Tomatoes Slipping Up? It Could Be Anthracnose

As summer heat ramps up, you might notice your ripening tomatoes developing small, sunken spots that seem to grow darker and more rotten by the day. If that sounds familiar, you could be dealing with anthracnose, a common fungal disease that affects ripe or overripe fruit, especially under warm, wet conditions.

Anthracnose is caused by several species in the Colletotrichum genus, and it's particularly problematic when tomatoes are left on the vine to fully ripen. The disease appears as small, circular, water-soaked lesions that eventually darken and may develop concentric rings. Over time, these spots may enlarge and soften, making the fruit unmarketable and prone to secondary rot.

Conditions that Favor Anthracnose
This fungus thrives in warm (75–85°F), humid environments—conditions often found in mid to late summer. Rain, overhead irrigation, and dense foliage can contribute to prolonged leaf and fruit wetness, which increases disease severity. Spores can survive in soil or on plant debris and splash onto lower fruit during rainfall or irrigation.

Management Strategies
Managing anthracnose requires an integrated approach:

• Cultural Controls:

• Practice crop rotation, avoiding planting tomatoes or other solanaceous crops in the same spot more than once every 3–4 years.

• Remove and discard infected plant debris at the end of the season.

• Mulch under plants to reduce soil splash and keep fruit from contacting the soil.

• Stake or cage plants to improve air circulation and keep fruit off the ground.

• Harvest promptly—overripe fruit is most vulnerable.

• Resistant Varieties:
  While true resistance to anthracnose in tomatoes is limited, some varieties may show better tolerance. Selecting crack-resistant and firm-fleshed types may help reduce damage.

• Chemical Control:
  Fungicides can help, especially in wet seasons. Products containing chlorothalonil, copper, or azoxystrobin are labeled for home garden use. Apply preventatively when fruit begins to develop and repeat as directed on the label, particularly during extended wet periods. Be sure to rotate fungicide classes to prevent resistance.

Anthracnose won’t usually kill your tomato plants, but it can significantly reduce the quantity and quality of your harvest if left unmanaged. Regular monitoring, good sanitation, and timely harvesting are your best lines of defense.