Farm Progress

NO-TILL KNOW-HOW with Dr. John Bradley

February 1, 2001

6 Min Read

Weed Control Strategies for No-till Crop Production Using the proper weed control strategy is crucial to success in no-till. A burndown application of a herbicide that cleans your fields of all existing vegetation before planting, combined with follow-up herbicide applications using correct rates and timing, are key elements of a successful weed control strategy. Controlling weeds usually becomes easier, more dependable and less expensive in a no-till system, especially when combined with the technology of Roundup Ready[R] crops and Roundup UltraMAX[TM]. Clean fields before planting are important in all crops. By a "clean field" I am referring to a field where all live vegetation, including cover crops and/or weeds, has been terminated before no-till or con-till crops are planted. Starting with a clean field results in better yields for any system, but in a no-till system it should be your number one priority.

COTTON Emerging cotton seedlings can not compete effectively with weeds for moisture, sunlight and nutrients - especially in the spring when young plants are struggling to establish a sufficient root system. Experienced no-till growers have found that a two-application burndown strategy is most effective, since cotton-growing regions are optimum environments for early weed growth. Roundup UltraMAX is simple to use and very effective. However, it is important to remember that application timing is critical for best results. To conserve soil moisture, control cover crops with at least 26 ounces of Roundup UltraMAX per acre, two to three weeks before planting, or as soon as the cover is 20 to 30 inches tall. To get optimum control on weedy fields, set your sprayer to maintain at least 30 percent overlap above the tallest vegetation.

For economic reasons as well as effective in-crop weed control, it is important to match correct rates per acre to weed size, especially when dealing with ryegrass. Treat one- to three-inch weeds in Roundup Ready cotton between cotton emergence and the fourth true-leaf stage (before the fifth cotton leaf is the size of a quarter). During this growth phase, either one or two over-the-top applications of Roundup UltraMAX can be made, depending on the severity of weed infestation. If two applications are needed, these should be timed to allow for incremental cotton growth of at least two nodes AND a 10-day minimum time period between applications.

A broadcast sprayer and a post-direct hooded or shielded sprayer should take care of all herbicide applications in a no-till situation. For applications after the fourth true leaf stage in Roundup Ready cotton, a post-directed application of Roundup UltraMAX should provide total coverage across rows. Nozzles should be set to keep the spray at or below the cotyledon scar to avoid contact with cotton leaves.

One of the biggest advantages to using a no-till system combined with Roundup Ready technology is the elimination of residual herbicides where possible. According to comparisons among different tillage systems on Monsanto Centers of Excellence (COE) research farms over a three-year period, a no-till program produced more than $20 profit per acre over conservation tillage and $45 profit per acre over conventional tillage. The additional profit per acre was primarily due to lower overall herbicide costs. The treatments with the lowest cost across all COE locations were non-residual, no-till systems with Roundup Ready cotton. All treatments or comparisons had the same effective weed control.

SOYBEANS Weed control in soybean fields has become much easier since the introduction of Roundup Ready soybeans, especially when no-tilled. When using Roundup UltraMAX with Roundup Ready soybeans, growers can control most weeds, large or small, annual or perennial. And, Roundup UltraMAX can be applied over the top of Roundup Ready soybeans anytime between emergence through flowering. Many growers also find that the Roundup Ready system is easy to use because they can eliminate tank mixes with residual herbicides, and they no longer have to worry about crop injury to soybeans while trying to keep weeds in check. Most growers who have adopted Roundup Ready soybeans have found that properly timed Roundup applications are all that is necessary for effective weed control, which ultimately leads to the most profitable system for conservation tillage. Use of other herbicides in a tank mix with Roundup UltraMAX often adds expense and increases the risk of crop injury or carryover, depending on the other herbicides being considered. After years of research, Monsanto has concluded that Roundup UltraMAX alone is the best choice for most weed control situations.

Just like cotton, an effective no-till soybean production system starts with a burndown application of Roundup UltraMAX. In the Delta and Mid-South, I usually recommend 24 to 26 ounces per acre for preplant burndown. Typically in the Southeast, a preplant burndown application from 24 to 48 ounces per acre should be used. Of course, these are general rates. Actual rates should be based on weed species and size. Another application of Roundup UltraMAX may be used approximately two to three weeks after planting, when weeds are two to four inches tall in the Delta and Mid-South and three to six inches tall in the Southeast. New flushes of weeds should be controlled with sequential applications of Roundup UltraMAX. Timing of sequential applications should be based on weed size and will vary according to location and environmental conditions. The combined total of preplant, in-crop and preharvest applications of Roundup UltraMAX should not exceed three quarts per acre. Refer to the Roundup UltraMAX label for more information on recommended rates and timing of herbicide applications for specific weeds.

CORN For effective weed control in no-till corn, once again, it is important to start with a clean field. I recommend using Roundup UltraMAX on Roundup Ready corn. Roundup UltraMAX may be applied on Roundup Ready corn before, during or after planting corn. For in-crop applications on Roundup Ready corn, the label offers options for using Roundup UltraMAX alone or in tank mixes. Read the label directions for more detailed instructions on correct timing and application rates of Roundup UltraMAX on Roundup Ready corn.

Monsanto also has a complete line of preplant residual and post-emergence herbicides that can be used in a no-till corn system. Some of these herbicides include Harness[R], Harness Xtra[TM], Bullet[R], Degree[TM], Degree Xtra[TM], Permit[R] and Lasso[R]. See your local Monsanto dealer or representative for specific herbicide recommendations.

Grain/commodities harvested from Roundup Ready[R] corn and Roundup Ready corn with YieldGard[R] is approved for U.S. food and feed use, but not yet approved in certain export markets where approval is not likely to be received before the end of 2001. As a result, the Grower is restricted from introducing such grain/commodities into channels of trade where the potential for export to such markets exists. The Grower must channel such grain/commodities for feeding on farm, use in domestic feed lots or other uses in domestic markets only. Growers should refer to Monsanto's Technology Use Guide for information on crop stewardship regarding the potential movement of pollen to neighboring crops. For assistance in locating domestic outlets for all other corn grain/commodities, view the ASTA web site at or contact Monsanto at 1-800-768-6387.

ALWAYS READ AND FOLLOW LABEL DIRECTIONS. Roundup herbicide brands will kill plants that do not contain the Roundup Ready[R] gene. Harness[R], Harness Xtra[TM], Bullet[R], Degree[TM], Degree Xtra[TM], Permit[R] and Lasso[R] are restricted use pesticides. Harness is not registered for use in the state of New York. Roundup UltraMAX[TM], Roundup Ready[R], Harness[R], Harness Xtra[TM], Bullet[R], Degree[TM], Degree Xtra[TM], Permit[R] and Lasso[R] are trademarks of Monsanto Company. [C] 2001 Monsanto Company.

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