Alternative seed treatments to Gamma-HCH for controlling cabbage stem flea beetle on oilseed rape

Summary

The project had the overall aim of identifying potential replacement seed treatments to gamma-HCH for use on oilseed rape and was set up at short notice following the withdrawal of the treatment in summer 1999. The specific objectives were

To test candidate seed treatments against a gamma-HCH standard and an untreated control at three sites in the Midlands, east and south of England.
To evaluate materials in terms of both their impact on adult feeding damage and larval numbers in the plants to enable an estimation of the effect of treatment on damage and future risk of damage.
To measure adult flea beetle activity at the sites to enable a between site comparison of the level of challenge and the persistence of control.
Experiments were conducted at three sites with a recent history of high numbers of cabbage stem flea beetle at Bridgets in Hampshire, Boxworth in Cambridgeshire and Brewood in Staffordshire. Seed for all treatments was provided by Uniroyal of the variety Pronto with a fungicide treatment of carboxin plus thiram (Anchor) already applied. This seed was then overdressed with insecticide seed treatments at various rates of application by Uniroyal, with coded product A1597, Bayer, with UK805, and Aventis, with fipronil.

The three sites were sown as soon as conditions allowed after the middle of August, on 23 August at Bridgets and Brewood and 2 September at Boxworth. Sowing rate was 4.5 kg/ha and the thousand seed weight 5.55g. The crops emerged quickly at Bridgets and Brewood, but at Boxworth emergence was delayed by dry seedbed conditions. Vigour was assessed visually and plant populations were counted a few days after emergence and when emergence was complete. A sample of fifty plants was removed from each plot at the end of the flea beetle feeding period and the percentage leaf area damaged by flea beetles on the cotyledons and the first true leaves was assessed. A further sample of plants was removed in late November or December and the numbers of cabbage stem flea beetle larvae in the petioles were counted. Flea beetle activity from the time of sowing to the end of October was monitored with two yellow water traps at each site.

Aims

The project had the overall aim of identifying potential replacement seed treatments to gamma-HCH for use on oilseed rape and was set up at short notice following the withdrawal of the treatment in summer 1999. The specific objectives were

To test candidate seed treatments against a gamma-HCH standard and an untreated control at three sites in the Midlands, east and south of England.
To evaluate materials in terms of both their impact on adult feeding damage and larval numbers in the plants to enable an estimation of the effect of treatment on damage and future risk of damage.
To measure adult flea beetle activity at the sites to enable a between site comparison of the level of challenge and the persistence of control.
Conclusions

Cabbage stem flea beetle caused economic levels of damage at two of the three sites, giving the candidate seed treatments a thorough test. Of the three materials tested Bayer's UK 805 was the most effective in reducing flea beetle damage. It achieved an efficacy score of 176 relative to 100 for gamma-HCH. Other less developed products were tested at different rates. A1597 from Uniroyal achieved scores of 80, 96, 89 and 123 at the four different rates tested and fipronil from Aventis scores of 120 and 140 for two rates.

Implications for levy payers

This was a pilot study using provisionally formulated products that may differ from the final versions if developed through to commercial release. Three potential replacements for gamma-HCH seed treatment have been identified. Of these Bayer's UK805 is closest to market, approval being under consideration for approval under PSD's emergency procedures at the present. If approval is obtained in time this product may be available for use this autumn. As well as controlling attack by both species of flea beetle UK805 has been confirmed as providing a good level of aphid control and may also reduce slug damage. The other two materials are still under development but could provide useful alternatives in the future.