Chapter 14: Weed management

In Chapter 3: Site Preparation weed management programs were reviewed for bringing a pasture into ginseng cultivation. Options for pre-plant weed control include:

Pre-plant weed control practices
Broadcast translocated herbicides (Roundup, Crossbow, Garlon, others)	Repeated mechanical tillage during dry weather to uncover the root systems of perennial weeds
Cut or girdle trees, pull or push out stumps with roots attached	Grow cereal cover crops (1 or more rotations) to choke out weed growth

Complete control of perennials
The goal of the pre-plant weed control program is too eliminate 100% of all perennial weeds, including their root systems, prior to seeding the beds in mid September. The root systems of perennials including Canada thistle, field bindweed, and quackgrass spread by underground rhizomes. During tillage, rhizomes will be broken into smaller pieces. If these pieces are exposed to sunlight they will dry and be killed. However, if the pieces are large enough they can survive tillage and resume growth. Canada thistle is one of the worst weeds. Not only can the underground rhizomes re-grow, but seedheads (see Fig. 1) can blow seeds in from neighboring fields.

One application of a translocated herbicide may not be enough to completely kill all perennials. Ginseng growers should consider spraying a pasture in mid to late April, wait 2 weeks for the sod to die off, disc the field twice, and then wait to see if any of the perennials resume growth. The field should be carefully walked to look for any weed re-growth. There always seems to be a few perennials that will need selective spot spraying. Don’t neglect them! This is a crucial step that simply can not be overlooked.

Once the perennials have been taken care of, a cover crop of cereals grown during the summer will keep annual and biennial weeds from sprouting. It will also provide a significant amount of biosmass to till under to enrich the soil tilth.

Weed control options post-planting
Once the ginseng bed has been sown, a 1-2” thick layer of sawdust mulch is applied. While mulch will retain soil moisture and help deter slugs, its main purpose is to prevent light from striking weed seeds. As reviewed in Chapter 3 the majority of annual and biennial weed species have a light requirement in order to germinate. Even the most thorough weed management program prior to planting will not kill the vast number of weed seeds, which can lie dormant in the upper layers of the soil surface. They can remain dormant for years. As long as they don’t receive light however, they won’t germinate.

First year beds
Ginseng growers have found that even with a thorough weed control program prior to planting there will still be some weed in first year beds. During the spring months, as the young ginseng plants are first emerging, there will be weeds coming up as well. Growers in windy sites have found that it is hard to keep an adequate mulch layer on the planted beds the first winter. It may be necessary to re-apply mulch prior to emergence of the ginseng plants in the spring.

It is very important that weeds are pulled when they are first seen. They should come up fairly easily as they are growing in a fairly loose soil with mulch. If they are allowed to get too big however, pulling them up will also pull up the ginseng seedlings. Once weeds are pulled, be sure to smooth the sawdust mulch back in place to cover any exposed soil.

Second year beds
There will be fewer weeds during the spring of the second year. The sawdust mulch will have started to decompose and will have less tendency to blow away. The ginseng plants will have developed more of a shade canopy that will suppress weed seed germination. Some growers have stated that it may take only 4 hours every 2 weeks to walk through a quarter acre garden and pull any emerged weeds. Once again, if weeds are pulled when they are small and the mulch layer repositioned there should be very little impact on the ginseng plants.

Three and four year beds
By year 3 and 4 the ginseng plants will have started to completely cover the beds thus discouraging weed growth. The original layer of mulch may need to be replaced, as it will have decomposed extensively. Weed seeds blowing in from areas surrounding the garden will have an easier time becoming established unless mulch is re-applied

Herbicide use in established beds
Monsanto has a federal label for Roundup Ultra that can be used in ginseng. Northwest ginseng growers have found that one application to the beds in mid to late March, before the ginseng emerges, has been very effective in killing winter annuals, biennials, and any residual perennials that escaped the pre-plant weed control program.

Herbicide product

Application notes

Roundup Ultra, containing glyphosate, made by Monsanto Company

A nonselective, translocated herbicide with no apparent soil activity. Will travel to the root systems of perennial weeds, thus killing them. In non-bearing ginseng, apply Roundup with boom, shielded sprayer, hand-held, or wiper equipment. If used after the ginseng plants have emerged, avoid contact with any green foliage, stems, and exposed roots as severe injury to the ginseng can occur. Do not apply within one of harvest.

Pastures surrounding the ginseng garden
While the majority of the weed control effort will occur within the beds themselves, attention should be given to the area surrounding the garden. Many weed species produce seeds that can be carried by air currents. Surrounding pasture ground can be treated with broadleaf weed killers such as Crossbow (containing triclopyr and 2,4-D), or Weedmaster (containing dicamba and 2,4-D). When used during late April through mid June, these products will control the broadleaf weeds without harming the grass. A dense, vigorous stand of orchardgrass will out-compete annual bluegrass.

Turfgrass surrounding the garden
Ginseng growers can surround their gardens with turf grass to provide a firm surface to run machinery on. In areas west of the Cascades perennial ryegrass is the preferred turf species. A thick healthy stand of lawn ryegrass will produce few weeds. Less weed growth will ensure that fewer weed seeds will find their way into the ginseng garden.

A contaminant of turf grass is annual bluegrass (Poa annua). Annual bluegrass can survive the mild winters west of the Cascades and set seed all year long. These seeds commonly find their way into the ginseng garden. They can establish themselves if they land on a portion of the beds where the mulch is thin. If allowed to spread, annual bluegrass stands can overwhelm a first year field of ginseng. A new herbicide for turf, Prograss (ethofumesate) will provide effective pre- and early postemergent control of annual bluegrass in turf.