Herbicides should be applied soon to minimize the impact of winter annual weeds on wheat growth and development.
The most prevalent weed problems in wheat fields at this time are usually chickweed, purple deadnettle, henbit, marestail, field pennycress, and other winter annuals, along with dandelion.
Giant ragweed and Canada thistle are also starting to emerge. Several herbicides are available for control of winter annuals in wheat, but one of the following should be used where chickweed is present: Huskie; tribenuron (Express, Nuance, Victory); or a tribenuron/thifensulfuron premix product (Harmony Extra, Nimble, TNT Broadleaf, etc).
Huskie will control ragweeds and marestail, but 2,4-D should be added to tribenuron or tribenuron/thifensulfuron for control of these weeds.
Most effective control of dandelions will occur when they have resumed active growth, and it is still too early for control of Canada thistle and early-season summer annual weeds.
Control of dandelion is generally variable in spring. We have had the best results with combinations of tribenuron and 2,4-D, but this may not result in more than about 70% control.
Fields treated at this time for winter annual control should be scouted again later in April to determine if later-emerging populations of summer annual weeds, Canada thistle, wild garlic, or other weeds require another herbicide treatment. In fields without many winter annuals or dandelions, the best advice may be to delay herbicide application until later in spring, and select herbicides based on scouting.
Be sure to follow label guidelines to minimize risk of crop injury and yield loss. Labels for some products specify the number of tillers or leaves that wheat should have before treatment is allowed.
All labeled wheat herbicides can be applied prior to jointing, but the number of herbicide options decreases as wheat progresses through jointing and more advanced growth stages. Wheat should be dissected to determine growth stage, because size is not a good indicator of stage.
Weather and soil conditions can affect the risk of crop injury from certain herbicides. Injury from ALS inhibitors (Harmony Extra, Express, etc) is more likely when wet soils and cold temperatures are inhibiting wheat growth.
Most herbicides can be applied using 28% UAN as the spray carrier, although some labels do not provide much guidance on this. Results of OSU research indicate that wheat should tolerate application of herbicide in 28% UAN well into April, as long as the restrictions on herbicide labels relative to wheat growth stage are followed.
For products that are applied with surfactant, consult labels about the surfactant rate when applying in water vs 28%, since surfactant rates may be reduced to minimize the risk of injury when applying in 28%.
Guidelines and effectiveness ratings for wheat herbicides can be found in the 2009 Weed Control Guide for Ohio and Indiana.