Photo Credit: P. Wagner.
When controlling grassland weeds, the mindset of row crop weed control is put into practice too often. In most cases, broadcast control of weeds in grasslands is rarely necessary. Most often, spot or zone spraying can be used more effectively to manage the noxious and problematic weeds. What is zone spraying? Well, let us take a moment and consider this in a different context. For example, in basketball when a player is on defense, he is not chasing other players all over the court. Instead, he is defending a certain area and not the whole basketball court. This applies to weed control in grassland. Often, noxious and invading weeds are only in a few areas and do not require the whole grassland to be sprayed. Grasslands typically have about 80% of their biomass as grass, 15% as forbs (broadleaf plants), and 5% as shrubs.
Balancing Weed Control & Beneficial Plant Life
What happens when a grassland is broadcast sprayed for broadleaf weeds? Beneficial plants such as forbs are killed or injured, decreasing the overall diversity and health of grasslands. This is important in both grazing and non-grazing programs. For grazing programs, it is critical to understand that livestock, including cattle, will utilize a variety of native and non-native broadleaf plants in their diets to meet their nutritional and mineral requirements, if these plants are available. When targeting weeds with a broadcast application, it is common to severely impact or eliminate desirable broadleaf plants. In addition, it is often common that livestock will forage on weedy species as well. Achieving balance in investments into weed control while protecting non-target plants, which has merit both economically, ecologically, and in relation to livestock health and performance.
Often, as managers, we confine our understanding only to what we easily observe. Thus, we tend to think of grazing only in the context of what we easily see during daylight hours. Livestock, however have 24 hours a day that they can potentially graze. Often, what is unpalatable at a particular time of day may be more desirable at a different time, depending on the compounds active in the plant at the time. In non-grazed grasslands, the same principals apply for wildlife.
Value of Plant Diversity
The value of maintaining plant diversity can pay dividends in relation to insect and wildlife diversity. More plant diversity provides better habitat for insects and, in turn, supports wildlife communities. Insects act as a food source for wildlife including many bird species. Maintaining plant diversity can also help boost beneficial insects such as pollinators, dung beetles, and natural enemies of common insect pests. For pollinators, individuals including bees, butterflies and moths, beetles, and certain types of flies use many of the broad leaf plants (forbs) for sources of nectar and pollen. An abundant pollinator community benefits grassland health and may even help improve production of nearby crop fields. Furthermore, healthy grasslands creates opportunities for alternative uses like recreation.
The very first and best investment into grassland weed control is to consider the following questions: Why do I have this weed? What is the source? Is this a result of current or previous management? Can I manage this problem effectively? Is it noxious or problematic? Can I take advantage of this problem? Remember, a grassland with only grass is not a healthy grassland.
Resources for chemical spot treatment of Pasture/Range and Noxious weeds: