METHODS - doerc200002

ERDC TN-DOER-C20

March 2001

demonstrations of this strategy will be discussed: Herbert Hoover Dike, Lake Okeechobee, FL, and

Eagle Island CDF, Wilmington, NC.

METHODS: An innovative technology for wiping herbicides was identified from participation in

the National Roadside Vegetation Management Association (NRVMA) annual conferences. Ex-

hibits of new equipment and techniques were presented at annual conferences in 1995 and 1996.

A wiper applicator was displayed by Cross Equipment Company, Inc. (CECI), Sebring, FL, at the

1995 annual NRVMA conference in New Orleans, LA, and at the 1996 annual conference in

Minneapolis, MN. Mr. Dana Ritenour, CECI, described the effectiveness of the wiper applicator

and agreed to demonstrate the use of the wiper to control undesirable weedy vegetation on dredged

material at Corps projects in cooperation with the U.S. Army Engineer Research and Development

Center (ERDC).

Lake Okeechobee, FL. The first demonstration was at Lake Okeechobee on the Herbert Hoover

Dike, which was constructed with dredged material removed from Lake Okeechobee in the1970's

to establish an inner rim canal. The dredged material was predominantly sand and marl with a soil

pH of 8.5. Contractors for the U.S. Army Engineer District, Jacksonville, had been fertilizing and

mowing vegetation on the approximately 282-km- (175-mile-) long dike system for a number of

years. Mowers had cut the desirable vegetation Bahia grass and Cynodon dactylon (Bermuda grass)

extremely short, below 25.4 mm (1 in.), resulting in suppressed regrowth of these species.

Undesirable vegetation such as napier grass and Spanish needle had become established on large

areas of the dike (Figure 3). High levels of fertilizer were applied for maximum growth of Bahia

grass when the presence of that species was extensively reduced. Consequently, the undesirable

vegetation continued to grow and spread to even larger areas of the dike. Management of vegetation

was changed in 1995, after ERDC was asked to assist the Jacksonville District to reduce fertilizer

applications and provide guidance and demonstration of innovative technologies in vegetation

management on dikes and levees constructed from dredged material. The Florida State Water

Management Districts were requiring all nutrient inputs to Lake Okeechobee to be reduced. The

loading of nitrogen and phosphorus was required to be reduced to control nutrient-related eutrophi-

cation in Lake Okeechobee and to improve the water quality of the lake under the South Florida

Ecosystem Restoration Program.

Soil samples were collected for each mile of the Herbert Hoover dike from each side of the dike for

the entire dike system. The soil samples were sent to the University of Florida at Gainesville for

soil fertility testing. Minimum fertilizer for the maintenance of desired vegetation was recommended

based on the soil test results. These fertilizer rates were applied to the dike. In addition to reduction

of applied commercial fertilizer being evaluated, other ways to improve soil fertility using available

residual materials and management of vegetation were considered. The application of recycled soil

manufacturing technology (RSMT) and the use of plant species such as perennial peanut (Arachis

glabrata Benth. cultivar Florigraze) that required less fertilizer and mowing were also evaluated in

the demonstration. Demonstration plots were established using RSMT by incorporating cellulose

in the form of yardwaste (Figure 4), bagasse (Figure 5), melaleuca compost (Figure 6) and lake

debris (Figures 7 and 8) in combination with biosolids such as N-Viro Soil (reconditioned sewage

sludge) and BionSoil (reconditioned animal manure). These plots improved the soil fertility

substantially but also increased the growth and amount of undesirable weeds whose seed had

accumulated in the dike soil over the years (Figure 9). Consequently, weed control was required on