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Dr. Larry Nelson (right) and Coalition President Newt Hardie During Early Tests of Sheeting (September 2004)

Introduction: In August of 2004, Dr. Larry Nelson from Clemson Extension Service explained his idea that plastic could possibly be used to kill kudzu foliage. A member of the Spartanburg Menís Garden Club volunteered to use plastic at several places in the South Pine Street area where other non-chemical methods were being tested. This paper recaps the tests using plastic over kudzu.

  1. Summary
    1. The heat under plastic sheeting definitely does kill the kudzu foliage.
    2. Browning of some leaves is visible in 3 to 4 days. The kudzu foliage is completely killed in two to three weeks depending on various factors such as: Outside temperature, how well the plastic is held in place, and how much movement of air takes place under the plastic.
    3. It was difficult to hold the plastic in place when used over mature, two foot, three foot, and higher, substructures of kudzu.
    4. Where the kudzu was low to the ground (immature and one foot high or less), the outline of the foliage kill was quite visible and sharp.
    5. Vines extending out from under the plastic were unaffected. This was evidenced time and again. A vivid example was where plastic was wrapped around the trunk of a tree which had kudzu growing up the tree and into limbs above the plastic. None of the leaves above the plastic turned brown.
    6. If the plastic is removed after complete foliage kill, the kudzu usually comes back. The speed of recovery and aggressiveness of the vines appears to be dependent on two factors.
      1. The length of time covered by plastic before removal.
      2. The original height of the kudzu substructure.
  2. The Plastic
    1. Four-mil plastic was used first since the volunteer had some at home. While it worked satisfactorily, six-mil provides more weight to partially crush the substructure of kudzu and is less subject to being blow back by the wind. The six-mil did not tear even though heavy strain was applied when straightening after wind shift and rain shift.
    2. Midway through the two months of testing, Dr. Nelson suggested the use of clear plastic so as to admit more sunlight and possibly raise the temperature under the plastic. Several tests were set up with clear plastic. Even though the "clear" version has a distinctly whitish cast, the browning of top kudzu leaves was visible without removing the plastic. Although these applications were not sufficient to conclude which plastic was superior, the black appeared to work better.
    3. The polyethylene sheeting was 20 feet wide and 100 feet long and weighed 57.4 pounds. It cost $45.97 at Home Depot.
    4. It was difficult to carry 57 pounds of rolled and folded plastic into the kudzu. The best method for handling seemed to be to toss the roll onto the kudzu such that it unrolled in the process, walk through the kudzu to the remaining package, pick it up, toss again so that it unrolls further, and repeat the process until the full 100 feet is laid out. At this point the plastic was unfolded, then pulled to full width on each side, and then straightened. The whole process took about 20 to 30 minutes for each roll.
  3. Holding the Plastic in Place
    1. Small rocks were not effective for weighting down the plastic and kudzu substructures. Heavy rocks worked well in most cases but were not readily available and could only be transported a few at a time even with a wheelbarrow. This approach requires high labor commitment and only a few spots were anchored thusly at each test. Gaps of 10 and more feet — often 20 feet — between stones were normal. This did not allow for a good "seal" and permitted wind to get under the plastic.
    2. Rain formed puddles in various places — largely depending on the kudzu substructure. Water is heavy. Where it collected, the plastic was anchored quite well because the kudzu underneath was pinned to the ground. The indentation caused by the water tended to pull the plastic away from its original position even when held down by large rocks. This effect tends to reduce the span of the plastic and would be a negative factor where two plastic panels come together. After a rain it was often difficult to move the plastic or to remove the water.
    3. Rainwater can be used in lieu of rocks to hold the plastic down by walking parallel to the edge of the plastic and approximately two feet in from the edge. The weight of the worker crushes the kudzu beneath, and the path of footsteps creates an indentation roughly similar to a shallow ditch along the edges. Once this is done, rainwater collects in puddles along the edge and holds the plastic in place.
    4. 3M Tape with adhesive on one side was tested where plastic was laid parallel to a paved road. In this case sand prevented a secure bind and the adhesive was not strong enough to prevent the wind blowing the plastic back.
    5. A number of methods for holding down the plastic were tried. Tent stakes and long nails through hard plastic edging strips were partially effective.
    6. Tape used for binding edges of carpeting was used to hold two strips of plastic together. This worked reasonably well although not perfectly.
  4. The Heat
    1. The area under the plastic got hot quickly during summer sunlight. Dr. Nelson described the process as "cooking" the kudzu.
    2. An effort was made to use thermometers to determine temperatures under the plastic. However, the thermometers available and the documentation were not sufficient for meaningful learning.
    3. Several factors influence the temperature under the plastic.
      1. Outside temperature.
      2. The presence or absence of shade.
      3. The completeness of closure at the edges of the plastic. This, in turn, is influenced by the height of kudzu substructure and bushes/stumps under the kudzu.
      4. The amount of breeze that got under the plastic.
      5. The "seat of the pants" impression gained by the volunteer was that it did not really matter whether the outside daytime temperature was 70 degrees or 90 degrees. Top kill definitely took place even in late fall when temperatures were 10 and more degrees below the summertime highs. This, if proven to be true, gives more flexibility as to timing (summer vs. cooler spring and fall) and the conditions under which the use of plastic (shade and clouds vs. full sun) is effective.
  5. Miscellaneous
    1. A distinct odor is noticeable under the plastic as the kudzu "cooks".
    2. An unusual number of anthills formed under the plastic. Volunteers must be careful about ant bites. High top boots, long sleeves, gloves, and insect sprays on all three are recommended.
    3. New growth is at first tender. The volunteer had some success in using an industrial string trimmer to remove this foliage and sprouts when the original kudzu substructure was six to twelve inches off the ground.
    4. Placing 100 feet of plastic in a mature field of kudzu is not easy. The worker must walk/stumble into and over the mass of kudzu.
    5. Rather than placing two or three lengths side by side at the same time, it may prove less labor intensive and more cost effective to lay out one strip, leaving the equivalent of two strips uncovered. Then after the top kill, the plastic might well be moved sideways to cover the adjoining and untreated kudzu. After the second top kill, the plastic might be moved to the remaining third area with less effort than laying out the original length. This length of plastic could then be shifted sideways back to the original area for a second treatment.
  6. Thoughts for Further Exploration
    1. At what temperature does heat kill the foliage quickly?
    2. How long does it take to kill the foliage at temperatures lower than the quick kill?
    3. How long does it take to kill the immature vines and how long to kill the mature vines?
    4. Is there some method that would kill the foliage on the vines that extend out from under the plastic?
    5. It was virtually impossible for one worker to get the plastic up over seven foot and higher kudzu covered structures such as large bushes and dead tree trunks in the field. Scaffolding of these types will need to be cut down before laying plastic.
    6. Obviously, study of the optimum length of plastic application is important. Users, however, can simply leave the plastic in place until top kill is complete.
    7. How many applications are required to completely kill the kudzu roots? This may be influenced by the maturity and size of the kudzu roots.
    8. Perhaps a combination of methods might prove superior to the exclusive use of plastic. For example, plastic then string trimmer, then plastic.
    9. Would a plastic treatment first, followed by spot treatment with a relatively mild herbicide be effective enough to replace an original application of harsh chemicals?
    10. If the plastic is not removed, is a complete kill possible through use of plastic? If so, how long would it take to achieve a complete kill of kudzu roots?
    11. Since Kudzu foliage dies quickly at the first frost, would the use of "steam" from dry ice achieve a quick kill? If so, would it be practical to vent the cold vapor from dry ice under a plastic covering?

Conclusion: Plastic has promise in containing and removing kudzu. It is not a panacea and is labor intensive but definitely has applications. We appreciate Dr. Nelsonís suggestions.

Newt Hardie
November 2004

Use of Plastic Sheeting in Fields of Debris Covered Kudzu: Our experiment/testing area is a kudzu covered field that has been used as a dump for construction materials in years gone by. The dumping was probably purposely done to fill in a section of the field that slopes down to a creek. We found large blocks of cement, a large conduit, etc. These form a mound running along the area we will be using for tests.

The mounds of construction materials make that area impractical for mowing. This is not a unique situation. Unfortunately, our world has a lot of kudzu covering up acres and acres of trash. The plastic rolls of sheeting might work nicely for killing the foliage of the kudzu growing amongst the mounds of material.

This is a good example of how plastic sheeting might work well to defoliate kudzu where other treatments cannot be used because of rough ground. We will incorporate this into our test and use photos to document this usage.

April 2005

The polyethylene sheeting does work well in defoliating kudzu amongst construction mounds. The leaves die within a week or two. This treatment knocks back the foliage and permits a clear view of what materials are under the kudzu. The effect is to achieve a temporary condition similar to the dormant season.

Because the tops of the construction materials were several feet high, the temperature under the sheeting was not warm enough at the ground level to kill the kudzu crowns.

Rain water collected in the low areas and pulled the sheeting inward toward the water. The weight of the water lowered the sheeting to within a few inches of the ground. However, the water acted as a cooling agent and reduced the temperature below that necessary to achieve crown kill. The standing water provided a breeding ground for mosquitoes which we combated with droplets of motor oil.

In summary, we achieved foliage kill but no measurable crown kill. Kudzu leaves began coming back within a few weeks. After a month or so, there was no visible difference between the area treated with plastic sheeting compared to similar terrain that was not treated.

Newt Hardie
December 2006