Tidbits on Spring Weed Control in Wheat and Barley

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

List of recommended herbicides for winter wheat and barley in Delaware (additional herbicides are labeled).

Note Osprey and PowerFlex are not labeled for barley.

Points to consider:

Be sure to prioritize scouting those fields that have a history of poor weed control.  That includes those no-till field that did were not sprayed with glyphosate or fields that only received vertical tillage prior to planting.

In our trials, PowerFlex applications in the spring can cause crop stunting and yield loss. Injury and yield loss does not occur with all spring applications but occurs enough that I warn folks about it and only recommend it when no other option is available.  We do not see injury with fall applications of PowerFlex and have not been able to determine what causes this injury.

Small grain herbicides are going out in the spring at a time when weather is often less than ideal for herbicide performance. Cutting rates increases the likelihood of poor herbicide control. Starane Ultra is an herbicide I often hear folks using at rates less than 5 fl oz as a way of cutting costs.  I have found that we really need to use at least 5 fl oz to get best control.

Annual ryegrass populations with resistance to Group 2 herbicides (Osprey and PowerFlex) have been reported in Delaware. No reported resistance issues with Axial products in Delaware; however, resistance has been confirmed in Maryland.

Annual bluegrass and roughstalk bluegrass control is best with Osprey (with 80 to 85% control the best we can expect). However, Osprey should not be applied within 14 days of nitrogen application due to crop damage.

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

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 and Quelex are the most common options to suppress/control resistant chickweed.  Metricor or Tricor (metribuzin) has a state label for use in winter wheat and barley.  Metricor or Tricor are the only formulations 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 metribuzin to fields with ALS-resistant chickweed, treating 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 significant injury with green-up applications.  When using a sensitive variety, applications in late March and into April did cause significant injury and yield reductions.
• We have not tested malting barley varieties, but feed barley has exhibited good crop safety to Metricor or Tricor.
• Do not apply with nitrogen.
• The label allows tankmixtures with other small grain herbicides.
• Use of non-ionic surfactants (80/20) is okay, but do not use with crop oils or MSO.
• 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 plant vegetables after small grain harvest.

Refer to the label for additional precautions, rates and timings.

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

Ivyleaf speedwell control is another difficult weed to control.  UD research has found suppression with a combination of Harmony Extra with either Starane Ultra, 2,4-D or Quelex.  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 within a few weeks of flowering to prevent seed production. Using a competitive cover crop is another alternative to limit seed production of these winter annual weeds.