Winter Wheat Fields Are Greening Up Already

Spring green up. What does that mean?

Green-up is not a growth stage per se, but it is a descriptive reference to how the field looks a darker green color as the weather warms up in the spring and plants come out of dormancy and the new growth covers the winterkilled tissue. In PA, this usually happens between mid-March (southeast PA) and late April (northern tier). However, with the warm winter we are experiencing this year, many fields in southeast PA are already greening up. Plant growth stage at green-up will depend on several factors like planting date and fall weather conditions. For example, two neighboring fields, one late planted and the other early planted may green up at the same time – the late planted can be at Feekes stage 3 while the early planted can be at Feekes stage 5. It is important to scout the field for accurate growth staging.

Why is green up important?

As the plants are coming out of dormancy, this is a time of fast growth that requires scouting and timely management.

What to scout for

Growth stage

This guide from the University of Wisconsin is an excellent resource for staging fields. Pay attention to fields at the Feekes stage 5 (the developing head is located just above the crown and is less than 1/8" long). This is the last stage in which 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.

Stand counts

See this video explaining how to perform a stand count. Yield potential of winter wheat is decreased when the number of (alive) plants falls below 20-25 plants per square foot. These numbers are based on an average of 3 heads per plant. Therefore, it is also important to look at the condition of the tillers. For example, if there are 20-25 (alive) plants per square foot but plants have less than 3 healthy-looking (usually with 3 or more leaves) tillers, yield potential will likely be decreased.

Winter survival

Winter survival can be assessed visually by estimating the percentage of dead foliage for a field or field management zone. If the percentage is high, and especially if this is coupled with a low stand count estimate, a simple winter survival test can be performed by digging up plants and looking for root regrowth at room temperature (bag test). See how to do a bag test at the end of this article.

Management decisions

Nitrogen (N) fertilizer

Wheat takes up most of its required N between Feekes stage 6 (first node visible above soil surface, commonly known as jointing) and Feekes stage 10.5.2 (flowering, anthers visible). Therefore, delaying N fertilization past Feekes stage 6 often decreases yield. Similarly, applying N fertilizer too much in advance of Feekes stage 6 may exacerbate N losses and decrease yield. That said, with wet conditions limiting field access, applying N anytime 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, although research done in Ohio and the West has shown little yield advantage of splitting spring N applications. The optimum spring N rate is specific to each field and year, but a general rule of thumb based on PA research is to apply 1 lb. of N per bushel of expected wheat yield. 

Herbicides

As wheat approaches the stem elongation and jointing growth stage, be cautious of certain herbicide applications. Once wheat has passed Feekes 6 (i.e. when the first node of the stem is visible), 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: Edition, Treaty Extra, Nimble, others), Harmony SG (similar products: Treaty, Harass, Volta), and Finesse can be applied to wheat until the flag leaf is visible (before Feekes 8). Maestro, Huskie, Stinger, and Starane can be applied to wheat up to boot stage (before Feekes 9). Refer to wheat growth stage graphic (Figure 2.5-1, pg. 465) from the 2023-24 Penn State Agronomy Guide for more details.

Each spring there are questions about the 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 stages 6 and 9, sensitivity to 2,4-D gradually increases as wheat growth stage advances. Thus, the risk of injury increases as wheat growth stage advances between stages 6 and 9. Severe injury is highly probable when 2,4-D is applied at Feekes 9 and 10. In most cases, herbicide injury can set back the growth of the crop and potentially cause reduced yields since the crop can't recover in a timely manner.

It is recommended that the application of 2,4-D to wheat be made after wheat has reached Feekes 3 but prior to Feekes 6. If growers choose to apply 2,4-D at later stages, they need to understand the associated risk. This 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 on wheat past Feekes 6 is to use another broadleaf herbicide with a wider application window that is effective on the weeds present in the field.

Tank mixing liquid N with herbicides

Liquid urea-ammonium nitrate fertilizer (UAN) is a common spray solution carrier for herbicides in wheat in our region. We typically recommend no more than a 50:50 water/UAN ratio. The most common herbicide used in this manner is 2,4-D ester at 1 pint/A (2,4-D amine is difficult to mix in UAN). 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 to these mixtures will likely increase the risk for crop injury. This risk increases with later wheat growth stages because more leaf area is exposed to the treatment and recovery time is shorter. Applications of 2,4-D should be made in the spring to actively growing wheat following tillering (Feekes 3) but prior to jointing (Feekes 6). To minimize this risk:

• Do not apply more than 20 lbs of nitrogen per acre in the form of UAN when using a surfactant with herbicide.
• Do not apply more than 40 lbs of nitrogen per acre in the form of UAN when no surfactant is used.
• Avoid high-temperature, high-humidity days. Late afternoon applications carry less risk of leaf burn.

Below are the specific adjuvant recommendations for Harmony SG and Harmony Extra SG:

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.

Plant growth regulators

The application window for some plant growth regulators coincides with or follows the green-up phase. For example, the window for Palisade EC (trinexapac-ethyl) application on wheat is Feekes 4 -7. Our recent research on Palisade EC indicated that across different N management strategies, Palisade EC decreased wheat height by 5-10% and had no effect on grain yield but decreased straw yield by 5-10% when Palisade was split applied between Feekes stages 5 and 7.