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

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. Before you blame dead plants on plant pathogens, check to see if this could be due to a lightning strike.

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.

According to a University of Nebraska publication, lightning strike happens in poorly drained areas in the field where a pool of water may collect. Plants affected by lightning may show ozone injury symptoms. Lightning discharges ozone after the strike. Plants that are not completely killed by lightning may have other pathogens develop such as stem canker. However, stem canker does not need lightning in order to develop in soybeans.

Source: Emmanuel Byamukama, iGrow