A much-cursed Weed

Pseudanthemum variable

Few growers in this region are not plagued by this pest, variously known as Kirkwood’s Curse or Mackinney’s Menace after the two nurseries that have been blamed for introducing it to orchid collections. It is actually a plant native to the dry sclerophyll forests along the eastern coast of Australia. It is cultivated and sold by some plant nurseries as the “Butterfly Plant” because it is said to be attractive to four or more species.

The plants are fast-growing and commence seeding at an early stage. Seed capsules explode on maturity, scattering seed which can be wind-borne over a range of several metres. Once you have it, it will quickly spread through your orchid collection and throughout your garden. Orchid potting media provide the ideal hosts. Plants have a long taproot, often bifurcated, usually similar in length to the height of the plant. Most attempts to pull plants out of a pot or the ground result in breakage at ground level, leaving behind the root system which will promptly re-grow. The only way to effectively remove the weed from potted orchids is to re-pot, removing all traces of the taproot from the plant’s root ball. For plants with tightly matted roots, this can be difficult. An alternative, sug- gested by Wayne Turville at Australian Orchid Nursery (Melbourne), is to paint the leaves of the weed with concentrated (50%) Glyphosate. You would need to be very careful not to get any Glyphosate at this strength on your plant and watering should be with held for at least 48 hours

Plants containing this weed in the pot can be deemed to be not in “Show Bench Condition” as defined by the AOC Judging Handbook. To avoid the risk of spreading this pest to other growers, exhibitors at shows or meetings should ensure that all such plants are removed from pots beforehand.

Author: Charlie McMonagle