Dr Andrew Brown, product development manager at Becker Underwood, said: "Biopestides is a new market and lots of growers need a lot of help."
Common failings were nozzle sizes and pressure levels, he said. Beneficial nematodes, for example, had soft bodies and were up to 1mm long.
Sprayers needed to use large noz- zles to jet the nematodes on to the plants and lower pressure to avoid "shearing" the creatures into pieces.
Switching off artificial lights and avoiding spraying in sunlight, meanwhile, prevented nematodes drying out and dying," he advised.
"The industry has lots to do to make the product easier to understand or better to use," Brown told the conference hosted by the Association of Applied Biologists.
One grower, for example, improved success simply by bending the end of a spray lance upwards to enable the dowsing of caterpillars that hugged the underside of leaves.