Science into practice: Are sulphur-based fungicides bad for Encarsia?

Over the past five years, the previously successful prophylactic bio-control strategy for whitefly in tomato crops of weekly releases of parasitic wasp Encarsia formosa seems to be failing.

The situation has been exacerbated by the need to apply remedial insecticidal treatments, which has disrupted bio-control of other pests, jeopardising the industry's pesticide-free goal. One theory, which HDC project PC 293 explored, was that glasshouse whitefly problems coincided with an increase in the use of sulphur-based products to control powdery mildew.

A grower survey confirmed a higher incidence of whitefly in recent years. However, 15 of the 23 companies who responded did not mention sulphur. Records from the Tomato Working Party did not show a significant increase in sulphur use over the five years covered by the survey.

There was a clear varietal effect, with the greatest incidence of damaging whitefly infestations occurring in cherry tomato cultivars. Neighbouring crops of less susceptible varieties may have been placed under additional invasion pressure.

Excessive de-leafing may also have had a bearing on whitefly incidence in long-jointed cultivars, particularly in older and lower glasshouses where parasitised scales are often removed before adult Encarsia have emerged.

A practical laboratory study investigated whether sulphur-based products masked the chemical signals female Encarsia follow to find their host. There was no evidence that applying sulphur as a high-volume spray or a vapour interfered with the wasps' searching behaviour. There appear to be a number of factors involved that could be contributing to whitefly problems on individual sites.

Horticultural Development Company

For details on all HDC activities, visit

Have you registered with us yet?

Register now to enjoy more articles and free email bulletins

Sign up now
Already registered?
Sign in

Before commenting please read our rules for commenting on articles.

If you see a comment you find offensive, you can flag it as inappropriate. In the top right-hand corner of an individual comment, you will see 'flag as inappropriate'. Clicking this prompts us to review the comment. For further information see our rules for commenting on articles.

comments powered by Disqus

Read These Next

What challenges and opportunities lie in store for tomato growers?

What challenges and opportunities lie in store for tomato growers?

The British Tomato Growers Association (TGA) conference today (21 September) heard a range of perspectives on what changes lie in store for the sector and how to anticipate them.

Buoyant demand for UK apples but frost and labour remain concerns

Buoyant demand for UK apples but frost and labour remain concerns

As the British apple season begins, English Apples & Pears (EAP) is warning that growers will feel the effects of both a late frost in spring and also constrained labour supply.

Tomorrow's tractors

Tomorrow's tractors

These machines have advanced rapidly over recent years but what does the future hold? Sally Drury looks ahead.

Follow us on:
  • Facebook
  • LinkedIn
  • Twitter
  • Google +
Horticulture Jobs
More Horticulture Jobs

Pest & Disease Tracker bulletin 

The latest pest and disease alerts, how to treat them, plus EAMU updates, sent direct to your inbox.

Sign up here

Professor Geoffrey Dixon

GreenGene International chair Geoff Dixon on the business of fresh produce production

Read Professor Geoffrey Dixon