Should we be using biocontrols?

Garden Organic's research manager Anton Rosenfeld demystifies biocontrols and shares advice on their use

- Anton Rosenfeld

The prospect of a biological control can sound both attractive and alarming at the same time. In effect, we are unleashing an army of tiny creatures to fight off the pests that are spoiling our plants. So many gardening catalogues offer biocontrols and the concept sounds great, but should we be doing this? Is it considered organic? to gardeners are not toxic to humans and of little risk to the environment.

The most common types are mites, predatory wasps and microscopic worms called nematodes. They are suitable for organic growers, but in fact they have been used much more widely because they have many advantages over synthetic pesticides. There is no risk of contaminating produce, and pests don’t develop resistance to biocontrols in the same way that they do to chemicals.

HOW TO USE THEM 

You need to think ahead. It’s best to apply a biocontrol just when you notice pest numbers increasing as most are less effective at dealing with severe infestations. They are generally ordered in the post, so will take time to arrive and they should be used soon after receipt.

Mites and wasps are most effective when used in a glasshouse as when used outside they tend to move away from where you have put them. Nematodes are watered into the soil, and move much more slowly, so can be used outside without fear of them escaping.

Most biological controls will function best within the range 10-30C (50-86F), although the nematodes can tolerate soil temperatures down to 5C (41F). It’s really important to stick to the instructions about how and when to apply them, or you will be wasting your money.