Every year, usually about late August, farmers sometimes notice reddish to purple corn or sorghum leaves and plants (Figure 1). Usually, these are isolated single plants and other times, they occur in patches in the field. Growers often question if they are seeing disease or perhaps nutrient deficiency. Upon closer inspection, these plants often have reduced grain set or are entirely barren.
While the distribution of the red to purple color could be linked to several growing season stresses such as temperature, drought, disease, or simply genetics, the color is most often caused by an overabundance of photosynthetic sugars and a pigment called anthocyanin that builds up due to the lack of grain production. Sugars produced daily by photosynthesis move within the plant and are used to produce grain; however, when grain set is poor or nonexistent, the sugars and anthocyanin accumulate in the plant. Occasionally, single leaves or the top parts of the plant are affected on plants with normal grain set. This normally occurs due to insect feeding or other damage to plant structures that do not allow the sugars in the leaves to transport to the developing grain. I’ve often noticed that insects such as corn leaf aphids find these plants more attractive due to the increased sugar content.
While the presence of the reddish plants is not the problem, it is an indicator of plant stresses that signal reduced grain production. Farmers should take note of the distribution of the plants within the field as a clue to identify those stresses.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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