Weed Control in Wheat and Barley

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Since many small grain fields did not get an herbicide treatment last fall, they may need to be sprayed as soon as the fields dry out to control weeds before weeds get too large and before small grains get too large and interfere with spray coverage.

List of recommended herbicides for winter wheat and barley in Delaware (additional herbicides are labeled but not recommended).

Herbicide Maximum Stage Rotation to Soybeans Rotation to Vegetables
Axial XL Pre-boot No restrictions 30 days
Harmony Extra Before flag leaf emergence 7 days 45 days
Huskie Flag Leaf emergence 120 days 9 months
Quelex Flag leaf emergence 90 days 15 months
Starane Ultra Early boot stage 120 days in MD

90 days in DE, VA

4 months
Sentrallas Before flag leaf emergence 120 days

90 days in DE, MD, VA

4 months
2,4-D After tillering before jointing No restrictions 3 months
Dimetric EXT At “green up stage” No restrictions at least 4 months

 

Considerations
Annual ryegrass populations with resistance to Group 2 herbicides (Osprey and PowerFlex) have been reported in Delaware. There have been no reported resistance issues with Axial XL in Delaware; however, resistance has been confirmed in Maryland. A word of caution, Axial XL is the same herbicide family as Hoelon (Group 1) and there was Hoelon-resistant annual ryegrass in the region in the past.

Common chickweed control is becoming more challenging with the spread of ALS-resistant common chickweed (resistant to Finesse, Harmony Extra, Osprey, and PowerFlex). Spring application of Starane Ultra, Quelex, and Huskie are options to suppress/control the resistant chickweed. Delaware Department of Agriculture and Winfield have approved a state label (24c) for use of Dimetric EXT for winter wheat and barley. The active ingredient is metribuzin. Dimetric is the only formulation of metribuzin with this special label in DE and MD. In addition to chickweed, UD Weed Science has also had encouraging results with control of ivyleaf speedwell, jagged chickweed, henbit, and knawel when applied to weeds 3 inches or less. We know some varieties differ in their sensitivity to metribuzin, and most varieties have not been tested. So, we recommend limiting Dimetric EXT to fields with ALS-resistant chickweed, treat early-spring, and being cautious on varieties with no previous experience.

  • Winter wheat is most tolerant if treated at green up timing. UD Research has used Shirley, a sensitive variety, and have not documented injury with green-up applications. When using a sensitive variety, applications in late March and into April did cause significant injury and yield reductions.
  • Do not apply with nitrogen.
  • Do not use on sandy soils with organic matter less than 0.75%; which includes sandy knolls in portions of some fields.
  • We recommend use of metribuzin only in fields planted with a grain drill (not recommend on fields where seeds were broadcast and incorporated with vertical tillage tool or disc).
  • Be sure to use the rate recommended for your crop stage.
  • Do not double-crop vegetables after small grain harvest.
  • Refer to the label for additional precautions, rates and timings.

Jagged chickweed control has not been very good with any herbicide or herbicide combinations when applied in the spring. In our trials, Dimetric EXT was the most effective treatment. Harmony Extra plus Starane Ultra provides some suppression. No other treatment provided better suppression in our trials.

Henbit is the most common weed in winter wheat and it can be difficult to control with most small grain herbicides applied in the spring. Harmony Extra, Huskie, and Quelex will suppress henbit, but seldom completely kill the plants. But suppression in combination with a competitive small grain canopy is often sufficient to stop henbit growth.

Ivyleaf speedwell control is another difficult weed to control. UD research has found suppression with a combination of Harmony Extra with either Starane Ultra or 2,4-D or Quelex applied alone (Quelex plus Harmony Extra was not included in our trial). PowerFlex also provides suppression but can cause injury to wheat with spring applications.

There is always interest in applying wheat herbicides with nitrogen, so be sure to read all herbicide labels carefully because some products can be tankmixed with nitrogen but only if the nitrogen is no more than 50% of the spray solution (nitrogen is mixed 1:1 with water.

A longer-term approach for weed control is to prevent winter annual weeds from producing viable seeds in the years the field is not planted with small grains. Jagged chickweed and henbit will start flowering in mid-March and need to be treated by early April to prevent seed production. Using a competitive cover crop is another alternative to limit seed production of these winter annual weeds.

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