Proceedings Crop Protection in Northern Britain 2010

Proceedings Crop Protection in Northern Britain 2012 pp: 145-150

PESTICIDE USE patterns IN SCOTTISH Cereal Crops 2000-2010: Potential Impact of EU Thematic Strategy for Pesticides

J Hughes, G Reay, and L Thomas

Pesticide Survey Unit, SASA, Scottish Government, Roddinglaw Road, Edinburgh, EH12 9FJ

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Summary: Whilst there has been little variation in the proportion of Scottish cereal crops treated with pesticides, both the number and weight of applications have increased over the past decade. The overall trend primarily reflects changes in fungicideapplications. The number of herbicide applications has also increased although the quantity applied has remained static, whilst the quantity of insecticides applied has greatly decreased over time. The implementation of the EU thematic strategy for pesticides may significantly reduce the number of pesticides available to Scottish cereal growers, particularly in relation to fungicides.

INTRODUCTION

Cereals account for over 80% of Scottish arable cultivation, with a total market value of ca.£400 million per annum (Anon, 2010). Around 450,000 haare grown annually, predominately consisting of spring barley, winter wheat, winter barley and oats (ca. 55, 25, 15 and 5% of the crop respectively). Fluctuations in overall area, and of constituent crops, are associated with factors such as climatic conditions at planting, grain prices and changes in agricultural subsidies.The aim of this paper is to present pesticide application data for Scottish cereal cropsover the last decade and to discuss the influence that the newly introduced EU thematic strategy for pesticidesmay have on future pesticide use patterns.

METHODS

Pesticide application data were obtained from the dataset collected by SASA during biennial arable pesticide use surveys (Kerr & Snowdon, 2001; Snowden & Thomas, 2003; Snowden et al., 2005; Struthers, 2007; Reay, 2009; Reay et al., 2011).The surveys are conducted by collecting data from a random sample of farmsclassified by size and geographic region. National estimates of pesticide use are produced from the sample data by applying raising factors based on crop census areas.Pesticide use expressed as ratio of spray area to treated area is the total area of pesticides applied, including multiple applications during the growing season, divided by the area of crop treated, this does not equate to number of applications.

EU Council Directive 91/414/EEC, concerning the placing of plant protection products
on the market, has been replaced with a thematic strategy for pesticides. Thisconsists of authorisation and statistics regulations (1107/2009/EC and 1185/2009/EC respectively)and an associatedSustainable Use Directive (2009/128/EC). A major implication of this legislationis that the pesticide approval processwill become hazard as well as risk based. This may result in some active ingredients currently on Annex I being withdrawn or substituted over time. Whilst the full impact of these changes is not yet known, the potential influence of this legislation has been investigated by comparing current pesticide use with predicted future approval status based on a Pesticides Safety Directorate (PSD) impact assessment (Anon., 2009).

RESULTS AND DISCUSSION

Almost all Scottish cereal crops receive pesticideapplications and the proportion treated has been fairly constant over the last ten years (Table 1). However, both the ratio of the total spray area to treated area and the average quantity applied has increased over the last decade. These trends are discussed in relation to each of the main pesticide groups.

Table 1.Pesticide Application Data 2000-2010.

Fungicide Use Patterns

Whilst there has been little change in the proportion of cereal crops treated with a fungicide since 2000, the ratio of spray area to treated area increased by 35%. i.e. a greater number of products were applied to the crop. The quantity of fungicide applied has also increased, particularly between 2002 and 2004, when average dose rates doubled (Table 1).The 2004 increase in quantity was primarily due to greater use of chlorothalonil, a chloronitrile fungicide, which is applied athigher rates (Figure 1). Chlorothalonil use increased from 1 to 16% of total fungicide spray area (with a corresponding increase from 4 to 44% of total weight) between 2002 and 2004. This was primarily a consequence of the development of resistance to strobilurin fungicides inSeptoria tritici. Consequently, the strobilurins show a drop in use over the decade, from 26% of total fungicide area in 2000 to 16% in 2010. As strobilurins are active at very low application rates, their decline also influenced the increase in dose rate. The amine fungicides (including fenpropimorph, and spiroxamine) have also shown a gradual decrease in use over the last decade (from 20 to 13% of total fungicide area) whilst use of triazole compounds has remained unchanged, accounting for 30 to 40% of fungicide applications.

Herbicide Use Patterns

Herbicides were consistently applied to more than 90% of cereal crops over the reported period.As with the fungicides a similar, albeit less pronounced, trend of an increasing spray area in relation to treated area is displayed (Table1). Despite the increase in spray area the average quantity applied shows no significant variation. This is influenced by a10% increase in use of the sulfonylurea compounds over the decade (Figure 2). Sulfonylurea herbicides are applied at low rates and their increase has coincided witha reduction in use of the higher dosage aryloxyalkanoic acid herbicides (in particular mecoprop-p), which have declined by a third over the same period. Another major change was the removal of the urea herbicide isoproturon from the market in 2009, which previously accounted for 9% of total herbicide application area.

Insecticide Use Patterns

The percentage of cereal crops treated with insecticides is considerably lower and more variablethanfungicides and herbicides (Table 1). This is largely due to greater temporal variability in pest pressureand applications being more reactive than preventative. Whilst there has been no change in the relative proportions of spray area to treated area,dose rate has decreased markedly over the last decade. The particularly high quantity applied in 2000 was due to extensive use of organophosphates, which have very high application rates, for aphid control. Thereafter, the main trend has been a steady decrease in organophosphate use, from 27% of spray area (93% of weight) in 2000 to 8% spray area (85% of weight) in 2010. In contrast,use of pyrethroids, compounds which are applied at very low rates, has increased from 69 to 90% of total area (5 to 14% weight) over the same period.Carbamate insecticide use has shown little change over the reported period, remaining low throughout (ca 4% area).

Figure 1.Spray area of total fungicides and main fungicide groups applied to cereal crops 2000-2010.

Figure 2.Spray area of total herbicides and main herbicide groups applied to cereal crops 2000-2010.

Figure 3.Spray area of total insecticides and main insecticide groups applied to cereal crops 2000-2010.

Potential Effect of EU Thematic Strategy on Pesticide Availability

The active ingredients most likely to lose approval status, according to the prediction of the PSD impact assessment, based on the EU thematic strategy, are listed in Table 2. Were these compounds to be removed from the market reduced fungicide availability would be the most serious threat to Scottish cereal production.

Many of the major cereal fungicides are listed as likely to lose approval under the new legislation. Five triazoles, notably epoxiconazole and tebuconazole, which cumulatively account for 20% of the 2010 fungicide spray area, are at risk due to their potential endocrine disruptor status. In addition, when compounds that the impact assessment state may come off the market are taken into account a further 4 triazoles (difenaconazole, propiconazole, prothioconazole andtriadimenol) and an imidazole compound (prochloraz) are included. These compounds account for a further 16% of the fungicides applied in 2010 and are all Demethylation Inhibitors (DMI). DMI fungicides are an important group of broad spectrum compounds of economically important cereal pathogens, and are particularly important for Septoria tritici control. In addition, chlorothalonil is predicted to be a candidate for substitution. Chlorothalonil currently accounts for 17% of fungicide spray area and is an important component in control strategies for Septoria tritici, Rhynchosporium secalis, Ramularia collo-cygniand Fusarium spp. Overall, the loss of these fungicides would have major repercussions for both disease control and resistance management strategies, leading to resistance issues for theremaining compounds.

Table 2Active ingredients most likely to lose annex I approval (PSD impact assessment, 2009) and 2010 use data

* includes multiple applications to the crop area during the growing season

** for separate each group (fungicides, herbicides, insecticides)

Both the herbicides and insecticides are predicted to be comparatively less affected than fungicides. The herbicides most likely to lose approval cumulatively accounted for 10% of the 2010 herbicide application area. The most significant loss being pendimethalin, which was applied to 66 k spray hectares (4% of spray area) and is important for pre-emergence black grass control in cereals. When actives that may be removed, notably chlorotoluron, and those that are candidates for substitution, such as diflufenican, are considered, compounds applied to around a fifth of the current spray area are at risk and,as such, weed control options would be severely reduced.

In relation to insecticides, only two actives applied to cereal crops are predicted to be likely to be removed; bifenthrin and esfenvalerate. Both active ingredients, which cumulatively accounted for ca 3% of 2010 insecticide spray area, are at risk due to their classification as persistent, bioaccumulative and toxic (PBT) compounds. Deltamethrin and dimethoate, each accounting for ca 3% of total current spray area, may also be at riskas potential endocrine disruptors. Dimethoate is particularly important for control of wheat bulb fly in cereals and all four of these insecticides areimportant pest control options for winter wheat and barley. However, the most serious threat to cereal crops in relation to insecticide losses is the pyrethroid lambda-cyhalothrin, which is predicted to be a candidate for substitution. Lambda-cyhalothrin accounted for 40% of the total insecticide spray area in 2010 and is applied to all cereal crops.

In conclusion, pesticide input is integral to cereal production. The proposed changes to pesticide availability, particularly in relation to fungicides, have the potential todramatically change current pesticide application regimes. Were the predictions from the PSD impact scenario implemented there would be significant difficulty maintaining both pest control and resistance management with the remaining compounds, leading tonegative impacts on yield and the Scottish agricultural economy.

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