Guidelines for Liquid Fertilizer Carriers and Small Grain Herbicides

Recently, I have had questions regarding the use of small grain herbicides in fertilizer carriers. In addition to those related to application timing and adjuvant utility. Liquid urea-ammonium nitrate (UAN) fertilizer is a common carrier for herbicide sprays 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 herbicides 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 (Feeke's stage 3) but prior to jointing (Feeke's stage 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.

Other herbicides have more specific guidelines for mixing with liquid fertilizer and adjuvants, such as nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO). Herbicides such as Harmony SG, Harmony Extra SG, Osprey, PowerFlex HL, Quelex, and others can be applied in a UAN carrier, but certain guidelines must be followed, and temporary crop injury may occur.

Axial XL and Axial Star: May be mixed in a spray solution containing up to 50% liquid nitrogen fertilizer. Add Axial XL/Star to the water first. Mix thoroughly, then add the liquid nitrogen fertilizer in an amount no greater than 50% of the final volume. Under certain environmental conditions, this mixture may cause crop burn.

Metribuzin: Application via a liquid nitrogen fertilizer carrier is typically not recommended. However, the label does not explicitly forbid it; but it warns that crop injury may occur if metribuzin is applied in combination with liquid fertilizer, especially with the addition of NIS. Do not use COC or MSO.

Osprey and Osprey Xtra: Fertilizer spray solution should not exceed 15% liquid nitrogen (1.5 gallons of liquid nitrogen in 10 gallons of spray solution per acre), and it must include NIS of 0.25% v/v (1 quart per 100 gallons of spray solution). When MSO is used, ammonium nitrogen or ammonium sulfate fertilizers are not recommended. Do not topdress with nitrogen fertilizer within 14 days following Osprey application.

PowerFlex HL: Carrier should not be composed of more than 50% liquid nitrogen fertilizer and should not exceed 30 lb of actual nitrogen per acre. Use NIS at a maximum of 0.25% v/v instead of COC. An independent liquid ammonium nitrogen fertilizer application made within 7 days before or after a PowerFlex HL application may result in transient leaf burn or stunting. Do not make a liquid fertilizer application during this period unless the risk of crop response is acceptable.

Pixxaro: May be applied in spray solutions containing liquid fertilizer. When Pixxaro is applied with liquid fertilizer, non-ionic surfactant, crop oil concentrate, or methylated seed oil is not needed.

Quelex: Spray solutions containing liquid nitrogen fertilizer can be used. If NIS is included, use a maximum rate of 0.25% v/v. Do not use COC or MSO if mixed in liquid fertilizer.  Additional adjuvants are not needed if tank mixing with 2,4-D ester or MCPA ester and liquid nitrogen fertilizer.

Aside from these products, other herbicides may allow the use of liquid nitrogen fertilizer as a carrier, but make sure to review the product label for details.