Gibberella ear rot can be especially severe in corn-wheat rotations as the fungus is also responsible for head blight in small grains.
What Conditions Cause Gibberella?
Gibberella zeae overwinters on the residue of corn and small grains. In small grains, this disease is known as Fusarium head blight, and in corn, Gibberella. Gibberella zeae enters kernels during the silking timeframe of about a week. Storms and rainy weather during silking increase the chances of the disease infecting ears.1 Additionally, wounds from birds or insects create openings for the disease to enter ears.
Once infected, mold develops often moving from the tip to base of the ear. Severely infected ears can look mummified when the ear husk and cob fuse together. Mold color can begin as white, but characteristically turns a dark-red or pink color.2
Gibberella also infects stalks following pollination via wounds in the stalk and through the roots and causes the lower stalk to softened and become straw-colored as plants die. Pith tissue disintegrates leaving the vascular strands in tact. The inside of a rotted stalk has a pink-to-red discoloration. Small, blue-black fungal bodies called perithecia form on the surface of the lower stalk and can be easily scraped off.
Perithecia are produced between temperatures of 41°F and 86°F and relative humidity ranging from 75.5% to 100%. However, they do not mature and produce spores until temperatures are between 68°C and 86°C with relative humidity between 85% and 100%.3 The spores can be spread by air or rain splash.
Yield Impact on Corn
High-yield scenarios favor Gibberella; however, there are differences between corn products and their susceptibility to the disease. Disease pressure is influenced by the timing of silking, weather and insect pressure. Therefore, it is likely to see field-to-field variability in disease pressure.
Deoxynivalenol (vomitoxin or DON) levels in grain can reduce feed quality and prices at elevators. DON levels may be greater in corn products planted later in the season.4 A mycotoxin test is recommended to check on loads coming in this fall as DON levels should be 5 ppm for beef and feedlot cattle older than 4 months. DON levels are to be 1 ppm for swine, young calves, and dairy animals.5 Mycotoxins are concentrated in the dust and lighter, shriveled kernels, and contaminated grains should be cleaned to remove these fine particles. If the corn is to be used for silage, it is recommended to have a mycotoxin test as well.
Stalk quality is compromised when Gibberella infects stalks, and early harvest may be necessary if there is the potential for significant lodging.
Gibberella Ear Rot and Stalk Rot in Corn
Corn Product— Products are rated for Gibberella and ratings are on a scale of—Below Average (BA), Average (A), and Above Average (AA) for tolerance to the disease. Characteristics that resist animal and insect damage are desired. Different corn products are likely to have different silking dates, and silking dates aligned with stormy humid weather increase the risk of infection. Researchers in Canada are working to identify inbreds with resistance genes to provide plants able to defend against infection through silks or kernel wounds.4
Insect Protection— European corn borer (ECB) and Western bean cutworm (WBC) are insects that feed on kernels and open up ears to infection. Traits protecting against ECB and WBC should be chosen when planting into a field with previous heavy pressure from Gibberella or Fusarium head blight.
Fungicide— a ground rig or aerial application should be used to spray just after tasseling to protect silks from being infected when they begin to senesce. Gibberella is not strong enough to colonize on a healthy or dead silk.1
Combine Adjustments to Reduce DON—when Gibberella is more limited to ear tips, those smaller and lighter kernels can be blown out of the combine and left in fields using the following adjustments:
- Screens on bottoms of clean grain and return elevators. Bottom door can be taken completely off to leave light, infected kernels in the field.
- Screen on the unload auger if possible.
- Set the concave wide with the rotor/cylinder speed set slow.
- A closed back portion of the chaffer (sieve) increases the wind blast forcing additional light kernels out the returns and over the back of the sieve. Some good kernels may be lost; however, it may be acceptable considering a field with high DON levels.6
Fall Field Work—Fall tillage in combination with shredding plant debris may assist in plant residue breakdown reducing inoculum.
1 Hein, T. 2016. Preventing gibberella ear rot. https://www.topcropmanager.com/fungicides/preventing-gibberella-ear-rot-18911#
2 OMAFRA. 2014. Identifying corn moulds. Crop Talk. http://www.omafra.gov.on.ca/english/crops/field/news/croptalk/2014/ct-1114a9.htm
3Manstretta, V. and Rossi, V. 2015. Effects of temperature and moisture on development of Fusarium graminearum perithecia in maize stalk residues. Plant Microbiology. Vol. 82. pgs. 184-191.
4Hein, T. 2012. Gibberella ear rot: the latest on hybrid offerings. https://www.topcropmanager.com/genetics-traits/gibberella-ear-rot-the-latest-on-hybrid-offerings-6135#
52017. RG-8 Regulatory Guidance: contaminants in feed. Canada Food Inspection Agency. http://www.inspection.gc.ca/animals/feeds/regulatory-guidance/rg-8/eng/1347383943203/1347384015909?chap=0
6RealAgriculture Agronomy Team. 2018. Corn school: fine tuning the combine to reduce DON levels. https://www.realagriculture.com/2018/11/corn-school-fine-tuning-your-combine-to-reduce-don-levels/.