By Daren Mueller
The spring has certainly looked a little different than previous years. What does it mean for disease development? With some of our more destructive diseases – sudden death syndrome (SDS) and white mold – the rains have certainly increased the chances of disease developing. Each season these diseases have two hurdles to clear: early season conditions that set up the disease, and mid to late-season conditions that make a disease situation worse. Let’s take a quick look at how this year’s weather matches up with previous years.
White Mold
Since 1999, the four years in which white mold was most prevalent across all of Iowa are: 2004, 2009, 2015, and 2019. See Tables 1 and 2 to compare weather from northwest (NW), north central (NC), and northeast (NE) Iowa. I used the weather data from the Iowa Mesonet.
Table 1. Precipitation totals (inches) for white mold years (2004, 2009, 2015, 2019) compared to 2024.
* Through June 20, 2024
Table 2. Average temperature (F) for white mold years (2004, 2009, 2015, 2019) compared to 2024.
* Through June 20, 2024
Sudden Death Syndrome
Since 1999, the four years in which SDS was most severe across all of Iowa are: 1999, 2010, 2014, and 2016. See Table 3 and 4 to compare weather from these same three locations in Iowa.
Table 3. Precipitation totals (inches) for SDS years (1999, 2010, 2014, 2016) compared to 2024.
* Through June 20, 2024
Table 4. Average temperature (F) for SDS years (1999, 2010, 2014, 2016) compared to 2024.
* Through June 20, 2024
What Does All This Mean?
In the four years with the most white mold, the precipitation at three arbitrarily selected weather stations in northwest, north central, and northeast Iowa was 16% greater than the 30-year average in April, May, and June. Also, the temperature was 0.7% cooler than the average during these same months. For the four years with the most SDS, there was 33% more precipitation than the average year during these three months at these same weather stations. Also, the average temperature was 1.8% warmer than the average. In 2024, we have seen 37% more precipitation than average and temperatures that are 2.9% warmer than average. While the increased precipitation should increase the risk of both diseases, the warmer temperatures may slow disease, particularly white mold development.
Development of both diseases also relies on continued favorable weather conditions. For the four white mold years, the average precipitation in July and August was 12% greater than the average and the temperature was 3.9% cooler. For SDS, the average precipitation was 33% greater than the average, and the average temperature was 0.6% cooler than the average. While moisture levels are ideal for white mold and SDS, they will need to continue through July and early August for disease to really develop. Temperatures also will need to cool for white mold development.
What does this mean for fungicide applications?
For SDS, there are NO foliar fungicides that work. We continue to hear reports of recommendations for fungicides to be applied at R1 for SDS control; however, our data shows that all foliar fungicides have no effect on SDS. If you want to read up on this, here is a research summary on these foliar applications.
For white mold, recommendations for foliar fungicide articles are a bit trickier. In recent years, we have encouraged folks to hold off on their first fungicide application until R2 or even R3. However, with the rainfall we have had, keep a close eye on the fields with a higher risk of white mold. You may need apply the fungicide a little earlier at R1 to R2, especially if the rain continues and it cools down. A useful tool to monitor the risk for white mold is Field Prophet, which is available at no charge. Finally, remember that not all fungicides are equally effective against white mold. Please check out the Crop Protection Network fungicide guide for efficacy ratings for white mold.
Source : iastate.edu