Bob Hochmuth, Mark Warren, Shannon Carnevale, Lara Milligan, Jay Capasso
Introduction
As the saying goes, “when thunder roars, go indoors”. Whether you’re in the fields or just out enjoying some of our beautiful natural areas, if you see lightning or hear thunder it is time to retreat to the safety of an indoor space. UF/IFAS, the National Weather Service, and the National Lightning Safety Council all recommend seeking shelter inside a proper building – one with four walls, a foundation, and a roof. Picnic shelters are sometimes mistakenly used as lightning shelter when out camping, hiking, or on sports fields – but these can actually increase your risk of a lightning injury. If you don’t have a building nearby, retreat to a fully enclosed vehicle. I’m sorry to say, that golf carts, 4×4’s, convertibles, and old jeeps (without doors) do not provide a safe shelter from lightning. Go indoors and wait 30 minutes after the last thunder boom before returning to your outdoor activities.
Thunder is the byproduct of lightning, and you can’t have lightning without thunder. You may be thinking, “What about heat lightning?” Heat lightning is normal lightning that is far away, so far away that you cannot hear the thunder boom. Also, it’s far enough away that you don’t see the actual strike. What you are actually seeing is the reflection of the lightning flash on higher altitude clouds and through the distant horizon. The reddish or orange hue of heat lightning is caused by “atmospheric scattering” of the light, especially when viewed near the horizon – just like how a sunset appears redder than the sun appears at midday.
When Lightning Strikes in a Watermelon Field
Florida is the national leader in both lightning strikes and watermelon production. One of the most interesting things you might see is when lightning hits a watermelon field. The power of the electricity in a strike “etches” a line across the watermelon fruit through the vines laying on the fruit (Image 1). In addition, we often see a hole melted or blown in the drip tape or plastic mulch (Image 2). This is sort of a novelty in agriculture, but a very interesting one. We usually see at least one area in a watermelon field in the Suwannee Valley region of Florida each year. Think about it, all lightning strikes must hit somewhere, so why not a watermelon field?
Lightning frequently occurs throughout Florida during thunderstorm events. The most frequent type of lightning strike is the electric discharge from the atmosphere to the ground. The actual strike point in a field is very small, but the discharge in energy can result in damage well beyond that point. When lightning strikes in a watermelon field, it generally results in the sudden appearance of irregular, circular spots with dead or severely damaged plants, with little or no recovery of the plants (Image 3). The thing here is that it is a much more sudden death than even Fusarium wilt. The actual point of entry can usually be identified within the center of the dead spot. In addition, the evidence of a strike often can be found in the plastic mulch, which is seen as a small, melted spot, not a tear in the plastic, sometimes associated with a small depression in the soil where the actual strike hits. The energy is transferred down the drip tube which typically has some water inside, and in severe cases, a section of the drip tube melts resulting in leaks upon the next irrigation event. The lightning energy may follow along the drip tape (down the row) or along the vines and you may see other melted plastic areas. We have seen a couple instances where even the drip tape was melted down the line. We have almost always been able to find the small, melted plastic holes. In many cases the lightning ran down the vines that were on top of a watermelon fruit and it etches a burn line in the fruit rind. If watermelon fruit are present, the energy goes through the vines and etch or burns tracks in the surface of the fruit. This same type of damage can occur in any other crop grown, not only watermelon.
4
