Implementation Guidance for the Control of Undesirable Vegetation on Dredged Material

ERDC TN-DOER-C20

March 2001

Implementation Guidance

for the Control of Undesirable

Vegetation on Dredged Material

PURPOSE: The purpose of this technical note is to provide guidance for implementing selected

management practices to control undesirable vegetation on dredged material.

BACKGROUND: Dredged material is normally removed from navigable waterways or from

aquatic environments and placed in confined disposal facilities (CDFs) or in other upland environ-

ments. Natural colonization is allowed, although in many cases undesirable vegetation such as

Phragmites communis (common reed), Salix sp. (willow), Populus sp. (poplar and cottonwood),

Bidens bipinnata (Spanish needle), and/or Pennisetum purpureum (napier grass) becomes estab-

lished. Recently, CDFs have filled, and new CDFs are extremely difficult to find. Removal and

beneficial use of dredged material are becoming more desirable to provide storage space for future

dredged material. However, undesirable vegetation has interfered with CDF operations and the

potential beneficial use of dredged material as a high-quality material. Elimination of undesirable

vegetation will enhance the quality of the dredged material for use in beneficial products such as

manufactured topsoil, engineered soil capping material, building blocks, and construction flowable

fill. Under the Dredging Operations and Environmental Research program, demonstration projects

were conducted to develop management strategies to control undesirable weedy vegetation on

dredged material.

INTRODUCTION: When dredged material is placed in a CDF and/or an upland environment to

construct dikes or levees, various management strategies are used ranging from no management to

different degrees of management. No management normally results in a wide variety of aggressive

vegetation colonizing the site. In many areas, the vegetation that will establish is common reed or

Phragmites (Figure 1), willow, poplar, and cottonwood as well as any weeds that might exist in the

adjacent surroundings (Figure 2).

There are many approaches to controlling undesirable weedy vegetation for various situations:

selective herbicide spraying, mowing, fire, and/or tillage. In some cases improper mowing of

vegetation has actually resulted in increased amounts of undesirable vegetation. In these cases,

mowing was too close to the ground, eliminating desirable vegetation such as Paspalum notatum

(Bahia grass) and allowing undesirable vegetation such as napier grass to become established

(Figure 3). Selective herbicide sprays have been used successfully for specific locations. Tillage is

used in agriculture in combination with selective herbicides. Fire is used in certain situations to

control undesired vegetation. Fertilization and soil management have been used in combination with

mowing. In situations where spraying, fire, and tillage are not permitted, the wiping of selective

herbicides can be more appropriate and effective in combination with minimum mowing.

This technical note describes an innovative management strategy for maintaining desirable vegeta-

tion while controlling undesirable weedy vegetation on dredged material where use of some weed

controls such as fire, herbicide spraying, and tillage is not allowed or practical. Two examples of