Image
Photo by Paul David Blakeley. © Copyright 2005. All Rights Reserved.

Kudzu does not thrive in shade. It relishes sunlight. When light is deficient, leaves are small and pale. In the complete absence of light, kudzu grows pale sprouts without leaves. The inventor Jack Callahan is working on the idea of planting tree seedlings in kudzu patches. The concept is to grow shade and stunt the growth of kudzu. The challenge, of course, is to protect the seedling from being swamped by the kudzu for many years!

Perhaps the best direct way to shade-out kudzu is to lay opaque materials on top of kudzu. This can be plastic sheets, or mulches of spreadable material (especially effective are grass clippings), even discarded vinyl billboard signs. I turns out that materials lying on top of kudzu in the fierce summer sun of the southeast U.S. is more important as a "thermal treatment" instead of a "shade treatment". Merely "shading out" kudzu stunts its growth, but it does not kill it.

Using a thermal treatment on kudzu might bring to mind the use of fire. On the other hand, using heat produced by the sun is a well known method for sterilizing soil, and is called solarization. Such heat can also kill kudzu foliage. Even a miniature hothouse is a treatment possibility! The Coalition first heard the idea of using polyethylene sheets to treat kudzu from the late Dr. Larry Nelson at Clemson University, who was a member of the Coalition Board of Directors.

Preliminary tests in 2004 used black polyethylene (plastic) sheets. The first photograph shows Coalition cofounder Newt Hardie (left) and Larry Nelson. Note the wrapped tree trunk in the second photograph that was intended to prevent vines from climbing into the tree. But alas, it didn't work. The vines climbed the tree by sneaking underneath the sheet, as the closeup in the third photographs shows! September 2004.

Image Image Image

Vines continue to grow out from beneath the sheeting and are unaffected by the treatment. Kudzu is not completely killed under sheets. Instead it produces pale sprouts due to light deficiency, as seen in the photograph. September 2004.

Image

Clear sheets or black? There's more than enough kudzu for testing . . . September 2004.

Image Image

Light Absorption by Black Plastic Sheets

All objects absorb some light, and that absorbed light causes an object to heat up. The darker the object, the greater the amount of light absorbed. The brighter the light, the hotter the object becomes. A black object (which absorbs the most light) placed in sunlight (which is very bright) gets quite hot. So, black sheets on top of kudzu get very hot; the hot sheet heats the air and kudzu beneath it; and, this heat could kill the plant.

The Greenhouse Effect from Transparent Plastic Sheets

Plastic sheets transmit visible light, but block the escape of heat. So, clear sheets on top of kudzu lets visible sunlight in; the sunlight is absorbed by the plant and ground beneath the sheet; the absorbed light is converted into heat which cannot escape from underneath the sheet, and, this heat could kill the plant.

Which Type of Sheet is Best?

As the previous descriptions explain, the heat from black and clear plastic sheets are due to different causes. It is not possible to know ahead of time which method delivers the most heat to kudzu. Depending on circumstances, either type of sheet might deliver more heat to the plants beneath them.

However, at this time we do not know whether heat is the most important factor for controlling kudzu using plastic sheets. For example, perhaps it is better to prevent light from reaching the kudzu to prevent photosynthesis (black plastic sheet), and thereby starve the plant during heating. On the other hand, perhaps it is better to allow light to reach the kudzu during heating so photosynthesis occurs when the plant is too hot (clear plastic sheet), and thereby over-stress the plant. Only tests can reveal which type of sheet, and for what reasons, works best to control kudzu.

Lou Adams
July 2005


PROJECT TITLE: An Alternative to Herbicides for Controlling Kudzu in Riparian Zones and Other High Risk Areas.

PROJECT COORDINATOR: Dr. Larry Nelson

ORGANIZATION: Dept. of Forestry and Natural Resources, Clemson University

Address:
272 Lehotsky Hall
Clemson University
Clemson, SC 29634

Telephone: 864/656-4866
Fax: 864/656-4786

E-mail address: lnelson@clemson.edu

EXECUTIVE SUMMARY

Kudzu [Pueraria Montana (lour.) Merr] is a well-established, invasive weed problem in the southeastern United States. It grows at the exclusion of other native species and is estimated to occupy more than a million forestland acres. In urban areas it occupies vacant lands and provides cover for rodents, snakes and other pests. The primary recommendation for controlling kudzu involves the use of herbicides. Currently registered products can be effective but the best products are generally prohibited near streams or wetlands and present a risk to sensitive crops, shade trees, gardens and other sensitive urban areas. An alternative control method is needed. This proposal discusses the use of black plastic sheeting to overheat and provide top-kill of kudzu plants. Alternate periods of covering and uncovering to allow for consecutive periods of top-kill and re-growth will be used to gradually deplete the regeneration capacity of roots. Success would allow kudzu control in areas that are nearly untouchable with herbicides. Control could be accomplished without risk to water quality or other plants and this method of control would be of benefit on both rural and urban sites.

Background and Justification

Kudzu be very difficult and expensive to control even with the best herbicides. In order to convert kudzu sites to productive forest, cropland or other uses, total eradication is a necessity. The vines can grow at a rate of one foot per day, can form roots at each internode and can rapidly reoccupy a site if plants or plant parts escape treatment.

Effective herbicides are available for controlling kudzu. However, the best products for eradication are Tordon 101M and Tordon K. Both products contain picloram and are restricted use products that cannot be used on stream banks or where entry into water is likely to occur. Glyphosate formulated as Rodeo and Accord and triclopyr as Garlon 3A can be used in and near water, but these products are less effective than the Tordon products and must be applied several years in succession for effective control. An alternative control method is needed for this situation. One possibility is the use of black plastic coverings for use on stream banks and as buffers between streams and areas where broadcast herbicide applications are acceptable. This method would also be highly desirable for kudzu patches on urban sites where herbicides might damage shade trees, gardens and other sensitive plantings. Black plastic applied during the heat of summer provides effective top kill of a variety of plants. Trials are needed to determine whether plastic coverings can be used economically to provide top-kill and eliminate regeneration capacity of the roots.

Objective

Evaluate the effectiveness of black plastic covering for eradicating kudzu.

Approach and Procedures

Tests of plastic covering will involve treatments of alternate periods of time in which the kudzu is covered and un-covered to allow for re-growth. Treatments will cover the period of June 1 through September 30, 2005. The objective is to provide top-kill of the kudzu and depletion of carbohydrate reserves in the roots. Treatments will include:

  1. Alternate covering for 1 week, and three weeks uncovered.
  2. Alternate covering for 1 week and four weeks uncovered.
  3. Alternate covering for 1 week and five weeks uncovered.
  4. Alternate covering for 1 week and six weeks uncovered.
  5. Cover for the entire growing season.
  6. Control — no covering.

(The sequence of covering and uncovering for each treatment would be repeated until the end of the growing season.)

If one week is not long enough to provide total top-kill, the above treatments will be changed to include 2 weeks of covering with the same uncovered growth periods.

Plots will be 0.1 acre in size and arranged in a completely random or randomized complete block experimental design with three replications. Percent control will be evaluated using standard analysis of variance.

The study will be conducted on the Clemson Experimental Forest or on another appropriate site in the upstate of South Carolina. It will be initiated in spring of 2005 (mid April or when the kudzu begins to grow), and treatments will continue until the first heavy frost (mid to late November). Evaluations of percent control will be conducted in early May of 2006. Results will be used to determine the desirability of continuing treatments through the 2006 growing season.

All work will be conducted by Clemson University personnel (Larry Nelson, graduate student and technicians).

This work could lead to extensive and improved kudzu control in riparian zones, and would enable control on difficult urban sites in cities such as Greenville, Spartanburg, York and other upstate towns with extensive infestations.

Budget

Expenditure Justification Cost
Graduate Student & Labor Field work, data collection and analysis,
report writing. Assistantship - $11,000
Labor ($6.25/hr X 75 hr)
$8,000 (grad-student)
$460 (labor)
Materials Plastic sheeting (20 x 100 ft rolls @ $45.97
each x 39 rolls = $1,800), plot
markers, labels, rebar ($300)
$2,100
Travel To and from the site. (60 miles X 12 trips
X $.35/mile)
$250
    $10,810

Outcomes

The overall success of this project would lead to a reduction in the use of herbicides for kudzu control and would provide a control option on sites where water quality is a primary issue.

As the Clemson Forestry herbicide specialist, I receive dozens of inquiries each year on how to control kudzu on sites with streams, near sensitive crops, beneath desirable shade trees and on urban and suburban sites where effective herbicides cannot be used. I am currently in discussions with the Spartanburg Men's Garden Club on kudzu control options within the city limits. This proposed project, might provide an immediate control option for Spartanburg and other infested municipalities. It would also provide a control option that does not exist along streams and wetland areas where water quality is a critical need.

The success of this program could be incorporated into our overall outreach program on invasive pest plant species. The information would be distributed to counties through brochures, publications and our web page. Results would be readily accepted by the South Carolina Chapter of the Southeastern Exotic Pest Plant Council and other groups interested in controlling invasive plants.



The Coalition worked closely with Larry Nelson. We also visited each other. Here are photographs of a Coalition trip to visit Larry and his graduate student Casey Newton (in tan duck bill hat and light blue shirt) at Clemson University to discuss their research. We were especially interested in their method of monitoring temperature underneath sheets using thermocouples with digital readouts. August 2005.

Image Image
Image Image
Trip Photos by Paul David Blakeley. © Copyright 2005. All Rights Reserved.

Here are the handouts provided by Larry Nelson during our visit, which summarize the status of an ongoing experiment with black polyethylene sheets. Click on either one to see larger images and to read the text.

Image Image

After the sudden death of Larry Nelson in August 2006, his graduate student Casey Newton completed the research. Casey and associates created a poster (530 KB PDF) that summarizes the results of this research. He graduated from Clemson University with a Masters Degree in August 2007. The following story in the Fall 2007 issue of "Clemson Impacts" reported on Casey's graduation. Click on it to see a larger image and to read the text.

Image