't do about these garden monsters, let’s first understand how JBs function. JBs emerge in June from grubs in lawn turf, the eggs of which were laid in the lawn the previous summer by JB adults. Here is a very good diagram, prepared by the University of Minnesota, showing what happens:
Life cycle of Japanese beetle: egg, grub, and adult stages. In June, the grub turns into a pupa. It emerges from the soil in late June and July as an adult, to mate and lay eggs. Females live for a few weeks feeding on trees, shrubs and roses in the morning, returning to the turf in the afternoon to lay more eggs. Eggs hatch in July and grubs are almost full grown by late August. Grubs dig deep in the soil for the winter months and then move upward in spring as the soil warms. Grubs do best in warm, slightly moist soil that has plenty of organic matter and tender grasses. However, they can survive in almost any soil.
Note that the grubs are coming to the surface in April and May and are feeding on the roots of your lawn as we speak. So there is something you can do about the grubs in your lawn right now. If you turn over a couple of square feet of turf around your rose garden and find one inch long white grubs, you can apply a grub control product, such as “Grubex” or “Menard’s Grub Control” to your lawn right now and probably kill them off. I have been doing this (and other things like Milky Spore and nematode treatments) for the last seven or eight years and I can simply say that I have wasted my time and money. Why? Well, I’m sure I killed off the JB grubs in my lawn, but what about the thousands and thousands of grubs in my neighbors’ lawns and in the turf of several golf courses in my vicinity. The U of M says that JBs fly thousands of feet from where they emerge (think roughly a mile here) and they are looking for their favorite food… read ROSES! So it might make me feel good to think I killed off the JB grubs in my lawn, but I am completely helpless when it comes to killing off the grubs in neighboring lawns and golf courses a mile away. I don’t mean to say that you shouldn’t try to kill the grubs in your lawn (especially, the “U” says, in August and September each year), but that is probably more important in preserving the quality of your lawn than keeping JBs from eating your roses.
As mentioned above, Milky Spore has not proven effective, probably for the same reasons, i.e. it might work on the grubs in my lawn but the majority of invading JBs come from a five mile radius around me, not from my property. Here's what the University of Minnesota JB article says about it:
Milky spore disease – is caused by the bacteria Bacillus popilliae and is sold under the names of Japidemic Doom and Milky Spore. Recent trials with these formulations have not reduced Japanese beetle grub numbers in turf.
As mentioned above, Milky Spore has not proven effective, probably for the same reasons, i.e. it might work on the grubs in my lawn but the majority of invading JBs come from a five mile radius around me, not from my property. Here's what the University of Minnesota JB article says about it:
Milky spore disease – is caused by the bacteria Bacillus popilliae and is sold under the names of Japidemic Doom and Milky Spore. Recent trials with these formulations have not reduced Japanese beetle grub numbers in turf.
That said; let’s take a look at how to try to control adult JBs on your roses. Note I said “try” because there is really no completely satisfactory solution. So, here’s the most important point of this article: The best way to control JBs is with your fingers and soapy water! Don’t be fooled by the easy solutions presented by insecticides; just like killing the grubs in your lawn, the JB adults you kill with insecticides are just the tip of the iceberg that is flowing up and down your street into your garden. The only sure-fire way to deal with JBs is to pick or shake them off your roses into a can of soapy water. JBs are really quite vulnerable to this method because their primary defense mechanism is to simply drop off the plant they are destroying, down to the dirt or grass. They don’t sting or bite and they move pretty slowly, especially early in the morning and at dusk, so the “trick” here is to hold your can under the target JBs and pick or shake them off the plant into the soapy-water. I’m as squeamish as the next person about picking bugs with my fingers, so I wear nitrile surgical or milking gloves (that I get in the dairy-farm department at Fleet Farm) and I use a plastic 2 lb. coffee can, which has a built-in handle and a big opening. I squirt a little dishwashing soap in the can and fill it about half-full with water. The soap breaks the surface tension of the water and they are very helpless once they hit it. While this process is laborious, especially because it goes on for two months, through thousands of JBs, there is some pleasure in watching the little demons meet their end, knowing that every JB you drown will never fertilize or lay an egg for next year’s hatch. Each night, I dispose of the dead JBs either by flushing them down a toilet or putting them in my yard-waste bin (covered). Note that they become very smelly if you leave them in the soap-water overnight.
This is important! Don’t be tempted to squish JBs and throw them on the ground after you pick them off your roses (even though it would give you (and me) so much pleasure to do so). When you squish a female JB her sexual-attractant pheromone is spewed out and brings in every male in the neighborhood!
Likewise, don’t buy JB traps. They use that same sexual pheromone to bring JBs to the traps, and many more JBs come into your yard than ever find their way into the traps. If you are just compelled to buy traps, buy them for your neighbors and keep them out of your own yard! Oh, and be sure to empty your neighbors’ traps every day, because all those dead JB females just keep attracting more suitors, which are bound to find your roses. Here’s what the “U” has to say about JB traps:
"JB traps: are they useful in controlling JB adults?"
“Pheromone traps contain a lure with the scent of geraniums and rose (geraniol) and 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.” (Emphasis mine.)
Insecticide Control of JB Adults
Note: After several years of experimenting with insecticide control of JBs, I am firmly convinced that it is the wrong approach in the home or small public garden for the simple reason that it massacres all other beetles in the garden, most notably the lady beetle, which is perhaps the most important beneficial bug for controlling a variety of insect garden pests. Also, all of these insecticides harm pollinators, especially bees, as well as virtually all other beneficials such as wasps, syrphid flies, lacewings, minute pirate bugs etc., as well as predatory mites, which attack a large variety of pests such as aphids, thrips and two-spotted spider mites. Once I began controlling JBs with insecticides, many of my bees disappeared and I experienced an infestation of all the pests listed above; a lesson well learned! It has taken me two years to re-establish beneficial bugs in my gardens and I will never again spray insecticides to control JBs.
Having said that, there comes a time in very large public gardens and the gardens of commercial growers when JB infestation occurs and it’s just too hard and time consuming to hand pick them. I vividly remember a visit in 2007 to the lovely Elizabeth Park Rose Garden in Hartford, CT, in which the JB infestation was absolutely shocking, and nothing was being done to stop it. The garden was literally in ruins, which was unacceptable. That same situation occurs with commercial rose growers who cannot let their crops be ruined. At some point, these large gardens and nursery farms must revert to insecticide control, unfortunately at the expense of killing off beneficial insects; i.e., the lesser of two evils. Note: After several years of experimenting with insecticide control of JBs, I am firmly convinced that it is the wrong approach in the home or small public garden for the simple reason that it massacres all other beetles in the garden, most notably the lady beetle, which is perhaps the most important beneficial bug for controlling a variety of insect garden pests. Also, all of these insecticides harm pollinators, especially bees, as well as virtually all other beneficials such as wasps, syrphid flies, lacewings, minute pirate bugs etc., as well as predatory mites, which attack a large variety of pests such as aphids, thrips and two-spotted spider mites. Once I began controlling JBs with insecticides, many of my bees disappeared and I experienced an infestation of all the pests listed above; a lesson well learned! It has taken me two years to re-establish beneficial bugs in my gardens and I will never again spray insecticides to control JBs.
Until recently, the only insecticides that were even mildly effective on JBs (i.e. imidacloprid and carbaryl) were also very hard on the environment, particularly on bees and other beneficials. Also, they just killed the JBs that landed in the first couple of days, while swarms of these monsters just kept on coming.
In 2011, it was brought to my attention by a commercial pesticide applicator that one of the pyrethroids, Lambda Cyhalothrin, sold as Demand CS, might be effective in controlling JBs. I tested it in the summer of 2012 and was very surprised and pleased at how effective it was. When I used it the first time, I had an infestation of hundreds of beetles in my beds. Immediately upon spraying, the beetles literally went away and did not come back for upwards of five days, at which time their numbers were few enough that I could resume picking and drowning them. After about a week, I sprayed again and the process repeated itself. I continued to do this for the rest of the summer until the JBs were finished hatching.
Demand CS utilizes a unique capsule suspension of the Lambda-Cyhalothrin which keeps it active on the roses for upwards of a week. This apparently acts as a repellant to JBs, since they will not land on the plants when the insecticide is present. The University of Minnesota website on JBs mentions the Pyrethroids (and Lambda Cyhalothrin specifically) as effective control insecticides for JBs. Here's that URL again:
http://www1.extension.umn.edu/garden/insects/find/japanese-beetles/ .
Note, in particular, that the "U" does not mention toxicity to bees with Lambda Cyhalothrin, whereas most other pyrethroids are shown to be toxic to bees and other beneficial insects. However, I noted, subsequent to my trials in 2012, that there was, indeed, an effect on beneficial insects in my gardens, especially on lady beetles and, to a lesser extent, bees. In particular, I experienced the worst infestation of aphids I have ever seen, causing us to take other insecticide steps. In a large public or commercial garden that may be the lesser of two evils and a price worth paying to control the JBs. In any event, our experience would indicate that Lambda Cyhalothrin is the best all-around insecticide alternative for JB control.
Note, in particular, that the "U" does not mention toxicity to bees with Lambda Cyhalothrin, whereas most other pyrethroids are shown to be toxic to bees and other beneficial insects. However, I noted, subsequent to my trials in 2012, that there was, indeed, an effect on beneficial insects in my gardens, especially on lady beetles and, to a lesser extent, bees. In particular, I experienced the worst infestation of aphids I have ever seen, causing us to take other insecticide steps. In a large public or commercial garden that may be the lesser of two evils and a price worth paying to control the JBs. In any event, our experience would indicate that Lambda Cyhalothrin is the best all-around insecticide alternative for JB control.
Imidacloprid (Merit) is still useful in JB control as a way of killing JB grubs in the turf and as a systemic in trees, particularly against emerald ash borer. It can also be used as a systemic in roses, applied as a soil drench in May, but note that it is only effective if the JBs land on the stems and leaves of the plants. In other words, it is not effective in the blooms, which is where most JBs (and bees) land.
Please note that imidacloprid (Merit) has been shown to be toxic to bees and is suspected as a leading factor in bee colony collapse disorder. For that reason it has been banned in Europe and parts of Canada and there is a move afoot to ban it in the U.S. In my opinion, therefore, it should be used only as a turf grub control, if at all. One caution: If you use Imidacloprid on your lawn to kill JB grubs, do not apply it around any edible fruit trees you might have, since it is absorbed by the fruit and you will end up eating it; not a good idea.
ConclusionThere is only one completely safe solution to JB control in the rose garden: i.e., pick them off and drown the buggers. A beneficial side-effect of that method is that it requires you to be in the rose garden at least twice a day and results in a more thorough job of deadheading and assessing other issues, not to mention enjoying the beauty of your roses. For large public gardens and commercial nursery farming operations, Lambda Cyhalothrin (Demand CS) works better than other insecticides I have tried and appears to be the lesser of evils in damaging beneficials, despite the fact that it wipes out all beneficial beetles.
By all means, also read the University of Minnesota piece, at the URL address cited earlier in the article. You can also find it by doing a Google search for: Japanese Beetles, Minnesota.
If you have questions or ideas, please let me know. at: jfalkersr@gmail.com or 612 385-6226.Jack Falker
August 5, 2015
