The biology, phenology and management of Australian weed-camel melon (Citrullus lanatus (Thunb.) Matsum. and Nakai)

Abstract

Citrullus lanatus (camel melon) is an important summer weed of Australian fallows, and can rapidly develop monocultural stands in sandy soils receiving adequate soil moisture. As a general review on the biology of C. lanatus, this paper reviewed the current published literature (including our recent published studies) and also summarised extensive field and laboratory studies performed on its biology, phenology and management in the South-West Slopes of New South Wales. Recent population genetics studies conducted in Australia have shown that the species is monotypic, and was introduced as a single colonisation event in the mid 1800's. Our studies showed genetic diversity in C. lanatus to be non-existent across Australia and invasive ranges and highest in the native range in Africa. Further genetic analyses have shown the species in Australia is identical to Citrullus lanatus var. citroides, the citron melon, native to Africa and now naturalised across Africa, Asia and North America, where it is a weedy nuisance or occasionally a food source for livestock and humans. Although limited genotypic diversity may facilitate potential biocontrol strategies for Citrullus lanatus in Australia, biocontrol may be difficult due to its close genetic similarity to commercial watermelon, a major horticultural crop in Australia and more globally. In Australia, field germination was observed to occur during a two to three-month period between late spring and summer, when warm soil temperatures occurred and field establishment was typically observed after significant rainfall events and was associated with soil moisture availability. Controlled environment seed dormancy findings indicated that dormancy was significantly reduced by storage at ambient laboratory temperatures over eighteen months. Seed dormancy was transient and appeared to be both physical and physiological in nature, and was dependent on the period of after-ripening during the post-harvest period. Key reproductive attributes, including high seed production, self-compatibility and pollination facilitated by several non-specific pollinators have likely resulted in increased spread of this weed in Australia and more globally. Management of C. lanatus is achieved using IWM strategies including pre and post-emergent applications of herbicides as well as limiting fruit production by cultural practices including mowing, grazing and cultivation.