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houndstongue although, in most cases,
<br />the fresh plant is considered unpalat-
<br />able by livestock and is generally
<br />avoided. Hounds[ongue contains
<br />pytroli-zidine alkaloids or PAs which
<br />may cause liver damage or failure in
<br />horses and cattle but not sheep.
<br />Poisoning can potentially occur when
<br />houndstongue is cut and dried with
<br />harvested hay or when animals are
<br />confined to a small azea lacking
<br />desirable forage.
<br />Poisoning occurs when animals
<br />consume sufficient quantities of plant
<br />material with high pyrrolizidine
<br />alkaloid concentrations. PA levels are
<br />generally highest in immature plants
<br />(1.5 to 2.0 percent dry weight) and
<br />decrease with maturation. The acute or
<br />chronic nature of poisoning depends
<br />on the PA concentration, amount eaten
<br />and rate of ingestion. Some clinical
<br />signs of PA poisoning for cattle
<br />include:
<br />Slight disinterest in food
<br />Stands off by itself,
<br />reluctant [o move
<br />Stands with head lowered
<br />for much of [he day
<br />Kicking at belly
<br />Gradual weight loss,
<br />slow to gain weight
<br />Diarrhea or constipation;
<br />severe straining
<br />Nervousness, convulsions,
<br />photosensitivity, jaundice, coma
<br />To prevent poisoning, do no[
<br />confine animals in a pasture lacking
<br />proper forage and avoid harvesting
<br />houndstongue in hay crops. Should
<br />poisoning occur, owners must remove
<br />the animal from pasture as soon as
<br />possible and consult a veterinarian. If
<br />the animal retains a mild appetite it can
<br />be placed on a low protein, high
<br />energy diet (e.g., timothy hay).
<br />Control
<br />Long-term control of houndstongue
<br />requires an integrated weed manage-
<br />ment approach. The most effective
<br />method of weed management is
<br />preventing their spread and estab-
<br />lishment, Practices which reduce
<br />the spread of weeds include: limiting
<br />weed seed dispersal, containing
<br />current infestations, minimizing soil
<br />disturbances, detecting and eradicat-
<br />ing weed introductions early,
<br />establishing competitive grasses and
<br />proper grazing.
<br />Adopting rangeland management
<br />strategies which maintain competi-
<br />tive grasses and desirable forage can
<br />help prevent some instances of PA
<br />poisoning. In azeas susceptible to
<br />invasion, proper livestock grazing
<br />should include altering timing,
<br />frequency and level of defoliation
<br />to allow a full recovery of desirable
<br />grass species. This grazing regime
<br />promotes litter accumulation to
<br />allow proper nutrient cycling and
<br />enhances the vigor of desirable
<br />grasses which limits the invasion of
<br />rangeland weeds.
<br />Several strategies exist for
<br />integrated houndstongue manage-
<br />ment. Surface cultivation, roguing
<br />(digging, scraping or ripping) and
<br />hand-pulling are considered ineffec-
<br />tive means of houndstongue control
<br />because plants are capable of
<br />regenerating from the root crown.
<br />However, severing the root
<br />crown 1-2 inches below the soil
<br />surface with a spade and removing
<br />topgrow[h can be effective in
<br />controlling small infestations.
<br />Mowing a[ ground level can reduce
<br />regrowth by 60 percent as well as
<br />seed production in some cases.
<br />First-year rosettes can be con-
<br />trolled using picloram (Tordon
<br />22K®) applied at 1 quarUacre in
<br />spring, summer or fall. An eazly
<br />spring application of 2,4-D amine (1
<br />quart/acre) before bloom can provide
<br />up to 97 percent control of second
<br />yeaz rosettes. This vestment is
<br />effective along waterways.
<br />Metsulfuron (Escort®) is recom-
<br />mended for use in pastures and
<br />disturbed azeas. Escort® may be
<br />applied to rangeland infestations
<br />(Z/10 [o s/10 oz./acre). Escort® should
<br />be applied mid-June when plants are
<br />actively growing. It is important to
<br />always add a recommended nonionic
<br />surfactant to the spray solution.
<br />Reapplication may be needed in the
<br />first year of control [o prevent seed
<br />production. For complete control,
<br />annual herbicide reapplications may
<br />be needed.
<br />To date, five biological control
<br />agents are being screened for their
<br />potential use on houndstongue.
<br />These include a root weevil
<br />(Mogulones cruciger), a seed weevil
<br />(Mogulones borreglnis), a stem
<br />weevil (Mogulones trisignatus), a
<br />root beetle (Longitarsus
<br />quadriguttatus) and a root fly
<br />(Cheidosia pasquorum). The screen-
<br />ing of Mogulones cruciger has been
<br />completed. Al] five insects, if found
<br />sufficiently host-specific, will be
<br />released in Montana within the next
<br />few yeazs.
<br />Note: Information in this document is
<br />provided for educational purposes only.
<br />Reference to commercial products or
<br />trade names does not imply an
<br />endorsement of them by the MSU
<br />Extension Service.
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<br />t furtherance of cooperative extension work in agriculture and home eco- q_6 (Range and Pasture)
<br />nomics, ads of May 8 antl June 30, 1914, in cooperation with the U.S.
<br />Department of Agriculture, LeRoy Lun, Interim Vice Provost and Director, Reprinted March 203 (5003035
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