Troubleshooting Disease Symptoms in Wheat
In general, the wheat crop is looking pretty good across the region, but there have been some not-so-good looking fields. This spring’s abnormal weather patterns have lead to some interesting symptom development in wheat. In my travels across the county and state and in conversations with colleagues in the area, several wheat fields have been exhibiting disease-like symptoms that are not readily attributed to any one disease.
The symptoms include general yellowing of plants, yellow leaf tips, and/or flecking on the leaves (Figure 1). The flecking on the leaves is a symptom that can be caused by many different biotic and abiotic factors, but when entire fields are affected it is generally associated with a condition called physiological leaf fleck (Figure 2). Leaf flecking can be caused by periods of cloudy weather followed by bright, sunny weather, which we have certainly had this spring. However, similar symptoms can also be associated with viral infections and bacterial pathogens. Bacterial infections in wheat are not very common in our region; however, wheat samples in nearby Delaware tested positive for the bacterial wheat pathogen, Clavibacter michiganensis subsp. tessellarius (Cmt, Figure 3). Both physiological leaf fleck and Clavibacter m. tessellarius are believed to have little-to-no impact on yield.
A second disease that we are seeing associated with these yellowing leaf tip symptoms is Barley Yellow Dwarf Virus (BYDV) and Cereal Yellow Dwarf Virus (CYDV). Both viruses have similar disease cycles and are vectored by aphids, primarily in the fall. What is interesting is that BYDV symptoms are typically also associated with bronzing of the leaf tips; however, these particular wheat samples did not exhibit these classic symptoms. Additionally, some plants that were exhibiting bronzing/purple leaf tips did not test positive for BYDV or any other viral pathogens, which leads me to this takeaway point—disease symptoms in wheat can be very tricky to decipher, especially when weather events complicate symptom expression. Wheat can be particularly sensitive to freeze, cold, and even sunny weather events in the spring, especially if weather conditions fluctuate. In many cases, symptom expression in response to environmental stressors can mask, uncover, or mimic disease issues. Furthermore, disease symptoms are not always “textbook,” so relying on visual identification is not enough to properly diagnose problems.
Moving forward with wheat cultivation, it is important to keep this information in the back of your mind as you troubleshoot symptoms, and it is a good idea to utilize all the resources at your disposal, such as crop consultants, labs, and Extension professionals, to help diagnose problems.
This article appears in June 2022, Volume 13, Issue 2, Agronomy news.