Field Demonstration of Simultaneous Establishment of a Pili Grass Ground Cover and Native Hawaiian and High-Value Hardwoods

Dr. Joe DeFrank, UH Weed Specialist
Poamoho Experiment Station O‘ahu

UPCOMING Forestry Field Day ~ Jan. 25, 2005

Poamoho Experiment Station

Contact: Dr. Joe DeFrank, UH Weed Specialist


Photo 01: Demonstration site prior to Pili/herbicides/ Tropical hardwood demonstration, 02/11/04.


Photo 1
Photo 02. Pili grass planted after weed flush and kill. Pre-herbicides applied after planting, 06/17/04. Photo 2
Photo 03. Pili grass growth 84 days after planting and prior to first mowing, 09/03/04.
Photo 3
Photo 04. Teak planted into Pili grass mulch on 09/17/04.
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Photo 05. Poamoho forestry demonstration after 2nd mowing on 11/23/04. Photo 5
Photo 06. Teak growing well in Pili mulch 67 days after planting on 11/23/04.
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Photo 07. Koa 2.5 years old in previous ground cover demo with emoloa (all dead now) plots to left, Pili grass center and bare ground/plastic weed mat to the right on 11/21/04.
Photo 7

Objectives: Demonstrate simultaneous establishment of grass ground cover of Pili grass and Hawaiian hardwoods.

In this reporting period maintenance work was conducted on an existing Koa/Pili grass mixed planting at the Poamoho Station. This work included pruning Koa tress to reduce wind damage and mulching established trees with Pili grass clippings. Chemical herbicides were also used in the Koa/Pili grass planting to determine the response of the grass to incidental contact with herbicide sprays. A spray mixture containing Gramoxone Extra (paraquat) and Goal 2X (oxyfluorfen) was applied to weeds mingled with the Pili grass and encroaching upon the base of the Koa trees. Applications were made with a backpack sprayer to simulate small farm technology anticipated in Hawaiian plantings. Weed control from the spray application was excellent and the Pili grass showed injury only on foliage that was contacted. Pili grass recovered from the herbicide injury and no harmful effects were observed on the Koa trees.

This experimental maintenance spray application provides evidence that weeds in a mixed planting of Koa and other tropical hardwoods with a Pili grass ground cover can be successfully controlled with currently available herbicides. This clean up spray application will be an important and useful tool for growers that want to use Pili grass in their tropical hardwood forest plantings.

Outputs and Outcomes

An important outcome during the current reporting period is the demonstration of successful post emergence weed control in a mixed planting of Koa and Pili grass with currently available herbicides. Successful weed control in any mixed species planting is difficult without causing injury to desirable species. The successful demonstration of the Goal/Gramoxone spray mixture will be helpful in requesting support to legalize this experimental technique from the companies representing these herbicides.

An extension to the project will be required to more fully address the objectives of this project.