A few winter wheat fields scouted last week were found with symptoms caused by non-living (abiotic) agents. Some of the symptoms observed include physiological spots, yellowing lower leaves, and gray spots. Growers are wondering if these are diseases that something can be sprayed on to manage.
Physiological spots are numerous small chlorotic spots on wheat leaves (Figure 1). These can be found on almost every plant in affected fields. Physiological spots may develop due the genetic reaction to the environment or resistance to infection. They usually do not develop further but remain as chlorotic spots and do not cause economic yield loss. Nothing can be done to manage these spots.
Figure 1. Physiological spots developing on a wheat leaf.
Yellowing Lower Leaves
Yellowing of lower leaves is usually observed in fields that have excessive tillering (Figure 2). The lower leaves become shaded due to insufficient light. Sometimes the yellowing on lower older leaves may be due to nutrient deficiency such as nitrogen. Splitting nitrogen application may help in reducing overtillering.
Figure 2. Wheat plants with yellowing lower leaves due to overtillering.
A few fields had grayish spots on top leaves (Figure 3). The cause of these spots is not known.
Figure 3. Gray spots on top leaves.