With our recent cold night temperatures and warm days we may see damage to small grain crops. Damage symptoms can vary based on what stage the plant is in, other components of the weather such as rain or snow, and soil types.
Cold soil temperatures and temperatures that fluctuate greatly between day and night can cause odd symptoms on young coleoptiles and emerging foliage called color-banding. Color-banding occurs when tissue near the soil line discolors as a result of being exposed to very cold or warm soil, especially when there is a marked difference between soil and air temperatures. This results in yellow (Figure 1), and purple discoloration that often extends the width of the coleoptile or leaf. White bands can be seen when in the spring when warm soil contacts the plant (Figures 2 and 3)Affected plants are often near each other and the impacted leaves may have multiple bands that result from new growth being exposed to the fluctuating temperatures and sometimes referred to as ‘rugby stripes’. Although these symptoms can be dramatic, it’s unlikely to kill the plant.
Plants can also be damaged by exposure to cold air temperatures and frost. These plants can have leaf twisting (similar to a corkscrew) in older leaves (Figure 4), reddening or purpling at leaf tips (Figure 5), a general sickly-yellow coloring (Figure 6), or water-soaking which can make the tissue appear darker. Sulfonylurea herbicides can also produce purple to red pigments in some plants. Areas that are more prone to cold or frost damage include: low spots, areas with wind exposure, dry soils, and fields/areas with high crop residue as the crop residue prevents the heat from the soil from radiating to the plant. Early season nitrogen may make the plants more susceptible to this type of cold damage if the nitrogen application caused accelerated growth.
Fields with a high proportion of clay may be prone to soil crusting. Crusting events occur when soil particles re-disperse as a result of rain or irrigation and reform into a dry, dense covering. This crust becomes too solid for seedlings to germinate through. As a result the seedlings appear curled from attempting to grow up through the hard surface (Figures 7 and 8). Seedlings that do emerge will likely grow fine into the winter. Trillate and Trifilluralin chemicals can cause distortion that can look similar.
If you suspect cold damage: check the distribution of the symptoms in the field, paying attention to low spots and exposed areas. Next, check the root system as a poor root system may indicate root rot rather than cold damage as the cause of the symptoms.
As with any questionable symptoms, the Plant Pest Diagnostic Clinic is here to help! To get more information or to send a sample, follow the directions on the Plant Pest Diagnostic Clinic website.