Observed more closely, the plot treated with the black sheet is darker and the kudzu appears "composted". Less organic matter is visible. Any kudzu found under the black sheet is in the form of pale sprouts. Sprouts are pale due to insufficient sunlight (etiolation). July 2005.
The plot treated with the clear sheet has more organic material (more ground is visible), and is lighter (drier?). Any kudzu found under the clear sheet consists of bunches of prolific green sprouts. July 2005.
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.
Both types of sheets knock down foliage, either as a way to access root crowns for surgical removal, or as a way to reveal debris that is otherwise hidden as shown in the photograph below. Thereby exposed to view, the debris is more easily removed for disposal. August 2006.
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.
Here is an example of using an area rug, before and after it is applied to a patch of kudzu. Note how much the kudzu compresses under the weight of carpet, illustrating the relatively low density of kudzu biomass. June 2007.
This photograph shows a vinyl billboard sheet over kudzu on uneven ground. Our original idea was that the heavy weight of carpet and billboard sheets would compress the underlying biomass, limit air circulation underneath, retain heat, and thereby accelerate decomposition. The Coalition finds that temperatures beneath these materials are not as high as under plastic sheets. Foliage kill is incomplete, and kudzu crowns are not killed. However, the Coalition finds these materials useful for flattening a tall mass of kudzu. May 2007.
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.
When all pieces were rounded up and folded for winter storage, the count was: 1 clear polyethylene sheet, 3 black sheets, 3 rugs, and 4 carpet pieces, for a total of 11 applications at this one site! The photograph shows the resulting stack. November 2007.
We find that it is much easier to fold and roll up these materials in the middle of the day because cool or cold morning temperatures make them much less flexible. Also, ants love the heat under sheeting. Be prepared for attack when moving or removing polyethylene sheets because these little critters can bite! Especially fire ants.
Sheeting: The Bottom Line