Weed of the Month – August 2014


(Gomphocarpus cancellatus)

(Photos: plant, monarch butterfly and caterpillar; flower bud; E. Cousins; Cape Jervis)

This woody weed from South Africa grows to about 1 metre high, and competes with natives for space, nutrients and water. It has escaped cultivation as an ornamental, and has invaded many reserves and national parks. The plant seed is spread by wind and water; its sap can be an irritating or toxic to some people, so use gloves when dealing with infestations. Hand pull small plants; use cut-and-swab or drill-and-fill techniques to poison large ones. If infestations are kept under control, the cotton bush does bring one benefit. Over the winter, you’ll notice the plant has many white-purple flowers…and often plenty of caterpillars, devouring the soft leaves and stems. These are the larvae of the Monarch butterfly, which have been plentiful around Cape Jervis this year. The Monarch is not truly an Australian native (though a resident for hundreds of years!), but apparently the larvae of the Lesser Monarch, which IS an Australian native butterfly, also uses this bush as a food source!

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