Target spot on tomatoes — symptoms and treatment

Severity: medium

What is Target spot

Target spot of tomato is caused by the fungus Corynespora cassiicola. It causes concentric ring lesions resembling a target — the pattern that gives the disease its name. The lesions are worst on the lower leaves, and the fungus also marks the fruit near the stem end. It is a warm, humid-weather disease that thins the canopy from below, and its habit of scarring fruit costs you crop directly, not only through lost leaves.

Symptoms

On the leaves the disease produces brown spots marked with concentric rings, so that a mature lesion looks like a shooting target drawn on the leaf. The larger lesions are on the lower leaves, where they expand until they merge and the leaf is lost; the disease then works up as the canopy below dies away. On the fruit, spots develop near the stem end — a plant showing ringed leaf lesions is worth checking around the shoulders of its fruit.

• Early: brown spots on the leaves, heaviest on the lower foliage.
• Progressing: spots enlarge into lesions with distinct concentric rings; fruit spots near the stem end.
• Advanced: lesions merge, leaves die, the canopy thins from the bottom upward.

Be careful here: Target spot is the near-twin of Early blight (Alternaria solani). Both make concentric ring lesions, both hit the lower leaves hardest and both mark fruit at the stem end, and telling them apart by eye is unreliable. In practice this matters less than it sounds — the cultural controls are the same and both are treated at first symptoms — but if you need certainty, have a sample identified.

Causes and conditions

Corynespora cassiicola survives on infected crop debris and spreads by spores carried on wind and splashing water, which is why overhead irrigation and rain move it through a planting so efficiently. Infection depends on the leaves staying wet, so warm, humid weather with extended leaf wetness from rain or dew favours it strongly. Anything holding moisture in the canopy makes it worse: plants set too close, unpruned foliage low on the stem, still air between the rows, watering from above.

Treatment

Pruning and spacing — cultural

Timing: throughout the season. Remove the lower leaves, where the largest lesions form and where air moves least. Space plants for good air circulation so the canopy dries after rain and dew. Avoid overhead irrigation, which both wets the foliage and splashes spores between plants.

Chlorothalonil + Azoxystrobin — chemical

Timing: at first symptoms. Apply the fungicide mixture at first symptoms. Alternate active ingredients to prevent resistance — repeated use of a single active ingredient invites a population that shrugs it off. Pre-harvest interval: 14 days.

Pesticide registrations vary by country — check local approval before use.

Prevention

• Space plants generously and prune the lower canopy so air moves and leaves dry quickly.
• Irrigate at the base rather than overhead, and water early in the day.
• Clear and destroy crop debris after harvest — it is where the fungus survives.
• Rotate away from tomatoes rather than replanting into the same ground each year.

Frequently asked questions

Can I eat fruit with target spots on it? Cut away the spotted tissue near the stem end and the rest is usable; badly marked fruit is best discarded. If you have sprayed, respect the pre-harvest interval of 14 days.

How do I tell Target spot from Early blight? Honestly, often you cannot by eye. The good news is that the response overlaps heavily: prune and space the plants, keep the foliage dry, and spray at first symptoms. If the identification must be certain, submit a sample.

When should I spray? At first symptoms, not on a fixed schedule. And when you repeat, alternate active ingredients rather than reaching for the same product every time.