Agronomy Blog

Fall Weed Control – Plant Clean, Stay Clean

by Jesse Grogan | Oct 5, 2017

Fall weed control delivers clean, weed free fields in the early spring. Winter annual weeds like marestail, chickweed and henbit; biennial weeds like wild carrot; perennials weeds like dandelion and quackgrass are controlled. Warmer soil temperatures and planting conditions improve in clean fields. Fall emerged marestail, many resistant to glyphosate and ALS herbicides, are hard to control in the spring due to increased plant size and physiology.  Set up a program to kill emerged weeds at the time of fall application. “Kill what you see”.  The cost of fall applications should be kept low and simple so that funds go to spring residual weed control.  A simple fall weed control program would be glyphosate and 2, 4-D. Wait for weed emergence in October and apply in warm conditions until Thanksgiving. Residual herbicides applied in the fall aid in the control of weeds that could emerge through the winter. But, fall applied residuals can carry over into the spring crop and cause crop injury or be depleted by early spring. Level of control is dependent on the weather and geography. Use of residuals in the fall is a debated topic among farmers and weed scientists.

Jesse Marestail in field_Jesse_2843 citedAcreage of Roundup Ready 2 Xtend® soybeans is increasing at a rapid rate. This technology offers another option for improved weed control with specific dicamba products labeled for soybeans. One of the best options is burn down or early season application of dicamba when temperatures are cool. Mark Loux at Ohio State has reported that dicamba can be slightly better for controlling emerged marestail than 2, 4-D in early season. A spring burn down program with residuals should be used against weeds that could emerge in the summer. A superior spring program can minimize the need for post herbicide application in crop, especially for marestail. An aggressive residual program is more effective for the control of glyphosate resistant weeds like water hemp.

Do not depend on fall applied residuals to control weeds until an early post application. It is a decision each grower needs to make based on weed pressure they experience and how they plan to use resources in their operation. Fall weed control is beneficial, especially before soybeans. Factors to consider:

  • There are several effective herbicide programs to control rosettes for marestail and other winter annual weeds such as chickweed and henbit, biennials such as wild carrot and poison hemlock and perennials such as Canada thistle and dandelion. 2, 4-D is almost always used and combined with other herbicides before corn or soybeans. Glyphosate, Canopy® and metribuzin are used before soybeans. Canopy® is the only herbicide likely to have control of weeds after soybean planting. Glyphosate, Basis® and Simazine are used before corn. Other treatments are also available such as dicamba, Autumnâ, saflufenacil (Sharpen®, Verdict®, Optill®), or chlorimuron (Classic®, Synchrony®). Best control of dandelion is with 2, 4-D or dicamba with Canopy® before soybeans or Basis® before corn.
  • Soil conditions improve in the spring with fall weed control. Soils tend to warm up faster when clean and free of growing or decayed mats of weeds. Fall weed control is a benefit when heavy weed pressure develops with frequent rains and warm weather, such as this fall. Weed control in the early spring could become difficult if cool and wet weather persists before planting, preventing timely spraying with equipment. Fall weed control makes planting in a dry, high quality seed bed more likely.
  • Control of fall weeds such as henbit and purple dead nettle will help reduce the amount of Soybean cyst nematode pressure by reducing potential reproduction of alternate host plants. Relatively weed free fields are also less likely to experience heavy black cutworm damage as adult moths do not find egg laying sites in emerged weeds.

Fall weed control is a great option for managing winter annual, biennial and perennial weeds. Cost effective and simple control measures are available. Soil conditions can be much better in the spring for earlier planting and fewer complications from weeds or residues. Time is approaching for fall weed control from the middle of October to Thanksgiving.

Sources and Additional Information:

  1. Bradley, Kevin. 2013. Considering Fall Herbicide Applications: It’s not JUST about the weeds. University of Missouri, Division of Plant Sciences, Columbia, MO
  2. Legleiter, Travis and Bill Johnson. 2014. Starting Next Year Now: The Utility of Fall Herbicide Applications. Purdue University, Department of Botany and Plant Pathology, Weed Science, West Lafayette, IN.
  3. Loux, Mark, 2017. Are Fall Herbicide Treatments Necessary in Xtend Soybeans. C.O.R.N. newsletter. 2017-31.
  4. Roundup Ready Plus Herbicide Solutions. Post-Harvest Weed Management-NORTH.
  5. Roundup Ready Plus Herbicide Solutions. Post-Harvest Weed Management-SOUTH.

Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
Sharpen®, Verdict®, and Optill®  are trademarks of BASF Corporation. Autumn® is a registered trademark of Bayer Crop Science LP. Canopy®, Basis®, Classic® and Synchrony® are registered trademarks of DuPont de Nemours and Company. Genuity® and Roundup Ready 2 Xtend® are registered trademarks of Monsanto Company. All products are trademarks of their manufacturers.
LG Seeds and design are trademarks of SCA Limagrain.

Download a copy of this Technical Bulletin: Tech_350 - Fall Weed Control