While we are seeing more rain, the drought has turned green corn plants into various shades of yellow and brown. However, there are a few other colors you may see in a field. Read below to know what the different colors may indicate:
Reddish-Purple
Early season reddish-purple streaking may be a sign of phosphorus deficiency. However in late season corn, this purple hue can be a sign of anthocyanin production. Anthocyanins are naturally occurring pigments that form to absorb excess light and help corn tolerate excessively sunny conditions, similar to how melanin protects our skin. These pigments make plants shades of reddish-purple. Additionally, anthocyanins can be caused by a buildup of sugar in leaves, which may indicate that the sugar is not being fully utilized or the flow of sugar is disrupted. Drought conditions can lead to small or missing corn ears, resulting in unused sugar. Stress and stalk damage may disrupt sugar flow.
Figure 1. Purple streaking from corn plant with no ears (Paul Smith)
Orange
If orange specks are observed on corn, it may be corn rust. Immediate treatment may not be needed, but it is essential to monitor the corn for development and spread to determine the appropriate management approach. See corn rust and southern rust for more information.
‘Dusty’ black/gray
Common smut has been prevalent this season, as it is favored by hot, dry conditions and worsens when kernels are injured. Infected corn kernels are full of black spores that may spread, contributing to a dusty black appearance on surrounding leaves. It is recommended to remove the infected kernels (galls) or ears before they rupture to minimize spread. The spores can survive in the soil for 5-7 years, though cultural practices that manage ear rots are also useful at managing common smut.
The late season rainfall we are experiencing also provides conducive conditions for saprophytic fungi, such as Alternaria spp. that grow on dead leaves and husks. These fungi do not usually cause ear damage and do not need to be managed.
Figure 2. Dusty black spores on corn with smut (Rob Coltrin)
With tar spot of corn spreading throughout the Midwest and Southeast regions, black spots are a concern for every corn grower. Tar spot has not been reported in North Carolina, though it is important to familiarize yourself with the disease. If tar spot is suspected, please contact your extension agent. Extension agents should report suspected cases to extension pathologist, Daisy Ahumada: daisy_ahumada@ncsu.edu.
For more information on other causes of changing corn leaf colors, see the following:
