Even in a Drought Late Season Soybean Diseases Can Still Show Up
The 2012 growing season has been one of great variability in terms of the weather and its impact on soybean diseases. Early stand issues were mainly caused by crusted soils due to driving rains or shallow planting into dry soil. Very few soybean disease related questions have been expressed……until now. Last Friday (8/3/12) I walked a field near the Arlington Ag Research Station. It was expressing classic Phytophthora root and stem rot (PRR) symptomology. Yesterday I also received similar questions out of the LaCrosse area. As you examine the symptomatic plants it is important that you differentiate PRR from stem canker as they can easily be confused.
Yesterday I also saw the first report of sudden death syndrome (SDS) from @FS_Mark. Weather conditions will likely limit the severity of SDS statewide however this pathogen was confirmed north of Eau Claire in 2010 so vigilance in those areas that have received rainfall is important. As always make sure that the disease identification is correct for SDS, since foliar symptoms are similar to brown stem rot (BSR). In particular, make sure to examine the whole plant, including stems (looking for internal browning due to BSR) and roots (looking for a root rot and also a bluish hue that is the fungus of SDS). Do not just rely on the foliar symptoms to verify your diagnosis of either disease.
Lastly, in spite of the heat during flowering across the state, we will still see white mold somewhere in the state. This is not necessarily a surprise as we do find the disease each growing season. Based on our current observations and reports though, it appears that the disease intensity will be low, although variation to the soybean variety is be evident.
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