Aspergillus Ear Rot
Aspergillus ear rot (AER) is a major disease of corn that can produce aflatoxin, a carcinogenic mycotoxin. There is a diversity of species within the genus of Aspergillus associated with causing ear rot. Two of the most common species are Aspergillus flavus and A. parasiticus.
Symptoms: The most common symptom of Aspergillus ear rot is the presence of yellow to olive-green patches of spores on or between the kernels. While any part of the ear may be infected with the disease, symptoms are often seen at the tip of the ear that has received damage either from biotic or abiotic factors.
Favorable conditions: Aspergillus infection and development is favored by hot, dry temperatures (86ºF), and is most severe under drought conditions during pollination and grain fill.
Plant stress plays an important role in AER and aflatoxin production. Conditions such as hillsides, sandy soils, nutrient deficiency, and dense plant populations can result in severe infections.
Yield effect: The majority of the time, yield loss caused by AER rot is associated with drought stress. This can make it difficult to estimate the damage done solely by the disease, but the pathogen can reduce the weight of infected kernels. An indirect impact on yield is monetary loss due to price reductions or rejection at grain elevators due to aflatoxin levels that are above action threshold. It has been estimated that aflatoxin contributes $163 million loss annually for US corn growers (Wu 2006).
Management: Pre-harvest management strategies start with planting a variety that is adapted to the southern region, along with moderate or above rating for drought tolerance. Managing overall plant health by providing optimal conditions for growth such as the use of fertilizer, correct planting population, and optimum watering during silk to late-dough stage. Managing secondary plant stressors such as weeds, foliar diseases, and insects is part of disease management for AER. No fungicides are labeled for use for AER, however there is also a biological control (Afla-Guard® GR, Syngenta – Labeled for use in TN) in which a species of A. flavus that does not produce aflatoxin is applied in the field at growth stages V7 – R1.
Mycotoxin: The production of aflatoxin is the most detrimental aspect of AER, as it is carcinogenic. Aflatoxin levels may increase after harvest if grains aren’t dried below 15% moisture and stored in at least 50ºF. The presence of aflatoxins affects grain quality and marketability. The FDA has established action thresholds for aflatoxin in human and animal food/feed set at 20 ppb (TABLE 2).