AURORA - Nursery crop researchers at Oregon State University's North Willamette Research and Extension Center (NWREC) in Aurora are testing new ways to efficiently prevent weeds from growing in nursery containers.

They hope that new methods will prevent weeds in container-grown stock while protecting water quality. Hannah Mathers, nursery crops specialist at the OSU center, and her colleagues are comparing the effectiveness of "novel" methods of weed control in nursery-grown container stock. These methods include:

  • Bark mulch treated with preemergent herbicides "Goal" or "Surflan."


  • Collars of fabric that cover the surface of the pot soil and let the plant through, called "Geodiscs." These let water and air in, but keep light out, thereby preventing weed growth.


  • Collars of plastic called "Environ Lids" that snap over the top of the pot, but let the woody plant stick out.


  • Paper mache pellets, a by product of newsprint production called "Penn Mulch." These absorb twice their volume of water.


  • Wool pellets, a by-product of sheep shearing, called "Wulpack." These also absorb twice their volume of water.


  • Perforated plastic bags that the pot is inserted into, called "Weed Bags." The plastic bags let water and air in, but keep out light.

The researchers are comparing these novel methods to the effectiveness of weed control of three types of more traditional pre-emergent herbicides including Snapshot, Surflan and Goal. And they are looking at the effects of these on nursery plants in the pots.

Preliminary results indicate that the Geodiscs are working well to control weeds in the containers. But they are hard to put on. The Weed Bags are also extremely effective, but also are labor intensive, said Mathers.

Organic growers might be particularly interested in some of these novel methods. Since they don't use chemical herbicides, weeds are their number one problem. "Nursery growers estimate that they spend $500 to $2,000 per acre for removal of weeds by hand," said Mathers.

Nurseries traditionally depend on aerially broadcast granular preemergent herbicides to prevent weeds from germinating in container-grown stock. But because some of it lands on the ground rather than on the surface of the soil in the pot, these granular herbicides pose potential water quality problems.

Misdirected herbicide granules can be quite common, said Mathers. One study in Alabama measured as much as 86 percent of the granular herbicide falling between the pots, onto the ground, not on the soil surface of the pot, she said.

Also, pre-emergent herbicides don't get rid of weeds already growing in nursery plant pots.

Lost granules can leach into the soil, run-off to other sites and affect other non-target vegetation. Herbicides are known to contaminate ground and surface waters more than insecticides, she explained.v The Oregon nursery industry, the biggest agricultural industry in the state, is producing at least half of its landscape plants for the nation in containers, rather than grown in the ground, she said.

Weeds compete with the container-grown nursery crop for resources. They absorb nutrients and water, block light and prevent good air circulation around a nursery plant. Weeds can also reduce the marketability of a container-grown crop. "If the customer observes poor weed control and perceives that the nursery has sloppy or inferior control of weeds, it may make a poor reputation for the seller," Mathers said.

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Hannah Mathers, 503-678-1264