I received a notice that the California Department of Food and Agriculture (CDFA) has plans to combat the Asian Citrus Psyllid (ACP) which has been detected on citrus trees near my location in Fallbrook, California. I scanned the letter, it’s a large PDF file of about 10 megabytes. In short, county agents will be spraying citrus trees in the affected area with a pyrethroid, a short acting contact insecticide, and using a ground application of imidacloprid, a long-acting systemic insecticide to combat the ACP.
The county also had an open house, for folks with questions. I attended the open house, but did not take pictures, unfortunately it didn’t occur to me to bring a camera. I was advised that opting out of the program is easy, a notice is put on the garage door, giving 48 hours before the application is made. If one wishes to opt-out, one must call an 800 number that’s said printed on the notice to do so. This pesticide application is designed as an opt-out, rather than opt-in, making it rather aggressive, presumably due to the fear that the ACP is causing the folks working at CDFA.
Unfortunately some of my other questions, very basic, were unanswerable by the folks giving the open house. Bees are very important with respect to the pollination of many food crops. Imidacloprid kills bees. That fact as warning is clearly stated on multiple companies’ MSDS and pesticide information sheets, it does not seem to be in dispute. It has also been linked to bee colony collapse. I was assured that the dose they were using would not kill bees, according to the first CDFA representative I spoke with. My next question was, “Have you studied the bee population density?” This was apparently a hard question, as a couple of other folks needed to be consulted. According to an Adrian Gonzales, a representative of CDFA in attendance at the local open-house meeting, the answer was “No.” So I asked, “How can anyone know how many bees have or have not been killed, unless the bee population is first studied before an application, then studied for a sufficiently long period of time afterward?” They took my email address and told me I’d be contacted, and I was in fact contacted in just a few short days.
According to K. David Kim, staff scientist at the California Department of Food and Agriculture:
“Although imidacloprid is highly toxic to bees, the way CDFA (and their contractors) apply it, the exposure, and therefore risk, to bees is quite low. The imidacloprid is applied to the soil, where it is taken up by the tree and concentrated in the foliage. The only potential exposure to bees is during the bloom, where it has been found in the pollen. Studies at UC Riverside are being performed looking at this exposure route.”
I also received a separate reply from a Jason Leathers at CDFA, who was “not aware of any research projects on bees in the Fallbrook area.” At the open house, I was assured there were no plans to replace any of the bee populations that may be injured or killed by this ACP treatment program.
Imidacloprid is known to be a long-lasting systemic insecticide that, when applied to the ground typically used in horticulture, has a “field dissipation half life” with a rather wide range of values anywhere from 26.5-to-229 days. If, due to varying soil conditions, the degradation half life is the shorter figure, it seems to represent a risk to bees several months later during the spring bloom; if the degradation half life is the latter figure, then the pesticide may still be having a rather strong effect several years from the date of soil application. This long field dissipation half-life is reminiscent of how imidacloprid is claimed to continue killing termites for from 5-to-10 years following a single application when applied under the slab of a home.
Thus the lack of bee population studies both before and after an application of imidacloprid is a notable omission in California’s ACP extermination plan. Because of the long field-dissipation half-life, it seems to me these studies should be conducted for several years. The folks at CDFA seem primarily concerned with killing the psyllid. It seems there are few alternatives that do not result in the spread of the insect.
After the open-house meeting, I learned that imadicloprid is toxic to earthworms, at levels as low as 50 PPB (0.05 PPM). This is of concern to organic gardeners, as earthworms are one sign of a fertile soil (also see a wonderful story about an earthworm farm of the 1800s, a longer version appears here). Just as with bees, the long sub-surface half life of imidacloprid (where there is no light) suggests a single application is likely to affect earthworm populations for a significant, if unknown, period of time. According to K. David Kim:
“Imidalocprid is longer lasting, and yes it is toxic to earthworms at the applied rate, but the application is only around the base of the trees and there is very little movement of the pesticide laterally.”
The reason imiadicloprid is claimed successful with termite eradication is that as the insects move, they cannot detect the poison to avoid it.
The reasons I became an enthusiast of organic methods of soil husbandry are due to an informal experiment I performed back in the 1980s. I had planted 6 or 7 rose plants in the existing topsoil, without any organic amendments, at a residence my wife and I rented. I began by fertilizing them with synthetic fertilizers. Aphids massively infested the buds and stems. Typically, folks either spray poisons to kill those, or use a systemic insecticide (judging from products sold at nurseries); since I didn’t and still don’t like to use poison if it can be avoided, I used soap mixed with water (I didn’t use detergent). It worked well, unfortunately, it needed frequent applications, I was needing to spray soap and water every couple of weeks to keep the aphids under control. I started fertilizing the roses instead with top-soil dressings of steer manure which was supplied in 1 cubic foot bags, which according to the label at the time was not really only manure, but was manure composted with “forest products” (in other words the product at the time was mislabeled, it was “compost”, not “steer manure”). I also stopped all synthetic fertilization. The next year, the roses only had a few or occasional aphids here and there, nothing that seemed to constitute “an infestation”. I tried applying synthetic fertilizers again, and shortly thereafter, massive numbers of aphids re-infested the plants. I again stopped the synthetic fertilizers, and returned to only the use of manure fertilization. The next year, again, just a few aphids appeared here and there, it was not worth the trouble to spray. In looking back on this, I’ve come to believe that synthetic fertilizers acts to make plants, particularly roses, “taste good” to aphids, which are considered plant-sucking insects. The effect I noticed is possibly related to the purity of chemical fertilizers, and the impurities of organic fertilizers. My axiom with respect to rose plants: as synthetic, chemical fertilizers were increased, the need for pesticide applications also increased.
Like aphids, the Asian Citrus Psyillid is a “sap-sucking” insect, and is possibly why the folks at CDFA believe a systemic insecticide is expected to kill them.
It is troubling that the state of California is suggesting the use of a systemic insecticide on food crops — citrus: oranges, lemons, grapefruits, etc. — which backyard growers in all likelihood consume. It is also troubling that the systemic insecticide chosen, imidacloprid, has such a long degradation half life in soil. The lack of a plan to study and *mitigate* its local effect on bees is also very troubling.