How to Treat Leaf Spot (Before It Spreads to Your Other Plants)

The strawberries in your garden, the succulents in your kitchen, and even the grass in your lawn are all susceptible to leaf spot. But what exactly is leaf spot, what causes it, and most importantly, how can you control its spread? Read on for our experts’ tips.

• Matt Ramosowner of Plant Sensation & Co., a company that designs and creates outdoor plant displays
• Joel BurnsedAgricultural and Natural Resources Agent and County Extension Coordinator with the University of Georgia

What is leaf spot?

Leaf spot is a plant disease caused by fungus or bacteria, explains Matt Ramos, owner of Plant Sensation & Co. “Leaf spot is typically caused by fungus or bacteria that infect the plant through wounds, cuts or natural openings in its leaves,” Ramos says.

Leaf spots can vary in size, shape, and color, depending on the specific cause (fungal or bacterial pathogen) and can even fluctuate on a single plant. Spot colors can range from yellow, red, orange, tan, green, brown, and black. Smaller spots usually indicate a more recent infection, while larger spots have had time to mature and spread.

According to Ramos, while leaf spot isn’t always a death sentence for your plant, it weakens it and can spread to other plants if left untreated. In some cases, it can cause leaves to drop prematurely, preventing any potential fruit from ripening.

How to identify leaf spot

If multiple areas of your plants have discoloration, it may be a leaf spot. The spots may appear on the upper or lower sides of the leaves at first. Some may appear almost translucent or lighter in color, but others may be darker. While these areas are not perfect circles, they are often circular. If left untreated, the spots can grow large enough to connect and form large areas.

When a bacterial pathogen is involved, the middle of the leaf spot sometimes falls off, creating holes in the leaves. Shoots, buds, and flowers can also be infected when a bacterial pathogen is involved.

Causes of leaf spots

Although almost any plant can be susceptible to leaf spot, there are different varieties and causes of leaf spot depending on the type of plant. For example, a bacterial leaf spot common on lettuce leaves was first discovered in 1918 and causes small, water-soaked spots on the leaves that eventually develop into lesions. Cherry leaf spot, on the other hand, is caused by the fungus Blumeriella jaapii and attacks not only the leaves of some varieties of cherry trees, but also the stems and fruits.

However, there is one common denominator for all types of leaf spots: they thrive in humid conditions. Prolonged periods of rain can often lead to the spread of fungal outbreaks, and high humidity levels are also favorable conditions for the spread of bacterial spots.

“These pathogens thrive in moisture and can spread rapidly under favorable environmental conditions,” Ramos says. “Especially when the plant or leaves have wounds, cuts and openings.”

How to treat leaf spots

Early detection and action is essential, so keep a close eye on your plants. Examine the undersides of leaves to identify spots early. It is imperative to remove infected pieces and dispose of them properly. Don’t just throw away the trimmed pieces nearby, bag them up and remove them from your property.

According to Joel Burnsed, agricultural and natural resources agent and county extension coordinator at the University of Georgia, leaf spot cannot be “cured.” However, when it comes to fungal infections, “fungicides can be applied to prevent further spread.”

Ramos suggests doing additional research or contacting a local professional for advice before attempting any treatment yourself.

How to prevent leaf spots

To prevent leaf spots, it is essential to control the humidity of your plants as much as possible. Reduce overhead watering to prevent moisture from pooling on your leaves and try to water only at the base. If this is not possible, water your plants early in the day so they have plenty of time to dry out.

It is important to leave adequate spacing between mature plants to reduce moisture, so plant accordingly and prune if necessary. Some fungi can jump and spread through surrounding weeds, so it is imperative to keep these nuisances at bay. Also, be sure to prune infected areas immediately and dispose of them in a sealed bag.

“Sometimes fungicides can be applied as a preventative measure to prevent leaf spots from occurring,” Burnsed says. While this may not be necessary as often during dry periods, it can be an effective way to prevent leaf spots caused by fungal infections.

Finally, be careful when inspecting plants before purchasing them. The last thing you want to do is add a diseased plant that could wreak havoc on a thriving, healthy garden.

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