Keeping Disease at Bay

by Matt McIntosh

Mould can be a boon for some things (penicillin and some types of cheese come to mind). But in the field, however, it’s definitely not a good thing.

Fungi, and the diseases they cause, can significantly impact both the quality and the quantity of a crop – from grapes and tomatoes to wheat and corn. The severity of fungal pressure depends on many factors, and farmers keep a close eye on their fields in order to anticipate – and hopefully prevent – harm to their plants. High fungal pressure can drastically reduce how much farmers can produce, and can even have health implications in some cases.

Fungicides are one tool commonly used by farmers when they see infection rates getting too high or when they anticipate a significant problem due to environmental conditions.

With footage from Real Farm Lives

What’s a fungicide?

Fungicides are a type of pesticide used to stop the spread of fungal pathogens. These products can either control disease during the growth of crops, improve the storage life and quality of harvested crops, or increase the productivity of a crop. Just like over-the-counter products available for home gardens, different fungicides will address different issues. A product designed to target a specific disease in corn, for example, will not be effective against diseases unique to vegetables like tomatoes and cucumbers.

Farmers growing crops which are particularly susceptible to specific diseases will apply fungicides more frequently than those growing less susceptible crops. Generally speaking, cool and wet conditions at the wrong time of year can drastically increase the risk of fungal pathogens spreading in a given crop. Other factors, such as how susceptible the particular crop variety is, are also at play. However, this also means some conditions (e.g. warm and dry weather, resistant crop varieties, etc.) actually help to prevent infection.

Indeed, fungicide use is not universal or consistent across different crops. Whatever they are growing, farmers determine if the disease pressure (what’s called a “disease threshold”) is high enough to warrant control. Fungicides and the application process cost money and time after all, so the risk to the crop in question has to exceed that cost.

Fungicides are also used in conjunction with other disease control measures.

In orchards, for example, large fans are often used to keep the air moving. Doing so helps keep airborne moisture at bay, thus supressing fungal development. Another example involves giving plants the right nutrients at the right levels, supporting growth patterns which are less susceptible to pathogens. These and other control strategies are part of a practice called “integrated pest management,” where farmers use specific tools to address specific problems and in conjunction with one another.

Like with other pesticides, resistance is an ongoing concern. While natural resistance is always a factor, repeated use of the same fungicide on the same fungus and in the same area can lead to heightened resistance to the control product. This is another reason farmers rely on a variety of control methods rather than just fungicides.

Fungus and fungicide safety

Like other types of pesticides, the use and availability of fungicides are controlled by Health Canada’s and the federal Pest Management Regulatory Agency. Health Canada must deem products safe for people and the environment before farmers can use them. Re-evaluations of approved products occur every fifteen years, if not earlier, to account for new scientific information.

Regulations also dictate fungicides be accompanied by very specific information about the product, including what amount of it should be used, and how it should be applied. Farmers follow these instructions to ensure they protect their crops without damaging them or the wider environment.

Some fungal pathogens can themselves pose a risk to human health and animal health, if severe enough in a given crop.

The fungal disease vomitoxin can make cattle sick, for example, if enough of it is present in a corn crop harvested for feed. A popular example in human history is ergot, which, along with also being a problem for livestock, has been suggested as the cause of apparent mass hysteria events like the Salem Witch Trials in the late 1600s. While this remains a popular hypothesis and is not a proven fact, it does illustrate how some fungal pathogens could affect human health in a time before modern food safety regulations.

The good news is Canada’s food safety system is modern, and highly effective at preventing food safety concerns.