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Cause Fusarium spp. are known to cause a crown rot of corn, both on field and sweet corn. Crown rot has been observed on sweet corn in the Willamette Valley. These fungal pathogens are able to colonize other plant species, especially grassy plant species. These soilborne fungi can also survive in affected plant residues, on other infected hosts, as well as in soil. Sometimes pathogen populations reach high levels in fields when corn is planted after grass seed. Dry, hot conditions favor the development of crown and stalk node rot while wet, compacted soils promote Fusarium root rot. Excess nitrogen or imbalanced applications can favor development of crown rot; heavy manure applications have been associated with crown rot of field corn.
Symptoms In affected fields, crown rot may be present as early as the 6-leaf stage, and commonly by silking. Affected plants usually show leaf firing, starting from the base of the plant and progressing upwards. After pollination, plants may wilt during high temperatures and leaves may exhibit a subtle-to-obvious change in green hue. Crown rot is characterized by dark-brown or black-colored rot of inner tissues in the crown. By harvest and often much earlier, stalk nodes appear reddish-brown to dark black in color and can range from a small portion of the node affected to a strip of rot almost ¼ inch wide throughout the node plate. Stalk nodes typically rot progressively up the stalk; however, nodes that bear ears may be darker than nodes immediately below. Internodes can sometimes show discoloration of a few vascular elements but internodes are not typically symptomatic and do not rot.
Little rot of roots is observed at the 4- to 6-leaf stage. Often rot spreads from the crown into brace roots and side tillers, resulting in a mass of rot below soil that can be mistaken for root rot. The severity of disease in affected fields depends on varietal susceptibility, pathogen population levels, and environmental conditions.
Cultural control
- Frequent cropping with corn will lead to a buildup in pathogen population levels. Avoid planting sweet corn after grass seed in problem fields.
- 'Jubilee' and related varieties are very susceptible to this disease so the use of other varieties will aid prevention for fields where the pathogen propagules are present.
- Apply balanced nitrogen applications and avoid an excess of N.
- Irrigate more frequently for shorter periods so as to avoid drought stress as well as overly wet soils.
- Residue levels may enhance the population of pathogen so maximizing residue breakdown could be important in problem fields.
Chemical control Seed treatment with various fungicides can aid in controlling rot of the mesocotyl but isn't thought to offer protection against crown rot later in the season.
Biological control
- Bexfond at 7 to 14 fl oz/A. O
- Heads Up at 0.035 oz/34 fl oz water/180 lb seed will stimulates pest suppression system of plants. Efficacy unknown. 12-hr reentry. O
Reference Miller, N.L., and Ocamb, C.M. 2009. The relationship between yield and crown disease of sweet corn grown in the Willamette Valley of Oregon. Plant Health Progress: doi:10.1094/PHP-2009-0831-01-RS.