Wet Weather and Late-Season Fungicides

Wet weather is continuing to be a problem throughout the state, and many questions are popping up regarding late-season fungicides. 

With funding from Ohio Soybean Council, we conducted a “high-input” trial in 2013 (9 locations) and 2014 (7 locations) to examine the use of a strobilurin fungicide at the R3 growth stage (initial pod development).  There was a positive yield response to fungicide application at 6 out of 16 locations (~38% of the time).  Of the responsive sites, the average yield increase due to fungicide was 7 bu/ac (range of yield increase was 3 to 12 bu/ac).  The table below shows the disease ratings, rainfall, and flooding events that occurred at the sites responsive and unresponsive to fungicide application.

 

RESPONSIVE SITES

UNRESPONSIVE SITES

Average brown spot in bottom of canopy

(R6 growth stage)

7.1%

(leaf area affected)

1.4%

(leaf area affected)

Average frogeye leaf spot in top of canopy

(R6 growth stage)

2.4%

(leaf area affected)

0.5%

(leaf area affected)

June + July rainfall

12 inches

11 inches

Number of locations with standing water for at least 24 hrs.

0

2

 

The sites responsive to fungicide had greater leaf area affected by brown spot in the bottom canopy and frogeye leaf spot in the top canopy.  The responsive sites had slightly greater rainfall in June and July than the unresponsive sites. 

What really stands out and is very pertinent to this year: Two locations had standing water for at least 24 hours in early July.  Both locations were unresponsive to fungicide application.  Additionally, the yield at these two locations yielded on average 40 and 38 bu/acre…These two locations had bigger issues limiting yield than disease. Flooded fields often have reduced root and shoot growth, limited nitrogen fixation, reduced photosynthesis, and increased physiological stress.  In our two flooded fields, disease was not the yield-limiting factor.

 

 

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.