Friday, August 24, 2012

Invader in the Lawn



A small-leafed, weed with purple flowers is spreading over my lawn. It has nasty stickers and a long tap root.  Sensitive plant is one name of this weed; sleeping (or sleepy) grass is another.  The name comes from the fact that the leaves close when they are touched. In Hawaiian it is called pua hilahila.

This invader commonly grows in well drained soils that have been disturbed such as lawns, orchards, pastures and roadsides.  It does not grow under forest canopies.  It is a real scourge as it crowds out other plants and grows up into taller ones.  It appears from sea level to about 4,000 ft. in elevation. The sensitive plant can also be a fire hazard in dry terrain. 

Control
Physical:  Hand weeding is obviously difficult due to thorns and a strong, woody root.  In pasture land, it can be controlled by intensive grazing where cattle will kick the pua hilahila out of the way to get at the grass beneath. 

Chemical: The sensitive plant can be controlled with the herbicides Roundup and Garlon. Roundup will also damage or kill your lawn. In lawns, herbicides containing the active ingredient 2,4D (Crossbow, Trimec Southern) are fairly effective and should not damage the lawn.  Damage can occur to carpetgrass when Trimec Southern is applied. Locally it has been observed that no damage occurs when applying Garlon to many of our lawns. When in doubt, spray a small portion of the lawn and wait for 2 weeks to see if any damage occurs.  If plants are disturbed before spraying, the leaves will fold up and the herbicide will be ineffective. For further information go to the following website: http://www.ctahr.hawaii.edu/invweed/WeedsHI/W_Mimosa_pudica.pdf