Conditions this year have led to the development of a less frequently seen black mould, Cladosporium. Development of Cladosporium ear and kernel mould took place due to early frost damage to corn that had not yet reached maturity, coupled with wet harvest conditions. Cladosporium fungi often infect kernels damaged by insects, hail or frost. When grain with high moisture content is frosted, micro-fractures in the pericarp occur. Starch oozes out from these openings and serves as the food source for Cladosporium. Cladosporium appears as gray to black or very dark green streaks scattered over the ear and can have a powdery appearance. It can also cause greenish-black streaks in the kernels. The variety of colours this mould exhibits is directly related to its stage growth. The symptoms usually start with a white powdery mycelial growth in between the kernels (Figure 1) which quickly develop to a dark green or gray fungal mass (Figure 2). The black colour notes later stages and all colours of green and gray can be seen through the stages in between (figure 2). Initial discolouration often starts on the kernel base attached to the cob and will eventually progress and cover more of the kernels and cob (Figure 3).

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Figure 1: Initial Cladosporium ear rot development on corn kernels recently exposed to frost.
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Figure 2: Mature dark green fungal growth of Cladosporium ear rot on corn kernels.
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Figure 3: Cladosporium growth on corn kernels base and cob


This disease can be fairly common but usually does not cause extensive damage to the ears, and does not cause any feeding toxicity. If you rub the surface of the kernels where this mould is located, the discolouration can be completely removed. Although the mould will continue to grow at low temperatures, drying the grain to normal storage moistures will stop the growth due to the lack of moisture. Cladosporium rarely causes yield loss nor grain quality challenges. However, misdiagnosis of this disease can lead to dockage at the grain elevator.


Since many ear mould or rot pathogens remain viable in the soil for several years, carefully scout fields with a history of ear mould, even if management practices are employed to decrease pressure.

Some options to help decrease the risk of ear mould infection include crop rotation, heavy tillage, planting hybrids with insect protection traits, and good fertilization. Planting a package of hybrids with different maturities and Crop Heat Unit (CHU) requirements to flowering, as well as rotating germplasm planted in the same field from year to year, are also good practices to help reduce the impact of ear moulds. Proper grain drying and storage are important when this and other diseases are evident. Here are some tips for harvesting and storing grain from fields with prevalent ear mould infection.

  • Allow corn to mature in the field to 22 to 25% moisture content. If lodging concerns exist, harvest early since down corn is more likely to mould.
  • Consider tilling and rotating away from corn for 2015.
  • Combine should be adjusted to minimize kernel damage and maximize cleaning.
  • Corn should be dried to 13 to 14% moisture content prior to storage.
  • Grain should be stored at cool temperatures (2° C to 7°C) after drying.
  • Grain should be checked periodically for temperature, wet spots, and insects.
  • Consider applying antifungal treatments to grain.


Since some moulds can be toxic to livestock proper identification is needed before using it for feed. Always send a sample of suspect corn to a toxicology lab for analysis. If concentrations of a mycotoxin are present, a veterinarian or an Extension specialist can help determine if it is safe to feed to livestock. Please contact your local agronomist on where to send samples if you have concerns about feeding your harvested grain to livestock.

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Figure 4: Cladosporium infected kernels compared to a normal kernel.