The 2019 wheat harvest is well underway in South Dakota, with many acres of winter and much of the spring wheat crop left to harvest. To date, reports on yield and quality have been variable, depending on when the crop was seeded, weather conditions at important growth stages (such as flowering and grain fill) and disease pressure throughout the season.
Disease Impact at Harvest
Two diseases which can impact wheat at harvest are Ergot (Figure 1) and Fusarium Head Scab (FHB) (Figure 2). These are both fungal diseases that infect HRW and HRS wheat during flowering when conditions are conducive. At certain levels both diseases can also result in producers taking discounts or having product rejected at the elevator. Ergot thresholds in grain are very low (0.05 % which is like 10-15 ergot bodies per kilogram) due to its potential to cause health issues in humans and animals. FHB can reduce both yield and test weight, but it is usually the level of deoxynivalenol or DON (vomitoxin) that is associated with scab infected grain which results in rejection or dockage at grain elevators. Current FDA level of DON for human consumption is 1 ppm and 5-10 ppm for livestock (depending on type).
Minimizing Harvest Losses
Some steps can be taken at harvest to help minimize losses from these diseases. Scouting fields just prior to harvest can help producers determine if these diseases are present and to what extent. It is possible these diseases may be worse in some areas of a field than in others. For instance, since ergot is often present in grasses in the ditch, it may occur at higher levels in areas adjacent to these grassy areas or on field edges. These areas can be harvested and stored separately, so as not to contaminate wheat from areas of the field where the disease incidence is much lower. This gives the producer the opportunity to sell the wheat from the good areas of the field without deductions.
Typically FHB will impact an entire field if the field is ripening evenly. This might not be the case in situations where part of the field was seeded later for some reason or different varieties were used within a field. In these situations it is possible part of the field may be more impacted by the disease. Again checking fields prior to harvest could help producers limit losses. However, it may be difficult to accurately assess for FHB if wheat heads have already turned color.
In any areas where FHB is a concern, producers should slow their speed and adjust their combine settings to throw as many scab infected kernels out the back of the machine as possible. The same can be done with ergot infested wheat. Ergot bodies are usually larger than wheat kernels, making it possible to use conventional grain cleaning equipment to separate it out. Gravity tables are also successful, especially if the wheat has good test weight. Ergot bodies have a lower density than wheat. At times it may be necessary to use a color eye to clean out the ergot.
Grain infested with DON should be cleaned before it is stored. Even after cleaning this seed should not be stored at moisture levels over 22 %.
- Friskop, Andrew, Extension Plant Pathologist, NDSU, Ransom, Joel, Extension Agronomist, NDSU. Deoxynivalenol (DON) in Small Grains, 2017
- Brent Turnipseed, SDSU. SDSU Seednews, Volume 23, Issue 2, August 2015.
- Friskop, A., Endres, G., Hoppe, K., Mostrum, M., Ransom, J., Stokka, G., Ergot in Small Grains. NDSU 2018.