The cost of controlling the major pests and diseases of sugarcane to the sugarcane industry in Australia was estimated to be $111 million in 1996 (McLeod et al. 1999). The major pests and diseases that cause losses in sugarcane production include canegrubs, feral pigs, ratoon stunting disease (RSD), sugarcane rusts, chlorotic streak and soil-borne diseases (McLeod et al. 1999).
Various biological agents including bacteria, fungi and viruses cause diseases of sugarcane. Diseases of sugarcane that have been identified in Australia are listed in Table 3.
Disease control in sugarcane is based on an integration of legislative control, resistant varieties, and other management procedures. Long-term disease management in Australia focuses on the development of disease resistant cultivars (McLeod et al. 1999). Short term spraying options are available, but their economic viability may not be sustained. Hygiene is important to disease management strategies, particularly for diseases transmitted through cuttings such as RSD and leaf scald. Cutting one infected stalk may lead to significant infection to the next 100 cuttings which are subsequently cut by the same blade (Croft et al. 2000). Machine harvesters can also transmit the disease.
Many sugarcane diseases are also managed through the use of disease-free planting material supplied through Cane Protection and Productivity Boards. To obtain such planting material hot-water treatments are used to disinfect planting material. Long hot-water treatment (3 hours at 50ºC) is used to control RSD. Soaking in ambient temperature running water for ~40 hours followed by 3 hours at 50ºC is used to control leaf scald bacteria. Short hot-water treatment (50ºC for 30 minutes) is used to control chlorotic streak and some insect pests (Croft et al. 2000). Minimising cultivation also can encourage healthy microbial communities and reduce disease-causing organisms (Allsopp et al 2000).
The RSD is caused by C. xyli subsp xyli which infects vascular tissues of sugarcane. The ratoon stunting disease of sugarcane is probably the most important disease of sugarcane. In Australia, the estimated lost from this disease was $6.3m/year (McLeod et al. 1999). The symptoms are poor growth and resulting in stunting shoots, which might not be obvious if most plants in the field are infected. The visual symptoms of red orange dots in the vascular tissues can be seen only when the stalks are cut and sliced (Croft et al. 2000). Yield loss often becomes more severe in subsequent ratoon crops.
Leaf scald (Xanthomonas albilineans)
Leaf scald is caused by a bacterium X. albilineans which infects the vascular tissues of sugarcane. It is found in most sugarcane districts in Queensland (Croft et al. 2000). The symptom of leaf scald is characterised by the long white to cream streak on the leaves. The severe infected leaves appear scald and rolling inwards. The top of the severe infected shoots turn chlorosis. Yield loss occurs through the death of infected cane stalks.
Leaf scald can spread by wind-blown rain, plant material, contaminating cutting equipments such as planters and harvesters (Croft et al. 2000). Leaf scald can infect many other grass weeds which are alternate hosts and act as a reservoir for the disease. Extremes of moisture and temperature conditions favour disease transmission.
Orange rust (Puccinia kuehnii)
Orange rust is caused by P. kuehnii. The symptom is distinct from the common rust caused by P. melanocephala. Pustules of the orange rust are orange while those of common rust are reddish brown. Leaf lesions tend to be grouped in cluster while those of common rust are distributed evenly on leaves. Pustules cause rupture to the leaves and allow water to escape from the plant, leading to moisture stress. Rain favours the development of orange rust but inhibits the development of common rust (Croft et al. 2000).
In 1999-2000, sugarcane crops in Australia were affected by the outbreak of orange rust, which had severely damaged the most widely grown commercial cultivar Q124 (Apan et al. 2003). Later, the new promising cultivar of high yield and resistance to orange rust Q205 was developed (Courtney 2002).
Sugarcane rust (Puccinia melanocephala)
Sugarcane rust is caused by P. melanocephala an obligate parasitic fungi. Estimated loss from sugarcane rust in Australia was $3.5m (McLeod et al. 1999). The symptoms started from tiny, elongated spots, light green to yellow on leaves. These spots later enlarge and turn to reddish brown. Yield loss depending on environmental conditions was estimated to be 10-20% in Australia (Bernard 1980) and 20-40% in USA (University of Florida 2004).
Pachymetra root rot (Pachymetra chaunorhiza)
Pachymetra root rot is a disease only found in Queensland sugarcane districts (Magarey & Bull 2003). The disease seems to favour high rainfall areas. In northern Queensland, surveys indicated almost every field is infected with the disease. The disease is characterised by a soft rot of the primary and some secondary roots leading to poor root development. Yield loss caused by Pachymetra root rot was estimated to be up to 40% (Magarey 1994).
Sugarcane smut (Ustilago scitaminea)
Sugarcane smut is a serious disease of sugarcane that can reduce yields by 20-30%. The disease causes severe stunting and is characterised by black, whip-like structures that form at the growing points of sugarcane plants. These whips replace the spindle leaves and are formed in the shoots developing from infected cane cuttings (Frison & Putter 1993). There was an outbreak of smut in Australia in July 1998 in the Ord River area of Western Australia. This outbreak was controlled and the disease has not been detected in eastern Australia (Croft et al. 2000). Short hot-water treatment and use of resistant varieties can control smut.
The movement of sugarcane and sugarcane machinery is restricted in Queensland by the Plant Protection Act 1989 (Qld) and the Plant Protection Regulations 2002 (Qld). Provisions under the Plant Protection Act 1989 (Qld) allow for inspectors to order the destruction of diseased cane.
Other fungal diseases of sugarcane are minor diseases (Table 3) and cause less impact on yield.
The cause of the disease is unknown but it is thought that the disease may be caused by virus. The disease occurs in sugarcane districts with wet and poorly drained fields. Lower incidence of the disease is generally found in drier regions (Croft et al. 2000). The symptoms are the yellow to white streaks on the leaf and on the midrib and leaf sheath. Older streaks change to yellow and more visible than younger streaks. Finally chlorosis starts to appear in the middle of the leave. Internal vascular bundle tissues may show reddish in colour. Yield can be reduced by 70% (Croft et al. 2000).
The disease is transmitted in soil by water. It is common in areas with poor drainage and flood prone areas. Chlorotic streak can also transmitted through cuttings. Infected cuttings show poor germination, slow and number of stool reduced.
Fiji disease is caused by Fiji disease virus (FDV) genus Figivirus, family Reoviridae. The symptoms is whitish galls raised on the underside of the leaf blade and midrib. Galls produced due to the disorder of cell proliferation in the phloem and xylem. The colour of the galls can vary from white to green and the surface of the gall is usually smooth. When the gall is old the epidermis may be ruptured and appear brown. At advance stage of infection, stem development slows down and successive leaves become smaller and stiffer, the whole top part develops a fan like appearance (Croft et al. 2000) .
Fiji disease can be transmitted by infected cutting, or by a vector: plant hoppers (Perkinsiella saccharicidae). Significant yield loss has been recorded in 1970s in Queensland (Croft et al. 2000). Due to the intensive management program put in place, no reports of the disease incidence since the 1980s.
Sugarcane mosaic is caused by a number of potyviruses (Table 3) such as the Sugarcane mosaic virus (SCMV). The mosaic symptom pattern appears in young growing leaves. Once old, infected leaves may appear more normal as the mosaic become green. The record of yield loss caused by sugarcane mosaic was 40% in some fields (Croft et al. 2000). Aphids are the vector for transmission of the disease. Seed produced by infected cane can also transmit the disease.
Table 3. Diseases of sugarcane that cause yield losses in Australia (Frison & Putter 1993; McLeod et al. 1999; Croft et al. 2000).
Disease free planting material and resistant varieties
There are many insects and animals that are pests of sugarcane. In addition some insects such as plant hoppers (Perkinsiella saccharicida) are known vectors of other diseases (Croft et al. 2000; Allsopp et al. 2000). Information below is summarised from ‘Australian Sugarcane Pests’ (Agnew 1997).
Animal pests of sugarcane are numerous and include ground rats, climbing rats, feral pigs, wallabies, foxes, the striped possum, the eastern swamphen and cockatoos. Ground rats (Rattus sordidus), wallabies, striped possums (Dactylopsila trivirgata), the eastern swamphen (Porphyrio porphyrio) and cockatoos (Cacatua galerita) are native to Australia and consequently are protected. Permits for control of native animals in cane fields must be obtained from the relevant Cane Protection and Productivity Board. Integrated pest management is now widely employed to discourage and control economically damaging pests. This includes strategies such as controlling weeds that may harbour rats (Allsopp et al. 2000).
Leaf and stem – sap feeding, damaged leaves more susceptible to fungal diseases
Leaf and stem – sap feeding
Leaf and stem – sap feeding
Leaf and stem – sap feeding
disease free planting material
2. toxicity and allergenicity
Section 2.1 Toxicity
Sugarcane is a well-established agricultural crop with a long history of safe use. Sugarcane has been cultivated in Australia for over 100 years. Commercial sugarcane is grown as a source of sugar (sucrose) for human food. By-products from processing sugarcane into sugar such as molasses and bagasse have been mainly used as food additives in stockfeed.
Sucrose is the primary product of plant photosynthesis and, therefore, common in food crops consumed regularly by humans and animals. Sucrose has an exceedingly long history of human dietary exposure. It has been classified as a non-toxic substance to humans (MSDS 2004). The LD50 of sucrose for rats is 30 g/kg body weight (MSDS 2004). Consuming sucrose in extremely large oral dosages may produce gastrointestinal disturbances. Although there is no direct evidences that link sucrose consumption with toxicity, there are several studies indicating that sucrose intake should be limited because it may be associated with health problems (Howard & Wylie-Rosett 2002). Studies found that a high intake of sucrose was associated with cardiovascular diseases, development of type II diabetes, obesity and hypertension (Howard & Wylie-Rosett 2002). In addition, it is well established that sucrose consumption increases the risk factor for dental caries (Rugg-Gunn & Murray 1983; Sreebny 1982).
A mixture of bagasse and molasses is used as cattle feed. When fed in large quantities and incorrectly, molasses may be toxic. The symptoms of molasses toxicity are reduced body temperature, weakness and rapid breathing. The animal may have difficulty standing (Perez R. & de Azucar 2004). Molasses toxicity often affects eye-sight and the animal may become blind. This indicated damage to the brain and the clinical syndrome was similar to that of cerebro-cortical necrosis. Necrosis in the brain readily develops and allows rapid diagnosis (Preston 1988). The necrosis is likely to be caused by either a decrease in energy supply to the brain because of thiamine deficiency or glucose deficiency.
Bagasse is the highly fibrous residue remaining after cane is pressed to remove sucrose. Like many other agricultural by-products such as cereal straws, bagasse is high in ligno-cellulose and may have a depressing effect on feed intake. The digestibility of bagasse is very poor because of the presence of lignin which protects carbohydrates from being digested by the rumen microbes (de la Cruz 1990; Leng 1991). To improve the nutritive value of ligno-cellulose materials for livestock, physical or chemical pre-treatments are required (de la Cruz 1990; Playne 1984).
Section 2.2 Allergenicity
Sugarcane pollen is transported by wind and therefore has potential to act as an airborne allergen. Allergenicity of sugarcane pollen was evaluated by Chakraborty et al. (2001). In the skin tests that were conducted, 70.58% of field workers with respiratory disorders showed highly reactive skin tests. The authors also tested rice and several other plant species and concluded that sugarcane pollen was the most significant allergenic type. However, there are no reports of any major allergic responses to the commercial hybrid cultivars of sugarcane in Australia.
In Australia sugarcane occurs almost exclusively in managed cultivation. In sugarcane districts, transient sugarcane plants may occur along roadsides or railways where it can establish after displacement during transport, but there is no indication that these form self-perpetuating populations.