Method and composition for protecting pavement structure from growth of plants in splits of the structure

A method and device are used for controlling growth of plants in pavement splits by preventing seeds from germinating and by preventing growth of plants from existing roots in the vicinity of the splits. The growth of plants is controlled for extended periods of time (2 to 20 years). A pre-emergence herbicide and a systemic herbicide are incorporated into a polymeric matrices. The polymeric matrices are formed into shaped objects, such as, bands or cords which are then inserted into splits. The split is then filled with a sealer which permits easy migration of the herbicides therethrough. The herbicides gradually released from the shaped objects at a rate sufficient to maintain a minimal effective level of herbicide outside said sealer for a predetermined period of time.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the field of controlling the 
growth of plants in splits found in cement or asphalt pavements. The 
invention, more particularly, relates to the field of long-term control of 
plant growth in the splits. 
Pavements are usually made of asphalt and concrete but can also be 
constructed by a variety of building materials such as stone, brick and 
cobblestone. Such pavement structures including sidewalks and curbs are 
usually engineered with seams and/or expansion joints. The expansion 
joints are intended to function to either prevent or limit the formation 
of cracks in the pavement caused by thermal/pressure excursions such as 
those caused by weather. 
Most commonly, cracks are caused by natural processes such as freezing and 
thawing of the pavement caused by weather conditions. Because of the 
freezing and thawing, the integrity of the joints in the pavement may be 
reduced or worse, cracks may form in the pavements. Further, enlargement 
of both the manufactured or naturally created splits can occur during 
severe cold weather when water infiltrates into the splits. As used in 
this specification and the appended claims the term "split" is defined to 
mean any type of divide in the pavement including cracks, joints and 
seams. 
The problem associated with splits in the pavement can be amplified by 
plants. The joints, the seams and the cracks in the pavement serve as 
natural collection points for wind dispersed plant seeds. Moisture and 
soil which accumulate in the cracks provide an ideal environment for 
plants allowing the seeds to sprout. Upon germinating, the plants 
accentuate the problem of crack enlargement by further inducing the 
cracks. Moreover, roots of plants in the soil below pavement can grow into 
plants through the splits in the pavement. 
In addition to enlarging the splits, the plants growing in the splits can 
also cause litter problems because they are capable of trapping litter, 
such as, paper wrappers as they are being blown about by the wind. This 
problem is especially troublesome on aircraft runways, tax-ways and 
aprons. Such plant growth may obscure the view of airport runway lights 
endangering the lives of airplane passengers. Moreover, the litter which 
accumulates in the runways due to the growth of plants in pavement splits 
can even be sucked into jet engine or into reciprocating engine intakes, 
to cause damage or malfunction of engines. 
To alleviate the plant problem, a quick temporary solution is provided by 
mowing. A more permanent method has been developed which requires the 
splits to be routed and then sealed with either asphalt or butyl sealants. 
In the most severe cases, repaving the runway, taxi-way or apron may be 
required. 
Although routing and sealing is effective for removing plants that have 
grown in the splits at the time the pavement is either routed and sealed 
or repaved, the method is not a solution for the long-term control of the 
plant problem in splits. That is, if the splits have been routed and 
sealed, the seal will eventually deteriorate thereby reopening the splits. 
Once the splits are reopened, the growth of plants in the reopened splits 
presents the same problems as those discussed above. Therefore, routing 
and sealing the splits does not alleviate the problem of plant growth in 
splits (including cracks, joints or seams). It continues to be a recurring 
problem. 
It is known in the art that plant seedlings may be controlled by the use of 
pre-emergence herbicides. For example, Soper, U.S. Pat. No. 3,257,190, 
Soper, U.S. Pat. No. 3,111,403, Lignowski and Scott, Trifluralin and Root 
Growth, 12 Plant & Cell Physiology 701 (1971), and Eshel and Katan, Effect 
of Dinitroanilines on Solanaceous Vegetables and Soil Fungi, 20 Weed 
Science 243 (1972), all teach the use of 2,6-dinitroaniline as a herbicide 
which eliminates germinating seedlings. Furthermore, Koestler, U.S. Pat. 
No. 4,360,376 teaches incorporating 2,6-dinitroaniline into a microcapsule 
capable of releasing it. Although these references teach the use of 
pre-emergence herbicides to control the growth of plants, they do not 
provide a practical solution which may be used in long-term control of 
plant growth in pavement splits, including joints, cracks or seams. 
By applying a herbicide in a single application to a split (a crack, joint 
or seam) in the pavement, the initial concentration of herbicide is much 
greater than needed. However, the concentration becomes too low to be a 
truly effective retardant with the passage of time. The concentration of 
herbicide in the applied area is lowered because of physical, chemical and 
even biological activity. 
Therefore, it is desirable to provide a method and device in which the 
herbicide can be metered out in the split at a preselected rate. 
Additionally, it is desirable to provide a method and device which 
protects the herbicide from degradation and physical loss from the split. 
Another problem with using pre-emergence herbicides, such as 
2,6-dinitroaniline is that such herbicides do not eliminate existing 
plants. In other words, the growth of perennial plants from existing roots 
is largely unaffected by presence of a pre-emergence herbicide in the 
split. 
A problem with prior art controlled release devices such as those disclosed 
in U.S. Pat. No. 3,864,114 (Green) is that the operation of the device 
disclosed in that patent is based on leaching the herbicide. Water 
penetrates the device and leaches out the herbicide. Generally, water 
degrades the herbicide in a relatively short period of time of about 2 to 
6 weeks. 
In light of the problem encountered by the growth of plants in pavement 
cracks, joints, and seams, there presently exists a need for a method 
and/or device which prevents such growth for extended periods of time. 
Such an arrangement would help minimize the amount of destruction and 
danger caused by plant growth in highways, airport runways, sidewalks and 
generally in any type of use of concrete and asphalt. 
Thus, one object of the present invention is to provide a product and a 
method for controlling, for a prolonged period of time (2 to 10 years) the 
growth of plants in splits by preventing seeds from germinating and also 
by preventing the growth of plants from existing roots. 
Another object of the present invention is to provide a controlled-release 
device and a method in which the release of the herbicide is driven by 
temperature. 
A further object of the present invention is to provide a controlled 
release device and method in which the release rate of the herbicide and 
its effectiveness can be predetermined. 
A still another object of the present invention is to provide a controlled 
release device and method in which the herbicide is protected from 
chemical and biological degradation prior to being released from the 
device. 
A yet further object of the present invention is to provide environmentally 
superior controlled release herbicide device and method in which the 
herbicide is localized and does not spread far into the soil surrounding 
the system. 
A still further object of the present invention is to provide herbicidal 
device which can be easily inserted into the splits and which is retained 
in the splits for a prolonged period of time. 
Other objects of the present invention will become apparent to those 
skilled in the art upon studying this disclosure. 
SUMMARY OF THE INVENTION 
Briefly, the present invention provides a method and a device for 
controlling or preventing plant growth for a prolonged period of time of 2 
to 10 years. The method and the device prevent seeds from germinating for 
extended periods of time in splits found in pavement and also prevent the 
growth of plants through the splits from roots of plants in the soil near 
the splits. A pre-emergence herbicide is incorporated into a matrix for 
controlled release. The polymer in the controlled release device must be 
capable of incorporating a herbicide. After the herbicide is incorporated 
into the polymer, the matrix is molded into shaped objects, such as, a 
band, a cord, or capsules which can then be placed into splits found in 
the pavement. The shaped objects are inserted into a split and are capable 
of maintaining a minimal effective level of herbicide for a predetermined 
time period. The shaped object or objects are then preferably encased by a 
sealer which protects them from deterioration and physically maintains 
them in the split. 
In areas where plant roots may already exist in the soil or where root of 
trees or other valuable plants are not in the vicinity of the split, the 
present invention provides a combination of two types of shaped controlled 
release objects containing herbicides: one containing a pre-emergence 
herbicide to prevent seeds from germinating and a second containing a 
systemic herbicide to prevent the growth of plants from roots already in 
the soil. The objects are preferably sealed by a resilient polymeric 
sealer, such as, butyl rubber. 
In accordance with a preferred embodiment of this invention, the 
pre-emergence herbicide can consist of a 2,6-dinitroaniline such as 
trifluralin. The systemic herbicide can be any approved systemic herbicide 
that is compatible with polymers and has an acceptable release rate, such 
as tebuthiuron marketed under the trade name Spike by Dow-Elanco or 
glyphosate marketed under the trademark Roundup by Monsanto Company. The 
polymer can be selected from a group consisting of thermoplastic polymers, 
thermoset polymers, elastomeric polymers and copolymers thereof. Once the 
herbicide, such as, the trifluralin is incorporated into a polymer of the 
controlled release device, it is extruded to form a shaped object, 
preferably a band, which can be conveniently placed into the splits. The 
band is then sealed in place by a sealer, which permits the herbicide to 
easily migrate there through, and is preferably resilient. The sealer is 
preferably either silicone or urethane or butyl rubber. 
By placing a slow release device, such as, a band capable of slowly 
releasing a pre-emergence herbicide into the pavement cracks, joints or 
seams, an advantage is realized over the prior art in that seeds which are 
inevitably collected in such areas are prevented from successfully 
germinating. More importantly, the herbicide is released at such slow 
rates that the protection can last for long periods of time, generally 2 
to 10 years, and as much as 20 years. In addition, the use of devices 
containing a systemic herbicide prevents the growth of plants from roots 
already in the soil in the vicinity of the split. 
The present invention, together with attendant objects and advantages, will 
be best understood with reference to the detailed description below read 
in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The plant control mechanism of the present invention comprises using a 
first polymeric matrix incorporating a pre-emergence herbicide and a 
second polymeric matrix incorporating a systemic herbicide. The present 
invention provides a method of preventing germinating seeds in splits of a 
pavement structure, which are either artificially or naturally created. The 
seeds are prevented from germinating for a prolonged period of time, 
generally 2 to 10 years and as much as 20 years. The prolonged protection 
against plant growth is effected by placing controlled release devices 
containing a pre-emergence herbicide in form of a shaped object, such as, 
a band in the splits and sealing the shaped objects with a sealer which 
permits the herbicide to easily travel therethrough. 
The present invention also provides a method for preventing the growth of 
plants from roots existing in the soil near the structure. This is done by 
incorporating a systemic herbicide in a polymeric matrix which can be made 
into a shaped object. The systemic herbicide is preferably released over a 
period of at least about 2 years. The object or objects are then placed in 
the split and sealed with a sealer which permits the systemic herbicide to 
easily travel therethrough. Since a long term solution to plant growth is 
desired, the present invention incorporates the herbicide or herbicides 
which are used to control the plant growth into a polymeric matrices to 
form controlled release devices. The term "controlled release device" 
refers here to a device which produces controlled and sustained release of 
a herbicide from its matrix to its surface. The device provides a method 
for the controlled release of the herbicide into the surrounding 
environment. The herbicide released into the environment (generally soil) 
surrounding the system establishes an effective zone of action. Thus, the 
polymeric delivery system of the present invention maintains an effective 
dose of the active herbicide for a substantial length of time in a zone 
surrounding the device. If both a pre-emergence herbicide and a systemic 
herbicide are used in a system, two overlapping zones are formed, the 
systemic herbicide zone is generally larger because the pre-emergence 
herbicide generally travels only about a centimeter into the soil whereas 
systemic herbicides of this invention are slightly more water soluble and 
therefore are carried by water a little farther into the soil. 
The controlled release systems of the present invention provide advantages 
over single application methods which typically result in higher than 
necessary concentrations immediately after treatment which subsequently 
within a relatively short period of time degrade to a level below the 
minimum effective doses. Moreover, the preferred device of the present 
invention releases herbicides at a high rate initially and a lower, steady 
rate thereafter. The high initial release rate is preferably effected by 
applying a sealer at an elevated temperature, preferably in a molten 
state. This release profile assures that the split becomes protected in a 
relatively short period of time and that, subsequent to reaching the 
minimum effective level only the amount of herbicide necessary to replace 
the degraded herbicide is released. This release profile diminishes 
potential environmental and health problems of the treatment and reduces 
the cost of the treatment. 
Thus, by using a controlled release device, the concentration of the 
pre-emergence herbicide can be maintained at a concentration above the 
"minimal effective level" necessary to stop germinating plants. Similarly, 
the systemic herbicide is released from the controlled release device at a 
rate that maintains its concentration in the above its minimal effective 
level. As used in this specification and the appended claims, the term 
"minimal effective level" is defined with respect to pre-emergence 
herbicides to mean the level of herbicide necessary to prevent seeds from 
germinating. The term "minimal effective level" is defined with respect to 
systemic herbicide as the level of systemic herbicide that is necessary to 
prevent plants from growing. 
It has been found that polymers serve as effective release devices because 
they can act as both reservoirs and release-regulating mechanisms for the 
herbicide. Moreover, they can protect the herbicide from degradation. A 
more detailed description of "controlled release devices" is given in U.S. 
patent application Ser. Nos. 06/555,113, filed Nov. 23, 1983, which is a 
continuation in part of 06/314,809, and 06/314,810 both filed on Oct. 26, 
1981; 07/086,757, filed Aug. 18, 1987, 07/072,080 filed Jul. 10, 1987; and 
07/091,918 filed Sep. 1, 1987. The contents of these applications being 
incorporated herein by reference. 
Preferably, a pre-emergence herbicide is selected on the basis of being 
capable of effectively retarding or preventing germination of seeds. In 
pavement applications, 2,6-dinitroanilines have been found to be suitable 
retardants. By way of example, some suitable 2,6-dinitroanilines are 
trifluralin commercially available as Treflan, benfluralin available as 
Benfin, insopropalin available as Pearlan, oryzalin available as Surflan, 
ethalfluralin available as Sonalan, pandimethalin available as Prowke and 
profluralin available as Tolban. Preferably, the 2,6-dinitroanilines are 
trifluralin and benefin. The most preferred 2,6-dinitroaniline is 
trifluralin. The preferred concentration of pre-emergence herbicides in 
the polymer matrix range from about 10 to about 25 of the total weight of 
the matrix, especially preferred is the range from about 15 to about 20 
percent. 
Any systemic general purpose (non-selective) herbicide can be used in 
connection with the present invention. The selection of a specific 
herbicide depends on the application. Examples of preferred systemic 
herbicides suitable for use in the present invention include tebuthiuron 
marketed by Dow Elanco under the trade name Spike and glyphosate marketed 
by Monsanto Company under the tradename Roundup. Tordon and diuron are 
examples of other systemic herbicides that can be employed. 
Polymer selection for the controlled release device depends upon the 
extreme conditions found in concrete or asphalt. Temperatures can vary 
from below freezing to nearly 50.degree. C. Additionally, the pavement 
encounters various types of moisture such as water and ice. Finally, the 
selection of the polymer must account for the characteristics of the 
herbicides and provide the desired release rates. 
Preferred polymers capable of withstanding such adverse conditions and 
providing the desired release rates for the pre-emergence herbicide, such 
as, 2,6-dinitroaniline, include isoprene, low density (LD) polyethylene 
and high density (HD) polyethylene. However, it is possible to use other 
polymers selected from the group consisting of thermoset polymers, 
thermoplastic polymers, elastomeric polymers and copolymers thereof. By 
way of example, some other possible polymers include vinyl acetate, 
urethane, polyester, silicone and neoprene. The preferred polymers for 
systemic herbicides are silicones and urethanes. Silicones and urethanes 
are preferred primarily because their matrices provide a relatively faster 
release rate for polar compounds. It has been discovered that it is 
advantageous to release the systemic herbicide quicker than the 
pre-emergence herbicide. It will be recognized by those skilled in the art 
that other suitable polymers may also be used with the present invention 
depending on the particular use contemplated. The preferred concentration 
of systemic herbicides in the polymer matrix range from about 5 percent to 
about 10 percent of the total weight of the matrix, especially preferred is 
range from about 8 to about 10 percent. 
In addition, it is advantageous to add a filler and/or carrier to the 
controlled release device to optimize the loading of the polymer. The 
inclusion of such a substance allows greater amounts of herbicide to be 
loaded into the desired polymer while at the same time assisting in the 
release rate of herbicide. Carbon black is the preferred carrier. The 
preferred amount of carbon black is from about 2 to about 10 percent by 
weight of the total weight of the device. 
To form the controlled release device of the present invention, a 
pre-emergence herbicide, such as 2,6-dinitroaniline and a systemic 
herbicide, such as tebuthiuron, is incorporated into the polymer by 
mixing. The mixing should be sufficient to allow an even distribution of 
herbicide throughout the polymer. A more detailed description of the 
mixing is given in U.S. patent application Ser. No. 06/555,113 filed on 
Nov. 23, 1983 which is a continuation-in-part of U.S. patent applications, 
06/314,809 and 06/314,810 both filed on Oct. 26, 1981. Methods for 
obtaining the release rates are described in patent application 07/303,770 
filed on Jan. 30, 1989. 
Once loaded, the polymer matrices are then molded into shape objects, such 
as, bands and allowed to cool so as they would maintain the desired 
shapes. As shown in FIGS. 2 and 3, the bands can be molded, for example, 
into a cord 10 or a flat strip 20. Preferably, the molding is accomplished 
by means of extrusion which is known in the art. The band can be designed 
with varying diameters and with differing amount of herbicide. 
However, to prevent seeds from germinating for extended periods of time, an 
amount of the pre-emergence herbicide sufficient to establish and maintain 
a minimal effective level in a zone surrounding the device must be loaded 
into a polymer matrix. Similarly, to prevent the growth of plants from 
roots already existing in the soil, a sufficient amount of the systemic 
herbicide must be incorporated into the polymer matrix containing the 
pre-emergence herbicide or into a separate polymeric matrix to establish 
and maintain a minimal effective level of herbicide in the soil 
surrounding the device. It has been discovered that for the minimal 
effective level of 2,6-dinitroaniline is about 10 parts per million of 
soil. Similarly, it has been discovered that the minimal effective level 
of the systemic herbicide, such as, tebuthiuron is about 2 ppm of soil. 
Table 1 provides longevity estimates of "minimum effective levels" for the 
three preferred polymer cord systems at two loading concentrations, 15 and 
30%, and at four different cord diameters. The estimated release rates were 
calculated at a temperature of 45.degree. C. because of the high 
temperatures found on pavements. Table 1 is provided by way of explanation 
and illustration. As such, the table is not to be viewed as limiting the 
scope of the invention. 
TABLE 1 
______________________________________ 
Est Est 
Polymer/ Est Rel Rate Longevity 
Longevity 
Cylinder (45.degree. C.) 
(15%) (30%) 
dia (in) (.mu.g/cm2/day) 
(yr) (yr) 
______________________________________ 
Isoprene 
0.25 250 2.67 5.35 
0.312 250 3.43 6.87 
0.375 250 4.21 8.42 
0.5 250 5.76 11.52 
LD PE 
0.25 200 3.34 6.68 
0.312 200 4.29 8.59 
0.375 200 5.26 10.53 
0.5 200 7.20 14.40 
HD PE 
0.25 120 5.57 11.14 
0.312 120 7.15 14.31 
0.375 120 8.77 17.54 
0.5 120 12.00 24.01 
______________________________________ 
As can be seen from the table, the release rates of the herbicide can vary 
with the selection of the polymer matrix. However, a "minimal effective 
level" can be maintained for at least 3 to 5 years. Preferably, the 
concentration in parts by weight of the herbicide should range from about 
10 to about 30, the concentration of polymer from about 50 to about 90 and 
the concentration of filler from about 10 to about 30. 
Preferably, the crack which is to be processed is first routed to remove 
existing undesired plants. After the crack has been routed, the band 
described above is placed in the crack. The band which is preferably the 
size of the crack is generally embedded at a depth of about 1 to 2 inches. 
Once in place, a backer rod typically made of polyethylene can be put on 
top of the band. After the band is applied to the crack, the crack 
containing a band therein is sealed using a sealing material, such as hot 
butyl rubber, asphalt or even concrete. It should be noted that the 
mentioned sealants were used by way of example and do not limit the scope 
of this invention. 
Preferably, the sealant is applied immediately upon the insertion of the 
band because of the possible detrimental effects to the band caused by 
sunlight and the weather. However, a leeway of a few hours is permitted. 
Upon sealing the band, the heat given off by the molten sealant 
advantageously causes the band to give off an immediate burst of herbicide 
which eventually tapers to the desired steady state. 
FIG. 1 illustrates a preferred apparatus which may be used to implement the 
method of the present invention. The band, in the form of a cord 5, is 
transported to the work area where it will be placed in a crack on a cart 
generally shown at 6. The cart 6 comprises a reel 1 upon which the cord 5 
is wound. Below the reel 1 is a stationary clevis 3 through which cord 5 
travels. A wheel 4 also disposed beneath the reel 1 can be adjusted lower 
or raise the reel 1. The cart 6 preferably also includes a heating 
mechanism to heat the cord 5 to allow for easier application of the band 5 
in pavement cracks. The heating mechanism 2 may comprise, for example, a 12 
volt battery and an electrical resistance heating element. This heating 
mechanism is particularly useful since the rolled cord 5 will tend to 
retain its rolled shape, commonly referred to as a "memory effect." The 
heating of the rolled cord 5 by means of the heating mechanism will tend 
to eliminate this memory effect. Additionally, the heating makes the band 
or cord more flexible and thus easier to apply. 
After being transported, the band 5 is placed into the split in the 
pavement. However, before placement, the split must be routed. With the 
band in place, the split is resealed. The split can be resealed by a 
variety of sealants. Resilient polymers which permit easy travel of 
herbicides therethrough are the preferred sealers. Currently, the most 
preferred sealer is butyl rubber. However, asphalt is the most common 
sealing material. 
In conclusion, advantages are realized by placing a band capable of slowly 
releasing herbicide into pavement splits. One advantage is that the plants 
that collect in the splits are prevented from germinating. More 
importantly, the invention provides a long-term solution for the plant 
growth problem and thereby, eliminates the need for frequent repair and 
reseal of pavement structures such as runways and sidewalks. 
Referring now to FIG. 4, there is shown there a cross-section of a crack 
generally designed by a numeral 100 in a pavement structure 112 filled in 
accordance with the present invention by a system constructed in 
accordance with the present invention. The crack 10 is sealed by a sealer 
15 composed of butyl rubber. The sealer fits tightly against the walls 117 
of the crack 110. Inside the sealer 115 there is a controlled release 
device 119 in shape of a continuous cord. The controlled release device 
119 contains a pre-emergence herbicide, such as, trifluralin. Also inside 
the sealer 115, there is a controlled release device 121 which contains a 
systemic herbicide, such as Roundup.RTM. or Spike.RTM.. 
The matrix of device 119 is preferably made of a high density polyethylene 
and carbon black. The preferred composition of this device is high density 
polyethylene--70 parts, carbon black 5 parts and Treflan 25 parts. The 
matrix of device 121 is preferably made of silicone or urethane. The 
preferred composition of this device is silicone or urethane--90 parts and 
Spike--10 parts. The preferred silicone is silicone 3112. 
In operation, the crack 10 is first routed to remove dirt and plants 
therefrom. Then, the cord 119 and the cord 121 are placed in the crack 
110. The crack 110 is then filled with a molten butyl rubber seal 115. The 
seal 115 encases the cords 119 and 121 and physically maintains them in 
position in the crack 110. The butyl rubber protects the herbicides in the 
cords 119 and 121 from degradation. 
The heat from the sealer 115 causes a release of a significant dose of the 
herbicides from the polymeric matrices of cords 119 and 121. The 
herbicides traverse the butyl rubber and migrate to the interface between 
the wall 117 of the pavement 112 and the outside surface of the butyl 
rubber seal 115. It has been discovered that for trifluralin, the minimal 
effective concentration at the interface is about 10 ppm of soil. The 
pre-emergence herbicide generally travels only less than about one 
centimeter from the interface between the seal 115 and the wall 117 into 
the soil 125. The systemic herbicide, however, travels further into the 
soil 115 and establishes a herbicidal zone in the soil in which plants are 
prevented from growing. When a root, such as root 130 existing in the soil 
grows a shoot, such as, shoot 135, which enters the herbicidal zone, the 
systemic herbicide is absorbed by the shoot and/or root 135. The shoot 135 
and root 130 are destroyed. 
Similarly, pre-emergence herbicide forms a zone around the seal 115. If a 
seed, such as, seed 145 finds its way into a space between the seal 115 
and the wall 117, the pre-emergence herbicide prevents such seed from 
germinating. 
It should be apparent that a wide range of changes and modifications can be 
made to the preferred embodiments described above. It is therefore intended 
that the foregoing description be regarded as illustrative rather than 
limiting, and that it be understood that it is the following claims, 
including all equivalents, which are intended to define this invention.