Controlling Winter Annual Weeds
Record winter high temperatures are causing earlier weeds emergence, so now is the time to control winter annual weeds in alfalfa. Thin field stands combined with open soil surfaces and adequate moisture can result in high weed pressure. So, prior to alfalfa shoot green-up or dormancy break, scout fields for early green winter annual weed patches of pennycress, downy brome, mustards, cheatgrass and shepherd’s purse. Left unchecked, these weeds can lower first cutting hay yield, quality and palatability. Also, excessive weeds can extend dry-down and lengthen harvest time.
However, before applying any herbicide, scout current and potential weed pressure. Verify that fields have enough weeds to justify herbicide spray applications and then determine the best management options.
- Winter annual weeds can grow better during cooler spring temperatures than alfalfa, so dormant alfalfa herbicides such as MCPA Amine, metribuzin and Gramoxone® can still be applied.
- Pre-emergent herbicides such as Warrant®, Chateau® and Prowl H2O® can be applied soon after green-up, but these chemicals will not control weeds which have already germinated.
- Aim® herbicide will control early growing broadleaf weeds but not control grassy weeds.
- Poast® herbicide will control most growing weedy grasses but not downy brome.
- Pursuit® and Raptor® herbicides control growing henbit well during early alfalfa green-up, but control weeds best when air temperatures are warmer.
- Glyphosate products like Roundup Weathermax®/Powermax® will control growing weeds with warmer temperatures too; however, they must be used with Roundup-Tolerant alfalfa varieties.
Other new alfalfa field products include: Balan®; Trust®; Moxy®; Arrow®; Select Max®; Velpar; Karmex®; Sinbar®; Pursuit; Butyrac® and Raptor®. Our Nebraska Extension NebGuide EC130, “Guide for Weed, Disease, and Insect Management in Nebraska” provides additional information.
As winter annuals can quickly establish in hay fields, early season weed control is important for quality hay production. Timing is essential — control winter annuals before alfalfa breaks dormancy and before weeds render economic losses. For more information, see CropWatch’s alfalfa resources.
Mild Winter and Insect Pressure
This winter has been quite mild and dry across the state, with most locations experiencing periods of higher-than-normal temperatures and 77% of the state currently in drought. What do these conditions mean for insect survival this winter and pest pressure this spring and summer?
Because insects have a variety of methods they use for survival, we can only generalize when trying to predict future insect populations and pressure based on winter conditions. Insects that overwinter belowground, like grasshoppers, are generally less affected by mild winter conditions since soil temperatures are more constant. However, a shallow frost layer can increase survivability.
In contrast, for insects that overwinter aboveground, like alfalfa weevil, fewer cold days can increase survival, but a lack of snow cover can lead to exposure when temperatures do fall below freezing.
Conditions this spring can have a more significant impact on insect pest populations. A cool, wet spring can delay grasshopper hatching, while alfalfa weevil thrives in cool and overcast conditions. If this spring brings hot, dry conditions, grasshoppers will thrive while alfalfa weevil activity could be reduced.
In the end, it’s important to scout early and often so that insect pest populations can be monitored. And remember, if more pests survive due to this mild winter, so too will more beneficial insects survive to help moderate pest populations.
