Brassicas: Improving control of whitefly

Summary

The Problem:

Whitefly (Aleyrodes proletella) is becoming increasingly difficult to control on kale and Brussels sprout in particular. It is not clear why this is the case, although outbreaks appear to be more severe in hot, dry years (2003, 2006 and 2010). Research on the basic biology and ecology of cabbage whitefly was undertaken in the late 1930s and this provides very useful background information. More recently, there has been research on the overwintering status of cabbage whitefly (females overwinter in a state of ovarian diapause) and on development times on, and preferences for, different cultivars of susceptible brassica crops.

Most recently, research in the UK has focused on insecticidal control (data obtained in other HDC projects targeted at control of aphids on brassica crops) and a PhD project at the University of Greenwich (Simon Springate – supervised by Professor John Colvin) investigated the increasing importance of cabbage whitefly as a pest, and potential methods for its control. Populations of whitefly were tested for resistance to certain insecticides and it was shown that certain whitefly populations are resistant to pyrethroid insecticides. The potential for native predators, in particular a species of ladybird and parasitic wasps (Encarsia spp.), to control whitefly was also investigated.

There are a number of possible insecticide treatments to control whitefly. In HDC trials focused on brassica aphids some of these insecticides suppressed whitefly infestations and a novel insecticide also looked interesting. However, we still did not really understand how to put together a spray programme to suppress whitefly. There were also questions about the best ways to apply spray treatments to maximise control.

The HDC has recently been developing a portfolio of work addressing whitefly control on brassica crops and to date this has involved 3 projects:

FV 399 - The aim of the project was to evaluate insecticide spray programmes and application strategies that might improve control of brassica whitefly. This was addressed through 1) field trials, 2) pot trials and 3) spray application tests in a wind tunnel. In the field trials, all treatments were applied at fortnightly intervals, when the infestation was already quite high and Movento was the most effective insecticide product. The most effective programmes began with Movento and the most effective strategy was to separate the two Movento applications included rather than apply them consecutively. In the wind tunnel study, boom-mounted nozzle configurations did not give adequate under-leaf coverage of sprays regardless of nozzle type, application volume or forward speed. Dropleg spraying systems improved coverage on the undersides of leaves on Brussels sprout, but not on kale.
FV 406 – the aim of the project was to field test the impact of releasing parasitoid wasps (Encarsia tricolor) and explore the impact of early insecticide applications. Early insecticide application based on monitoring proved as effective as periodic application in controlling whiteflies on kale. Two applications of a coded product were comparable to existing systemic products. Release of parasitoid wasps provided control levels equivalent to insecticides at the point of release.
CP 091 - which is an HDC Studentship (Spencer Collins) on the biology of cabbage whitefly and is at the beginning of its second year. The overall aim of the project is to improve understanding of the biology and ecology of cabbage whitefly to help growers to minimise the development of whitefly infestations and to control unacceptable infestations effectively.

Benefits to industry:

The results of this project will be relevant to all brassica growers, but particularly to those producing Brussels sprouts and kale. The proposed project is complementary to the LINK project led by HDC: Sustainable Crop and Environment Protection - Targeted Research for Edibles (SCEPTRE).

The results will be delivered to industry through the HDC annual and final reports, a presentation at a BGA or other relevant industry meeting and an article in HDC News. It might also be appropriate to present the results and other new information as a supplement to the HDC Factsheet which is in preparation currently. The trials will be available for viewing at Warwick Crop Centre and at Elsoms’ trial site, by appointment or at the annual Open Days at both locations.

Sector:

Horticulture

Project code:

FV 406a

Date:

01 January 2014 - 29 February 2016

Funders:

AHDB Horticulture

AHDB sector cost:

£109,117

Project leader:

ROSEMARY COLLIER, UNIVERSITY OF WARWICK

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About this project

Aims and objectives:

The aim of this proposed project is to evaluate the components of programmes (insecticidal, biological and physical) that might improve control of brassica whitefly. It will focus particularly on the timing of treatments.

Project objective(s):

1. To investigate additional insecticide treatments for whitefly control.
2. To investigate the efficacy of parasitoid release and crop covers, alone and in combination, in suppressing whitefly infestations.
3. To investigate the most effective overall treatment strategy e.g. is it better to suppress infestations as soon as they start? Is there a certain stage in a ‘generation’ (e.g. when adults, eggs or larvae predominate) when it is best to apply treatments?
4. To investigate the most effective way to use Movento and other effective insecticides in terms of the interval between treatments.

5. To relate the findings of this project to brassica growers through publications (such as factsheets), HDC reports or presentations.