Harvest Considerations for Wheat

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Now that wheat has stopped flowering you may think the need to check your wheat fields for disease is over. Not so fast. Plan on checking your fields 18-21 days after flowering to assess for scab incidence and severity. Assessment of heads earlier than this may not allow adequate symptom development, and assessment later than this can result in misassessment due to natural senescence of the plant. Look for 1) severely symptomatic fields and 2) areas of fields where fungicide coverage issues may come into play (field edges, forest edges, near powerlines, etc). Assess at least 1 transect per acre of field. Without looking at plants, pick 25-50 heads as you walk through your transect. Typically we run 100 paces, picking heads along the way. Bring the heads back to the truck and set aside the heads with symptoms such as bleaching, partial bleaching, pink kernels (Figure 1). Count the number of heads with symptoms. If you have more than 10% symptomatic heads, this may indicate a potential scab and DON issue in the field. Visual symptoms do not mean you have a DON issue, but they do indicate increased probability for elevated DON.

Potential problematic fields or problematic areas of particular fields should managed as follows:

  1. Harvest problem areas/fields first (and remember that this year you may be able to harvest at higher moisture without dockage in some places)
  2. Dry down grain below 15% moisture ASAP (this will halt growth of Fusarium and potential production of DON by the fungus)
  3. Separate good or low level scab fields from fields with significant issues.


Figure 1. Wheat heads with symptoms of Fusarium head blight/scab.

As far as harvesting, you will need to look at adjusting your combine settings when harvesting symptomatic fields. The goal here is to remove any lightweight tombstones caused by Fusarium, which impact test weight and can contain significant DON contamination (in the hundred ppm range). One can argue that this results in loss of good grain along with bad grain and this is true in some cases. Research indicates that either opening the screen opening (from 70 mm to 90) and running at standard fan speed (1375 rpm) OR running at increased fan speed (1475 rpm) with a standard screen opening (70 mm) can dramatically reduce DON contamination. In addition, when taking into account yield and dockage, the gross income is significantly greater than harvesting with regular fan and screen opening settings. http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-04-11-0309. In the research, the potential for this practice to be profitable was particularly significant at low grain prices, and stable across levels of scab severity. Although combining high fan speeds with wider screen openings reduced DON and improved income, it was not as consistent across environments and situations as either increasing the fan speed or increasing the screen opening alone. As stated in the abstract “Results showed that, when harvesting grain from FHB-affected fields, the improvement in grain quality and reduction in price discounts with a combine adjustment could be great enough to counteract the reduction in harvested grain that results from the adjustment.” These data are not absolutes. However, the study does show that you can improve net income and reduce DON by either increasing fan speed or increasing screen opening.

Lastly, remember that management of scab starts with the selection of a moderately resistant variety. Application of a fungicide for scab suppression in a severe scab year is unlikely to save a susceptible wheat variety. However, the combination of a good, moderately resistant variety in addition to a timely fungicide application can put you in a more favorable position if a scab outbreak does occur. Use the Virginia Tech or University of Maryland misted nursery data to help you with variety selection.