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P. cinnamomi causes a rot of fine feeder roots, and root cankers in some species, leading to dieback and death of host plants. Other symptoms include wilt, stem cankers (with sudden death of tree), decline in yield, decreased fruit size, gum exudation, collar rot (if infected through grafts near soil level) and heart rot (e.g. pineapple). A symptomless invasion of the sapwood has been reported in some species (Davison, 2011).
Hygienic precautions can be applied to exclude P. cinnamomi from a place of production (Smith, 1988). Unsterilized soil or growing medium, or farm machinery, should not be brought in. Introduced plants should be kept apart until their phytosanitary status has been checked. All propagation should be done from healthy plants or seed. Cultural measures should be taken to reduce the risk of spread in case of introduction. If land does become infested, incidence of P. cinnamomi can be reduced, if not necessarily eliminated, by leaving the land under non-susceptible crops for at least 4 years, and by applying various control measures.
In southern Australia there is great concern about the impact of P. cinnamomi in areas of native vegetation. A good outline of management practices to reduce its introduction to, and spread within, such areas is given on the Project Dieback website (Natural Resource Management Western Australia, 2013).
A standard dieback signage system is used in Western Australia to indicate the dieback status of an area to help prevent the spread of propagules by humans, see Project Dieback (Natural Resource Management Western Australia, 2013).
Cultural control measures include alleviation of high soil moisture levels and improving aeration by increasing drainage, and attention to mineral nutrition. Elements of the soil microflora suppress P. cinnamomi in some soils and may be potential biocontrol agents. These factors were reviewed by Weste (1983). Soil solarization also controls P. cinnamomi on young avocado plants (Kotze and Darvas, 1983). Smith et al. (1983) reviewed the combination of measures for controlling the disease in nurseries.
The use of mulches rich in cellulose will often reduce populations of P. cinnamomi. Microorganisms which decompose cellulose also degrade the cell walls of P. cinnamomi, which are composed of cellulose and laminarin (Downer et al., 2001). Composted and uncomposted animal manures suppress P. cinnamomi (Aryantha et al., 2000) but the active ingredient is often ammonia which can be toxic to plant roots. Chitosan also inhibits fungal growth of P. cinnamomi (Napoles et al., 1997). Gypsum amended soil reduced root rot of avocado seedlings (Messenger et al., 2000a, b). In hydroponic conditions, increased copper (Toppe and Thinggaard, 2000), sand filtration (Os et al., 1999) and reduced oxygen (Burgess et al., 1998) significantly reduced disease. Soil solarization, in isolation and with cover crops, significantly reduced P. cinnamomi populations in avocado orchards (Lopez Herrera et al., 1997) and sunlight exposure reduced heart rot of pineapple (Yang RongYang and Zhou Chang, 1998).
There are numerous microorganisms which inhibit P. cinnamomi via parasitism, antibiosis and competition. Although none of these microorganisms has yet provided economical control, there is increasing evidence that these organisms play an important role in the natural suppression of P. cinnamomi in certain soils. This topic has been reviewed by Erwin and Ribeiro (1996). Bioenhanced mulches (Costa et al., 1996) and repeated applications of the bacterium Pseudomonas putida (Yang et al., 2001) suppressed P. cinnamomi infection on avocado roots. Earthworms were shown to transport biocontrol agents in potted soil which helped to alleviate avocado root rot (Singer et al., 1999). In vitro inhibition of P. cinnamomi was obtained with Byssochlamys nivea isolated from saline mud in western Australia.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: