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Chapter 5 - Weed Control, No. 13, Spring 1989

Inversion - A Weed Control Technique in Dryland Cereals

Don Wysocki

Recently, atrazine inversion under the label ''Cheat Stop 90" became an option for cheatgrass control in dryland cereal in Washington and Oregon (see Summer 1988 issue of this newsletter). The effectiveness and low cost of this method make it an appealing option. However the decision to apply this option should also be based on a thorough understanding of the inversion process. Don Rydrych, STEEP Researcher and Weed Scientist at the Columbia Basin Ag Research Center, Pendleton, a principle investigator in inversion research, provided the following historic prospective and explanation of the inversion technique.

Development of the Inversion Process

Initial work on herbicide inversion began in the early 1960's as part of a research effort on downy brome control. Funding for this early effort came horn the Washington Wheat Commission and later from the Oregon Wheat Commission. At first, this methodology was known as ''pre-plant drill incorporation" but Rydrych introduced the term "inversion," Early experiments conducted by Rydrych at Lind and Pullman, WA, included inversion of such materials as diallate (Fargo), simazine (Princep) and atrazine (Aatrex), In the late 1960's, work on inversion was at a standstill because of safety problems with old-style drills, objections to soil residual herbicides and uncertainties about registrations.

Downy brome problems particularly in conservation and no-tillage systems encouraged STEEP and commodity funded research in the 1970's and 1980's. Work on downy brome control was focused to develop safe selective herbicide registrations, which would hasten adoption of conservation tillage technologies. During this period, trifluralin (Treflan) was registered as a soil incorporated herbicide for downy brome control, diclofop (Hoelon) was registered as a soil incorporated herbicide for downy brome and wild oat control, and metribuzin (Sencor or Lexone) was registered as a postemergence herbicide for downy brome control. These provided some options for downy brome control and aided the development of conservation tillage systems.

Research at this time also focused on inversion of herbicides. Rydrych and others showed that metribuzin, atrazine, diclofop, IPC and ethyl metribuzin could be used successfully with inversion techniques. This led to the registration of atrazine (Cheat Stop 90) in 1988. Currently registration is being sought for inversion application of metribuzin, clomazone (Command), chlorsulfuron (Glean) and ethyl metribuzin (Tycor). These may offer additional options in the future.

The Inversion Technique

Inversion is a preplant surface herbicide treatment which relies on soil displacement and mixing during seeding. It can be used in conventional and conservation tillage systems. Herbicides are surface applied before seeding and soil mixing, and displacement during seeding redistributes the herbicide to areas away from the seed (Fig. 1). Drill openers throw treated soil away from the seed zone creating a safety zone in the seed row. Firming by the press wheels prevents treated soil from slipping back into the seed row. Hoe or shovel openers produce different herbicide distributions than double or single disk openers (Figs, 2 and 3). Hoe openers produce a wider safety zone because they move more soil out of the row. Nonselective herbicides require a wide safety zone to prevent crop damage. Consequently hoe drills are required for inversion of materials such as atrazine or trifluralin. Disk drills, however, can be used where cereals are tolerant of applied herbicides, such as diclofop.

Fig. 1. Herbicide distribution achieved by the inversion process.

Fig. 2. Herbicide distribution and safety zones produced by inversion using hoe openers.

Inversion is a shortened modification of standard soil incorporation. Standard incorporation uses a herbicide application and shallow tillage operation to produce a 2- to 3-inch herbicide zone at the soil surface (Fig. 4). Seed is then placed below this zone. Inversion uses the drill to incorporate and redistribute the herbicide and eliminates tillage operations. This conserves time, labor and plant residue cover. Thus the inversion process is well suited for conservation tillage systems.

Using inversion techniques requires agronomic practice similar to other farming methods. Fields should be free of emerged weeds using chemical fallow treatment, tillage aided herbicide treatment, or conventional tillage.

Fig. 3. Herbicide distribution and safety zones produced by inversion using double disk openers. 

Fig. 4. Herbicide distribution produced by standard soil incorporation.

Preplant herbicide is applied shortly (1 week or less is recommended) before seeding. During seeding, drill openers mix and redistribute the herbicide to permit establishment of the crop.

There are some precautions to consider when using an inversion program. The process will not work safely with nonselective herbicides (atrazine) when furrows slip or slump back into the seed row. This can happen because of steep slopes, excessively dry soil conditions, improperly adjusted drills or excessive drilling speeds.

Development of the inversion has been through the efforts of STEEP researchers, Wheat Commodity funding and industry support. Understanding the inversion process will assist growers in devising weed management strategies for their situations.

Use of Trade Names

Research results are given for information only and are not to be construed as a recommendation for an unregistered use of a pesticide. Always read and follow label instructions carefully. To simplify the information, trade names have been used. Neither endorsement of named products is intended nor criticism implied of similar products not mentioned.


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