Aflatoxin-producing fungi

Cause

Aspergillus flavus and A. parasiticus.

Damage

Major and widespread, particularly in dryland crops. Kernels contaminated with aflatoxin bring a reduced price and, in cases of very high levels, may be downgraded to oil quality.

High soil temperatures and drought during flowering and podfill are the major causes of aflatoxin contamination. Pods damaged by insects, disease or rain after a dry period or after harvest allow the fungus access to the kernels.

Symptoms

The greenish-yellow fungi are not always visible in harvested kernels. The toxins can only be detected in a laboratory.

Management options

Cultural
Irrigation will minimise the risk of pre-harvest aflatoxin. However, if the plant is allowed to stress just prior to maturity, the A. flavus mould can still invade the pod.

Dig as soon as the crop is mature.

Leaving peanuts in the windrow to dry to 13% moisture increases the risk of aflatoxin because of the chance of rain re-wetting the crop. The risk is much higher if the plants were moisture-stressed before harvest. Peanuts in well-inverted windrows have a lower risk because they dry quicker.

Harvest irrigated areas separately from dryland areas. This may mean turning in the middle of a row if the irrigator does not cover the paddock. Mixing peanuts from these dry ends of rows is a common way to end up with aflatoxin-positive loads from irrigated crops.

Clean out threshers, bins and elevators between seasons, as one contaminated nut can downgrade a whole load.

Start curing the crop within three hours of harvest to stop any further development of the aflatoxin. Harvested nuts should definitely not be left overnight before curing, even if only part of a bin is threshed.

Low soil calcium may increase the risk of aflatoxin where soil conditions are favourable for A. flavus mould development. Gypsum may reduce the risk of aflatoxin contamination.

Chemical registrations and permits
Check the Australian Pesticides and Veterinary Medicines Authority chemical database and permit database for chemicals registered or approved under permit to treat this disease on the target crop in your state or location. Always read the label and observe withholding periods.

Further information