Members' experiments

A survey of pests and diseases in vegetable crops in UK gardens and allotments

Each year we organise several citizen science experiments that our members can participate in to help inform the way we grow organically today. This experiment is 2020 - A survey of pests and diseases in vegetable crops in UK gardens and allotments.

Why we carried out a survey

In 2020, Garden Organic carried out a survey of pests and diseases in vegetable crops grown in gardens and allotments by its members. Our aims were to:

  • find out what measures people used against pests and diseases
  • find out which pests and diseases were most frequent and caused the most damage
  • build up a long term picture to identify trends over time and location that may be a consequence of climate change

What are the most popular methods of pest and disease control?

As organic pest control is about a holistic, preventative approach, it is encouraging that the most popular measures taken were all proactive, not just replacing conventional sprays with organic equivalents. The three most popular measures were using mesh netting, handpicking and growing plants to attract beneficial creatures, which were used by over three-quarters of participants regularly or every year.

Contentious measures

There are some control measures that we would not recommend. Washing up liquid was used occasionally by around half of the participants. Washing up liquid is a detergent and will often be applied in unknown doses so could damage plants and beneficial creatures and persist in the environment.

Most damaging pests and diseases

We ranked pests and diseases by how frequently they occurred at people’s sites and how much damage they caused. It will be no surprise that the slugs, cabbage white butterflies and pigeons were the top 3 most frequently occurring pests and were also likely to cause significant damage when they did occur.

Interesting trends

It was interesting that there were some sites that suffered very few problems from some key pests. Black bean aphid, carrot fly and brassica whiteflies were a problem for around half of the participants, but conversely, for a third of participants, they were only an occasional problem. Similarly, flea beetle and cabbage aphids were a problem for a third of participants, but half suffered only occasional problems.

Key trends in 2020

In 2020, black bean aphid was reported as a particularly bad problem causing crop loss at 30% of sites growing legumes. However, it was interesting that even in this bad year, there were still 41% of sites that suffered no damage at all.

Unravelling the reasons behind the differences between sites

It is encouraging that there was no damage from key pests at some sites, but it would be good to know the reasons why. Natural predators and parasitoids, plant nutrition and soil health, are all thought to play a role. Unravelling some of these reasons would help us greatly improve our ability to manage pests and diseases without the use of chemicals in our gardens.

Download the full report below.