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Ear Rots in Corn and Their Effects

  • Ear rots are often associated with insect feeding, weather (too hot and dry or too wet), wind and hail after R1, and hybrid characteristics.
  • Some ear rots produce mycotoxins, which may cause loads to be rejected by the elevator.
  • Scout corn fields from R5-R6 stage or prior to harvest to identify potential ear rot problems.

 

Controlling ear rots can be challenging, as several factors can elevate risk. Conditions that favor foliar disease, mainly wet and humid conditions persisting near R1, can increase risk of Fusarium, Diplodia, and Giberella ear rots. These pathogens survive on corn residue, and spores are dispersed with rain into shanks (Diplodia) or onto green silks (Giberella and Fusarium). When humid conditions persist in the 2-3 weeks after silking, the fungal spores germinate and can infect the associated ear. Less common are what are considered, "hot and dry" ear rots, including Aspergillus and Penicillium. These diseases require hot, dry conditions and somewhat stressed plants to infect ears.

 

What increases your risk for ear rots?  Hybrids with an upright ear position or ears that have exposed tips tend to be more prone to these diseases. All ear rots can be enhanced to a degree by damage caused by insect and animal pests and issues such as hail. This is because damage removes the protective husk, which allows the fungi direct access to moist and carbon rich developing kernels. Ear rot fungi also grow well and sporulate on and survive in / on corn residue. Therefore, fields in continous corn with production systems that favor large quantities of corn residue on the soil surface are at elevated risk for ear rot issues.  

 

The following are some management techniques that can help mitigate ear rot risk in fields with a history of issues:

1) Crop rotation and sizing residue to reduce the amount of corn present the next time corn is planted

2) Tillage to bury corn residue and reduce local inoculum levels.  The type of tillage is important, as benefit is related to the amount of residue left over on the soil surface.

3) Bale or remove corn after harvest to reduce the amount of corn residue in a field the next season. 

4) Apply a fungicide labeled for ear rot suppression during green silk. Silks contain a great deal of moisture and are more easily colonized and fungi grow can more rapidly than on dry, brown silks. Applying before silk emergence or once silks have started to turn will result in suboptimal efficacy. Ensure that adequate volume is used and that a deposition agent / surfactant is included to ensure adequate silk coverage.

5) Scout for ear rots around R5. 

6) Fields with elevated levels of ear rot (e.g. >10% incidence) should be harvested first. 

7) If storing grain, ensure that it is immediately dried to at least 16%. The reduced moisture helps stop fungal growth and therefore the continuued production of mycotoxins. 

 

Characteristics of common corn ear rots:

  • Fusarium – White to very pale pink fungal growth. Often sporadically "patchy" areas of ear impacted, but tips and entire ear may be affected as well.  Fusarium will also cause a series of fine lines radiating from the crown of the kernel, referred to as a “starburst” pattern (Image 1).  Kernels displaying the starburst pattern may be present without any additional mold growth. Infection is favored by wet weather in the three-week period after silking. Some Fusarium species can produce mycotoxins, including: Deoxynivalenol (also known as DON or vomitoxin), Zearalenone, Fumonisin, and Trichothecenes.
  • Gibberella – Pink to nearly red fungal growth that typically starts at the ear tips and progresses down the ear (Image 2). Infection is favored by cool, wet weather in the three-week period after silking. Can produce the mycotoxins – Deoxynivalenol (also known as DON or vomitoxin), and Zearalenone. Occasionally black melanized fungal structures resembling small BB's may be observed.
  • Diplodia – White fungal growth that starts from the base of the ear and progresses to the tip. Husks are often grey and droopy compared to surrounding healthy ears.  Fungal growth often causes husks to stick to the ear. No mycotoxins are known to be produced in Diplodia species that occur in the US.   
  • Aspergillus – Olive-green or gray-green mold at ear tips and between rows of kernels. This mold often has a velvety or dusty appearance. Usually occurs during very hot (near 100 F for a prolonged period of time), dry weather. It is often associated with damage to ear tips from insects or other causes and will continue to grow in storage.  Aspergillus produces the mycotoxin, aflatoxin, which is a carcinogen.  
  • Penicillium – Blue green to green mold often associated with damaged ear tips, from corn earworm feeding for example (Image 3). Penicillium also causes “blue eye” symptoms in stored grain. Penicillium produces the mycotoxin – ochratoxin.
  • Trichoderma – Starts as white mold between kernels. Becomes a very dark green to blue-green color and may grow over tops of kernels and underneath the husk. Often associated with frosted or injured corn. Trichoderma does not produce mycotoxins and is generally regarded as a minor ear or kernel rotting pathogen, usually occurring on scattered ears in the field.
  • Cladosporium – When mature, this fungus is very dark colored, black to dark green or dark brown. Some damaged kernels may be completely covered with this mold and appear black.  Black streaks may develop in infected kernels. Symptoms frequently occur after an early frost. Cladosporium does not produce mycotoxins. In some geographies, Cladosporium is quite common, but is less so in our area.

 

Not all ear molds produce mycotoxins. It is also important to realize that even if the molds are present, this doesn’t mean that mycotoxins will be present. The amount and type of mycotoxin produced is dependent on the host, pathogen, the strain of fungus, and weather conditions. The best way to determine if there are mycotoxins is to send a sample to a qualified private lab, USDA lab or university lab, for analysis.  

 

Image 1.  Fusarium “Starburst” Pattern on Corn Kernels (Source: GROWMARK, Inc.)

 

Ear Rots_Fusarium Starburst1-1.jpg

 

 

Image 2. Gibberella Infection on Corn Ear Associated With Insect Damage (Source: GROWMARK, Inc.)

 

Ear Rots_Gibberella infection2.jpg

 

Image 3. Penicillium Mold on Insect-Damaged Ear Tip (Source: GROWMARK, Inc.)

 

Ear Rots_Penicillium Mold3.jpg

 

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