by Daniela Carrijo and Dwight Lingenfelter

When it comes to winter wheat, now is the time to scout for accurate growth staging.

This is important for several reasons, but the first thing is to see where your winter wheat is.

The University of Wisconsin has a good online source for staging fields. An important note is to pay attention to fields at Feekes stage 5, where the developing head is located just above the crown and is less than one-eighth-inch long. This is the last stage where some herbicides can be used without causing leaf injury.

Further, after this stage, the developing head moves above the soil surface, and yield potential is decreased by wheel traffic damage. Here are some other tips for assessing your wheat fields and some early-season management tips:

Perform a stand count. Watch this video that explains how to perform a stand count.

Make sure you have a yardstick when you go out to the field. Count the number of plants in a 3-foot length, and do it in five or six locations in a field to get a good sample. The video has more information on a formula you can use to do your calculation.

The yield potential of winter wheat is decreased when the number of alive plants falls below 20 to 25 plants per square foot. These numbers are based on an average of three heads per plant.

It is also important to look at the condition of tillers. For example, if there are 20 to 25 plants per square foot, but plants have less than three healthy-looking tillers, yield potential will likely be decreased.

Assess winter survival. Winter survival can be assessed visually by estimating percentage of dead foliage in a field.

A simple winter survival test can be performed by digging up plants and looking for root regrowth at room temperature, also known as the bag test. Here’s information from Michigan State University on how to do it:

Manage N applications. Wheat takes up most of its required N between Feekes stage 6, where the first node is visible above soil surface — commonly known as jointing — and Feekes stage 10.5.2, where the plant is flowering and the anthers are visible.

Delaying N fertilization past Feekes stage 6 often decreases yield. Similarly, applying too much N in advance of Feekes stage 6 may exacerbate N losses and decrease yield.

That said, when wet conditions limit field access, applying N any time between green-up and Feekes stage 6, when field conditions allow, can be a good strategy.

Splitting applications during this period may reduce the risk for N losses, but research done in Ohio and in the West has shown little yield advantage to splitting spring N applications.

The optimum spring N rate is specific to each field and year, but a general rule of thumb based on research in Pennsylvania is to apply 1 pound of N per bushel of expected wheat yield. 

Use herbicides with care. As wheat approaches stem elongation and jointing growth stage, be cautious of certain herbicide applications.

Once wheat has passed Feekes 6, the risk of herbicide injury from 2,4-D, MCPA, Clarity/dicamba or Curtail increases, and application of these herbicides is not recommended.

In this situation, the remaining herbicide options for broadleaf weed control are Harmony Extra — similar products are Edition, Treaty Extra, Nimble and others; Harmony SG — similar products are Treaty, Harass and Volta; and Finesse up to when the flag leaf is visible, or before Feekes 8.

Maestro, Huskie, Stinger and Starane can be applied up to boot stage (before Feekes 9).

Each spring, we get questions about risks associated with 2,4-D or MCPA application to wheat past Feekes 6. Wheat tolerance of 2,4-D is highest between Feekes 3 and 6, and is lowest in Feekes 9 and 10.

Between Feekes 6 and 9, sensitivity to 2,4-D gradually increases as wheat growth stage advances. Severe injury is highly probable when 2,4-D is applied at Feekes 9 and 10.

In most cases, herbicide injury can set back crop growth and potentially cause reduced yields since the crop can't recover in a timely manner. It is recommended that application of 2,4-D be made after wheat has reached Feekes 3, but prior to Feekes 6.

Injury risk can be minimized by applying the amine form of 2,4-D or reducing the rate of a 2,4-D ester. A much better alternative past Feekes 6 is to use another broadleaf herbicide with a wider application window that is effective on weeds in the field.

Minimize risks of spray solution carriers. Liquid urea-ammonium nitrate fertilizer (UAN) is a common spray solution carrier for herbicides in wheat in the region. We typically recommend no more than a 50-50 water-to-UAN ratio. The most common herbicide used in this manner is 2,4-D ester at 1 pint an acre.

Application of herbicide in liquid nitrogen can cause leaf burn from the nitrogen, especially under hot, humid conditions, and the addition of other herbicides or fungicides will likely increase the risk of crop injury. This risk increases in later wheat growth stages because more leaf area is exposed to the treatment and recovery time is shorter.

To minimize risk, follow these tips:

Herbicides such as Osprey, PowerFlex HL and Quelex can be applied in a UAN carrier, but certain guidelines must be followed, and temporary crop injury may occur.

Manage plant growth regulators. The application window for some plant growth regulators coincides with or follows green-up.

For example, the window for Palisade EC application on wheat is Feekes 4 to 7. Our research on Palisade EC shows that across different N management strategies, Palisade EC decreased wheat height by 5% to 10% and had no effect on grain yield, but decreased straw yield by 5% to 10% when Palisade was split-applied between Feekes 5 and 7.

Carrijo is assistant professor and Extension specialist of grain crop production at Penn State. Lingenfelter is an Extension associate of weed science with Penn State Cooperative Extension.

Source: Penn State Cooperative Extension