Here is some interesting information about Japanese Beetle control from Prof. Daniel A. Potter of the University of Kentucky Department of Agriculture. I have corresponded with this professor, after finding one of his earlier articles about Japanese Beetles on the web, and he has been kind enough to summarize some research results that will probably be published within the next year. I mentioned to Prof. Potter that I would forward his comments to Gardenweb.com.
First, here is my summary: several different "conventional" and organic insecticides and repellents, which are advertised to reduce JB damage to plants, were tested by applying the products to linden tree foliage (one of JB's most favorite foods), "weathering" the treated foliage outdoors for varying time intervals of 1,3,7,14,19 days (to test durability of each product when exposed to the elements including rain), and then offering the treated and "weathered" foliage to JBs.
Some of the more effective products, from longest to shortest lasting, were:
1. Synthetic pyrethroids (deltamethrin, bifenthrin, lambda-cyhalothrin, permethrin, and cyfluthrin): all gave effective protection for more than 19 days. (I don't yet have the trade names in these products, or any information about the "inert" ingredients that are mixed with the pyrethroids.)
2. Sevin: protected for about 14 days
3. "Pyola" from Gardens Alive, natural (botanically derived) pyrethrins in a canola oil base, the most effective organic product: protected for about 5 days
4. "Neem-away" from Gardens Alive, neem oil product, protected for about 2 days
During the protected time span, JBs will not feed (or will not survive an attempt to feed) even when put right next to the "target" foliage. If, as other research suggests, JBs tend to follow a "feeding trail" marked by the pheromone scent of other JBs, it may be that JBs will not return in force to a protected plant (or garden) for some period of time even after the repellent wears off. Such an after-effect was not tested in the study.
Here now is the complete letter from Prof. Potter:
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Last summer one of my students evaluated a number of "organic" insecticides, as well as known or putative feeding deterrents for repellence or direct control of adult Japanese beetles on linden foliage. We sprayed individual intact linden shoots, allowed the residues to weather outdoors for varying 1, 3, 7, 14, or 19 d, and then harvested those shoots and challenged them in "no-choice tests" with 10 beetles confined with a treated or untreated leaf, or in "choice tests" wherein 10 beetles are offered a treated versus untreated leaf in an arena. We tested five synthetic pyrethroids (active ingredients were deltamethrin, bifenthrin, lambda-cyhalothrin, permethrin, cyfluthrin) and all of them gave at least 19 days residual control from a single application, despite frequent and heavy rains.
Sevin gave about 2 wks protection (longer than I would have thought), but did not last as long as the pyrethoids. Among the "homeowner-oriented organic products", the most effective were "Pyola" and "Neem-Away", both from Gardens Alive. Pyola is a combo of natural pyrethrins plus canola oil; it was effective out to 3 days, but not to 7 days post-spray. Pyola also was relatively rain-fast once the residues had dried. Pyola served as a feeding deterrent, and also gave rapid knockdown, although most of the exposed beetles eventually recovered in these lab assays. I think they would dessicate and perish in the field. One day old residues of Neem-Away were highly deterrent and gave good protection, but the effect noticeably was wearing off by 3 days, and the product seemed less rain-fast than Pyola.
Surround is a kaolin clay based emulsion that is sprayed on plant material to deter insects. It essentially whitewashes the plant material with a fine film of inert white clay. In our trials, surprisingly it did not deter the beetles from eating the linden foliage. Regardless, I don't think that Surround is well suited to use on roses or other flowering ornamentals because the white coating affects aesthetics. But it does have promise for fruit protection, where the clay residues can be washed from the fruit after harvest. We are also looking at Surround as a borer treatment (i.e., whitewashing tree trunks).
Keep in mind that these were one set of experiments on one plant species (linden), so results might differ on other plants. For example, we did not apply them to open rose blooms. But from what we saw, either Pyola or Neem-Away should give short-term residual protection and be effective if re-applied as-needed (every few days) during the period when Japanese beetles are abundant. Of course, neither will protect rose blooms that break bud and open "in between" sprays. Several of the "natural" plant extract-based products that we tested (and that claim efficacy against Japanese beetles) caused severe phytotoxicity (burned the leaves), so growers would be well advised to test such products on one or two plants before treating a whole garden.
As I am 100% Research and Teaching, I regret that I'm unable to answer all requests from the many individual gardeners who find me on the Web or telephone. We will be publishing this work in both scientific and popular articles, but probably not until sometime later in 2005. Also, we may be doing additional testing on roses. Feel free to follow up later on. Incidentally, there is a good Fact Sheet on Japanese beetle management that can be downloaded for free from the University of Kentucky Department of Entomology website.
Hope that helps.
Regards,
Dan Potter
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Q