Fusarium ear rot is caused primarily by the Fusarium verticillioides fungus, which also causes stalk rot, root rot and seedling blight in maize.
Symptoms may vary, or even be absent
Symptoms include scattered individual kernels or groups of kernels with whitish-pink fungal growth. These may also have a ‘starburst’ pattern of white streaks on the cap along the base of the kernel. Infection is more frequent on damaged ear tips and on kernels with pericarp injuries due to insect feeding damage.
This type of ear rot can also infect kernels without showing visible symptoms. Clean (first- grade) grain occasionally has an infection rate of up to 90% without showing symptoms.
F. verticillioides overwinters in maize stover, surviving in moist soil with poor aeration and little or no competition from other fungi and bacteria. The longer, slender branches (hyphae) of the fungus grow in the soil, first infecting the germinating seed and roots, and then moving up the plant.
The fungus also produces airborne spores that can be carried by insects, primarily the stalk borers Chilo partellus and Busseola fusca. These feed on infected plant tissue, then move to new plants, where they continue feeding. They leave fungal spores in their frass, and the infected stalks and seed release the fungus back to the soil.
Hot, dry conditions such as those in the north-western parts of South Africa’s maize-producing region promote the growth of the fungus.
Fusarium ear rot can cause yield and grade problems. The fungus can also produce a poison called fumonisin, which is highly toxic to horses and pigs, and has been linked to cancer in humans.
To reduce the incidence of the disease, plant a tight-husked hybrid adapted to local conditions, control ear feeding insects, avoid high plant populations, and maintain adequate nitrogen and other essential growth nutrient levels. Carry out crop rotation and sub-soiling in compacted soils to minimise plant stress.
If you anticipate a high infection level, adopt standard grain storage procedures such as drying the harvested grain to a moisture level below 16%. This prevents the development of fumonisim mycotoxin in stored grain. Aerate the stored grain regularly to reduce its moisture content and temperature to the desired levels.
Adjusting the combine harvester to avoid kernel damage during harvesting also reduces mycotoxin contamination.
Due to the common occurrence of these fungi in nature, sanitation practices to reduce the disease have not been very successful.
Sources: Flett B & Ncube, E: ‘Ear rots of maize: a continuous threat to food safety and security’ (ARC-Grain Crops Institute); ‘Ear rot diseases of corn’ (krugerseed.com).