Greasewood is an erect, spiny, woody perennial shrub that grows 1 to 1.5 meters tall. Flowers are small and light green to whitish. It has many thorns with thick, narrow, green leaves on rigid branches. Its bark is smooth and white.
Greasewood is a range shrub that livestock can generally eat safely in moderate amounts with other forage. It is moderately palatable. Death occurs when livestock eat large amounts in a short period of time. Losses generally occur in the fall and winter when sheep or cattle eat large quantities of leaves that have fallen to the ground or from the early growth in spring. The plant toxins, sodium and potassium oxalates, are found in the leaves with lower concentrations in other plant parts. The amount of toxin varies considerably in the different areas where it grows (from 10-22% of plant dry weight). Greasewood increases in toxicity as the growing season advances.
Where and When It Grows
Greasewood is adapted to the heavy saline soils of semiarid regions. It is confined to alkaline soils and may form the dominant vegetation on alkaline flats. It starts growing in early spring. The leaves remain succulent until fall, when they freeze, dry, and drop off. Buds remain on plants most of the year.
How It Affects Livestock
Signs of poisoning may develop 4 to 6 hours after an animal eats a toxic amount of greasewood. Greasewood poisoning in livestock is similar to that caused by halogeton resulting in hypocalcemia, renal necrosis and subsequent uremia. About 1 gm oxalate/kg body weight is lethal in sheep. This would be about 0.5 kg of green leaves and fine stems for a sheep or 1.5- 2.0 kg for a cow. To be lethal the plant must be consumed quickly without other diluting forages. Animals can become conditioned to oxalate ingestion by feeding oxalates at low doses for several days. In such animals the lethal doses are from 30-50% higher than non-conditioned animals.
Signs and Lesions of Poisoning
- Dullness, weakness, reluctance to move
- Breathing rapid and shallow
- Death occurs between 2 hours and several days
- Uremia, hypocalcemia, death due to interference with energy metabolism
- Renal tubular necrosis with crystals
How to Reduce Losses
Rumen bacteria can metabolize the toxin to a non-toxic form. Therefore, introduce livestock into heavy stands of greasewood slowly so as to allow time to adapt to the toxic substance in the plant (2 to 3 days). Make sure animals are full when first allowed to graze greasewood. Supply adequate water and a good variety of forage.
No treatments have definitively proven to be effective for greasewood poisoning. It has been suggested that oral dicalcium phosphate may decrease availability and absorption of the oxalates (0.25 kg per day). Although intravenous calcium gluconate reverses the hypocalcemia, it does not appear to alter all of the clinical or pathologic changes.
Greasewood can be effectively controlled with 2,4-D (1 kg ai/Ac). Two or more successive years of treatment may be necessary for effective control because of its resprouting ability. Follow all precautions for handling herbicides