Evaluation of foliar-applied copper hydroxide and citric acid for control of Gosss wilt and leaf blight of corn

Gosss wilt and leaf blight, caused by Clavibacter michiganensis subsp. nebraskensis (Cmn), is a re-emerging disease of corn (Zea mays) in portions of the midwestern USA. Although resistant corn hybrids have been developed for some regions, the availability of adapted resistant hybrids may be limited in other areas; therefore, chemical control could potentially serve as an interim control measure while resistant hybrids are being developed. A field experiment was initiated to evaluate the effect of copper hydroxide and citric acid on Gosss wilt severity and yield of corn. Chemicals were applied relative to inoculation with Cmn, and non-inoculated plots also were included. Treatments not inoculated with Cmn had significantly (P ≤ 0.05) lower Gosss wilt severity values compared with those that were inoculated, but no significant differences among treatments within Cmn-inoculated or within non-inoculated plots were observed. Neither Cmn-inoculation nor chemicals applied had a significant effect on corn yield. Overall, corn yields were reduced by approximately 9% in Cmn-inoculated plots compared with non-inoculated plots. From our research, application of copper hydroxide or citric acid was not a viable Gosss wilt management practice. Therefore, corn growers should continue to rely on cultural practices such as crop rotation and tillage to limit Cmn inoculum in fields, and grow resistant hybrids if they are available.