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LIGHTNING During thunderstorms, lightning can strike and affect a small portion of a field. In general, it strikes poorly-drained areas, often near the center of a center-pivot where the ground tends to be wetter. The size of the affected area relates to soil moisture and strength of the discharge. Most commonly the area struck by lightning is circular or ellipsoid with a well demarcated border. Normally, plants within the area are uniformly dead or dying with the destruction diminished along the border. Border plants may show ozone injury as ozone is produced by the lightning discharge. If soil moisture varies considerably in the area, damage may be irregular. At first glance, the area may seem to have been attacked by a pathogen such as black leg or stem canker. Symptoms appear in less than 24 hours starting with the lower stem. Stem tissue near the surface becomes soft, wet, and brown or black, similar to black leg but without the hollow center. The affected stem tissue will then dry up, changing to a lighter color with the surface turning very light, off-white. When cut longitudinally, the inside of the stem will show the pith collapsed, forming cross plates that look ladder-like. Depending on the lightning's discharge, stem symptoms move up the plant. The top of the plant collapses and dies quickly turning brown. Tubers are affected although symptoms don't appear until later. Their skin form large brown/black blotches on opposite sides where an electrical discharge passed. Some skin cracking occurs. A severe affect may result in a cooked tuber. The inside of the tuber may collapse forming a hollow area between the two outer blotches while the rest of the tuber may seem unaffected unless cooked. The tuber appearance is similar to that of bacterial ring rot. Affected tubers are prone to pathogenic invasion and usually decay in the field before harvest. Interestingly, other underground tissue, root and stem, are uninjured by lightning.
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