June 8, 2012

Note:  Also see in this week's CropWatch: Goss's Wilt of Corn Confirmed in Multiple Locations Across Nebraska

	Figure 1. Results from the 2009 Goss’s wilt management trial. Cumulative Goss’s wilt disease severity (expressed as AUDPC) in susceptible (Figure 1a., top) and resistant (Figure 1b, bottom) hybrids. (Each chart links to a larger, easier-to-read version.)
	Figures 2a and 2b. Results from the 2009 Goss’s wilt management trial. Treatment yields (bushels/acre) in susceptible (Figure 2a, top) and resistant (Figure 4b, bottom) 105-day relative maturity (RM) hybrids. (Each chart links to a larger, easier-to-read version.)

In 2009, a project was initiated to evaluate the effects of currently available products on the spread of Goss's wilt and on affected yield. In cooperation with the Monsanto Water Utilization Center in Gothenburg, 105-day Relative Maturity (RM) resistant and susceptible hybrids were mechanically wounded and inoculated with a suspension of Clavibacter michiganensis subsp. nebraskensis bacteria (the causal agent of Goss’s wilt) and treated with one of three treatment combinations at one of three application timings.

Treatments

Inoculation Treatments (indicated with shading at the top of graphs)

• Inoculated at corn growth stage V6 (pathogen introduced to plant)
• Not inoculated (pathogen NOT introduced to plant)

Wounded (indicated in yellow shading near the bottom of graphs)

• Injured
• Not injured

Pesticide Treatments (manually applied by CO2 backpack sprayer at 15 gpa)

• None applied
• Kocide® 3000 at 1.5 lb/ac
• Headline® EC at 6 oz/ac

Application Timing (listed on the bottom of graphs in pink shading under products)

• None applied
• Six days prior to inoculation/wounding (applied before pathogen introduction)
• Same day application made four hours after inoculation/wounding (applied at pathogen introduction)
• Twenty-four hours after inoculation/wounding (applied after pathogen introduction)

Treatment combinations were replicated six times throughout the experiment and arranged in a split plot randomized complete block design. Disease severity was estimated twice in each 30-foot long plot following inoculation and expressed as a cumulative rating (Area Under the Disease Progress Curve – AUDPC) where larger values indicate greater overall disease severity.

Disease severity and yield results from the experiment are shown in Figures 3 and 4.

Results

Overall, the greatest improvements in yield and disease severity were observed in the resistant hybrid compared to the susceptible hybrid that year. The average yield across treatment combinations (in the inoculated treatments) yielded more than 100 bu/ac more in the resistant hybrid than in the susceptible hybrid with 224 bu/ac compared to 120 bu/ac, respectively.

In both of the hybrids tested, the Kocide 3000 treatment made within 24 hours after inoculation resulted in the greatest decrease in cumulative disease severity in the inoculated treatments, although those differences were not always statistically significant. In that treatment, yield was greater than it was in other inoculated treatment combinations, but not always significantly so.

* Note: These results are from a single-year experiment at a single location and lacked statistically significant differences for some treatment combinations and further interpretation is not recommended. The second year of the experiment in 2010 was compromised due to severe weather damage that led to excessive plot variability and the results are not presented here.

**Note: The applications made in this experiment were made before disease lesions developed, so it’s unknown at this time how these treatments will perform in the presence of active disease lesions, as are being observed in several parts of Nebraska now.

Continued Research

Additional experiments are underway in 2012 at another location to test the effects of additional product and application timing treatment combinations. These experiments include several additional products.

Tamra Jackson-Ziems
Extension Plant Pathologist
Kevin Korus
Plant and Pest Diagnostic Clinic Coordinator