Copra mould, Aspergillus ear rot (of maize), yellow mould of peanut, storage rot of groundnut
Worldwide. In warm temperate and tropical countries on seeds and grains. The fungus is present in air, soils and water. Moulds of copra are recorded from Fiji, Samoa, and Solomon Islands.
Very wide; usually saprophytic (growing on dead organic matter, both plant and animal). Important as a post-harvest mould of maize, peanut and copra. In Fiji, it has been recorded as a neck rot of onions, but also on peanuts, maize and coconut, and in Solomon Islands it is recorded on discoloured and stored grains of rice.
In general, infections by Aspergillus flavus and aflatoxin production is more common in hot, dry years. In peanut and maize, for example, it is worse under conditions of drought, high temperatures (28-31°C), moist conditions with humidity of more than 85%, nitrogen deficiency (in maize), and insect damage. Insects, such as caterpillar borers and beetles, increase the amount of fungus and toxin for two reasons: (i) there is more damage for the fungus to colonise, and (ii) the damage releases moisture and that promotes fungal growth.
In peanuts, the disease is worse if there is moisture stress of more than 20 days near the end of the crop. It is worse, too, if the harvested crop is over mature, there is mechanical or insect damage to the pods, the moisture content of stored pods is great then 10%, or the peanuts are stored at high humidity.
The fungus survives in plant residues on or in the soil. Peanuts become infected from spores in the soil, and maize is infected by spores spread from plant debris to the silks of maturing maize ears by rain, wind, and also by insects. The fungus invades the kernels (seed), especially those that are injured. Some of the spores re-enter the soil at harvest, other spores stay with the ears to cause rots in storage.
Infection can occur in the field before harvest, or later, after harvest, during storage and transit. The fungus is most noticeable on stored copra (Photo 1), peanuts (Photo 2), maize (Photo 3&4), rice and other grains that have not been dried properly. Copra is turned a yellowish green, the colour of the spores of the fungus. The fungus can grow into seeds resulting in poor germination, and damaged seedlings. The disease is worse when insects damage the crop, and when plants are growing under stress.
Under certain circumstances the fungus produces toxins - called aflatoxins - which affect livestock, particularly pigs and poultry, as well as human beings. Aflatoxins can have a major impact on the value of the commodities susceptible to Aspergillus flavus.
In livestock, aflatoxin causes liver damage, reduces reproduction, reduces milk or egg production, causes birth defects, tumours, and weakens the immune system. In humans, it causes high fever, jaundice, oedema (water retention) of limbs, vomiting, swollen liver, and hepatitis.
Throughout the world, aflatoxin causes a huge problem to human and animal health as well as crop production. Wherever surveys have been done on peanuts or maize, they have found levels of contamination between 30-40%.
Look for a greenish-yellow mould on copra or on seeds that are discoloured and rotten.
There are peanut and maize varieties that tolerate Aspergillus flavus infection, but which do not support the production of toxins.
Treat seed with mancozeb (3g/kg) before planting. It is important to control insects during growth of the crop, in particular, caterpillars, termites, and beetles.
AUTHOR Grahame Jackson
Information from CABI (2015) Aspergillus flavus (Aspergillus ear rot) Crop Protection Compendium (http://www.cabi.org.cpc/). Photo 1 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia; Photo 2 Aflatoxin in peanuts. Department of Agriculture and Fisheries, Queensland Government. Photo 3 Department of Plant Pathology Archive, NCSU, Bugwood.org.; Photo 4 Harry Duncan, NCSU, Bugwood.org.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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