You’d think in a spring/early summer this dry that fungal diseases wouldn’t be a big issue. It’s true that the drier weather and warmer temperatures have reduced some disease pressures – but not all. Fungal diseases on tomato certainly fall in to the latter category.

It’s not uncommon to notice brown spots on tomato leaves this time of year. They are likely the result of infection by one of two diseases: Septoria leaf spot or early blight. Even in a dry year, tomato foliage tends to get thick, we water to keep them alive, and humidity is high. These conditions are a welcome mat for fungal infections.

Despite the name, early blight typically occurs after Septoria. Early blight spots are typically brown and larger than Septoria spots, often with a pattern of concentric circles resembling a target. Septoria spots are smaller and dark.

Leaves that are heavily infected can turn yellow and drop. Because the older leaves are the most susceptible, disease symptoms tend to start at the bottom of the plant and progress upward. Heavy defoliation can occur if preventative or reactive measures aren’t implemented.

Preventive measures can include mulching, caging, or staking the plants to help keep them up off the ground, hopefully putting them just a little further away from soil moisture. It will also increase circulation around the plants and encourage them to spread out, reducing optimum disease conditions.

Mulching is another option. It helps by reducing the amount of disease carrying water droplets that can splash up on to the plant either by natural rainfall or overhead watering.

You can’t do much about it this year, but it’s always a good practice to rotate the area in the garden where you plant tomatoes as well. If space allows, select an area that hasn’t been planted to tomatoes or related crops (peppers, potatoes, eggplant) for several years.

Because they are fungal diseases, fungicides are an option. Coverage is the key, so make sure you get fungicide applied to both the upper and lower leaf surfaces when fruit is about the size of a walnut (reapply following rainfall). Products containing the active ingredient chlorothalonil are good choices for fruiting plants because of its zero-day waiting period - meaning fruit can be harvested once spray is dry. If chlorothalonil doesn’t seem to be working, try a product containing mancozeb. The waiting period on this product is typically around five days, meaning harvest can’t occur until the preharvest interval has passed. Always read and follow label directions. If diseases have previously been a problem, start protection programs before you see disease pressure. Control on heavily infected plants is virtually impossible.