Farmers in the UK are trialling an alternative control method that uses plants known as trap crops to naturally ward off potato cyst nematodes (PCN).

PCN is the UK’s primary potato pest and is also prevalent in areas of Ireland. Around 65% of UK land used to grow potatoes is infected with PCN.

To control PCN, farmers currently rely on the use of pesticides, extending rotations and selecting resistant varieties.

However, one group of farmers in the UK are trialling an alternative method of control, using trap crops.

The theory behind trap crops

Trap crops are better described as plants which ‘deceive’ rather than ‘trap’ plants. The chemicals released from the trap crop roots signal the presence of suitable food and trigger the nematodes to emerge.

S. sisymbriifolium .

The nematodes begin feeding on the trap plant roots ahead of potato planting.

By consuming the trap plant, instead of their optimum host (ie a potato plant), the nematodes cannot accumulate enough energy to reproduce and complete their life cycle, thereby reducing the chances of subsequent infestation within the soil.

The trial

The farmers drilled the trap crop seeds in late June and July earlier this year, shortly after the cereal harvest. A second trial was sowed one month later.

Two species of trap crops have been used - Solanum sisymbriifolium (sticky nightshade) and Solanum scabrum (African nightshade).

S. sisymbriifolium has been shown to reduce PCN densities up to 80%, but has been difficult to establish in western Europe.

S. scabrum establishment and use is less well understood. However, the group decided to try this species in the trial.

The group hypothesised that deeper sowing might work better than shallow, so decided to compare establishment from two planting depths of 1.5cm and 3cm.

These solanaceous crops have not been selected over many generations to make them suitable for cultivation, but rather are wild plants recently brought into production.

In the wild, their seeds would grow from inside their fruit or inside animal dung. So, while we would expect small seeds to be drilled shallowly, they often fail to emerge.

Using handheld cameras and drones, the group measured trap crop ground cover. PCN counts were taken before sowing the trap crop and will be compared after trap crop destruction.

Initial findings

So far, the take-home messages are that earlier sowing, avoiding water-logged soils and higher seeding rates appear to be more successful to establish the crop.

Trap crop establishment varied considerably between farms, but S. sisymbriifolium sown at 1.5cm deep had the highest ground cover.

However, the group will have to wait until next year to start testing for PCN.

The trial was conducted by members of the UK’s Innovative Farmers programme, along with Andrew Wade (OptiGro), Ivan Grove (independent), Matthew Back (Harper Adams University) and Anne Stone (AHDB Potatoes).