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NEW HORTICULTURAL PEST Just as the bark beetle devastation approaches its end, another pest has decided to pay us a visit: the so-called flea beetle. If you haven’t seen them yet, you doubtless will very soon: tiny, roundish beetles, less than 1/8" long, deep black in color but (in certain light) with a greenish opalescence. It’s likely that they’ll be in a group—perhaps only 10 or 20, perhaps 100s or more, sometimes lending the odd impression that you are looking at a tree or shrub with black polka dots. When you see them they will probably be sitting immobile on a leaf, but when you disturb them they’ll jump off and hop vigorously about on the ground like fleas—hence their nickname. The term flea beetle actually covers some 4,000 species. I think the one we have may be Altica aenescens, which is the most common internationally, but it doesn’t matter greatly since one deals with all of them in pretty much the same way. They are worth dealing with, as they have begun to decimate plants entirely. Take a look at the elm trees near the intersection of Calle Celestial and Vista Colorado and you will see what these minute beetles managed to accomplish in no time flat. These are good-sized trees and their leaves are absolutely stripped into a lacy filigree. How the elms will respond I can’t say: Perhaps they’ll put forth another shoot of leaves, or perhaps they’ll go dormant for the season and start over next spring, or perhaps they’ll die. Among trees, elms seem particularly under attack, and examples are also to be found along Vista Sandia at the opposite edge of La Mariposa, which makes the point that the flea beetles have the territory covered. I first spotted flea beetles at our home chomping on Gambel’s oaks and scrub oaks, and after I eradicated them others showed up on roses. Credible anecdotal accounts among local horticulturalists have them infesting even some tough native plants that seem to withstand everything, including hollyhocks, lilacs, potentilla, and Apache plume, although I can report that they have steered clear of all those at our home. In any case, once flea beetles settle on a plant they consume the fleshy parts of the leaves with a vengeance, leaving behind only a lacy vestige. It seems clear that these are not desirable arrivals. (Amazing to say, a lot of flea beetle varieties were deliberately introduced to American ecosystems as a form of weed control. Don’t get me started.) The good news is that we have a fighting chance against them, and that we are fortunate to find ourselves aware of what’s going on right at the beginning of their life cycle here, unlike when we were gradually taken unaware by the bark beetles several years ago. Eradication of flea beetles falls in two phases, and neither is difficult. First, we want to obliterate the ones that are dining right now. If you are inclined towards organic control, the time-honored gardener’s technique of squishing them individually can not be bettered; but once you start squishing some, others will start hopping about and you will have to be quicker then me if you’re going to get them. If you are of the pesticide school, you may have some Sevin still sitting around from your bark beetle adventures, and that will bring them to a quick end. But Sevin is awfully strong stuff, and the preferred pesticide for flea beetles is fully effective while being far less hazardous to the affected plants and the rest of us who share their eco-system. The active ingredients you want are called pyrethrins, and what you require is widely available at garden and home stores in various commercial formulations, including ready-mixed spray bottles of insect killer. Pyrethrins do their job effectively and then degrade quickly, so they’re well suited to the job at hand. In fact, many mixtures of pyrethrins with canola oil or horticultural soaps are approved for various levels of certified organic gardening, and may even be applied up to a day before harvest – so this is clearly not some ominously dangerous chemical we’re playing with. In fact, pyrethrins are naturally occurring chemicals found in the glands of the flowers of Tanacetum cinerariaefolium, which is a cousin to common tansy, feverfew, and other species of the chrysanthemum family. If you find flea beetles dining on a plant, you may rest assured that they will also have been laying eggs in the ground beneath that plant. So killing the current bunch is only half the job. We must also take care of the next generation. The best solution for this is an organic one: the introduction of a vigorous population of parasitic nematodes. These are micro-organisms that love to dine on the larvae of pests like the flea beetle, but that behave only kindly to their good neighbors, like earthworms. You can buy parasitic nematodes at better garden centers, where they will have been kept refrigerated. For about $30 you get a little sponge impregnated with about a million of them (really!), and directions that walk you through the very easy method of how to make a brew of them in a 5-gallon bucket. Then you ladle a cupful or so around the bases of affected plants – more (I would imagine) for trees and large shrubs. A little goes a long way so it’s not an expensive proposition, and once you’ve applied the nematodes they’re off and reproducing. They can only help your soil in every way. In principle, that’s a plan for our neighborhood. Except for those who foreswear pesticides of any sort with unswerving orthodoxy (a defensible position), we might all traipse attentively through our properties armed with pyrethrin spray bottles – regularly, since these flea beetles are mobile and show up suddenly where they assuredly were not the day before – and blast away. We leave a marker of some sort at every plant we find infested and then return to douse the ground with parasitic nematodes. We might well be moved to do some preventative nematode treatment around favorite plants that don’t appear to be under attack, as it can only help the plant. I hope not to sound alarmist, and in truth I don’t think there is reason for the sort of hopeless desolation that attached to the bark beetle rampage. Horticulturists know that if it’s not one thing it’s another, and that whatever’s left standing at the end of the season is basically a miracle. In this case, we can help address the situation early on with minimal effort and expense, and with prompt attention there’s an excellent chance that we can minimize horticultural heartbreak down the road.
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