Date of this Version
Schlund, S. A. 2015. Goss's bacterial wilt development and Clavibacter michiganensis subsp. nebraskensis interactions with spray adjuvants. MS thesis, University of Nebraska.
Goss’s bacterial wilt and leaf blight of corn (Zea mays L.), causal agent Clavibacter michiganensis subsp. nebraskensis, was first confirmed in Dawson County, NE in 1969. Disease incidence decreased in the 1980’s due to various management strategies and disease developed sporadically until the early 2000’s when it re-emerged and was economically important. A Midwest, multistate survey conducted in 2011 suggested farming practices that may have contributed to the pathogen’s re-emergence. The use of agricultural pesticides was associated with Goss’s wilt. Since spray adjuvants are often used with pesticides, and physical characteristics of these adjuvants may enable infection of the leaf by epiphytic C. michiganensis subsp. nebraskensis, greenhouse and field studies were conducted to assess the effect of adjuvants on Goss’s wilt severity. A preliminary greenhouse study was conducted to determine if an epiphytic population of C. michiganensis subsp. nebraskensis could be established and initiate infection. The population became established and disease severity was higher when plants were less mature. To evaluate the effect of adjuvants on disease development with adjuvants, a greenhouse study was established. Adjuvants tested did not cause a consistent increase in disease severity between trials. An inhibition test was designed to determine if spray adjuvants inhibited bacterial growth in vitro at different concentrations. Results showed minimal inhibition at label rate for NIS, and consistent inhibition at 10X label rate for NIS with some inhibition for MSO and COC. Field studies were conducted in southwest Nebraska in 2014 and 2015. Disease severity was lower in adjuvant treatments in 2014. In 2015, no differences for disease severity or systemically infected plants were detected among treatments. These data indicate that spray adjuvants commonly used in corn production are not causing an increase in Goss’s wilt severity. Rather, adjuvants at higher rates may reduce the population of epiphytic C. michiganensis subsp. nebraskensis to below levels required for infection. Further research is needed before recommending non-label rate of these adjuvants under field conditions.
Advisors: Tamra Jackson-Ziems, Greg Kruger