Guidelines

Managing weeds in your fields should be targeted to the practices that allow you to optimize yields. Whether the field contains crops with Roundup Ready technology or not, certain weed management principles apply. Following are a number of key factors that can impact your ability to optimize your yields, along with associated tips to help you manage through your situations.

Actively growing weeds in your field at planting will compete with the crop and should be eliminated prior to planting.

  • Already established weeds rob crop seedlings of nutrients and water and reduce crop yield
  • When weeds are present at planting it is more difficult to get a crop established and may cause a poor stand
  • Weeds damaged by the planter are harder to kill with later herbicide applications
  • Waiting to control weeds with a postemergence herbicide application means weeds may be larger and harder to control

Excellent weed control in your field until crop canopy can be an indicator of good weed control throughout the season.

  • Weeds present at crop canopy are competing with your crop and could be reducing yield
  • Uncontrolled weeds can go to seed and provide a much larger weed seed bank for next season
  • Weeds make harvesting difficult and seeds may be distributed to additional fields via the harvesting equipment
  • Weeds at harvest can impact grain quality and lead to dockage for high trash levels

Include 2 or more crops in your crop rotation and ideally rotate to a different crop each year.

  • Crop rotation offers the ability to change cultural practices like planting dates and fertility programs which help reduce certain difficult-to-control weeds from becoming established
  • Crop rotation also allows for tillage or another herbicide program or additional modes of action which help prevent some weeds from becoming dominant in the system
  • Crop rotation can break insect and disease cycles by reducing plant material where they may overwinter

Use a broad spectrum soil active residual herbicide in the corn season of the crop rotation and in soybeans when tough-to-control weeds are present.

  • Early season weed control is imperative for maximum yield potential
  • Residual herbicides provide early season control and allow you the opportunity to better time postemergence applications
  • An early-season residual treatment reduces the overall weed pressure giving your postemergence program applied later a much better chance of success so weed shifts don’t become an issue
  • In soybeans weeds can grow beyond recommended treatment heights quickly and soybean yields can be reduced

The addition of a non-glyphosate herbicide reduces the sole use of glyphosate which can decrease the risk of developing of weed resistance.

  • A residual treatment helps control tough, yield-robbing weeds like waterhemp, lambsquarters, and common ragweed and can help lower the risk of weed resistance development
  • Use of a non-glyphosate herbicide adds another mode of action and reduces the sole use of Roundup® agricultural herbicides which will lessen weed population shifts
  • The use of residuals in corn and in some soybean weed management systems has shown increased yields because of reduced weed pressure

Use the full, labeled rate of Roundup or glyphosate herbicide based on the most difficult-to-control weed in the field.

  • Lower rates can allow weed escapes which may require a second trip to control, reduce crop yield and set seed for next season
  • The use of lower than labeled rates can lead to poor weed control and potentially “select” for resistant weeds
  • Recommended, full labeled rates are set after years of research show the best likelihood of commercially accepted control. Low rates, especially when spraying in less than ideal weather conditions, most often lead to poor results and dissatisfied customers. Plus, weed escapes build next season’s weed seed bank

Control weeds in corn before they reach 4 inches tall and in soybeans before they reach 8 inches tall.

  • Taller weeds become harder to control. If you allow weeds to continue to grow, a herbicide application may not give you adequate control and some may survive to create potential resistance risks
  • Weed competition studies were conducted with no preemergence herbicide products, but plots were maintained weed free after postemergence Roundup agricultural herbicide application. There was substantial yield loss in corn when weeds were allowed to grow more than 4 inches before postemergence application

The goal is to reduce weed populations from year to year, allowing for more efficient use of herbicides and other cultural practices to control weeds.

  • If weeds are allowed to survive and set seed, dramatically higher weed populations may result the next year. As an example, waterhemp can produce 300,000 seeds per plant
  • If you allow certain tough-to-control weeds to survive then you may accelerate shifting weed species to more difficult-to-control weeds. Shifting weed problems may require a substantially different weed management approach

Tillage can be very valuable in many situations and should be considered as an alternate weed control practice where appropriate.

  • Tillage serves as another way to control weeds and break certain weed patterns
  • Tillage reduces complete reliance on herbicides
  • Periodic tillage is a reliable cultural practice that also benefits your system by removing a build-up of trash on the soil surface and can even out ruts or rough spots in fields. However, only use tillage when necessary

Make glyphosate applications at the right time and right rate when required to achieve good weed control, but caution should be taken if glyphosate alone is used repeatedly over a 12-month period.

  • The selection pressure for resistance development increases as the number of glyphosate applications increases in a 12-month period.
  • Other chemistry products or tillage may be used to reduce the number of glyphosate applications
  • Periodic tillage can substitute for glyphosate-based burndown programs
  • Rotation to other crops, including Roundup Ready® crops where other chemistry is used, can break the cycle of multiple applications

Monsanto Company considers product stewardship to be a fundamental component of customer service and responsible business practices. As leaders in the development and stewardship of Roundup® agricultural herbicides and other products, Monsanto continues to invest significantly in research to understand the proper uses and stewardship of our proprietary herbicide brands. This research, done in conjunction with academic scientists, extension specialists and crop consultants, includes evaluations of: (a) some of the factors that can contribute to the development of weed resistance and (b) how to properly manage weeds to delay the development of resistance.

Glyphosate is a Group 9 herbicide based on the mode of action classification system of the Weed Science Society of America. Although rare in occurrence, any weed population may contain plants naturally resistant to Group 9 herbicides. The following general recommendations help manage the risk that weed resistance may occur. More specific recommendations are outlined in the Roundup Ready® crop sections of Monsanto's 2006 Technology Use Guide.

Weed resistance management practices:

  • Scout fields before and after herbicide application.
  • Start with a clean field, using either a burndown herbicide application or tillage.
  • Control weeds early when they are relatively small.
  • Incorporate other herbicides and cultural practices as part of Roundup Ready® cropping systems where appropriate.
  • Use the right herbicide product at the right rate and the right time.
  • Control weed escapes and prevent weeds from setting seeds.
  • Clean equipment before moving from field to field to minimize spread of weed seed.
  • Use new commercial seed as free from weed seed as possible.

Monsanto is committed to the proper use and long-term effectiveness of its proprietary herbicide brands through a four-part stewardship program: (1) developing appropriate weed control recommendations, (2) continuing research to refine and update recommendations, (3) education on the importance of good weed management practices and (4) responding to repeated weed control inquiries through a product performance evaluation program.

Report any incidence of repeated non-performance on a particular weed to the local Monsanto representative, retailer, or county extension agent.