How to Prevent and Manage Anthracnose on Beans, Cucumbers, and Tomatoes

If you’ve ever spotted dark, sunken lesions on your beans, tomatoes, or cucumbers, you might be dealing with anthracnose, a stealthy fungal disease that thrives in damp, warm conditions. One moment your plants look healthy, the next, fruit is blotched and rotting, and leaves are speckled and curling. It’s sneaky, fast-spreading, and deeply frustrating.But don’t worry, there are tried-and-true ways to prevent and manage anthracnose on beans, cucumbers, and tomatoes, and we’re here to share exactly how we do it.

What Is Anthracnose?

Anthracnose is caused by several species of Colletotrichum, a fungal pathogen that attacks both the foliage and fruit of plants. It spreads through infected seed, splashing water, and soil, especially during humid weather. It can affect many crops, but beans, tomatoes, and cucumbers are particularly vulnerable.

Common symptoms include:

• Small, water-soaked spots on leaves and stems that enlarge and darken
  
• Sunken, circular lesions with dark centres on fruit
  
• Premature fruit drop
  
• Leaf yellowing and wilting in severe cases

Rotate Crops

Anthracnose can survive in soil and plant debris, waiting to pounce again next season. To break the cycle:

• Rotate crops so that beans, cucumbers, and tomatoes don’t grow in the same bed more than once every 3–4 years
  
• Follow with non-host crops like brassicas or corn
  
• Remove all plant debris at the end of the season, don’t compost infected material

Healthy soil rotation is one of our top defences.

Space Plants for Airflow

This disease loves humidity. One of the easiest ways to keep things dry is by giving your plants space:

• Space beans, tomatoes, and cucumbers according to their mature size
  
• Train tomatoes and cucumbers vertically to keep foliage off the ground
  
• Prune lower tomato leaves and cucumber vines to increase airflow
  
• Avoid overcrowding, especially in greenhouses and polytunnels

Good airflow helps foliage dry quickly and discourages fungal spores from taking hold.

Water Smart, Not Wet

Overhead watering in the morning dew? That’s a fungal party waiting to happen. You can keep moisture under control by:

• Watering at the base of the plant only
  
• Watering early in the day so any splashes can dry
  
• Using mulch around the base to reduce splashback and conserve moisture
  
• Avoiding watering on cloudy, humid evenings

Dry leaves = fewer fungal problems.

Keep Tools and Hands Clean

Fungal spores can stick to tools, gloves, and even your boots. You can stay on top of hygiene by:

• Cleaning tools regularly, especially after working in infected areas
  
• Washing hands between handling different plant varieties
  
• Using dedicated tools for greenhouse versus outdoor beds

A bit of diligence can go a long way in reducing accidental spread.

Monitor and Remove Infected Plants Promptly

As soon as you spot the classic anthracnose lesions:

• We remove infected leaves and fruit immediately
  
• Bag and bin the waste, never compost it
  
• Disinfect pruning tools between cuts
  
• Keep a close eye on neighbouring plants

Early action can stop an outbreak in its tracks.

Strengthen Plants with Soil Health

We boost plant resilience by feeding the soil well:

• Apply well-rotted compost or organic matter regularly
  
• Add seaweed feeds or comfrey tea during fruiting
  
• Keep a balanced pH (around 6–6.8 for tomatoes and beans)
  
• Avoid high nitrogen fertilisers that cause soft, lush growth

Healthy plants are better equipped to resist disease.

Anthracnose might sound intimidating, but with a bit of planning and sharp observation, it doesn’t have to take over your garden. By using clean seed, rotating crops, spacing wisely, and maintaining good hygiene, you can prevent and manage anthracnose on beans, cucumbers, and tomatoes all without reaching for the chemical sprays.