As harvest begins, it is important to identify fields that may have ear rots to ensure timely harvest and proper storage of moldy grain. A different fungus causes each of these rots, and the environmental conditions at and just after silking influence which ear rot may be problematic in a given year.
Diplodia Ear Rot
Diplodia ear rot is caused by the fungi Stenocarpella maydis and Stenocarpella macrospora, and is very common in cornfields across the Corn Belt. This fungus survives in residue and infects plants around pollination. Humid weather and rains prior to and after pollination will favor disease development. Diplodia ear rot is identified by white fungal growth on the cob, often forming a mat of fungus across the ear (Figure 1). Infected kernels may also be brown-gray in appearance. Small, black fungal structures called pycnidia may form on the kernels or the cob. Caution is advised if feeding heavily infected grain to livestock.
Trichoderma Ear Rot
Trichoderma ear rot is caused by several different species of Trichoderma fungi. Affected ears have blue-green mold on and between kernels on the ear. Trichoderma ear rot can also cause corn kernels to germinate in the husk (called sprouting or vivipary). This disease is common in years when fall is wet and can affect injured ears. Ears with Trichoderma ear rot may weigh less than uninfected ears from the same field. Some Trichoderma species have been reported to produce trichothecene-type mycotoxins. Caution is advised if feeding heavily infected grain to livestock.
Managing Moldy Grain
Farmers should scout fields prior to harvest and determine the level of incidence of any ear rot in the field. If ear rots are observed in a field, affected areas should be harvested early and grain segregated to avoid contamination of non-infected grain. Grain harvested with suspected ear rots should be dried to below 15% moisture. If grain is kept above this moisture content, mold can continue to grow, and any mycotoxins present can continue to accumulate in grain. All grain contaminated by any ear rot fungus should be stored separately from good grain, and if stored long term, stored below 13% moisture to prevent further growth of fungi.
More resources on corn ear rots can be found on at www.cornmycotoxins.com.
Source: Kiersten Wise and Charles Woloshuk, Purdue Cooperative Extension Service