Grazing for noxious weed control requires a multi-year commitment. Although grazing does not immediately kill noxious weeds, it reduces seed production and growth, and stresses the plant. Each time the top of the plant is removed, it forces the root to use its reserves for re-growth, thereby weakening the roots and the plant. As seed production declines, fewer seeds are released to the environment. In time, weeds will be less able to compete with the desirable plant species.
Grazing can be part of an integrated control plan with chemical or other biological controls. Grazing can be used to remove old growth on noxious weeds, with the herbicide applied to the re-growth. This increases the effectiveness of the herbicide. In certain situations, noxious weeds may be grazed to suppress growth to the point where biological control methods becomes efficient. For example, in control efforts with leafy spurge, grazing is utilized to remove the old growth of the plant and control seed set, and then insects weaken the plant by eating the core of the stems and roots.
Current biological control measures for Russian Knapweed include a gall-forming nematode (Subanguina picridis) that was introduced to the United States in 1984, and has since been successfully established in Washington, Colorado, Montana, Oregon, Utah and Wyoming. This nematode forms galls on the stems, leaves and root crowns of Russian knapweed and weakens, but does not kill, the plant. It has not been found to readily spread long distances without assistance.
Continued research is being done to determine whether a gall-forming wasp (Aulacida acroptilonica) and a rust fungus (Puccinia acroptili) can be used effectively as biological control agents. There are currently no insects approved for management of Russian knapweed.
To determine if grazing with goats will be beneficial in a specific situation, the following considerations need to be carefully analyzed: 1) target weed(s) to be controlled, 2) desirable vegetation to be maintained, 3) environment and topography of the area and 4) management for the goats.
Some weeds and plants can be toxic to the animals that graze them, with the potential to cause serious or fatal health problems. Toxic plants must be identified so other means of weed control can be used. For some plants, grazing can be timed for the non-toxic stage. The University of Nevada Cooperative Extension has good reference material for identifying and controlling weeds in Nevada at (http://www.unce.unr.edu/publications/files/nr/other/EB9801.pdf ) or contact the extension office for assistance.
Goats prefer most plants early in the spring when they are tender but this may not be the optimum time to use grazing as a weed management tool. Plants expend the most energy as they are blooming and preparing for seed set. Grazing should occur as the plant is setting bud and into the bloom stage but before seed set. Grazing at this point should stop the seed set for the year. If grazed too early, the plant still has sufficient time to regrow, bloom and produce seeds. When weeds are grazed early, they should be allowed to regrow for a time and then be grazed again. Allowing time for re-growth prior to regrazing helps insure that goats will graze the weeds and not select the desirable vegetation. Grazing a plant two or three times within a season will weaken it, causing depletion of its root reserves.
As with other control measures, goat grazing must be applied properly to be efficient and effective. Using goats to control noxious weeds requires a long-term commitment. Due to extensive root systems and long-lived seeds in the soil, many noxious weeds can recover quickly after the grazing pressure is removed. An effective noxious weed control program requires proper management of goats and goals consistent with this type of program.
There are many goat producers in the area and some have developed businesses in which they rent or lease their goats for weed control. For more information on this topic go to: http://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1121.pdf "Management of Goats for Controlling
Noxious Weeds: A Primer" Shannon Williams, University of Idaho Lemhi County Extension Educator Bonnie Jensen, Owner, Weed Goats 2000, Salmon, Idaho
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