Rains Help Create Conditions Favorable For Disease

May 13, 2015
By Angie Peltier
A wet week. In a 7 day period between May 4 and 10, the Northwestern Illinois Agricultural Research & Demonstration Center (NWIARDC) received 2.21 inches of rain (Figure), an inch more than was received during the entire month of April! This rain largely put a stop to most field operations at the NWIARDC.
Figure. Note the dark rain clouds ready to drop rain on the SDS seed treatment trial just planted at the NWIARDC (Image credit: Marty Johnson).
Figure. Note the dark rain clouds ready to drop rain on the SDS seed treatment trial just planted at the NWIARDC 
Seed treatment trial planted. Due to the wet soil conditions, only one trial was planted during this week. Although soil conditions were likely a full day away from being 100% fit for planting, on May 7 NWIARDC personnel planted a replicated soybean seed treatment trial. This trial - established at the request of both the NWIARDC Advisory Committee and a company that develops biological seed treatments – will evaluate various experimental and labeled seed treatments for management of sudden death syndrome (SDS) in soybean.
Conditions required for plant disease. Three things must come together for plant disease to occur: a susceptible plant, a virulent pathogen, and an environment that favors the interaction between the host and pathogen. For this trial we did our best to bring together all of aspects required for SDS to occur. We planted a soybean variety that in a 2014 in-furrow fungicide and starter fertilizer trial had proven to be quite susceptible to SDS. We did not rely upon nature to provide our inoculum, but rather dried sorghum seed that had been previously soaked with water, pressure sterilized in an autoclave, and then seeded with the SDS pathogen (Fusarium virguliforme). A cone planter was used to deliver a known quantity of this inoculum into the furrows of the middle two rows of four-row plots. These thirty-two plots were then immediately planted to the same soybean variety untreated or treated with one of seven different seed treatments.
Soon after the last plot was planted, rain started to bring the third aspect required for disease – a favorable environment (Figure). This experiment was planted into a low-lying area of a field whose soil was already moist. The frequent rains received since planting, the cool air and soil temperatures forecasted for the near future and a drip irrigation system will be our (and Mother Nature's) best effort to secure an environment that favors development of sudden death syndrome and provide a good test for the different seed treatments.
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