With temperatures warming now is the time to revisit weed control in wheat.
- Wheat fields have resumed growth, time to think about weed control.
- Wild garlic should be controlled, even if densities are low to avoid market dockage.
- Be aware of plant back restrictions following some herbicides if soybeans will be planted after the wheat crop.
Warmer temperatures over the past few weeks have allowed winter wheat fields to green up and resume growth. During winter wheat green-up, there are a few field activities that need to be considered, including winter wheat herbicide applications. The following information will outline winter annual weeds to look out for, weed scouting tips, crop stage restrictions, and herbicide recommendations.
Some common broadleaf weeds to scout for in winter wheat are dandelion, purple deadnettle, henbit, chickweed, Canada thistle, wild garlic, and marestail. These weeds emerge in the fall and can remain relatively inconspicuous through the winter; however, they become competitive and troublesome during the spring if not controlled early. Summer annual weeds such as ragweed will be of less concern in the early spring and will be outcompeted by the wheat crop if managed properly. Grass weeds that commonly require spring herbicide applications in wheat include annual bluegrass, annual ryegrass, cheat, and downy brome.
The majority of wheat herbicides are labeled for application at certain wheat growth stages, and some commonly used herbicides have very short windows in which they can be applied. For example, 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring. Wheat growth stages and herbicide timing restrictions for other herbicides are outlined in Table 1.
Application of herbicides in liquid nitrogen fertilizer solution as a carrier is commonly done to reduce trips across the field. Caution should be taken when using liquid fertilizer as a herbicide carrier as moderate to severe crop injury can result, especially in cool, cloudy weather conditions. Many POST-applied wheat herbicide labels allow for liquid nitrogen carriers but require different rates and types of surfactants than if the herbicide was applied with water as the carrier. Table 1 includes precautions to be taken when applying wheat herbicides using liquid fertilizer as a carrier; further details and directions can be acquired from the herbicide label.
Another consideration when planning early spring herbicide applications is the plant back restriction to double crop soybeans. A large percentage of the herbicides listed in Table 1, especially those with activity on annual ryegrass and downy brome, have soybean plant back restrictions greater than the typical three-month time period between spring applications and double-crop soybean planting. The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double-crop soybeans after wheat. Refer to Table 1 for more specific soybean plant back timing restrictions.
Table 1. Spring applied wheat herbicide rates, crop stage restrictions, weed control spectrum, soybean plant back timing, and liquid fertilizer carrier recommendations.
Active Ingredient | Trade name(s) | Rate per Acre | Application Timing | Winter Annual Weeds Controlled | Liquid Fertilizer Carrier Recommendations | Soybean Plant Back Restriction |
|---|---|---|---|---|---|---|
| 2,4-D | Radar LV 4/400 | 1 to 2 pts | Tillering to before jointing | Prickly and wild lettuce, mustards, field pennycress, shepherd’s purse, horseweed (marestail), dandelion* | The use of liquid fertilizer as a carrier will increase the risk of crop injury | No restriction for early spring applications |
| Bromoxynil | Buctril | 1 to 2 pts | Emergence to boot stage | Mustards, henbit, field pennycress, shepherd’s purse | UAN used as a carrier in early spring may increase leaf burn, do not use fertilizer carrier after jointing | No restriction for early spring applications |
| Bromoxynil + pyrasulfotole | Huskie | 13.5 to 15 oz | After the 1-leaf stage up to flag leaf emergence | Purple deadnettle, henbit, prickly and wild lettuce, horseweed (marestail), mustards, field pennycress, shepherd’s purse, chickweed | Can be applied in a liquid fertilizer solution that does not exceed 50% nitrogen and is not being applied above 30 lb./Acre | 4 Months |
| Clopyralid | Stinger, Clean Slate | 0.25 to 0.33 pts | After 2-leaf stage until boot stage | Horseweed (marestail), Canada thistle, dandelion* prickly and wild lettuce | 10.5 Months | |
| Clopyralid + 2,4-D | Curtail | 1 to 2.67 pts | Tillering to jointing | Prickly and wild lettuce, mustards, field pennycress, shepherd’s purse, Canada thistle, dandelion*, horseweed (marestail) | UAN can be used as a liquid fertilizer carrier | 10.5 Months |
| Clopyralid + fluroxypyr | WideMatch / Truslate | 1 to 1.3 pts. | 3-leaf growth stage up to and including flag leaf emergence | Control of broadleaf weeds, including hemp dogbane, ragweeds, Canada thistle, marestail, and cocklebur. | Foliar-applied liquid fertilizers, used as a carrier for WideMatch, can cause yellowing or leaf burn of crop foliage | 10.5 months |
| Dicamba | Clarity | 0.125 to 0.25 pt | Emergence to before jointing | Prickly and wild lettuce, horseweed (marestail), shepherd’s purse, dandelion* | Conduct compatibility test as outlined by label prior to application | No restriction for early spring applications |
| Florasulam + MCPA | Orion | 17 oz | 3-leaf to preboot stage | Prickly and wild lettuce, chickweed, field pennycress, shepherd’s purse, mustards | 9 Months | |
| Halauxifen-methyl + florasulam | Quelex | 0.75 oz | 2-leaf to flag leaf emergence | Horseweed (marestail), henbit, chickweed, field pennycress, shepherd’s purse, mustards | Maximum of 0.25% v/v NIS should be used when applying with a liquid fertilizer | 3 Months |
| MCPA | Chiptox, Rhomene | 1 to 4 pts | Tillering to before jointing | Field pennycress, shepherd’s purse, mustards pigweed, prickly lettuce, horseweed (marestail) | The use of a liquid fertilizer as a carrier will increase the risk of crop injury | No restriction for early spring applications |
| Mesosulfuron-methyl | Osprey | 4.75 oz | Emergence to preboot stage | Ryegrass, bluegrass, wild oat, field pennycress, wild oat | Can be applied in a liquid fertilizer solution that does not exceed 15% nitrogen fertilizer. Maximum of 0.25% v/v NIS should be used when applying with a liquid fertilizer | 90 Days |
| Pinoxaden | Axial Bold | 15 oz | Emergence to preboot stage | Ryegrass | Can be applied in a liquid fertilizer solution that does not exceed 50% nitrogen fertilizer. Crop injury may be possible. | 90 Days |
| Propoxycarbazone-sodium | Olympus | 0.6 to 0.9 oz | Emergence to before jointing | Cheat, downy brome, purple deadnettle, horseweed (marestail), mustards, field pennycress, shepherd’s purse | Maximum of 0.25% v/v NIS should be used when applying with a liquid fertilizer carrier. Temporary crop injury may occur. | 12 Months and 24” of precipitation |
| Prosulfuron | Peak | 0.5 oz | Emergence to second node visible | Mustards, field pennycress, prickly and wild lettuce, shepherd’s purse, wild garlic, wild onion | Apply with NIS at 1-2 qt/100gal when using a liquid fertilizer carrier | 10 Months |
| Pyroxsulam | PowerFlex, PowerFlex HL | 3.5 oz | 3-leaf to jointing | Cheat, downy brome, ryegrass, chickweed, mustards, field pennycress, shepherds purse | Can be applied in a liquid fertilizer solution that does not exceed 50% nitrogen and is not being applied above 30 lb/Acre. NIS at 0.25% v/v should be added to solution. | 3 Months |
| Thifensulfuron + tribenuron | Harmony Extra TotalSol | 0.45 to 0.9 oz | After 2-leaf stage but before flag leaf becomes visible | Wild garlic and onion, field pennycress, mustards, chickweed, henbit shepherd’s purse, prickly and wild lettuce, horseweed (marestail), purple deadnettle | Include a surfactant at 0.5-2 pts/100 gal when applying in a carrier that consist of less than 50% nitrogen fertilizer. | 45 Days |
| Tribenuron | Express TotalSol | 0.25 to 0.5 oz | After 2-leaf stage but before flag leaf becomes visible | Chickweed, deadnettle, henbit, wild lettuce, mustards, field pennycress, shepherd’s purse | Liquid fertilizer carriers should have 0.06-0.25% v/v NIS added. Temporary crop yellowing and stunting may occur when applied in liquid fertilizer. This injury is occasionally severe, and risk of sever injury may increase under saturated soil conditions. | 45 Days |
* The highest labeled herbicide rates should be used to achieve control of dandelion plants with spring applications.
