Weather conditions were favorable for several different ear rots of corn in Indiana this year. Currently, Diplodia ear rot has been found most frequently in the state, and as we prepare for harvest, it is important to identify fields that may have ear rots to ensure timely harvest and proper storage of moldy grain.
Diplodia ear rot
Diplodia ear rot is caused by the fungus Stenocarpella maydis, and is very common in cornfields across the Corn Belt. This fungus survives in residue and infects plants during and after 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 (Figure 2). Small, black fungal structures called pycnidia may form on the kernels or the cob (Figure 3). The fungus is reported to produce several mycotoxins in South America and South Africa, however, no reports of toxic effects of grain on livestock or humans due to Diplodia ear rot have been reported in the United States.
Grain dockage may still occur, however, due to moldy grain.
Purdue University is conducting research on the fungus that causes Diplodia ear rot in hopes of improving management options available to farmers. If you have fields with suspected or confirmed Diplodia ear rot, please email Paty Romero at mromerol@purdue.edu.
Diplodia ear rot may be confused with other ear rots, such as Gibberella ear rot. 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.
Gibberella ear rot
Gibberella ear rot, caused by the fungus Fusarium graminearum, is common during cool, rainy years. The fungus infects during early silking and pollination, and is favored by cooler temperatures than Diplodia ear rot. This fungus produces a fungal mat on the ear, similar to Diplodia ear rot, but often with a pink or reddish color to the mold (Figure 4). Gibberella zeae produces the mycotoxin deoxynivalenol (DON), commonly referred to as vomitoxin. This mycotoxin can be extremely harmful to swine, and is carefully regulated according to the FDA.
Ear rot management
Preventative management of ear rots is critical, and can be accomplished by selecting less susceptible hybrids and reducing the amount of corn residue that can serve as a source for the fungus to overwinter through crop rotation and tillage. In-season management of ear rots is limited at this point, with few fungicides and anti-fungal products available for specific ear rots. Purdue research indicates that currently available fungicides do not have efficacy against these diseases.
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 mixing moldy and/or mycotoxin contaminated grain with high quality grain.
Silage and grain harvested with suspected ear rots should be dried to below 15% moisture. If grain or silage (with kernels present) is kept above this moisture content, mycotoxin 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.
All moldy grain should be tested to determine the presence and level of mycotoxins prior to use in livestock feed.
For more information on these ear rots and managing grain, please see here.
Figure 1. The fungus that causes Diplodia ear rot produces a white fungal mat on the cob.
Figure 2. Brown discoloration on ears can also indicate presence of Diplodia ear rot.
Figure 3. Black fungal structures, called pycnidia, are visible in cob tissue as a result of infection by the fungus that causes Diplodia ear rot.
Figure 4. A pink mold on the ear is a sign of the fungus that causes Gibberella ear rot (picture courtesy Charles Woloshuk).
