Disclosed are rope-like fumigants. The rope-like fumigants are sufficiently sturdy thick, or tightly twisted or braided that they can be generally vertically positioned without drooping at their top, even though they are considerably elongated. The rope-like fumigants are loaded with an insecticide, fragrance, or the like, and lit from the top. Very low cost materials such as jute, hemp, or the like form the base material for the fumigant. A holder is disclosed which retains the rope-like fumigant in a vertical position from its lower portion, while reducing the incidence of the fumigant's prematurely extinguishing. A method of controlling insects by use of the fumigant is also disclosed.

CROSS REFERENCES TO RELATED APPLICATIONS
 Not applicable.
 STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 Not applicable.
 BACKGROUND OF THE INVENTION
 The present invention relates to vertically disposed, rope-like structures
 that are ignitable from their top to dispense desired volatile materials,
 including, by way of example only, insect control actives such as insect
 repellents.
 The fact that certain combustible materials can be ignited and will then
 disperse an active ingredient as they continue to smolder is well known.
 Incense sticks and mosquito coils are examples of products made from such
 materials. See e.g. U.S. Pat. Nos. 4,959,925 and 5,657,574. The disclosure
 of these publications and of all other publications referred to herein are
 incorporated by reference as if fully set forth herein.
 The term "fumigant" herein means a burnable material that releases a
 volatile ingredient as the material burns, and preferably as it slowly
 smolders. A "volatile material" or "volatile ingredient," in that context,
 means any material that can be released by a burning fumigant including,
 by way of example only, fragrances, disinfectants, and insect control
 actives. The term "active" refers to a volatile material to be released in
 order to achieve the desired effect of the fumigant. For a fumigant
 intended to repel mosquitoes, for example, an insect repellant would be an
 "active." An "insect control active" is an active that repels, kills, or
 desirably modifies the behavior of insects. "Insects" herein means actual
 insects, as well as other small animals commonly controlled in conjunction
 with insects, such as spiders and the like.
 While conventional fumigants in the form of mosquito coils or repellent
 sticks are fairly inexpensive, they are often used in large quantity (e.g.
 thirty or so a month may be needed to control mosquitoes on an overnight
 basis). Further, these coils are most often used in countries having
 average annual income levels that are very low. In order to make such
 products more widely available, their cost must be reduced still further.
 This is particularly important in controlling the spread of malaria and
 certain other insect-borne diseases.
 There have been attempts to reduce the cost of mosquito protection by
 burning widely available, very inexpensive, smoke-producing materials that
 are used without any insecticide. However, efforts to control mosquitoes
 by burning materials of this type, such as by burning cow dung, are not
 very effective and can have other undesirable characteristics, such as
 excessive odor.
 Academic researchers in India have proposed the use of jute rope that has
 been impregnated with a mosquito repellant as a fumigant. This approach
 uses a relatively limp impregnated rope suspended from a hanger, which is
 lit on its lower end and permitted to smolder overnight. See M. Ansari et
 al., 31 Indian J. Malariology 57-64 (1994); M. Ansari et al., 29 Indian J.
 Malariology 203-210 (1992); and V. Sharma et al., 26 Indian J. Malariology
 179-185 (1989).
 Unfortunately, this technique produces inconsistent results as burning
 rates can not be precisely controlled and, especially, can be too rapid.
 Also, there is some fire risk if the characteristics of the rope are not
 carefully controlled. For example, fire can flash up the rope, contacting
 structures from which the rope has been hung. Metal mesh fire guards have
 been shown to attempt to control this risk. Further, a portion of the rope
 is sometimes wasted near its upper end, as contact with the suspension
 device snuffs the rope.
 Wax candles, having conventional fiber wicks surrounded by wax, are of
 course also well known. They are sometimes supported in a hollow core of a
 corkscrew-like wire, positioned on a flat surface. Some such candles have
 insect repellent (such as citronella) incorporated in the wax. However,
 such designs require the use of relatively expensive candle wax.
 Thus, there is still a need for improved fumigants, particularly those that
 can dispense insecticide or insect repellent at extremely low cost.
 SUMMARY OF THE INVENTION
 In one aspect, the invention provides a burnable fumigant. It has an
 elongated, preferably twisted or braided strand or otherwise formed rope
 or rope-like structure (preferably of at least 5 mm in diameter) which is
 sufficiently rigid that, when supported from its lower half, it maintains
 its upper half in a position sufficiently upright that the uppermost end
 of the rope-like structure remains at least level with or, preferably,
 above the remainder of the rope-like structure, even without an external
 support contacting its upper half. It is preferred that the upper half,
 when so held, droop no more than about 80 degrees from the vertical and,
 more preferred for easy holding and use, no more than 45 degrees. Ideally,
 the upper half should remain substantially vertical when so held. All such
 orientations will sometimes be referred to herein as being "functionally
 vertical." Preferably the rope-like structure remains functionally
 vertically disposed even when supported over no more than its lower third,
 better over no more than its lower fourth, and ideally over no more than
 its lower eighth.
 While the rope-like structure can include braided or twisted strands, it
 can also be made from strands formed into a rope-like structure by being
 compacted, felted, or similarly processed. The rope-like structure can be
 made of a very inexpensive material such as jute or other fibrous plant
 materials.
 There is an active on the surface of, impregnated in, or otherwise borne by
 the rope-like structure. The active preferably is an insect control
 ingredient, a fragrance, or a combination of the two. In especially
 preferred forms, the active includes an insecticide or an insect
 repellent. Two such actives are esbiothrin (d-trans chrysanthemate of
 d-allethrolone) and Pynamin Forte.RTM. (d-cis-trans-chrysanthemate of
 dl-allethrolone), both available from AgrEvo Environmental Health, Inc.
 and Sumitomo, respectively.
 In one embodiment, a strand or other longitudinally extending first portion
 of the rope-like structure has either no active or only selected actives.
 Another, co-extending, second portion of the rope-like structure does have
 one or more actives not present in the first portion and, preferably, also
 is colored, preferably with a dye, so that the second portion is visually
 distinguishable from the first portion. This provides a quality control
 feature to insure inclusion of a specifically treated strand in the final
 product, minimizes the amount of active needed for any given height and
 thickness of the structure, may also provide perceived value in the mind
 of the consumer, and can be used to visually distinguish among different
 actives or active concentrations in otherwise similar products. Thus, by
 way of example only, a product having a higher concentration of active for
 use in extreme conditions can be distinguished at a glance from a low
 active concentration product.
 The rope-like structure preferably is literally a rope between 5 mm and 15
 mm in diameter. With this diameter, tightly wound jute rope, held
 vertically from the bottom, typically can extend upwardly as much as 30 cm
 and remain functionally vertical. A length of rope held generally
 vertically from the bottom for burning from its upper end will sometimes
 be called a "rope candle" herein. The rope candle preferably is held up in
 a coil holder that supports it only from its lower half (preferably only
 from its lower third, more preferably from its lower fourth, or, ideally,
 its lower eighth). This reduces the likelihood that contact between the
 holder and smoldering rope will extinguish the rope prematurely.
 Another form of the invention provides a method of controlling insects. One
 positions the above fumigant such that it is functionally and preferably
 essentially vertically disposed and ignites an upper end of the fumigant.
 Preferably, the upper end is treated with an igniter material such as
 sodium nitrate.
 A wide variety of insect control actives are suitable for use with the
 present invention. Pyrethrum or pyrethroid type materials of the type that
 have been successfully used in mosquito coils are preferred. Especially
 preferred insect control actives (from the standpoint of expense and
 activity vis a vis mosquitoes) are pyrethrum, esbiothrin, Pynamin Forte,
 resmethrin, bioallethrin, allethrin, and mixtures thereof. Other insect
 control ingredients can also be used, such as the repellents citronella,
 lemon grass oil, lavender oil, cinnamon oil, neem oil, clove oil,
 sandlewood oil, and geraniol, and insect growth regulators such as
 hydroprene.
 A variety of known fragrances (e.g. those typically incorporated in incense
 sticks) can be used instead of or in addition to the insect control
 ingredient. A wide variety of volatile fragrances are well known to those
 skilled in the art.
 Because the rope candle is burnt from its upper end, the burning process
 proceeds much more uniformly and slowly than if it were ignited from its
 lower end, and with reduced risk of fire. Also, because the rope structure
 can be twisted or braided firmly, the fumigant is sufficiently vertically
 rigid that it does not so droop as to interfere with its functioning, at
 least over useful lengths up to about 30 cm. Compared to the length of the
 rope candle, only a relatively short holder is sufficient to hold the rope
 candle for use. Preferably the holder is made in the shape of a coil and
 is made of very thin wire. This insures only minimal contact at any height
 between the supporting coil and the burning portion of the rope.
 Consequently, the risk of the rope candle being extinguished by its holder
 is markedly reduced.
 The rope can be made from any of a wide variety of naturally occurring
 stranded plant materials. By way of example, only, while preferred ropes
 can be made from jute, other stranded structures can be made from portions
 of hemp, cotton, maize straw, rice straw, coir fiber, sisal, henequen
 fiber, and abaca fiber.
 These and still other advantages of the present invention will be apparent
 from the description of the preferred embodiments which follows. It should
 be appreciated that the following embodiments are merely the preferred
 embodiments. Thus, the claims should be looked to in order to judge the
 full scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 depicts a rope structure, generally 10. It is positioned in a holder
 11 which is made from a metal disk 12 to which is welded a metal wire coil
 13. Alternatively, the coil can be extracted out of the disk center after
 the center has been appropriately cut. There is a central hollow area or
 core 14 extending lengthwise through the coil and having a diameter
 sufficient to receive the bottom of rope structure 10.
 Rope structure 10 may be formed from braided or twisted strands or from
 strands formed into a rope-like structure by being compacted or felted.
 For example. FIG. 1 shows two strands 18, 19 being twisted together, but
 three strand or braided ropes can also be used. In the FIG. 1 embodiment,
 strand 19 is not impregnated with active while strand 18 is both
 impregnated with active and colored with a dye, prior to the strands being
 twisted into a rope.
 After the twisting, segments of the rope (typically between 8 cm to 10 cm
 long) can be cut. Preferably the top 21 of the rope structure 10 is dipped
 in an igniter solution (e.g. a sodium nitrate solution) to provide an
 igniter section 22.
 After insertion of the rope structure 10 in the core 14, the wire holder 11
 extends no more than a third of the way up the rope structure 10.
 Nevertheless, the rope structure 10 is sufficiently tightly wound and
 sufficiently wide so as to prevent its upper portion from drooping to an
 extent that interferes with the use of the invention. Drooping beyond 80
 degrees from the vertical so interferes, and preferably the rope structure
 droops no more than 45 degrees from the vertical.
 The rope structure 10 can then be lit from its top. Because the wire around
 the coil 13 is very thin (e.g. preferably not more than about 2 mm
 diameter), and because of the helical nature 24 of the preferred coil, at
 any vertical height only a small portion of the wire contacts the rope
 structure 10 and from only one side at any given height. As a result, the
 rope structure 10 will be able to burn almost entirely down to the bottom
 without being extinguished, whether by being snuffed out or by being
 extinguished by excessive conductive heat loss via the wire. Thus, there
 is less waste.
 In the alternative embodiment shown in FIG. 4, the rope structure 30 is
 braided. Preferably the braided structure, as a whole and after the
 braiding, is dipped into the active solution such that the active coats on
 the surface of the structure or even soaks into it. However, it is also
 possible to pre-treat a component strand that then is incorporated in the
 otherwise untreated rope in the braiding process.
 The impregnating/coating solution contains an organic solvent, such as
 isopropyl alcohol or a hydrocarbon such as Isopar M (from Exxon Chemical
 Co.). A dipping protocol is used that results in the rope structure
 holding from 1 to 3 mg of active per that length of the rope structure
 that will burn in one hour.
 When a dye is used in the dipping solution, it is preferably in the percent
 weight range of 0.001% to 0.1%. One preferred dye is the common fabric dye
 Malichite green. However, any suitable dye that does not produce
 detrimental fumes may be used.
 As indicated above, sodium nitrate is a preferred igniter material. It is
 applied in a 1 to 10% solution dissolved in water, most conveniently by
 merely dipping the end of the rope structure into the solution and then
 allowing it to dry.
 The burning rate of the rope can be adjusted by adding any convenient
 combustion rate-modifying material to the dipping solution. For example,
 when it is desired to retard the burning rate, boric acid (e.g. 0.2%) can
 be added to the dipping solution. This may be desirable where the type of
 plant material used has a tendency to burn too quickly.
 EXAMPLE
 A jute rope twisted from three primary strands was dipped in an isopropyl
 alcohol solution of Pynamin Forte at a concentration such that 8.75 mg of
 Pynamin Forte was deposited for each 15.4 cm (6 inches) of rope. After
 drying, the top end was dipped in an igniter made from a 1% aqueous
 solution of sodium nitrate.
 After the igniter had dried, the rope structure was then mounted in the
 FIG. 1 holder and lit at its upper end at around sunset in selected user
 test sites. Reports received indicated that the ropes provided mosquito
 protection comparable to that provided by conventional mosquito coils.
 Note that the rope may be made having widths and lengths either wider and
 less tall or narrower and taller than the embodiments depicted in the
 drawings. Further, more than one strand may be dyed in more than one color
 for various aesthetic, indicia, or trademark purposes. Also, various
 fragrances may replace and/or be used in addition to, the insect control
 active.
 Thus, the claims should be looked to in order to understand the full scope
 of the invention.
 Industrial Applicability
 Fumigants are disclosed that control mosquitoes at very low cost. Methods
 of using such fumigants are also disclosed.