With harvest in full swing, it is hard not to forget about weed control in wheat.  Primarily of concern is herbicide-resistant Italian ryegrass.  In the past, ACCase- (Hoelon) and ALS-inhibiting (PowerFlex and Osprey) herbicides provided control of this weed.  However, Italian ryegrass biotypes resistant to these products have developed, but that is not to say these herbicides will no longer work in your area.  For example, Osprey is still effective throughout most of Eastern North Carolina, but once you move into the Piedmont, ryegrass control by Osprey is hit or miss.  In areas with known ALS-resistant Italian ryegrass, Zidua is suggested delayed-preemergence.  Delayed-preemergence means 80% of germinated wheat seeds have a shoot at least ½-inch long.  If applied prior to this stage, injury may occur.  Zidua is a seedling-shoot inhibitor and will not control emerged weeds, therefore, it is important for fields to be clean prior to application.  Axiom applied spike (applied preemergence, Axiom can cause severe injury) also controls Italian ryegrass if a timely activating rainfall is received following application.  Another option on no-till or minimum-till fields (where stubble from previous crop has not been incorporated) is Valor SX applied preplant.  Valor must be applied at least 7 days prior to wheat planting and should be applied in combination with either paraquat or glyphosate to control emerged weeds.  Tillage should not be performed after Valor SX is applied.  Italian ryegrass control by Finesse is variable and growers should expect only suppression.  If Finesse is applied, plant only STS-soybean following wheat harvest.  Postemergence options for Italian ryegrass include Axial XL and Osprey.   Although most Italian ryegrass is Hoelon-resistant, Axial XL (also an ACCase-inhibiting herbicide) still seems to work in most areas.  Osprey may also control Italian ryegrass in areas yet to develop resistance and will also control small bluegrass.

Ryegrass in the non-treated control.  Received glyphosate 14 days preplant.

Ryegrass control by Valor SX plus glyphosate applied 7 days preplant

The herbicide TriCor, a metribuzin product from United Phosphorus Inc., has received 24(c) registration (special local needs) for use in Virginia for control of Harmony and Harmony Extra (group 2 herbicides) resistant common chickweed. The supplemental label is here: TriCor DF Herbicide 24(c) VA label. This is good news for small grains growers.

Research by Drs. Scott Hagood and Michael Flessner indicate that TriCor at 2 oz/a results in excellent common chickweed control when applied in fall or spring, with no significant injury to wheat. However, wheat injury can be a concern. Using crop oil concentrate or vegetable oil surfactants with TriCor increases the risk of crop injury, as well as when applying with fertilizer in combination with TriCor. Growers should select wheat and barley varieties that are tolerant of metribuzin if planning on using TriCor as certain varieties are more sensitive to metribuzin than others. Seed dealers may have information regarding metribuzin tolerance. Additionally, preliminary nonreplicated wheat variety sensitivity research by Drs. Wade Thomason, Carl Griffey, and Michael Flessner is included in this publication: https://pubs.ext.vt.edu/CSES/CSES-129/CSES-129-PDF.pdf. See pages 99 to 101.

Always make sure to read and follow the product label. Also note that TriCor is the only stand-alone metribuzin product legal for this use.

Example of wheat variety differences in sensitivity to metribuzin. Thomason 2015.