Weekly Word on Weeds

This is the first article this season from Dr.Joe Neal, weed scientist with the Horticulture Department from NC State University.


With freezing temperatures still in the forecast it is difficult to think about summer weeds. But, now is the time to begin summer annual weed management.

First line of defense: Mulches
Before ornamental plants leaf out, and herbaceous plants emerge, this is also a good time to apply a fresh layer of mulch to landscape beds. Not only does this conserve soil moisture and improve the aesthetics of the beds, it also will cover and shade weed seeds to prevent germination and establishment.

When mulches are not enough:
Preemergence herbicides work by preventing the establishment of weeds from seed. That means the herbicides must be applied several weeks before weeds germinate. Apply preemergence herbicides now to control spring-germinating weeds such as crabgrass, spurge and oxalis.

Common herbicides used in landscape beds include Barricade, Pendulum, Surflan, and Snapshot TG. Each works on summer annual grasses (like crabgrass) but differ in how well they control broadleaf weeds. Generally, Snapshot and Surflan are better on broadleaf weeds; Barricade tends to excel on spurge, pendulum may be a little better on horseweed. These herbicides also differ in their safety to ornamental plants. Granular formulations of herbicides are safer on ornamental plants than spray applications. But, when applied before budbreak, liquid applications may be made over the top of most woody ornamentals. In herbaceous ornamentals, you must be careful in your choice of herbicides. See Hort Information Leaflet No. 644 http://www.ces.ncsu.edu/depts/hort/hil/landscape-index.html for more information on weed management in color beds.

Freehand – a new herbicide labeled for use in landscapes and nurseries:
Freehand is a granular combination of pendimethalin plus dimethenamid-p. It controls many summer annual weeds including crabgrass, oxalis, and spurge. It is one of the few herbicides that controls doveweed. It is also as effective as Pennant Magnum for the suppression of yellow nutsedge.

WWWeeds notes will be archived on my web site. http://www4.ncsu.edu/~jcneal/

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.