Seeing Dead Soybean Plants in a Circular Pattern? Could Be Due to Lightning

By Emmanuel Byamukama
SDSU Extension Plant Pathologist

Lightning Strikes in Soybeans

What are the odds that a soybean plant can be killed by lightning? Very low! In a recent ten year period, Eastern South Dakota had an average of one to two strikes per square kilometer, per year. While quite uncommon for lightning to damage row crops, it does happen. Thunderstorms can have lightning that can burn soybeans plants leading to their death. Plants that looked just fine before the thunderstorm may suddenly start to show wilting symptoms and eventually die (Figure 1 and Figure 2). Before you blame dead plants on plant pathogens, check to see if this could be due to a lightning strike.

Figure 1. Soybean plants wilting a result of lightning strike one day after a thunderstorm on July 27, 2017 near Trenton, SD.

Figure 2. The same soybean field on August 11, 2017.

How can you determine if plants were killed by lightning?

• Determine when the symptoms were first noticed.
• Soybean plants affected by lightning will start to show wilting symptoms 1-2 days after the thunderstorm. Plants affected by lightning have black to dark brown discolored stems and petioles. They may have a scorched or burnt appearance.
• Look for the pattern of affected plants.
• Plants killed by lightning are aggregated in a circular or elliptical pattern.
• Rule out plant pathogens.
• While other diseases such as Phytophthora root rot, charcoal rot can also kill plants in aggregated pattern, rarely are all plants in an area killed at once. Charcoal rot usually develops in plants that have other stresses mainly moisture stress.