Brassicas: Treatments to control cabbage root fly

Project summary:

Recent HDC projects (FV 416 and 416a) and complementary research in SCEPTRE have focused mainly on control of cabbage root fly in transplanted brassica crops and the main method of application has been through pre-planting module drenches.  This research has centred on potential alternatives to Dursban WG for cabbage root fly control in the short and longer term.  In terms of the Approved alternative, Tracer, this has shown that Tracer-treated plants can be held on nurseries and with exposure to heavy watering for at least 2 weeks without significant reduction in performance compared with Dursban WG and that Tracer applied pre-planting is as effective as Dursban WG in control of damage in the root zone, but that Tracer is less effective than Dursban WG at controlling damage in the lower stem zone (between the module and the soil surface).  In 2014, there was also a small study in FV 416a on application efficiency in commercial nurseries and this raised some interesting questions about both the amount of insecticide applied to individual modules during the treatment process and also the sampling approach that should be used to assess this.  Finally, the SCEPTRE project has identified a number of new products with potential to control cabbage root fly. 

In the last few weeks it has become apparent that there have been problems in Cornwall in relation to damage to overwintering cauliflower crops by third generation cabbage root fly.  This has identified a need to re-assess control of cabbage root fly by means other than pre-planting module drenches as these do not seem to provide sufficient protection against damage to the lower stem area when modules are planted deep.

In addition there are a number of problems associated with the use of fine mesh netting to exclude cabbage root fly from swede crops, particularly associated with pest damage occurring under the netting.  Some work to determine when cabbage root fly eggs and larvae cease to be a threat to swede crops at the end of the season, in relation to the timing of removal of crop covers, is still ongoing in FV 416a, but further assessment of the problems associated with crop covers and evaluation of potential solutions is required.

The aim of the proposed project is to improve control of cabbage root fly in leafy brassica and swede crops.  Specific objectives are to: 1) assess the application efficiency of module drench treatments in commercial nurseries; 2) determine the utility of egg-sampling for determining the risk of damage to overwintered cauliflower plants in Cornwall by third generation cabbage root fly and identify appropriate methods of cabbage root fly control and 3) identify and summarise the key problems associated with use of crop covers to control cabbage root fly on swede crops and  determine whether changes in practice would improve control without compromising yield and quality.

The results will be delivered through the Final Report, an article in HDC News, the HDC Brassica Newsletter and a presentation at an industry meeting.  There may also be useful information that can be used in conjunction with the HDC cabbage root fly forecast, currently available on the Syngenta web site.

Benefits to industry:

Cabbage root fly is a serious pest of brassica crops and most crops are exposed to egg-laying by cabbage root fly females.  Recently, particular concerns have been raised about control of cabbage root fly in swede crops using fine mesh netting and in overwintered cauliflower crops, the latter being due to high pressure from third generation cabbage root fly. 

The results will be delivered through the Final Report, an article in HDC News, the HDC Brassica Newsletter and a presentation at an industry meeting.  There may also be useful information that can be used in conjunction with the HDC cabbage root fly forecast, currently available on the Syngenta web site. 

Aims and objectives:

Project aim:

The aim of the project is to improve control of cabbage root fly in leafy brassica and swede crops.

Project objective:

Objective 1 Assess the application efficiency of module drench treatments in commercial nurseries. 

Objective 2 Determine the utility of egg-sampling for determining the risk of damage to overwintered cauliflower plants in Cornwall by third generation cabbage root fly and identify appropriate methods of cabbage root fly control.

Objective 3 Identify and summarise the key problems associated with use of crop covers to control cabbage root fly on swede crops.  Determine whether changes in practice would improve control without compromising yield and quality.