Gibberella ear rot can be especially severe in corn-wheat rotations as the fungus is also responsible for head blight in small grains.
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, mould 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. Mould colour can begin as white, but characteristically turns a dark-red or pink colour.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 discolouration. 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 5°C and 30°C and relative humidity ranging from 75.5% to 100%. However, they do not mature and produce spores until temperatures are between 20°C and 25°C with relative humidity between 85% and 100%.3 The spores can be spread by air or rain splash.
High yield scenarios favour 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.
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:
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/.