As spring inches its way closer and pastures begin to green up, it is important to pay attention to the weed pressure that may start to pop up too. There are many options for managing weeds in a pasture system; however, it is important to understand the pros and cons of each management option and choose the one(s) that will best work for your personal operation.
It is crucial to positively identify the weed species before trying to control them. Improper identification can lead to failed control attempts. Numerous weed identification resources exist online or are available for smartphones. The Iowa State University Weed Identification Field Guide is a great resource for common Iowa weeds. Apps like iNaturalist and PictureThis are available for smartphones and quite adept at providing accurate identifications down to family, genus, or even species. Proper identification of the weed allows us to determine the best management tactics to use.
Preventative weed management tactics are those that are implemented in a system to try and avoid any initial or further establishment of weed species. These tactics might include actions such as transporting weed free hay, being sure to clean equipment after its use and before moving it to a new pasture. If new pasture is being established or areas are being interseeded, purchasing certified weed free seed can also help to prevent introducing any new weeds to the area.
Relying on biological resources is one of the lesser used methods of weed control due to its higher cost and higher risk of being able to obtain the desired results. These methods also require a much longer timeline to be able to reduce the weed populations and are often highly species-specific. Certain insect species may target specific weeds of interest to them (such as the chrysolina beetle to St. John’s Wort). Pathogens can also be released to create disease and impact the health and success of the weed population. Another biological control that could be consider is the use of goats. Goats are highly effective in controlling brush and woody plant species that other livestock species do not graze.
Herbicides are one of the most commonly used methods to control weed populations. Herbicides can be applied to the entire field, or they can be used as a spot spray. Applications are most effective when they are applied while the weed is in its most susceptible growth stage. Poor herbicidal weed control is often due to the herbicide being applied during a less susceptible weed growth stage. The appropriate growth stage for application is dependent on the life cycle of the weed.
Regardless of the herbicide used, be sure to pay close attention to the label requirements for hay harvest and grazing restrictions. Persistent herbicides (e.g. picloram, aminopyralid, etc.) may have further restrictions on moving any forage off-site. If a broadleaf weed is the target for control, consider the legume population since most herbicides used for broadleaf weeds will also eliminate legume forage.
Hand-digging or burning are two mechanical methods used to lower weed populations. While hand removal may be a reasonable task for some to manage weeds that reproduce via taproots, it is often too labor intensive to justify use in pastures. Prescribed burning is an effective option for some species, such as Eastern redcedar. Timing is key to target the species of concern.
During the process of pasture renovation, tillage may be an effective choice to manage weeds present in the field as it is a non-selective method of control.
The most common mechanical method is mowing. Clipping weeds before they reach reproductive stages can be effective at preventing seed production for many species. It will be most effective on biennial or winter annual species that produce seed atop a tall stem, but multiple mowing passes can be effective at preventing annual and perennials from producing seed as well. Biennials and winter annuals need to be mowed after bolting but before flowers produce viable seed.
Cultural methods can be easy to adapt in effort to reduce weed pressure as they revolve around maintaining a healthy stand of desirable forage. These tactics would include avoiding overgrazing so that the forage stand can outcompete the weed species, managing pasture traffic patterns, using well-adapted competitive forage species, and maintaining good soil fertility. The grazing style of the pasture can also be further managed to help with the forage growth, such as utilizing rotational, continuous, strip, or sequence grazing patterns.
Regardless of the weeds that are present in your pasture, there are viable control options that can be implemented for effective control. Staying on the forefront of the weed pressure will assist in being able to have an easier time controlling those weed populations.