Dieback disease

Thomas, B.J. (1981). Some degeneration and dieback diseases of the rose. Ann. Rep. Glasshouse Crops Res. Inst. 178-190. 

The major constraints to kava production in the South Pacific are due to various diseases and pests. Of these, a dieback disease is the most serious (Davis etal., 1996). Other diseases appear to have a lesser impact on plant productivity. Some insects and other pests have been shown to attack, though the kava weevil borer is the only insect recorded as causing serious damage. 

The first report of this disease was made in Fiji by Parham (1935) who described a wilt disease that in some instances caused major sections of the crop to be abandoned or destroyed. Later, it was found to occur in other kava-growing countries of Samoa, Tonga, and Vanuatu. Plant pathologists in Fiji have estimated that dieback disease causes annual crop losses of up to 60% (Brown, 1989 MAFF, 2001). 

Figure 3-1 Symptoms of kava dieback disease caused by cucumber mosaic cucumovirus (CMV).

Pares and co-workers (1992) showed that the cucumber mosaic virus (CMV) was present in leaves showing mosaic, mottled, and chlorotic symptoms. Subsequently, Davis and colleagues (1996) found that CMV was widely distributed in kava plants in all major kava-producing countries. They also showed that the symptoms of the dieback disease developed on plants inoculated with CMV, usually within three to four weeks after leaf symptoms first became visible. It is now accepted that the CMV is the main causative agent for the kava dieback disease. The disease is also aggravated by plant-sucking pests such as the leaf miner and aphids which create entry in the cells for the CMV, and by infections from soil borne nematodes, fungi, and bacteria. 

No adequate control measures have been developed against the dieback disease. The most effective precautions appear to be adequate spacing between plants and intercropping. Adequate field sanitation, use of virus free planting material, and pmning out of diseased plants are used effectively in many countries. 

E. carotowra pv. carotovora (Jones) Dye 1923 produced a black soft rot when inoculated onto injured (but not uninjured) kava stems. The symptoms were similar to those of the black soft rot characteristic of kava dieback disease. Thus, the bacterium was capable of killing kava plants which were already damaged, suggesting that this species may act as a secondary parasite under certain circumstances. 

Pares, R.D., Gillings, M.R., Davis, R.I. and Brown, J.F. (1992) Cucumber mosaic cucumvirus associated with kava plants showing symptoms of dieback disease in Fiji and Tonga. Australasian Plant Pathology, 21, 169—171. 

Diplodia. This disease has been reported from many areas of cacao production as caused by Botryodiplodia theobromae. It is associated with dieback of young branches and rotting of overripe pods. It is considered of little importance. 

Cane dieback. Causes Blueberry cane canker Fusiccsccum canker. Blueberry cane canker, most pre alent in the South, shows up as reddish, conical stem swellings. The next year these swellings become blisterlike, light gray, and then black and fissured. If this disease is a problem in your area, plant rabbiteye blueberries, which are not susceptible to cane canker. Or plant highbush cultivars resistant to cane canker, including Atlantic and Jersey . 

Shoots blacken, wilt, and die back. Cause Canker. Also known as dieback, this disease is caused by 2 fungal organisms and most often occurs during rainy weather. Prune and destroy infected shoots thin plantings to improve air circulation. Remove and destroy severely infected plants. If canker has been a problem, use preventive sprays of bordeaux mix. 

Symptoms When a lawn mower hits a tree, it can cut a thin horizontal groove into the bark. Repeated damage may cause branch dieback or kill the tree. Lawn mowers can also damage surface roots. These wounds provide entrance points for diseases and insects. String trimmers also pose a hazard careless use can cause the tool to strip the bark off the base of the tree, girdling and killing the plant. 

Cheo, P. (1970). Rose wilt or dieback-a new virus disease attacks rose in California. Lasca Leaves, 20 88-89. 

White, D.T., Blackhall, L.L., Scott, P.T. and Waldh, K.V. (1998). Phylogenetic positions of phytoplasma associated with dieback, yellow crinkle and mosaic diseases of papaya and their proposed inclusion in Candidates phytoplasma australiensce and a new taxon, Candidates phytoplasma australasia . International Journal of Systematic and Evolutionary Microbiology, 48 941-951. 

Davis, R.I., Brown, J.F. and Pone, S.P. (1996) Causal relationship between cucumber mosaic cucumvirus and kava dieback in the South Pacific. Plant Disease, 80, 194—198. 

There is considerable evidence that chronic exposure of a variety of plants to concentrations below these that cause irreversible damage, adversely affects plant growth, and decreases the resistance of plants to climatic stresses and parasitic diseases, and finally induces a progressive dieback. 

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