The DETRIMENTAL biological effects of herbicide; both pre- emergent and post emergent applications make it necessary to reevaluate our approach to the use and application of herbicides, and to find alternative methods to manage weeds effectively without the negative biological consequences of chemical weed management.
Herbicides such as Garlan, Roundup and a variety of other industrial hydrocarbon based synthetic chemicals commonly used for the management of weeds and undesirable plants are often applied carte blanc, that is indiscriminately. Weed management is a complex game of balance and does not necessarily exclude the application of herbicides as herbicides may be useful or appropriate under certain conditions. However, the negative side effects of herbicidal treatments are widely known and sustainable weed management will limit the use and application of herbicides in favor of more ecological approaches.The primary reasons that land managers have shifted away from the use of herbicides are manifold. Weeds have developed tolerances or even immunity to certain pesticides from repeated application and overuse of herbicide. These resultant “super weeds” are mutant varieties which are unaffected by herbicide or require substantial increase in herbicidal application. Unfortunately, soils, watersheds and aquatic and mammalian components of ecosystems have not developed these same tolerances, nor have the multitude of desirable plants; primarily our native grasses, herbs and forbs evolved biotic protective mechanism to counteract the herbicides.
As herbicides function on a purely chemical level-- that is, herbicides interact with the physiology of a plant chemically, grazing animals such as goats and sheep impact weeds on multiple levels effectively eliminating a plants capacity to reproduce and inhibiting or precluding vegetative growth. Additionally, grazing animals can positively impact soil chemistry and soil structure which is a further layer of weed mitigation.
On a physical level grazing can inhibit a plants ability to provide nutrients through it circulatory system, can inhibit a plants ability to photosynthesize, diminish a plants ability to store and deliver carbohydrate and or kill or eliminate a plant altogether.Chemically, grazers can alter P , K, N, levels in soils which is beneficial in areas where weeds have degraded soils and perpetuate conditions unfavorable for competing beneficial plants. Chemically amending the soil through grazing activity is also an effective bio-control for certain invasive weeds ex.. Italian thistle has a propensity towards soils that are potassium deficient, as grazers amend the soil with P, Italian Thistle , which is sensitive to P levels is less inclined or unlikely to invade.Another physical element of weed control with grazers is the hoof impact and its resultant effect on the physical structure of soils. Capped soils are often infested with weeds. Many weeds have elaborate tap root systems and are more tolerant to soils with poor aeration and water flow. Capped soils perpetuate weed cycles and inhibit beneficial competitor plants. Grazers break open capped soils reintegrating organic matter and stimulating new growth. The result of an “open” soil structure is improved circulation of plant nutrients and water, thus increasing the viability of the soil reducing erosion and encouraging non-weedy species to “out- compete” invasive plants.
These are general principles of weed management with grazing. The other requisite components for successful bio-control of weeds using grazing are grazing timing and grazing planning. It is imperative to time grazing according to plant cycles of the specific plants targeted for management so that grazing is administered during peak growth cycles or during periods when weeds are most vulnerable and effected by disturbance. Similarly, it is essential to administer grazing to most positively effect the beneficial vegetation that must be encouraged to compete and reestablish itself after and area has been treated for weedy infestation. Without reintroducing or reestablishing healthy, viable and preferably native vegetation, weed cycles will perpetuate themselves indefinitely as nature will inevitably fill the vegetative vacuum with more aggressive and adaptive weedy plants.
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