Establishment of, and preliminary impact studies on, the rust, Maravalia cryptostegiae, of the invasive alien weed, Cryptostegia grandiflora in Queensland, Australia

Abstract

The rust fungus Maravalia cryptostegiae, from south-west Madagascar, was introduced into Australia in 1995 as a classical biological control agent against the highly invasive rubber-vine weed Cryptostegia grandiflora, a woody climber endemic to Madagascar. The rust was released at 69 sites between 1995 and 1997 and is now established throughout the plant's exotic range in Queensland, estimated at over 40 000 km 2 . Dispersal was low in the first 3 -4 months but was virtually linear thereafter, and the rust spread over 100 km within the first year; after 3 years it was recorded 550 km away from the nearest release site. Spraying both dry and aqueous inoculum of uredinioid teliospores from the ground using mist-blowers, as well as from the air by atomizing spore suspensions, resulted in rust-induced defoliation, producing an overall reduction in fecundity and biomass of the weed. In sites with low water tables, weed growth decreased markedly, with a reduction in plant volume from 9 m −3 to 1 m −3 over a 4-year period. Both rust-and drought-induced stress combined to cause up to 75% plant mortality at some sites, and at all monitored sites, seedling recruitment was virtually nil. Improved growth of indigenous grasses amongst rubber-vine thickets has increased fuel loads and created opportunities to use fire as a component of an integrated approach to the management of this economically and ecologically damaging weed.

Tropical Vine Growth and the Effects on Forest Succession: A Review of the Ecology and Management of Tropical Climbing Plants

“…Australia has frequently witnessed the problems that can occur from the introduction of non-native species to control other non-native species. In Tomley and Evan's study, the rust fungus did reduce the growth and biomass of the rubber-vine without report of negative consequences (Tomley & Evans, 2004). In some cases, however, the introduction of a biological control agent has resulted in damage to native plants or the inadvertent invasive spread of that biological control agent.…”

“…By 1990, over 30,000 square kilometers were estimated to have rubber-vine cover. Tomley and Evans (2004) explain the subsequent attempt at biological control through the introduction of the rust fungus Maravalia cryptostegia from Madagascar in 1995. They describe, "The rust fungus induced defoliation of the vine and overall reduction of fecundity and biomass of the weed.…”

“…They describe, "The rust fungus induced defoliation of the vine and overall reduction of fecundity and biomass of the weed. Improved growth of indigenous grasses among the rubber-vine thickets increased" (Tomley & Evans, 2004).…”

Fallopia japonica, an increasingly intractable weed problem in the UK: Can fungi help cut through this Gordian knot?

“…Initially, any biocontrol agent takes time to catch up with its host and probably many years before the benefits can be seen. Nevertheless, the cost:benefit ratio can be massive, both from insect agents (McFadyen 1998) as well as from fungal agents (Evans 2000), especially rust fungi (Tomley & Evans 2004). …”

Population Biology of Plant Pathogens

“…(c) If the rate of increase during the growing season is such that random extinction is unlikely, infection will usually be limited by the upper density limits in a particular season, and there will be little correlation of levels across years. (Tomley and Evans, 2004). Variation in disease can cause substantial variation in seed yield of crop plants, as in the Bengal famine of 1942-1943, when exceptional environmental conditions caused yields of rice to drop by up to 80% (Tauger, 2003).…”