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Fusarium Head Blight (Scab) Risk and Factors to Consider (07/11/19)

There are several areas across the state in moderate to high risk for Fusarium head blight (FHB) on susceptible varieties that are flowering (Figures 1 and 2).

There are several areas across the state in moderate to high risk for Fusarium head blight (FHB) on susceptible varieties that are flowering (Figures 1 and 2). If a moderately resistant variety is being used, moderate to high FHB risk still exists for southeast and southwest North Dakota (Figure 3). All of these statements are based off maps generated by the Fusarium Head Blight Prediction Center (national model) and the NDSU Small Grains Disease Forecasting Website (state model). Risk will increase in the coming days for most areas of the state. Currently, the state and national model have similar trends, but also have noticeable differences prompting several questions on how to gauge FHB risk and what model should I use? This article will review both models and provide some insight on commonly asked questions.

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Differences between the national and state model

 Weather Data Source: The national model uses weather obtained by the National Weather Service that adjusts for topography and vegetation. The state model is solely dependent on the NDAWN station data. Regardless, the most important weather data variable being used is relative humidity as this drives FHB epidemics.

Time periods: The national model retrieves relative humidity data information for 15 days prior to the flowering date selected. The state model uses relative humidity for 7 days prior to the flowering date. The importance of using relative humidity data prior to flowering growth stages is that the Fusarium fungus needs several days of conducive conditions to start releasing spores that small grain spikes.

Host Susceptibility Selection: The national model currently has a selection tool to select market class (spring vs winter wheat) and host susceptibility (susceptible, moderately susceptible and moderately resistant). The state model does not have the market class criteria and has four classes of susceptibility:  very susceptible, susceptible, moderately susceptible and moderately resistant. Having a moderately resistant variety can drastically reduce risk in spring wheat.

Remember…These are prediction models

As with every model, predictive models should not be used as a sole source of information and decision making. Rather it should be used to help alert you to conditions that are conducive for FHB. We have seen the models perform remarkably well and also fail to predict epidemics. When I get asked about the risk for FHB in an area, I first consider the level of resistance of the variety used and then think about other factors that may give an indication of high humidity. For example, if dews are extending into the afternoon hours for consecutive days (pant legs are soaked when scouting), this paints a picture of an environment that will be at higher risk for scab.

Final thoughts

Currently, I believe the national model is doing a better job predicting potential FHB epidemics in the state. The national model has responded well to rain events, fog, long dew points, etc. The state model appears to be more conservative this year, but the model has been trending towards higher risk for several areas of the state over the past couple days.

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

 

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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