The Beetles Are Coming… The Beetles Are Coming!
By Jack Falker
Japanese beetles that is, and they are fast becoming the scourge of Twin Cities rose gardens. From my perch in Edina, 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 (Japanese beetles) burrowing deeply inside the bud, eating it from the inside out… sickening.
Let’s first understand where they come from and see what we can and can’t do about it. Japanese beetles emerge in June from grubs in lawn turf, the eggs of which were laid in the lawn the previous summer by Japanese beetle 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 Japanese beetle 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 Univeristy of Minnesota says that Japanese beetles fly thousands of feet from where they emerge (think multiple football fields here) and they are looking for their favorite food… read ROSES! So it might make me feel good to think I killed off the Japanese beetle grubs in my lawn, but I am completely helpless when it comes to killing of the grubs in neighboring lawns and golf courses a half mile or more 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 Japanese beetles from eating your roses.
By the way, the Univeristy of Minnesota article I’m quoting is definitely the best article I’ve seen on Japanese beetles (Go Gophers) and is available at this address: http://www1.extension.umn.edu/garden/insects/find/japanese-beetles/.
That said, let’s take a look at how to try to control adult Japanese beetles on your roses. Note I said “try” because there is really no completely satisfactory solution. So, here’s the “secret” of this article: The best way to control Japanese beetles 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 Japanese beetle
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 Japanese beetles is to pick or shake them off your roses into a can of soapy water. Japanese beetles 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 Japanese beetles and pick or shake them off the plant into the soap-water. I’m as squeamish as the next guy or gal 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 (Maxwell House), which has a built-in handle and a big opening. I squirt a little dish washing 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 many days, through thousands of Japanese beetles, there is some pleasure in watching the little demons meet their end, knowing that every Japanese beetle I drown will never fertilize or lay an egg for next year’s hatch. Each night, I dispose of the dead Japanese beetles 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 Japanese beetles 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 Japanese beetle her sexual-attractant pheromone is spewed out and brings in every male in the neighborhood!
Likewise, don’t buy Japanese beetle traps. They use that same sexual pheromone to bring Japanese beetles to the traps, and many more Japanese beetles 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 Japanese beetle females just keep attracting more suitors, which are bound to find your roses. Here’s what the “U” has to say about Japanese beetle traps:
Japanese beetle traps: are they useful in controlling Japanese beetle adults?
“Pheromone traps contain a lure with the scent of geraniums and rose (geraniol) and the sex pheromone of the Japanese beetle female. The pheromone is very powerful and will call in beetles from a few thousand feet. Research demonstrated that more beetles fly toward traps then are caught; resulting in surplus beetles that feed on your plants. Think twice before purchasing and installing a pheromone trap.”
Insecticide Control of Japanese beetle Adults
There comes a time in most large gardens, when Japanese beetles are present, that infestation occurs, and it’s just too hard and time consuming to hand pick all of them. At that point you have to revert to insecticide control. Until recently, the only insecticides that were even mildly effective on Japanese beetles (i.e. imidacloprid and carbaryl) were also very hard on the environment, particularly on bees and
other beneficials. Also, they just kill the Japanese beetles that land in the first couple of days, while swarms of these monsters just keep 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 Japanese beetles. I tested it in the summer of 2012 and was very surprised and pleased at how effective it is.
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 Japanese beetles 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 repellent to Japanese beetles, since they will not land on the plants when the insecticide is present. This may also be effective for treatment of several generations of spider mites for which Demand CS is also labeled.
The University of Minnesota website on Japanese beetles mentions the Pyrethroids (and Lambda Cyhalothrin specifically) as effective control insecticides for Japanese beetles. Here’s that URL again: http://www1.extension.umn.edu/garden/insects/find/japanese-
beetles/. Note, in particular, that they do not mention toxicity to bees with Lambda Cyhalothrin, whereas other pyrethroids are shown to be toxic to bees and other beneficial insects. I have noted in my trials in 2012 that there was no apparent effect on beneficial insects in my gardens. Another local rosarian, who also tried Demand CS last summer noted similar results.
Imidacloprid (Merit) is still useful in Japanese beetle control as a way of killing Japanese beetle 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 Japanese beetles land on the stems and leaves of the plants. In other words, it is not effective in the blooms, which is where most Japanese beetles land. Also, 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, in my opinion, should be used only systemically or as turf grub control, if at all. One caution: If you use imidacloprid on your lawn to kill Japanese beetle 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.
There is no easy, completely safe solution to Japanese beetle control in the rose garden. The best method of control is still the old-fashioned way of picking them off and drowning them. Lambda Cyhalothrin (Demand CS) does appear to work better than any other insecticide I have tried and appears not to do too much damage to beneficials. For more information, please read my “Minnesota Rose Gardener” blog posts regarding my experience with Demand CS on Japanese beetles in 2012: http://jack-rosarian.blogspot.com/2012/07/good-results-using-demand-cs-on-Japanesebeetles.html. 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, by all means let me know at: jack[at]falkerinvestments[dot]com or 612 385-6226.
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