Swingle citrumelo
Hybrids of grapefruit and trifoliate orange are referred to as citrumelos. Swingle has been the most widely and thoroughly tested of the many named and unnamed citrumelos throughout the world. It is a hybrid of Duncan grapefruit and trifoliate orange.
In Australia, Swingle initially attracted attention as an alternative to Troyer and Carrizo citrange for grapefruit, navel and Valencia oranges.
Tree size varies, depending on variety and soil type. Grapefruit are known to be very productive on Swingle overseas, while some navel oranges have performed well in Australia. It is thought to be more salt- and drought-tolerant than other trifoliate hybrids. Swingle will not perform well on shallow, poorly drained sites and highly calcareous soils.
Swingle is tolerant of Phytophthora spp., tristeza and the exocortis and xyloporosis viroids. It is resistant to nematodes and suitable for use in replant situations.
Compatibility
Swingle is incompatible with Eureka lemon and problems have been reported with some mid-season orange and mandarin cultivars. In WA there have been major incompatibility problems on Navelina and some orchards have suffered major decline and tree deaths at around 10 to 15 years old.
Recent problems with tree decline and death have also emerged with Daisy mandarin grown on Swingle.
Local experience
Swingle has been popular with many WA growers, particularly in the Bindoon/Chittering area. Recent incompatibility problems with Navelina and some other varieties have eroded that popularity.
It appears to be more salt-tolerant than some commonly used stocks and produces reasonable-sized, manageable trees. Experience suggests that vigour depends on soil type and climate. In general, it is more vigorous than Trifoliata — especially in the establishment years — and less vigorous than Troyer and Carrizo citrange.
In trials at West Gingin it has taken a while for trees to reach production and it is probably not suited to the light sands of this area. In trialing at Bindoon a number of trees of Newhall navel on this stock have showed symptoms of decline at around 10 years of age.