In Manitoba, cold temperatures during the day and freezing temperatures overnight have been one of the big stories the past week. Cereal crop types are more tolerant of freezing temperatures than other crops types; they can tolerant to temperatures as low as -6°C as their growing point below ground until the 5 leaf stage. However, symptoms of the cold temperatures has resulted in frost banding, or also called color or temperature banding, in cereal crops.
Often the bands appear in similar position on each seedling, so if you view the crop from a low angle, all the bands will line up. Depending on weather conditions, single and multiple bands can happen.
Figure 1. Colour banding in winter wheat in the Estevan area at the end of April 2013.
When do we see banding? Color or frost banding occurs on young cereal crop seedlings when temperatures at the soil surface fluctuate widely. Newly emerged plants will exhibit alternate color bands of pale green/yellow and green leaf tissue that correlates with high and low temperatures.
What creates it? Plant growth that occurs in the dark of night is not green but actually white, meaning parts of a leaf that emerges overnight remains white before dawn. When exposed to sunlight, the precursors to chlorophyll will start changing to chlorophyll (which is the pigment that makes plant leaves green), and the new growth turns from white to green.
When morning temperatures are cold in combination with sunny conditions, destruction of those precursors to chlorophyll can happen, resulting in less formation of chlorophyll. The end result is the plant tissue turns pale green or yellow. The intensity of banding is determined by the brightness of the early morning sunlight and the temperature. In severe cases, red plant pigments are formed that create brighter-colored bands on the seedlings. Banding is also more common in deeply seeded crops.
Will there be an impact to yield? Fortunately, affected seedlings usually grow normally with the banding with no effect on yield potential. In more severe cases, the bands may become necrotic and impact nutrient and water flow to the tip of the leaf.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD