Master Gardener Training Series: The Power of Plant Pathogens in History

This past week’s Extension Master Gardener Training with the Hanover Master Gardeners Association was equal parts informative and intriguing. We uncovered the dance between plants and their microscopic nemeses and how these organisms affected history.

We learned how agricultural challenges were overcome and still are best practices for today and we explored some historical oddities related to plants. This week we are talking about how fungi played a role in shaping our past. Let’s embark on a unique journey that takes us beyond the picturesque landscapes of flower-filled fields and into the lesser-explored territories of plant diseases.

Let’s dig in.

What is Plant Pathology?

According to the Virginia Cooperative Extension and our speaker, Stephanie Romelczyk, Plant Pathology is “the study of plant diseases which are any disturbance of a plant that interferes with normal growth and development, economic value or aesthetic quality and leads to the development of symptoms.” So the job of a plant pathologist is to help farmers determine what is happening to their plants, how to fix the problem, and to mitigate any potential crop loss. Throughout history, plant diseases have been responsible for some major historical events. Read below a few examples of the power of plant pathogens.

Bordeaux Mixture- a disease that almost eradicated the French wine industry

More on Bordeaux Mixture can be found here.

This first history lesson was one I was surprised that I hadn’t heard of given my past work in the wine industry. I had heard of the near eradication of our native grapes during prohibition, but I hadn’t learned about the plight and near destruction of French grapes until this class. In the 1860s, American grape vines were brought to France. Growers wanted to work on hybridizing American and French grapes to create new cultivars. There was a problem with this though…American grapes were resistant to powdery mildew and French grapes were not well adapted to this newly introduced fungus. No, the Bordeaux mixture isn’t a specialty wine blend. Good guess though...but rather an accidentally discovered fungicide that combats powdery mildew. The mixture is copper and lime. Pierre-Marie-Alexis Millardet noticed people were stealing his grapes from the roadside, he sprayed a copper and lime solution on the grapes to make them taste bitter and deter the grape poachers. He then noticed that the grapes by the road were healthy when the rest of his crop wasn’t so he sprayed the entire field with the copper and lime solution. It worked. Next time you’re at your Garden Center look at the organic fungicide ingredients. My guess is, that you’ll find that they are copper and lime-based. In addition to powdery mildew, aphids survived the trip to France and caused The Great French Wine Blight.

Grain Ergot- a disease that caused the fall of an empire and witch trials around the globe

More on Ergot & History can be found here.

Ergot is a fungus that has devasted grain crops for centuries. It’s pretty inconspicuous looking yet highly toxic to humans. The fungus contains LSD and mostly affects rye, but any cereal grain is susceptible to it. There are now rigorous screenings that help protect us from ergotism. Ergotism is responsible for the fall of the Holy Roman Kingdom when thousands of Cesars’s troops died leaving the empire open to attack. France and Germany are the result. Historians also believe that thousands of women who were burned at the stake during the witch trials of the Dark Ages in Europe along with the Salem Witch Trials may have been experiencing symptoms of ergotism.

Late Blight- a disease that caused the Irish Potato Famine

More on the Irish Potato Famine can be found here.

Once again a case of accidental spread of a microorganism…this time a water mold with its origins in North America made its way through the potato crops of Ireland. The Irish relied on potatoes for over 80% of their diets. They grew only a couple of varietals so if one plant was affected they likely all were. We know now that different varietals of plants offer different levels of resistance against pathogens. The mold Phytophthora infestans is responsible for late blight in potatoes and tomatoes. This type of blight affects all parts of the plant including lesions on the leaves and rot of the tubers (the part of the potato we eat). In 1845, Ireland experienced cool, wet weather which facilitated the spread of this destructive pathogen. The famine lasted from 1845-1849. During this time, around one million people died from starvation and 49% of US immigrations were from Ireland.

Chestnut Blight- a disease that led to endangered tree species

More on chestnut blight can be found here.

🎵“Chestnuts roasting on an open fire….Jack frost nipping at your nose.” You know how the rest of the song goes, but have you actually ever eaten chestnuts before? No, me neither, and I never actually thought about it until this class. They must have been popular for a song to be written about them right? What happened to them? We often hear about endangered or extinct species of animals, but did you know that we have plants that are also at risk of this as well? The American Chestnut tree and any tree in the Chestnut family fall into this category. The American Chestnut once made up nearly 50% of our eastern hardwood forests and were once a vital food source for the farmer’s pigs and his children. The pathogen that wiped out one of America’s most important tree species, Cryphonectria parasitica. It attacks the stomata of the plant. If you remember the blog post from two weeks ago, you know that stomata are the mouths of the plant. The fungus can forcibly eject itself and be carried by wind to neighboring trees. The spores can also spread through rainfall, birds, and insects. It is called blight because of how quickly it causes leaves to die off, however, it is a cankerous disease that continues to proliferate even after the tree has died. Quarantine and eradication are the only ways to manage the pathogen. Oregon and some parts of Europe have been successful at this. A 3rd example of a disease coming in on nursery stock. This time from China. China has the disease, but it doesn’t affect their trees in nearly the same way.

Corn Smut- A disease turned delicacy

More on huitlacoche (corn smut) can be found here.

Corn smut is a fungus and relative to mushrooms called Ustilago maydis. The fungus can overtake corn quickly when conditions are right. It attacks each kernel and creates a gall that is blueish-gray in color. American farmers despise this disease and have spent time, energy, and research to prevent this fungus from overtaking their fields. They’ve worked to develop resistant cultivars, fungicides, and have banned the importation of corn containing the pathogen. But one man’s “devil corn” is another man’s delicacy. In Mexico, they call corn smut huitlacoche. Traditionally, families would walk miles through corn fields to find this mushroom for special occasions. It is also sold fresh in supermarkets for use in tacos, quesadillas, and soups. Bonus: this fungal disease is full of lysine, protein, and fiber. If you see it on a menu, maybe give it a try. There are farms now trying to innoculate their crops to force the occurrence of the disease.

🧼📦Reason #547 why you should buy plants locally.

As you can see, the importation of plant material has had major implications on our health and the survival of native plant species. Another reason why buying local and planting native species is so important. Our invasive species of plants (Tree of Heaven and Bamboo are two I see most often in Ashland) and our non-native bugs (Spotted Lantern Fly, Japanese Bettles, Asian Jumping Worms, etc.) enter the country through imports. Yes, there are rules and regulations, but history tells us that protocols aren’t perfect. Please support your local farmers and nurseries that grow plants in-house. It’s incredibly important for the prevention of new diseases and invasive insects and buying locally has positive economic impacts. Win-Win! Okay off my soapbox!

Enjoy your weekend, Flower Friends! Get Dirty and Keep Blooming!

-Nicole Dillon, Breemar Flower Farm