Deer and the Looming Threat of EHD: Whitetails 365
Deer and the Looming Threat of EHD
As we gear up for 2025’s deer season, we’re praying for rain, and hoping the deer we passed to let grow, will make it to another hunting season. With that said, several reliable sources are predicting a continuation of the dry conditions that have plagued our landscape in recent years, and frankly, the evidence is already in. Our local precipitation levels for most of us are low, with the U.S. Drought Monitor currently labeling our area as “abnormally dry.”
For those of us deer addicts that are trying to figure out the weather patterns now to predict the fall, this season feels and sounds a lot like the drought back in 2012, which was one of the driest years I can remember and toughest on deer and deer hunters. We had a decent spring, but the dry spell that is stretching into the 2025 deer season is significant. Depleted groundwater means our deer herds will be increasingly reliant on surface water sources like those puddles, creeks, and shallow ponds that typically offer easy access to water. But what happens when these vital resources begin to vanish?
The answer is simple; deer will concentrate around the remaining water. This concentration of deer around dwindling water sources isn’t just a matter of convenience; it carries a potential consequence: an increased risk of Epizootic Hemorrhagic Disease, or EHD.
EHD and Drought
Over the past decade, Iowa has unfortunately become well versed with the devastating impact of EHD, a viral disease that primarily affects white-tailed deer, and now CWD, Chronic Wasting Disease is on the rise too. EHD is transmitted through the bite of infected tiny biting flies commonly known as “no-see-ums” or gnats. At one point, we would have one assumed that dry conditions would suppress the population of these disease-carrying insects. However, the reality, as the Iowa DNR has consistently pointed out, is quite the opposite.
When the rains fail and smaller waterways dry up, deer are forced to congregate at the remaining shallow, often stagnant, water bodies. We’ve seen small ponds dry up. They’re left muddy, with foul-smelling stagnate water. The deer are still drinking from these ponds. The deer will trample through the mud to get to the water, and with that mud is a breeding ground for insects, including a biting midge fly that can pass the disease Biting midges thrive in warm temperatures, mud, and stagnant water.
The reason that we’re concerned about this is that it just takes one deer infected with EHD, and several biting midges can feed on that deer. They then hang out in these areas, and infect healthy deer as they bite and feed off of them. As more and more deer gather to drink, the chances of a midge feeding on an infected animal and then spreading the virus to others skyrocket. This is why we often see condensed “pockets” where EHD was devastating.
During a drought, instead of a few midges scattered across numerous water sources, you now have a concentrated water source with flies buzzing around the few remaining wet spots. These tiny insects feed on an infected deer and then, as nature dictates, move on to the next, potentially healthy animal. The cycle continues, amplified by the sheer number of deer in close proximity. A killing frost will knock the insects down, but the summer and early fall months we see deer die off and the disease spread.
With drought, not only are the muddy water sources promoting disease, but limited access to clean water takes a toll on the deer themselves. Dehydration leads to stress, weakening their immune systems and making them even more vulnerable to diseases like EHD and the ever-present threat of Chronic Wasting Disease (CWD). We, as responsible sportsmen and women, have a vested interest in giving our deer populations every advantage to remain healthy.
The Iowa DNR’s records paint a stark picture, with severe EHD outbreaks occurring in 2012, 2013, 2019, and 2023. Observing the current weather patterns, it’s hard not to draw parallels to the summer of 2012, a year that brought significant drought and a subsequent surge in EHD cases. If you do find dead deer and suspect EHD, the Iowa DNR has an online reporting tool. You can help track the spread of the disease.
Providing a Water Source on Your Property
Given these concerning trends, now might be the time to consider a proactive approach: providing a supplemental water source on your property. This simple act can offer deer an alternative to those potentially disease-ridden, muddy watering holes, helping to disperse them and reduce the likelihood of EHD transmission.
Several options exist for creating water access on your property. There are fiberglass deer ponds, and we’ve seen some new designs in the past couple of years. These shallow, irregularly shaped ponds are durable, easy to move, and often have a natural appearance that doesn’t spook wildlife. While they may require refilling with a water tank, their lightness and natural look are significant advantages. Many hunters have found success with these, especially when positioned in areas frequented by rutting bucks, like your favorite timber stand, or by your blind.
The use of stock tanks is a topic of some debate. While some advocate for burying or partially burying them to reduce spooking, others simply place them above ground. If burying, be mindful of potential contamination from runoff, especially in bedding or feeding areas. You don’t want to position it in an area that will capture fecal matter. This promotes the spread of diseases. The goal is clean water, so consider the surrounding environment, don’t go putting your brand-new water source in a muddy area and compound your problem. Try to find rocky, sandy soil that doesn’t hold moisture for the midge flies to procreate. I also want a nice, elevated spot for placement of my water source for the obvious reason of contamination in the water.
At its core, deer survival hinges on three key elements: habitat, food, and water. If any of these are lacking, deer will inevitably seek them elsewhere. This is why we see EHD cases concentrated on particular pieces of land. By providing a reliable water source, you can attract and hold deer on your property and provide clean water. Water is a fundamental need. Ensuring its availability can make your property more attractive and encourage deer to spend more time there.
By offering a water hole, you can help alleviate the concentration of deer at potentially contaminated or midge-infested natural water bodies. Access to clean water reduces stress and supports a healthy immune system, making deer less susceptible to disease. You can also make your hunting better than ever with a well-placed water source. A strategically placed water source, especially during the rut, can be a magnet for thirsty bucks. This can be the difference between getting a shot at your buck or watching him walk just out of bow range.
While we eagerly await the soaking rains that our parched land and food plots desperately need, let’s not forget the immediate needs of our deer herd. The predicted drought carries the very real risk of exacerbating the EHD situation. By understanding the connection between dry conditions and disease, and by taking proactive steps to provide clean water sources, we can all play a part in supporting a healthy and thriving deer population in Iowa. Being an Iowa Sportsman isn’t just about the thrill of the hunt; it’s about being a responsible steward of the land and its wildlife, even when Mother Nature throws us a curveball.
By Aaron McKinney
July 2025
