Uintah County  
 

Weed Control

Traditionally, weed control has focused on one method to control weeds – herbicides. Where possible, the Weed Department uses IWM or “Integrated Weed Management” a method of weed control that utilizes two or more types of controls to control or eliminate certain weeds. With IWM, there are four basic methods we can use to control weeds – herbicide, biological, mechanical and cultural. Weed control is often far more effective when using multiple controls together.


Herbicide being used to control noxious weedsHerbicides are chemicals that affect the ability of the plant to grow properly. Pre-emergent herbicides are applied to the soil prior to seed germination, either in the fall or spring. These herbicides inhibit the weed seed's ability to germinate. Post-emergent herbicides are applied to actively growing plants. The plant then absorbs the herbicide through the foliage, stems/bark and/or roots. These herbicides affect the chemical balance of the plant causing growth irregularities which in turn kills the plant or destroys its ability to reproduce. Herbicides are engineered to affect certain types of plants – some are selective, killing only broadleaf weeds or only grasses while others are non-selective which may kill or damage any plant it may contact. Non-selective herbicides, such as Roundup® (glyphosate), used carelessly, often create areas for noxious weeds to invade by removing beneficial, competitive plants. Herbicides must be used cautiously to avoid off target damages that may occur to beneficial plants, animals, or yourself. Be sure to read and follow all label directions and precautions to ensure proper results.

It is also important for people to get away from the 2,4-D and Roundup® mentality. Although 2,4-D and Roundup® continue to have their place in weed management, recent technology has produced many specialized herbicides that are far more effective than 2,4-D or Roundup® for many noxious weeds. Additionally many plants are now developing resistance to Roundup (glyphosate). Although these herbicides may be far more expensive than 2,4-D and Roundup®, they often save you money in the long run because they can drastically reduce or eliminate the weed problem with fewer appilications. Less herbicide put on the land is better for your business and the environment. Contact the Weed Department to learn about other herbicide options.

Some folks have noticed that certain plants don't die after a herbicide application. There are two likely reasons for this. First is using the wrong herbicide. Most herbicides are formulated to kill certain plant species. These weeds are listed on the herbicide label. Second is there are several plants that have developed herbicide resistance. Herbicide resistance most often occurs when certain herbicides are used exclusively for many years in a row (5+ years). Contact your local weed control expert to learn more about herbicide resistance in your area.

Surfactants. As important as selecting the proper herbicide is, selecting and using a high quality surfactant is vital to the success of your weed control program. Weeds have many defenses against herbicides such as waxy cuticles, pubescence (the tiny hairs on the leaves and stems), extensive root systems among other things. Surfactants break down water tension allowing the herbicide to spread across the weeds surface allowing better translocated into the weed. Without the surfactant much, if not all, of the herbicide will run off or evaporate before it can be absorbed. Yes, surfactant cost more money, but without it you simply will not get anywhere near the full potential from your herbicides and you will be wasting money.

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Biological controls are the natural enemies of noxious weeds. Because most noxious weeds have been introduced from foreign countries they have few if any natural enemies here (insects, pathogens, herbivores, etc.) to keep them in balance with their new environment. With few, if any, natural controls many of these weeds compete aggressively with native vegetation, often displacing it. Animal and Plant Health Inspection Service (APHIS) is working to bring select natural enemies (typically insects and pathogens) of noxious weeds to the United States. APHIS tests each possible biological agent and possible mutations for a period of 5 to 7 years to ensure the agent will not harm any beneficial vegetation. Biological controls are not meant to eradicate target weeds, but they can be an effective way to bring them under control. Biological control agents are an important management tool for select weeds that are beyond control due to infestation size, inaccessibility, and/or herbicide resistance. Herbicide or mechanical control may be used to prevent additional weed spread from the main weed infestation.

Biological controls being used in Uintah County include:
Field bindweed Gall MitesAceria malherbae have been introduced near Jensen, Utah and appear to be having significant impact on field bindweed near the release site.

Musk thistle Seedhead Weevils and BeetlesTrichosirocalus horridus a stem borer weevil and Rhinocyllus conicus a seedhead weevil (below) are biocontrol insects that have been widely introduced in Utah. These insects now spread very well on their own and they can be found throughout Uintah County.

Musk thistle biocontrol

Leafy Spurge Flea beetles — Three species of flea beetles, Apthona nigriscutis (below left), A. flava, A. Czwalinea, were introduced to the counties leafy spurge population in 2008.

Long horn stem beetleOberea erythrocephala (below right) were also released on the leafy spurge population in 2008.

Leafy spurge flea beetles (Apthona nigriscutis) are an excellent biological control on leafy spurge Leafy spurge biocontrol

Saltcedar (tamerisk) Leaf BeetleDiorhabda carinulata (formerly D. elongata) (Below) have been released on several sites along the Green River in Uintah County. Adults (5-6 mm) emerge in May and June and begin laying eggs. Larvae emerge in about a week. Larvae morph through 3 instars (1st - 2 mm, 2nd - 4 mm, 3rd - 9 mm) over 21 days then pupate into adults in ground litter. Adults live for 15-20 days. When well established, D. carinulata may defoliate up to 1/2 mile of saltcedar per week. D. carinulata have spread to virtually every area in Uintah County.

Diorhabda elongata 3rd instar larvae and adult

Goats and/or Sheep — Goats and sheep have been used successfully to control Leafy spurge (below) and Russian knapweed in Uintah County. Goats and sheep gain weight readily on a diet of noxious weeds. They must be strictly confined to the areas of weeds so they will feed on the target species and they soon gain a taste for the "undesirable" vegetation.

Goats can be an excellent biological control for noxious weeds

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Mechanical controls involve the use of machinery to disrupt the life cycle of weeds. Plowing, digging, hand grubbing and chopping can be affective on select weeds. Annual and biennial weeds are most susceptible to these methods. Mechanical control alone is not normally a good option for Perennials. Perennials often benefit form these disturbances since they may reproduce from broken plant parts. However, combining with a follow-up treatment of herbicide is often very effective. Cutting Russian-olives or saltcedar trees and treating the stumps with select herbicides is very effective.

A BrushHog being used to mechanically control saltcedar

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Cultural controls utilize competition to control weeds. Many weeds can be controlled, but not usually eradicated, by planting and cultivating other competitive vegetation that is able to compete for available resources. Herbicide or fire is often used to clear away the existing weeds, then seeds are distributed prior to weed germination. This practice is commonly used following wildland fires to prevent noxious weeds from re-establishing too rapidly or easily.

Weed control manager preparing to apply grass seed for cultural control

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