While driving around Whidbey Island it is not hard to find one of the many problem weeds many of you face in your yard. It is HORSETAIL (Equiseteum arvense). It is one of the most common, invasive, and difficult to control weeds. One can measure the success of this plant by the fact that in an evolutionary sense, it is very, very ancient. In fact, at some point way back in botanical history, Horsetails and their relatives, the ferns, were the dominate vegetation. Some Horsetails grew to the size of trees, but, as the green world evolved and became dominated by seed-bearing plants, these giant Horsetails and most of the tree ferns became extinct. It is probably just as well, too; we have enough trouble with the Horsetails that persisted. Horsetails, like ferns, reproduce by spores rather than seeds. The earliest spring growth on Horsetails is manifested by so-called fertile stems. These are the growths that produce no foliage--only spores and plenty of them. There is a kind of a cone-like tip on these unbranched, early stems which can sometimes be up to 3 inches long. It is this organ that produces the fine, powdery spores which eventually blow all over and start new plants and colonies. Ferns do much the same thing, except that most of them bear their spores on the undersides of the fertile fronds. In addition to reproducing by spores, a Horsetail's profuse and deep root system can extend infestations to other areas. These dark, creeping, brown-woolly, tuber-bearing rootstocks may start on someone else's land; it could eventually invade your garden or landscape. Trying to dig out a Horsetail invasion is nearly impossible because any rhizomes, or those peculiar food-storing tubers, that are left behind in the soil will probably grow into brand new plants. In addition, these underground parts may be located from just a few inches underground all the way to a depth of 6 feet or more. After the fertile stems have popped up through the soil in early spring, the vegetative stems with many whorls of thin, green, jointed branches appear. These are the parts that do all the photosynthesizing and which are generally thought of as the foliage. Vegetative stems can be up to three feet tall. Although Horsetail is commonly found in dampish places, those of you with well-drained gardens invaded by them know only too well that damp soil is not necessarily a prerequisite for a healthy Horsetail invasion. In fact, they seem to tolerate and grow well even in soils that dry out considerably during the summer. Controlling this pest weed is definitely not easy because of the inherent toughness of the plant, and often because an invasion of this thing generally transcends property lines. If attempts to deal with it are not also made by neighboring property owners, the elimination of it by one gardener may be just about impossible. The methods of overcoming it will generally be dependent on what particular part of your property it's invading. Horsetail coming up in a planting of ornamental shrubs and trees can generally be kept down by pre-emergence applications of an herbicide called dichlobenil (Casoron). In order for this to prevent Horsetail from growing, it must be applied before the weed comes up in spring or after any existing Horsetail stems have been grubbed out. When a vegetable garden is being invaded the only options are hoeing the weed out on a regular basis or mulching with black plastic. Turf areas are not as seriously invaded as other areas since the regular mowing process tends to weaken the Horsetail. In driveways or other areas where no desirable plans are wanted a new herbicide is on the market which does well to control Horsetails. This product is triclopyr, sold under the trade name of Brush-B-Gon. This broad spectrum herbicide is a replacement for Amitrole-T which is no longer available to the homeowner. Triclopyr must be applied according to label and when the Horsetail is actively growing. This chemical will kill the root system, but may need to be applied more than once. It is more important to remember that Horsetail, like any persistent weed, can also be controlled by constant pulling and/or cutting, at least in theory. Any plant which is kept from growing and producing food for itself will ultimately starve to death and cease to come up. This approach requires close management of the problem at all times and for a period of two years or more. A brief publication called PNW 105 "Field Horsetail" is available from our office for 25 cents. It addresses the poisonous properties of horsetail for horses and livestock.



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