Question of the Week
Answer: I am pleased to provide you with information on non-chemical pasture weed control.
Ecological Weed Management in Pastures
It is important to remember that in agriculture we are dealing with a very complex biological system that operates in a particular ecological balance. Each region of the country, indeed each watershed and field might behave in very different ways because of differences in soil type and depth, indigenous plant cover, cropping systems, temperature, and water availability, not to mention field cropping history. By developing a cropping system or perennial pasture that utilizes nature’s own defenses and achieves ecological balance, a sustainable, pest-limited crop can be grown.
Do You Really Have a Weed Problem? In a highly complex, biologically diverse pasture, the very concept of weed infestation looses meaning. Many plants that are considered pasture weeds are highly palatable and nutritious during the vegetative stage. Take, for instance, dandelion and plantain. Both are numerous in many pastures, and producers can spend thousands of dollars spraying them with 2,4-D to try to kill them. They are, however, valuable plants that occupy different root zones, and so deliver nutrients from different soil depths. They are also very nutritious and palatable when young. These and many other “weeds” can be a valuable contribution to sustainable pastures. Even our so-called “noxious weeds” like knapweed and kochia can be grazed by sheep, goats, or cattle if just a little management oversight is applied. Weeds are basically a result of soil disturbance and human interference in nature, and if you think about it, without crop production, there would be no weeds. Weeds are merely plants that occupy space that humans do not want them to occupy. And we have many very good reasons for not wanting them to occupy certain spaces. In agriculture we have become very accustomed to applying pesticides to fields in order to eliminate unwanted plants and establish a favorable environment for the kinds of plants we choose to be there. But if we can look at our crop production and pasture systems as just that, “systems,” and begin to understand how plants and animals and humans interact on a given landscape, weeds will become much less of a problem. By managing croplands and pastures according to nature's principles we can significantly reduce weed problems.
How Weeds Get Started? Weeds enter an ecosystem only if they have been invited. In fact, many high producing pastures would succumb to weed infestations if management declined due to the presence of millions of seeds lying there, just waiting for the opportune moment to germinate and grow. A pasture that is managed to have high plant diversity, to remain vegetative for most of the growing season, and allowed adequate time for regrowth from a grazing event is better prepared to fight off germinating weed seeds. Even our most invasive species, when a seedling, cannot compete with the substantial, highly developed root system of a mature, leafy grass plant.
Techniques for Dealing with Problem Weeds in Pastures. Keeping weeds out of a pasture is much easier than trying to get rid of a bad infestation. Some management practices to consider for keeping pastures weed-free include:
• Terminate Low Producing, Weedy Fields
• Rotate Perennial Pastures with Annuals
• Integrate a High Density Rotational Grazing System
• Multi-Species Grazing
The afore-mentioned methods, used singly or in combination, can easily be incorporated into a pasture management system, setting up a situation in which weeds find it hard to get ground. When pasture stands such as alfalfa get too old, they often begin to decline and allow other plants to take over. Many times the grass component of the field will increase as alfalfa decreases, but in instances of low fertility or drought, annual weeds can take advantage of the open niche and become established. Terminating and reseeding the fields is sometimes then recommended. For some pastures that are terminated, you might consider planting them to winter wheat, or oats and winter peas for a season. These are in themselves valuable forage crops, and they help to break pest cycles while building soil all the while.
High density grazing plans also diminish weed invasion by reducing grazing selectivity. As an animal begins to consume all the plants in a given area, no one plant is favored. This gives grass an advantage. Grass, because of the lowered position of its growing point when vegetative, is more tolerant of leaf removal than broadleaf plants, which often elevate their growing points much earlier in the season. Very intensive systems can even favor grass over legume growth, so careful attention should be paid to the legume component of intensively grazed paddocks. Reseeding by frost-seeding, feeding seed to cattle, or broadcasting in the fall can be an effective way to maintain legumes in these systems.
Multi-species grazing refers to the practice of utilizing different livestock species to
(1) diversify farm income, (2) utilize pastures of different ecological types on the farm, and (3) manipulate the plant community to meet the production goals of the farm.
Cattle, sheep, and goats evolved eating different plant types. Cattle typically consume, in order of preference, grasses, forbs, and shrubs; whereas sheep will consume forbs, grasses, and shrubs and goats will seek shrubs, forbs, and grasses.
Sheep have been effectively utilized on western native ranges to control invasive species such as spotted knapweed and leafy spurge. Cattle that are grazing in conventional rotations often remain on western ranges for weeks at a time during the summer, and are moved when a set stubble height of key grass species like bluebunch wheatgrass or rough fescue is attained. When cattle, being primarily grass-eaters, remain in a pasture for long periods of time, they tend to exhibit grazing selectivity and choose vegetative grasses and young forbs over knapweed and other noxious weeds. Ranchers who have allowed a band of 800 or more sheep to graze for several days before or immediately after the cattle have seen significant knapweed usage by the sheep, with minimal grass utilization. Applying pressure with diversified livestock to knapweed, other forbs, and grasses in equal amounts will increase range biodiversity significantly over time. Sheep can be used as an alternative enterprise by taking value from wool, lambs, or by contract grazing on other parcels to control noxious weeds. Goats have a similar utility in areas with shrub infestation, and have been successfully used to control kudzu, English ivy, scotchbroom, and Chinese tallowtree in many parts of the country.
Last of all, know your pastures. Make it a point to understand the soil types and how they change with the aspect and slope of the land. Obtain some reference guides (Extension is a great place to find these) that will assist you in identifying the plants on your farm or ranch. The more you know about what your pastures will produce, the better position you will be in to make appropriate management decisions.
Remember – the principle concern in managing unwanted pasture plants is to
(1) encourage forage growth over weed growth through selection of appropriate livestock species and proper timing of grazing, (2) ensure adequate soil fertility through nutrient cycling, species diversity, and incorporation of legumes, and (3) rotate fields, even perennial fields, every now and then to break weed cycles. Perennial pastures can be rotated with cereals, summer annuals, or even vegetables to interrupt weed and problem insects.
Rotational Grazing and Paddock Size
Consider developing a rotational grazing system to take full advantage of the benefits of nutrient cycling as well as the ecological balance that comes from the relationships between pastures and grazing animals. High density stocking for short periods helps to build soil organic matter and develops highly productive, resilient pastures. For more information see ATTRA’s Rotational Grazing and Paddock Design, Fencing, and Water Systems for Controlled Grazing. Also available is Jim Gerrish’s Management-intensive Grazing: The Grassroots of Grass Farming, available from Green Park Press.
A rotational grazing management plan need not be complex. It merely has to direct the grazing animal to eat when and where you want them to in order to keep the plants in their growing (vegetative) stage. The basic principles of rotational grazing management include:
1. proper timing of grazing (corresponding to plant physiological stage)
2. proper intensity of grazing (duration on the pasture)
3. residue or plant height after grazing
In order to efficiently utilize the dry matter available a rotational grazing system should be implemented. Rotational grazing allows for more effective forage utilization by increasing herd size on smaller paddocks, thereby decreasing grazing selectivity and giving the farmer more control on what and when the livestock eat.
It is important to allow the pasture plants to get to sufficient height prior to turning the cattle onto the pasture. By waiting until the grass is 5 to 10 inches high, depending on species, the roots have become well developed and the plants can handle defoliation. Grazing intensity, or duration, can be taken care of by designing a suitable rotational grazing system. Rotational grazing, as the name implies, involves moving the cattle periodically from pasture or paddock to paddock. For instance, a good rule of thumb is to split a pasture into 10 or more paddocks with electric wire or electric tape, and stock each paddock heavily for a short amount of time. By doing this you are forcing the cattle to eat all that’s there, including weedy plants they might otherwise not eat. However, before the animals eat the plants to the ground, you move them to the next pasture. This takes into account the third principle. It’s important to leave several inches of grass to allow adequate leaf area for subsequent regrowth. Depending on the species, you will need to leave from 2 to 6 inches of plant stubble at moving time. An 11-paddock rotational grazing system that allows animals to graze each pasture for 3 days will give each paddock 30 days of rest. Most grasses will need 15 to 50 days of rest between grazing events to allow adequate regrowth, depending on season, moisture, and plant type.
Overgrazing. It is important to remember that overgrazing is not really a function of how many animals are on a pasture, but how long they remain there. In grazing management, time is the most important factor to consider in establishing a sustainable grazing system. Continuous grazing allows livestock to selectively graze the most palatable plants over and over. The problem with this isn’t necessarily in the selective grazing, but in the fact that the grazed plant does not get the time to regrow before it is grazed again. New growth is more palatable and contains more nutrients than older growth, so animals will come back for a second and third bite as long as they are in the pasture. A grazing system should allow the animal to be in the pasture long enough to take only that first bite. Frequent movement from pasture to pasture is a way to ensure that all plants have ample time to re-grow after grazing. In addition, for pastures with adequate water during the growing season, a very high stock density encourages animals to graze the pasture more uniformly than if the pasture was lightly stocked. In this situation the “weedy” species are being grazed at the same intensity as the “good” species.
Managing for Drought. Drought is a natural ecosystem process. The concept of an “average” or “normal” precipitation or temperature is a fabrication that humans use to try to understand complex systems and attempt to predict behaviors and outcomes. Whether in a humid zone or an arid environment, a producer will experience relative wet and dry years. Dealing with the dry years is a real challenge to livestock operations that rely on water to grow the plants and recharge the aquifers and streams that feed the animals. Having a drought plan is a very important component of a well-thought out farm or ranch management plan.
A drought-management option that deserves serious consideration is for a producer to maintain cow numbers at 75 percent of carrying capacity for “normal” years, and utilize the extra forage in wet years for high value animals such as stockers. In dry years the pastures will be better able to accommodate current cow numbers. Another option is to slow down rotations during dry years, thereby allowing more paddock or pasture rest time. This option can be effective especially when the herd is split between different pastures to minimize the impact on drought stressed plants.
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