Crofton weed (Ageratina adenophora) is an erect, perennial herb or small soft-stemmed shrub. It has numerous, woody branched stems that are densely covered in sticky hairs when young which can be green, reddish or purplish in color. A. adenophora become slightly woody and turn brownish-green or brown in color when mature. Its roots are yellowish in color and give off a distinct carrot-like smell when broken or damaged. It's leaves are broad, slightly crinkled, trowel-shaped, and toothed with chocolate-colored petioles. Crofton weed produces dense clusters of white flowers in the spring and summer. A. adenophora is native to Mexico, but has been introduced to many countries as an ornamental in the nineteenth century.
Crofton Weed Toxic Components
A. adenophora is highly toxic to horses if ingested. Unfortunately, crofton weed is palatable to horses, and if available to them in pastures, they will seek it out to consume. Following several weeks of grazing the plant, horses will start to cough frequently, quickly followed by exercise intolerance, depression, and death.
Consumption of the plant by horses causes whats known as “blowing disease” in Hawaii and “Numinbah disease” or “Tollebudgera horse disease” in Australia. Symptoms might take several years to become noticeable. In Zimbabwe, it was the cause of mortality in three horses.
- Frequent Coughing
- Made Worse With Exercise
- Exercise Intolerance
- Shortness Of Breath
- Condition Loss
- Respiratory Distress
- Heart Failure
PHYSICAL CONTROL: Small areas of scattered plants can be dug out with a mattock. Crowns must be removed to prevent regrowth.
MECHANICAL CONTROL: Slashing is often used to control heavy infestations on accessible land. Regular slashing will reduce flowering and seedset, thus reducing spread by seeds. It will also reduce the vigour and density of Crofton weed infestations and, combined with competitive pastures, will eventually bring them under control. The slashed and dried plant, however, is still attractive and toxic to horses. Take care to keep horses away until the plant has been completely removed from the paddock.
CHEMICAL CONTROL: Chemical treatment appears to work most effectively during late summer and autumn. When spraying Crofton weed with herbicides it is important to ensure that spray does not drift onto desirable plants and to maintain operator safety.
Well-managed, competitive pastures are important in preventing weed invasion and this principle also applies to Crofton weed. Dense pasture swards suppress seed germination and livestock eat young seedlings with the balance of their feed. Therefore, fewer plants grow to maturity. Goats are known to eat Crofton weed. The degree of weed control by goats depends on the stocking rate, weed density and the availability of other suitable feed. Using goats to help control widespread infestations may be worth considering, although some knowledge of goat husbandry and fencing is necessary. The same group of goats should be used for only one or two seasons to avoid risk of chronic health problems.
BIOLOGICAL CONTROL: A fungus that was accidentally introduced, Cercospora eupatorii, and a native crown-boring insect (Dihammus argentatus) also attack Crofton weed