By Ryan Klamfoth, Pioneer field agronomist
The recent cool weather has delayed corn maturation and harvest. Additionally, the lower temperatures create an ideal environment for development of ear molds. The four most common types of corn ear molds in Ohio include: Aspergillus, Diplodia, Fusarium, and Gibberella.
These fungal pathogens survive in the soil and on crop residue allowing them to infect developing corn ears. When the proper moisture and weather conditions are present, the silks become infected by the fungal spores. The amount of ear mold present within a field can be impacted by the interaction of planting date, hybrid maturity, and rainfall/humidity during grain fill. Scoring hybrid differences are extremely difficult since the infection is very situational and often a severity scale at one location is completely inverted at another location.
Although this infection occurs at silking, the mold is often not present until the middle or end of grain fill stages. Infected ears first appear to have a tight husk or pinched husk tip that does not loosen. These tight husks are a symptom of the infection that has already occurred and not the cause of the ear mold. Ear molds are detrimental in several ways. First, the mold interrupts the grain fill process causing premature black layer to kernels which reduces yield and kernel size. In addition, ear molds reduce kernel quality making feed less palatable to livestock and potentially causing storage problems if the corn is not properly dried. Lastly, mycotoxins present in the grain can be carcinogenic when consumed or cause illness in people or livestock.
Aspergillus ear rot is known for its green mold color. It is often found in association with an injury point in the plant tissue such as insect feeding. Aspergillus is considered by many to be the most carcinogenic of the four ear rots. Less common Trichoderma ear rot also has green mold, but it is a darker green and is not associated with mycotoxins.
Diplodia ear rot can be identified by its white color of mold. Diplodia starts at the base of the ear and often creates a thick mold that encompasses the entire ear. Unlike the other three ear molds, Diplodia is not associated with any of the problematic mycotoxins that cause illness.
Fusarium ear rot is diagnosed by its randomness throughout the ear, groups of kernels may be moldy and rotten while others appear to be unaffected. It can also be identified by a chalky white star-burst pattern within the kernel or darkened and discolored kernels that appear randomly.
Slight amounts of white fuzzy mold may also be associated with Fusarium ear rot.
Gibberella ear rot is perhaps the easiest to identify. The infection is most prominent at the tip of the ear and produces a noticeable pink mold. At times low amounts of mold are found or a white mold that has not yet turned pink can be seen. If the bottom of the ear appears healthy and normal but the tip is infected, odds are it is Gibberella ear rot.
Penicillium ear rot, Nigrospora ear rot, and Cladosporium ear rot are other types of ear rots that are less common and are not associated with significant mycotoxin levels.
Unfortunately, the presence of ear mold cannot be stopped or reversed once the infection has occurred. Frequent rainfall throughout August, September, and October can further development and severity of these ear molds. Mycotoxin levels in grain can increase as harvest is delayed and rainfall events continue. Timely harvest and drying of infected fields is the best management practice to limit increases in mycotoxins. Field scouting should be used to determine harvest priority for each field. In situations where mycotoxins are high, consider combine adjustments that will blow the lightweight infected kernels out back onto the field. This practice could potentially reduce mycotoxin levels making grain more marketable. Allowing corn to dry naturally in the field to 15% moisture is not a recommended practice in fields where mold or mycotoxins are a concern. Grain from fields with a presence of ear mold should be dried to 15% moisture, and even more ideally 13%, to minimize problems in stored grain. Fines from infected grain tend to contain higher mycotoxin levels.
Care should be taken to prevent, minimize, or remove fines in effort to manage mycotoxin levels. While mycotoxins and ear mold are associated with one another, levels of each may vary and visually inspecting grain samples is not a good indicator of mycotoxin levels. Collecting ears for testing from a field can be misleading since ear molds and mycotoxins can vary greatly within different areas of the field. Dust from grain with ear mold can be carcinogenic. Use a quality respirator rather than a disposable mask for tasks such as operating a sweep auger.