Sheet Comparison

Both types of sheet kill substantial numbers of kudzu crowns, with the clear sheet producing significantly better results (more plant kills). This difference is not visually obvious until the plots are left uncovered for a week so that any surviving crowns send out shoots. Prolific sprouting under the sheets (both black and clear sheets) reveals a plant's survival mechanism: When under life threatening stress, go for broke!

One other difference observed between black and clear sheet treatments is that vines growing over the sheet show much more heat stress on black sheets than clear sheets. It is not difficult to understand why: Black sheets under summer sunlight are much hotter than the surfaces of clear, translucent, or white sheets. June 2005.

When either sheet lays on thick kudzu growths, rainwater collects in pockets that form in the sheets. This helps keep sheets in place against the forces of wind, and keeps sheets pressing down on kudzu for improved thermal contact. Unfortunately, the cooling effect of water works against the desired thermal effect: Cooking kudzu. And, these pockets of water breed mosquitos during the summer. This is undesirable, so we poked holes in the bottom of such pockets to allow rainwater to drain. Of course, this ends up watering the very plants that we wish to kill! Holes also weaken a sheet, eventually resulting in tears after long exposure to sunlight. July 2005.

Besides black and clear plastic sheets, experiments with carpet and rugs (at right in photograph), and used billboard signs are underway. Billboard signs are printed vinyl sheets, specially treated to survive exposure to the elements (including ultraviolet light, UV, from the Sun). One potential advantage of billboard signs is that once used, the sheets are available to the Coalition at no cost. Notice in the photograph how the dead kudzu is more "flattened" where the carpet was placed (right of center), than where the plastic sheet was placed (left of center). August 2006.

While these materials permitted air, and sometimes light, to penetrate, they were effective in reducing the kudzu mass to almost nothing because of their heavy weight. Most foliage under the rugs died. But few if any kudzu crowns were killed.

When Coalition volunteer Gill Newberry saw the results of the first tests in the Coalition experiment area, she immediately set out to apply the idea at Peter's Creek Preserve, where she is custodian. In addition to polyethylene sheets already in use, Gill placed rugs and large pieces of carpeting on top of kudzu. Some pieces were small, but all aided in the suppression of kudzu. These photographs show one example, covered (left) and uncovered (right). November 2007.

Laying plastic sheets on kudzu is a simple and quick way to treat a relatively large area without much labor. The ground need not be flat or free of debris.
A hot summer sun begins to flatten and kill the top foliage in a few days. The greenhouse effect cooks the plants when sheets are clear.
Leaving sheets in place for one full season of treatment kills half or more of the crowns, permanently eliminating the plants.
Leaving sheets in place for two full seasons kills 90% of the crowns, permanently eliminating the plants.
Black sheeting is more effective killing kudzu than clear sheeting, especially in partially shaded site where fully blocking light is more effective at keeping shade tolerant plants under control, and the Greenhouse Effect alone is insufficient to kill crowns.
The method is useful as a first treatment for relatively small areas that quickly "knocks down" (kills) foliage, in preparation for a different and more effective treatment that eliminates any surviving kudzu. That is, the method makes it easier to access kudzu crowns on the ground, either for surgical crown removal or chemical treatment. For relatively large areas, sheeting is useful following skid loader treatment to kill more crowns, as preparation for treatments requiring access to crowns.
Other plants are killed by this method: It is not selective. It essentially sterilizes the soil surface, killing all plants, whenever sheets are close to the ground.
Mosquitos breed in rainwater puddles that form on sheets.
Material costs are high, about $1,400 per acre for the kind of sheet materials found in hardware stores. This is more expensive than using herbicides, but less expensive than labor intensive methods.
1. Clear plastic sheets found in hardware stores for attic and basement use are susceptible to damage by UV (ultraviolet) light in sunlight. The damage causes sheets to split and fracture after about 6 weeks of exposure to the summer Sun. Black sheeting does not appear nearly as susceptible to this kind of damage.
2. Polyethylene sheets are available with UV blockers to greatly extend the useful life of sheets, at additional cost. The Coalition purchased 6 mil UV protected sheeting (T4 greenhouse film) from Jade Systems (828-891-5115), manufactured by Covalence Specialty Plastics (Monroe, LA). A 100 foot roll of 20 foot wide clear sheeting cost about $160 (about $3,500 per acre), which includes delivery. A similar roll of black sheeting (nursery black greenhouse film) costs about $120. In both cases freight is about 20% of the total cost. These are all 2007 prices.
3. The Coalition has not seen splitting or cracking failures of clear sheeting after almost two growing seasons. However, it becomes less clear, essentially turning white. By becoming more reflective of sunlight, it becomes less effective at producing high temperatures via the greenhouse effect. Lower temperatures kill fewer kudzu crowns.
Click here to see how sheeting fits in with other kudzu control methods for small property owners.