Proceedings Crop Protection in Northern Britain 2010

Proceedings Crop Protection in Northern Britain 2014 pp: 21-26

INSECTICIDE USE ON SCOTTISH OILSEED RAPE CROPS: HISTORICAL USE PATTERNS AND PEST CONTROL OPTIONS IN THE ABSENCE OF NEONICOTINOID SEED TREATMENTS

J Hughes, G Reay and J Watson Pesticide Survey Unit, SASA, Scottish Government, Roddinglaw Road, Edinburgh, EH12 9FJ E-mail: [email protected]

Summary: Oilseed rape is a profitable break crop and an important component of Scottish arable agriculture. This crop has a wide range of insect pests, resulting in high insecticide input which combines seed treatments and foliar sprays. The organochlorine seed dressings used in the 1990s were replaced with neonicotinoid treatments from 2002 onwards; whereas over the last two decades sprays have been consistently dominated by pyrethroid insecticides. The restriction of neonicotinoid seed treatments will leave only foliar sprays available for crop protection which will limit the options for controlling pests of newly emerged crops.

INTRODUCTION

Oilseed rape has been cultivated in Scotland since the early 1980s (Anon, 1984) and during the last decade approximately 35,000 hectares have been grown each year (Anon, 2012a). In 2012 oilseed rape was the third most commonly grown arable crop in Scotland, accounting for 7% of the total combinable crop area.

Oilseed rape is grown as a break crop in arable rotations, helping to suppress the build up of weeds, disease and insect pests associated with cereals and potatoes. Its cultivation also offers farmers the opportunity to use plant protection products with different modes of action to combat existing pest populations.

Oilseed rape is predominately used to produce food grade oil and recently a market has developed for locally produced cold pressed rapeseed oil. A smaller area of crop is grown for biodiesel production. The pulp left after oil extraction is used for protein meal for animal feed. The market value of the 2012 Scottish crop was £39.4 million (Anon, 2013) and in recent years high market prices have led to oilseed rape becoming a more profitable break crop than peas or beans, which together accounted for less than 1% of the 2012 combinable crop area.

However, oilseed rape has a wide range of insect pests and crops are at risk from damage from seedling establishment through to seed development. The pest pressure oilseed crops are exposed to is reflected by their high insecticide input. In 2012, 94% of winter oilseed rape was treated with an insecticidal seed treatment and 70% of the crop received a foliar insecticide. In comparison, insecticidal seed treatments and sprays were applied to only 6 and 37% of the winter wheat crop respectively (Watson et al., 2013). This paper looks at trends in oilseed rape cultivation and insecticide use over the last 20 years and discusses the options available in the future, particularly in relation to the potential absence of neonicotinoid seed treatments. METHODS

The pesticide use data presented in this paper are taken from the dataset collected by the Pesticide Survey Unit at Science and Advice for Scottish Agriculture (SASA), a division of the Scottish Government’s Agriculture, Food and Rural Communities Directorate.

Biennial surveys of pesticide use on arable crops are conducted as part of the UK Government’s statutory post-approval monitoring programme. The surveys are conducted by collecting data from a random sample of Scottish farms stratified by size and geographic region. Estimates of total pesticide use are produced from these sample data by ratio estimation; the data are multiplied by raising factors calculated by comparing the sampled area of each crop in each stratum with the total crop areas recorded in that year’s agricultural census. Details of data collection and estimation can be found in the individual survey reports published on the SASA website (http://www.sasa.gov.uk/pesticides/pesticide-usage).

RESULTS AND DISCUSSION

Scottish Oilseed Rape Cultivation 1992-2012

Oilseed rape is an important component of the arable crop rotation. The overall area, and the proportion of spring and winter varieties grown, has varied over time in relation to climatic conditions at planting, market prices and changes in agricultural subsidies. However, over the last decade cultivation has been fairly steady at ca 35,000 ha, with more than 80% being winter sown varieties, with a mean yield of ca 3.5 t/ha (Figure 1). The yield increase from 2000 onwards was primarily due to greater cultivation of winter varieties which are higher yielding than spring sown crops (Figure 1). The poor yield in 2012 has been attributed to the difficult climatic circumstances in that year. Overcast conditions extend flowering and shorten the maturation period resulting in smaller seeds with lower oil content. Heavy rain can also result in pod shattering and premature seed shed.

Key Insect Pests and Historical Insecticide Use (1992-2012)

Oilseed rape has a wide range of insect pests and crops are at risk from damage throughout their life cycle. At seedling establishment, winter crops are vulnerable to damage from flea beetles, mainly the cabbage stem flea beetle (CSFB) Psylliodes chrysocephala whose larvae bore into the stems allowing water to enter the plant which can cause winter kill if it freezes. Other autumn pests include adult Phyllotreta spp. flea beetles which feed on rape foliage, rape winter stem weevil (Ceutorhynchus picitarsis) larvae which feed in crop stems and aphids such as Myzus persicae which transmits Turnips yellow virus (TuYV). Oilseed rape is also vulnerable to pollen beetle (Meligethes aeneus) damage at flowering and cabbage seed weevil (Ceutorhynchus assimilis) and brassica pod midge (Dasineura brassicae) damage during seed pod development.

In order to combat this wide range of pests, oilseed rape has historically been treated with a combination of seed treatments, to protect against insects colonising the crop at emergence, and foliar sprays to prevent damage from species occurring later in the season (Figure 2). 80 4

70 3.5

60 3 Y . Area of spring oilseed rape ) i a e h l

Area of winter oilseed rape d

0 50 2.5

( 0 Yield t o 0 , n 1 n (

a 40 2 / e h r e c A

t a p 30 1.5 r o e r ) C . 20 1

10 0.5

0 0 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 Year

Figure 1. Oilseed rape cultivation area and yield 1992-2012 (data source: Anon, 2012b).

Thiamethoxam Seed Treatement Clothianidin (formulated with beta cyfluthrin) Seed Treatement 100 Imidacloprid (formulated with beta cyfluthrin) Seed Treatement Lindane Seed Treatement .

90 Foliar Insecticides d e t 80 a e r t 70 p o r c 60 d e e s 50 l i o f 40 o e g

a 30 t n e c 20 r e P 10 0 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 Year

Figure 2. Percentage of oilseed rape crop treated with insecticidal seed treatments and foliar sprays 1992-2012. Oilseed rape crops have received consistently high insecticide input over the last two decades (Figure 2) and, unlike cereals, insecticidal seed treatments are a basic component of the crop protection programme. In the 1990s, the seed treatment used was lindane, an organochlorine compound which was applied to between 60 and 80% of crops. Lindane approval was withdrawn in 1999 and its use declined to 20% in 2000 in anticipation of its 2001 final use date. As lindane was being withdrawn, imidacloprid, a new broad spectrum systemic neonicotinoid insecticide, was approved for use on oilseed rape crops. Imidacloprid was approved in 2000 and first encountered, on 14% of the crop, in 2002. The area of crop treated with imidacloprid increased over time, with an estimated 81% treated in 2008. Two other neonicotinoid compounds, thiamethoxam and clothianidin, were subsequently approved for use on oilseed rape crops in 2007 and 2008 respectively and have since overtaken imidacloprid use. In 2012, imidacloprid, thiamethoxam and clothianidin were applied to 11, 36 and 46% of the crop respectively, representing total neonicotinoid coverage of 93%. Both imidacloprid and clothianidin are co-formulated with the pyrethroid beta-cyfluthrin.

In relation to foliar applications, over the last 20 years the percentage of the crop treated has varied between 44 and 79% (Figure 2). Foliar sprays are reactive so display temporal variation based on pest pressure. Figure 3 presents the total area of sprays, including multiple applications to the same area. Foliar applications are dominated by pyrethroid compounds, which have accounted for more than 90% of the total spray area throughout the presented period. The pyrethroid compounds used have varied over time. In the 1990s alpha- cypermethrin and cypermethrin were the principal compounds applied (accounting for 60 to 90% of spray area); whilst in the 2000s the majority of pyrethroid use was lambda cyhalothrin and tau-fluvalinate (accounting for 60 to 70% of spray area).

60 Non pyrethroid insecticides (carbamate, organochlorine, organophosphate, neonicotinoid, pyridine and oxadiazine compounds) 50 Pyrethroid insecticides .

0 0 0 , 1 ( 30 d e t a e r t

a 20 e r A

0 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 Year

Figure 3. Total spray area of foliar insecticides, including multiple treatments to the same area, 1992-2012. This dependence on pyrethroids reflects that most insecticides approved for use on oilseed rape belong to this class. Currently, pyrethroids account for 54 and 76% of approved actives and products respectively (Table 1). In addition, multiple pyrethroid applications may be made during the growing season, whereas the neonicotinoids (acetamiprid and thiacloprid) and indoxacarb are limited to a single application. Most pyrethroids also have approval for use during flowering, unlike indoxacarb and pymetrozine.

The non-pyrethroid sprays have also varied over time; in the early 1990s they were almost exclusively lindane (organochlorine, last approved use in 2001) and pirimicarb (carbamate). Organophosphate (dimethoate and chlorpyrifos) sprays were applied in the early 2000s until their approval was withdrawn for use on oilseed crops. In the mid to late 2000s very few non- pyrethroid sprays were recorded, those that were being pirimicarb and pymetrozine (which was approved in 2003). However, in 2012 foliar use of non-pyrethroids increased from the 0 to 5% displayed in the previous eight surveys to 9% of the total spray area. The compounds recorded in 2012 were pirimicarb, pymetrozine and for the first time the neonicotinoids acetamiprid and thiacloprid and the oxadiazine compound indoxacarb.

Table 1. Foliar insecticides with current approval for use on oilseed rape

Chemical Group Active Ingredient No. Products Example product(s) Carbamate Pirimicarb 16 Aphox Acetamiprid 1 Insyst Neonicotinoid Thiacloprid 3 Biscaya Oxadiazine Indoxacarb 3 Steward Alpha cypermethrin 9 Alert, Fastac Beta cyfluthrin 1 Gandalf Cypermethrin 10 Permasect C, Toppel 100 Pyrethroid Deltamethrin 14 Bandu, Decis Lambda cyhalothrin 31 Hallmark, Komodo Tau-fluvalinate 4 Mavrik Zeta cypermethrin 6 Fury 10 EW, Minuet EW Pyrethrum Pyrethrins 2 Pyrethrum 5 EC Pyridine Pymetrozine 2 Plenum

Future Options for Pest Control

The European Union has adopted a proposal (Regulation (EU) No 540/2011) prohibiting the use of clothianidin, imidacloprid and thiamethoxam on oilseed rape from December 2013. This restriction will be reviewed, although not necessarily rescinded, after two years. As there are no alternative insecticidal seed treatments approved for use on oilseed rape, only foliar use of the compounds listed in Table 1 will be available for crops sown in 2014. The absence of seed treatments has implications for control of pests colonising newly emerged crops. Whilst these can be treated with sprays, there are inherent difficulties in doing so. Effective management of early season pests will require a quick response, allowing control of CSFB before they lay eggs and aphids before they transmit viruses. This will require increased vigilance by farmers and as sprays cannot be applied until crops have sufficient leaf area, they may be of limited use when pest colonisation occurs at cotyledon or first leaf stage. In addition, spray applications are reliant on weather conditions, and if delayed may be too late to prevent damage. Another concern is the resistance status of the two main autumn pests. Whilst there is currently no reported resistance to neonicotinoids in the UK, resistance to both pyrethroids and pirimicarb are reported to be prevalent in Myzus persicae (Anon, 2012c) leaving very few options for their control. In addition, CSFB resistance to pyrethroids has been reported in Germany (Heimbach & Muller, 2012) leading to concern that it may also develop in the UK. Where pyrethroids are ineffective, this may lead to increased use of the other foliar options such as pymetrozine. However, the loss of the neonicotinoids will increase resistance pressure on all remaining active ingredients.

Overall, the absence of neonicotinoid seed treatments may make control of autumn pests challenging. The economic impact is difficult to estimate, although some reports have suggested it might be significant. A greater number of sprays will be required, although this will be offset to some extent by a reduction in the cost of applying a seed treatment. However, higher seed rates may be necessary to mitigate damage by autumn pests and yields may be affected. The average yield loss on untreated crops from CSFB is around 1% and from TuYV is 15% (Nicholls, 2013).

In conclusion, insecticide input is integral to oilseed production and historically growers have used a combination of seed treatments and foliar sprays. In the absence of seed treatments, farmers will have to rely on sprays, and this may have a detrimental effect on profitability. The extent of the effect on rape cultivation and economic return will not be clear until the 2014/15 crops are harvested. However, when considered in the wider context of other potential restrictions to oilseed rape pesticides, such as metaldehyde and key rape herbicides, due to implementation of the Water Framework Directive (Twining & Clarke, 2009), oilseed rape growers face considerable uncertainty about the availability of future pest control options.

REFERENCES

Anonymous, 1984. The Digest of Agricultural Statistics. London: MAFF, HMSO. Anonymous, 2012a. Results from the June 2012 Scottish Agricultural Census. Scottish Government. (http://www.scotland.gov.uk/Publications/2012/09/1148). Anonymous, 2012b. First estimate of the cereal and oilseed rape harvest 2012. Scottish Government. (http://www.scotland.gov.uk/Publications/2012/12/5477) Anonymous, 2012c. Annual Project Report 2012 Combating resistance to aphicides in UK aphid pests. HGCA/AHDB Report. Anonymous, 2013. Economic Report on Scottish Agriculture: 2013 Edition. Scottish Government Environment and Forestry Directorate, Rural and Environment Science and Analytical Services (http://www.scotland.gov.uk/Publications/2013/06/5219/0) Heimbach U, Muller A, 2012. Incidence of pyrethroid-resistant oilseed rape pests in Germany. Pest Management Science 2013; 69: 209–216. Nicholls CJ, 2013. Research Review No. 77. Implications of the restriction on the neonicotinoids: imidacloprid, clothianidin and thiamethoxam on crop protection in oilseeds and cereals in the UK. HGCA. Twining S, Clarke J, 2009. Future of UK winter oilseed rape production. Crop Protection Association Agricultural Industries Confederation: ADAS. Watson J, Hughes J, Thomas L, Wardlaw, J 2013. Pesticide Usage in Scotland: Arable crops 2012. Scottish Government. (http://www.scotland.gov.uk/Publications/2013/10/8375)