Phenology of the Diamondback Moth (Plutella xylostella) in the UK and Provision of Decision Support for Brassica Growers.

In the UK, severe infestations by Plutella xylostella occur sporadically and are due mainly to the immigration of moths. The aim of this study was to develop a more detailed understanding of the phenology of P. xylostella in the UK and investigate methods of monitoring moth activity, with the aim of providing warnings to growers. Plutella xylostella was monitored using pheromone traps, by counting immature stages on plants, and by accessing citizen science data (records of sightings of moths) from websites and Twitter. The likely origin of migrant moths was investigated by analysing historical weather data. The study confirmed that P. xylostella is a sporadic but important pest, and that very large numbers of moths can arrive suddenly, most often in early summer. Their immediate sources are countries in the western part of continental Europe. A network of pheromone traps, each containing a small camera sending images to a website, to monitor P. xylostella remotely provided accessible and timely information, but the particular system tested did not appear to catch many moths. In another approach, sightings by citizen scientists were summarised on a web page. These were accessed regularly by growers and, at present, this approach appears to be the most effective way of providing timely warnings.

Effect of different soil textures on leaching potential and degradation of pesticides in biobeds.

Biobeds can be used to intercept pesticide-contaminated runoff from the mixing/washdown area, creating optimum conditions for sorption and biodegradation such that the amount of pesticide reaching adjacent water bodies is significantly reduced. The biobed is built on the farm using locally available materials, which include, straw, compost, and topsoil. The topsoil acts as the inoculum for the system and is likely to vary in terms of its physical, chemical, and microbiological characteristics from one farm to another. This study therefore investigated the effects of using different soil types on the degradation and leaching potential from biobeds. Three contrasting topsoils were investigated. Leaching studies were performed using isoproturon, dimethoate, and mecoprop-P, which were applied at simulated disposal rates to 1.5 m deep biobeds. Annual average concentrations were similar for each soil type with leaching losses of even the most mobile (Koc = 12-25) pesticide <1.64% of the applied dose. Greater than 98% of the retained pesticides were degraded in all matrices. Degradation studies investigated the persistence of individual pesticides and pesticide mixtures in the different matrices. DT50 values for isoproturon, chlorothalonil, mecoprop-P, and metsulfuron-methyl applied at 4 times the maximum approved rate were similar across the biomix types and were all less than or equal to reported DT50 values for soil treated at approved rates. When applied as a mixture, DT50 values in each biomix increased, indicating that interactions between pesticides are possible. However, DT90 values of <167 days were obtained in all circumstances, indicating a negligible risk of accumulation. Studies therefore indicate that substrate will have little impact on biobed performance so it should be possible to use local soils in the construction process.

Leaching of pesticides from biobeds: effect of biobed depth and water loading.

Pesticides may be released to farmyard surfaces as a result of spillages, leakages, and the decontamination of tractors and sprayers. Biobeds can be used to intercept and treat contaminated runoff, thus minimizing losses to the environment. Previous studies using lined and unlined biobeds showed that water management was the limiting factor for both systems. While lined biobeds effectively retained pesticides, the system rapidly became water logged and degradation was slow. Studies using unlined biobeds showed that >99% of the applied pesticides were removed by the system, with a significant proportion degraded within 9 months. However, peak concentrations of certain pesticides (Koc < 125) were unacceptable to the regulatory authorities. These experiments were designed to optimize the design and management of unlined biobeds. Experiments performed to investigate the relationship between biobed depth and water loading showed that biobeds need to have a minimum depth of 1-1.5 m. The surface area dimension of the biobed depends on the water loading, which is controlled by the nature and frequency of pesticide handling activities on the farm. Leaching losses of all but the most mobile (Koc < 15) pesticides were <0.32% of the applied dose from 1.5 m deep biobeds subject to a water loading of 1175 L m(-2). These were reduced to <0.06% when a water loading of 688 L m(-2) was applied and down to <0.0001% for a water loading of 202 L m(-2). On the basis of these data, a 1.5 m deep biobed, subject to a maximum water loading of 1121 L m(-2) and with a surface area of 40 m(2) should be able to treat < or =44000 L of pesticide waste and washings such that the average concentration of all pesticides, other than those classified as very mobile, does not exceed 5 microg L(-1). This level of treatment can be improved by further reduction in the hydraulic loading.

Degradation and leaching potential of pesticides in biobed systems.

Biobeds provide a potential solution to pesticide contamination of surface waters arising from the farmyard. Previous work has shown that biobeds can effectively treat spills and splashes of pesticide. This study investigated the potential for biobeds to treat much larger volumes and amounts of pesticide waste not only arising from spills but also from washing processes. Two systems were assessed using a range of pesticides at the semi-field scale, ie a lined biobed system and an unlined system. Studies using the lined biobeds demonstrated that water management was crucial, with biobeds needing to be covered to exclude rain-water. Once covered, the top of the biobed became hydrophobic, restricting moisture loss and resulting in saturated conditions at depth. The drying out of the top layer coincided with a measured decrease in microbial biomass in the treated biobeds. Applied pesticides were effectively retained within the 0-5 cm layer. Whilst all pesticides tested degraded, low moisture content and microbial activity meant degradation rates were low. Studies using unlined biobeds showed that only the most mobile pesticides leached, and for these > 99% was removed by the system, with a significant proportion degraded within 9 months. Peak concentrations of the two most mobile pesticides did however exceeded the limits that are likely to be required by regulatory bodies. However, it is thought that these limits could be reached by optimisation of the system.

Persistence of the fungicides thiabendazole, carbendazim and prochloraz-Mn in mushroom casing soil.

The persistence of the fungicides thiabendazole, carbendazim and prochloraz-Mn in mushroom casing soil was determined following their application at rates commonly used in the UK mushroom industry. Following drench applications, the concentration of all active ingredients was always higher in the top half of the casing soil layer than in with the bottom half. When carbendazim and prochloraz-Mn were applied using half the recommended volume of water per unit area, there was a tendency for carbendazim concentrations to be even higher in the top half of the casing soil, compared with the standard treatment, while concentrations of prochloraz-Mn were similar, irrespective of the volume of water used. Carbendazim and prochloraz-Mn concentrations in the top half of the casing layer decreased to < or = 13 mg kg(-1) by day 28/29, following different applications, whereas the thiabendazole concentration was consistently high during the course of the crop, being < or = 83 mg kg(-1) at day 31. Fungicides that do not persist at high concentrations in mushroom casing soil for the duration of the crop may not give good control of mushroom pathogens, particularly if the fungicide concentration falls to a level which is close to the EC50 value.

Pesticide degradation in a 'biobed' composting substrate.

Pesticides play an important role in the success of modern farming and food production. However, the release of pesticides to the environment arising from non-approved use, poor practice, illegal operations or misuse is increasingly recognised as contributing to water contamination. Biobeds appear to offer a cost-effective method for treating pesticide-contaminated waste. This study was performed to determine whether biobeds can degrade relatively complex pesticide mixtures when applied repeatedly. A pesticide mixture containing isoproturon, pendimethalin, chlorpyrifos, chlorothalonil, epoxiconazole and dimethoate was incubated in biomix and topsoil at concentrations to simulate pesticide disposal. Although the data suggest that interactions between pesticides are possible, the effects were of less significance in biomix than in topsoil. The same mixture was applied on three occasions at 30-day intervals. Degradation was significantly quicker in biomix than in topsoil. The rate of degradation, however, decreased with each additional treatment, possibly due to the toxicity of the pesticide mixture to the microbial community. Incubations with chlorothalonil and pendimethalin carried out in sterile and non-sterile biomix indicated that degradation, rather than irreversible adsorption to the matrix, was the main mechanism responsible for the reduction in recovered residues. Results from these experiments suggest that biobeds offer a viable means of treating pesticide waste.