Early fall color could be a sign of leaf disease. Here are 2 things to know

I had a brief conversation with a non-gardening friend last week. She asked me if all gardeners hate fall because, as she put it, “everything dies in the fall.” I looked her square in the eye and responded, “we love fall ... precisely because everything dies!”

Not exactly the response she was expecting.

For the non-gardeners out there, allow me to explain. When it gets cold, the mosquitoes die. When it gets cold, the chiggers die. When it gets cold, those bedraggled tomato plants you’ve been trying to keep looking like something other than a burn pile ... they mercifully die, too. Spoiler alert to the non-gardeners, we’ve been quietly waiting, and waiting, for “everything to die.”

Of course, on the upside, fall also brings that annual explosion of fall foliage that adorns calendar covers and fills tour buses with leaf-peeping tourists and their expendable dollars each year.

Fall foliage color ... I’ve covered it many times (and likely will again in another month or so) because it is a marvel of plant physiology and biochemistry. But all fall color is not created equal. Particularly this time of year, just before the time fall color hits its full stride, we encounter early bits and pieces of foliage color — some to be celebrated, some to be admired, and some to be concerned about.

Early signs of fall foliage color change can be a sign of plant stress. It can be caused by a disease pathogen. It can even be a species’ adaptation to dry fall conditions. Of course, it can also be perfectly normal for some early coloring species. The trick is, figuring out which is which.

Is early fall leaf color caused by leaf disease?

Plants spend all spring and summer fending off constant attacks by a horde of insects and disease pathogens. Sometimes the plant wins. Sometimes the horde wins. Sometimes the plant puts up a good fight, but by September it just runs out of gas and gives in. Whether it is powdery mildew on peony leaves, shot hole fungus in weeping cherries, or bacterial blight on buckeyes, some plants just lose the battle this time of year, leaves turn yellow and drop from the branches.

The good news with this type of early fall color is that by this time of year, the leaves have generally done what the plant needed them to do. All season long the leaves produced all the sugars and other compounds the plants needed to grow through this season and prepare for the next. With herbaceous perennials such as peonies, when the leaves start to look all gray and yellow, I take that as a sign from the gardening gods that it’s time to cut them back to the ground. They’re tough. They can take it. And, quite honestly, when they get that way they’re too ugly to leave in place. This kind of early fall color rarely occurs in a plant. Generally, this early fall color shows up fairly uniformly across the whole plant.

But some disease-caused early fall color is a sign of bad things to come. Some of our favorite tree species, from maples to redbuds, are susceptible to what’s known as vascular wilt diseases. These, mostly fungal pathogens, work by essentially clogging up the tree’s plumbing in the trunk and branches. While you can have plenty of moisture in the soil and a healthy root system, trees infected with vascular wilts can’t get enough water up to the leaves. The result this time of year can be isolated branches (or in advanced cases, whole plants) going into a stress reaction type of fall color production. Vascular wilts can be diagnosed by dark streaking below the bark in young branches but the tip-off is usually large individual branches going to color prematurely.

Is early fall leaf color caused by drought avoidance?

Plants are pretty darned amazing. Like animals, they have spent a few zillion eons evolving capabilities that allow them to survive and thrive over the long haul. For some trees, that has meant evolving the capacity to resist droughts — to extract tremendous amounts of water from seemingly bone-dry soil — a bur oak, for example. Others have figured out how to deal with droughts by developing the ability to be tremendously frugal with their internal water use — prickly pear cactus.

But there’s a third way to deal with the ever-present fall droughts we experience in middle America — drought avoidance.

Some plants take the early signs of approaching fall — shortening days, decreasing temperatures, and yes, even increasing drought conditions, as a signal that it’s time to stop growing — it’s time to drop their leaves. And this happens throughout the tree’s canopy rather than on specific branches.

Rather than hang on to their leaves until later in the fall and make a big splash out of the season, black walnut, tulip poplar, osage orange, and a whole host of other tree species simply cut the cord. They drop their leaves now to cut their (water) losses. If like mine, your tulip poplar has started littering the lawn with paper-bag-brown leaves, it’s not sick. It has just recognized the inevitable and cried "Uncle."

This isn’t a sign that your tulip poplar or black walnut is sick, diseased, or otherwise unhappy. It is just a sign of an amazing bit of adaptation developed over the ages and in response to a pretty consistent weather pattern. In essence, trees developing this adaptation are not all that different from Darwin’s finches evolving special beaks to crack particular seed shells, or a monarch caterpillar’s ability to accumulate milkweed toxin to limit predation by birds.

Pretty cool stuff going on out there ... as everything prepares to die!

Paul Cappiello is the executive director at Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.

This article originally appeared on Louisville Courier Journal: Early fall color could be a sign of leaf disease. Here are 2 things to know