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Wednesday - November 12, 2008

From: Kahului, HI
Region: Hawaii
Topic: Invasive Plants
Title: Invasive introduced sandburs in Maui, Hawaii
Answered by: Barbara Medford

QUESTION:

I live in Maui, Hawaii & I have a serious problem with Cenchrus spinifex and/or Coastal sandbur grass (weed!) it is everywhere, in my flower beds, in my gravel yardscape. Every time I pull it out it drops its very prickly burs that stick to everything and cover the ground, so how do I eradicate it without killing my other plants? The burrs/seeds are all over the ground where I pulled out the grass. How do I prevent them from growing? So frustrated!

ANSWER:

A grass itself, grassbur is a common, troublesome weed in pastures, lawns and other turf areas. This is one of those plants where we must admit a plant native to North America is a pest. Of course, it's not native to Hawaii, but there it's an introduced pest. Either way, you don't want it in your garden.

Grassbur thrives in overgrazed or otherwise struggling turf, especially nutrient-poor turf. Healthy turfgrass will typically outcompete Cenchrus. Improved turf health is the surest strategy for ridding the lawn of grassburs.

You said you were experiencing the sandburs everywhere. To give you some idea of how to develop a healthy turf that will resist the sandbur, read our How-To Article on Native Lawns. Also, here is an article about Sandburs and some possible controls. One disadvantage we have here is that the Lady Bird Johnson Wildflower Center is dedicated to the care and propagation of plants native to North America, which means we are not going to have grasses native to Hawaii in our Native Plant Database. Go to this site from the Maui County Extension Office, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. That webpage has contact information, and possibly they can help you select lawn grasses or ground covers that will crowd out the sandbur.

You really can't prevent the seed (sandbur) from growing. What you have to do is get to the plants before they set seed. You need to learn to recognize the plants when they are juveniles, before they get the burs on them, and get them out of the ground at that stage. Their native habitat is sandy or thicker soils, especially on disturbed ground. So, plowing up an area won't help a bit, it will disturb that soil and make fallow ground for a whole lot more grassburs to plant themselves. You can't spray weedkiller in the flower bed or the lawn, because it will kill the desirable plants, also. You might try careful squirts of a dilute weedkiller on the plants in the gravel yardscape; just be careful to do it on a windless day, so it won't drift onto something you don't want dead. But the main prevention of more sandburs is preventing the seeds from setting. Get them out of the ground first.