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3.3.2 Mechanical Control <br />Mechanical control of noxious weeds can be an effective tool to physically disrupt <br />noxious weed growth and seed development. A combination of mechanical methods may <br />be used including tilling or disking, mowing, hand-held weed trimmers, mulching, hand - <br />pulling, hoeing, or livestock grazing. Mechanical weed control practices must be applied <br />with correct timing to maximize their effectiveness in preventing vegetation development <br />or seed production. Re -grading areas and burying infestations with clean soil can be used <br />to control heavily infested areas that chemical control is not enough to control the <br />infestation. Removing flower and seed heads from a noxious weed plant and disposing of <br />them properly can prevent dispersal of additional seed but does not eliminate the existing <br />infestation without other control measures. <br />Annual weedy species may be readily controlled with mowing or physical removal. <br />Many biennial noxious weed species can be dug up if the majority of the root system is <br />removed ant he the plant is disposed of properly. Most perennial species shave extensive <br />root systems with significant carbohydrate reserves. For such weed species mowing may <br />only control seed production without seriously affecting the plant's survival. Targeted <br />weed species should be correctly identified to determine if they will be effectively <br />controlled by mowing or other mechanical methods. Mowing should occur prior to <br />flowering and setting seed. Mowing after seed production has occurred may aid in the <br />spread of weed seeds. Disking or tilling areas containing perennial noxious species may <br />increase infestation due to root sprouting. In most cases mechanical control methods <br />cannot be used alone and are not effective against hardy perennial weed species. <br />3.3.3 Biological Control <br />Biological control of noxious weeds can be an effective tool to physically disrupt plant <br />growth and seed development of very large infestations of weeds. Biological weed <br />control methods and practices must be applied with appropriate timing to maximize their <br />effectiveness in preventing seed production. It must be noted that the use of biological <br />controls normally does not eradicate an infestation of weeds; rather they are capable of <br />reducing weed species vigor and reproduction. The Colorado Department of <br />Agriculture's Biological Pest Control Program has on-going biological control programs <br />for several noxious weed species, primarily B and C List species. <br />3.3.4 Chemical Control <br />Chemical control of noxious and pest weeds can be the most effective tool to disrupt <br />plant growth and seed development. Properly timed herbicides applications can prevent <br />seed production, disrupt plant establishment and growth, or kill noxious weed plants. The <br />physiologic effects of an herbicide on plant growth and development must be understood. <br />Properly identifying the weed species and timing the most effective chemical control <br />method for the phase of the plant's growth cycle is critical to effective weed control. <br />To avoid development of resistance to a particular herbicide through repeated use over <br />prolonged periods of time, herbicides with varying modes of action should be used. Also, <br />herbicides must be applied according to the manufacturer's label recommendations (i.e. <br />application rate, method, and timing). Herbicides should be applied using calibrated spray <br />Cresson Project Weed Management Plan 5 <br />