Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Over the last two weeks we have started to hear about problems with ear rots in some fields, in particular Diplodia and Fusarium ear rot. Ear rots can be caused by a number of different fungi, and can impact grain quality and yield. Another potential issue resulting from some ear rots is the development of mycotoxins, which can be harmful to livestock and humans if consumed.
In general, ear rots are derived from corn residue on the soil. The diseases tend to infect when we have wet weather from silking to about 2 weeks after the start of silking. Insect damage and delays in planting or slow grain drying or harvest can increase ear rot severity and incidence. The fungi often colonize the silks and then use the silk as a means to enter the developing ear although some (i.e. Diplodia) can also infect husks or the shank. Late season rains can increase ear mold severity and potential impacts on quality. The best means to manage ear rots is to rotate corn with another crop such as soybeans or vegetables, select resistant hybrids (when available), and manage insects. Do not expect a fungicide to have much impact on ear rots. Early harvest and drying to 15% moisture can limit additional fungal growth impacts on grain quality. To scout for ear rots inspect at least 10 ears for every 20 acres of field (minimum of 30 per field) prior to harvest. If you encounter ear rots at significant levels, send a sample to the Diagnostic Clinic to have it properly identified. Table 1 provides you a cheat sheet on some of the more common ear rots in corn.
Table 1. Ear rots commonly encountered in corn.
| Disease | Distinctive Symptom | Mycotoxins | Notes |
| Aspergillus ear rot | Stunting, small ears, powdery olive green growth in between kernels | Aflatoxin (carcinogen and toxin to liver) | Dry areas of field often affected more severely |
| Cladosporium ear rot | • Dark, green/black blotched or streaked kernels.• Scattered throughout ear. Green fuzzy growth between kernels. | none | Often associated with insect damage |
| Diplodia ear rot | • Straw colored husks, white/grey growth in between kernels• Black pin head structures produced late season on husks kernels, etc.
• May cause premature germination. |
none | Disease often progresses from base to tip of ear but entire ear can be affected. |
| Fusarium ear rot | • Kernels show a whitish “starburst” pattern• Sometimes kernels have grey to pink “cap”
• Often scattered throughout ear |
Fumonisin | More severe when hot dry weather follows flowering. |
| Gibberella ear rot | • Pink to red mold grows in between kernels.• Typically only impacts part of ear | Deoxynivalenol (DON)Zearalenone | Often starts at ear tip and works down to the base of the ear |
| Trichoderma ear rot | • White mold that turns green/blue and powdery.• Whole ear affected. | none | More severe when wet weather precedes harvest. Often associated with mechanical damage to ear. |