Crop Protection in Sugar Beet

摘要

SUGAR BEET CROP PROTECTION IN SUGAR BEET Mike May from IACR-Broomrsquo;s Barn in Suffolk UK discusses crop protection in sugar beet especially in the UK but also throughout Europe cereals (approximately 80 follows winter wheat). The ideal drilling dates are between 10 March and 10 April but this can be delayed by the weather. Drilling earlier than this will put the crop at risk of bolting (producing flowering stems instead of harvestable roots) as a result of vernalisation by periods of cold weather. Harvesting (Figure 1) starts as soon as the factories open (mid-late September) and on light soils may continue until the factories close (mid- February). On heavier soils harvesting is usually completed before Christmas. Beet awaiting delivery to the factory is stored (usually in outdoor clamps but sometimes in redundant buildings).Delivery is governed by a system of permits that are allocated by the sugar factory staff. Drilling dates in different countries are governed by the weather and there is both a spring and an autumn drilled crop in Spain. The autumn drilled area is in the south around Seville whilst spring drilling is carried out further north. The UK has one of the longest campaign lengths (opening of factories) at approximately 150 daysndash;around 100 days is the norm in most other European countries. Introduction Sugar beet is an important crop in the UK. Not only is it relatively profitable for the farmer but it also provides an important spring sown break for many combinable crop rotations that are dominated by winter wheat.Just under 30 of the worldrsquo;s sugar (sucrose) is produced from sugar beet and the rest from cane (Licht 1999). In Europe sugar beet is grown under a quota system governed by the EU. In 2001 sugar beet were grown on around 175,000 ha in the UK; this compares with 188,000 ha in 1998 (see Table 1 for European production). The main reasons for the reduction in area in the UK are increased yields through improved agronomy and varieties and favourable weather plus low prices for any surplus sugar that is produced in excess of the growerrsquo;s contracted quota. Sugar prices are set on an EU basis and UK growers have been disadvantaged owing to the high value of the pound;. In 2000 farmers received just over pound;27 tndash;1 of roots (adjusted to 16 sugar content) grown within their contract but approximately pound;6 tndash;1 for any surplus delivered to the factory (this comapres with over pound;37 tndash;1 and pound;11 tndash;1 respectively in 1996).Therefore there is no incentive for farmers to grow much more sugar beet than they require to meet or maintain their contracted tonnage. However the vagaries of the season especially drought means that most growers sow extra area (10ndash;15) to preserve their contract. Most sugar beet crops in the UK are preceded by winter Table 1. Top and bottom five European sugar beet producing countries (this data is from a variety of sources therefore discrepancies and variations may exist) France Germany Turkey Italy UK Greece Switzerland Ireland Finland Portugal Average area 1995ndash;1998 (rsquo;000s ha) 425 530 400 275 175 45 25 25 35 2 Average raw sugar production (t handash;1) 10.9 8.2 5.0 6.1 8.6 Average sugar yield 1995ndash;1998 1995ndash;1998 (rsquo;000s t annumndash;1) 4630 4380 1970 1680 1500 320 220 200 160 10 Growing costs and changes in production The total cost of growing sugar beet in the UK is around pound;1100 handash;1 (Nix 2000).Crop protection is an essential element and cost around pound;25 million (approximately pound;150 7.2 8.8 8.4 4.9 5.7 Total Western Europe Total Eastern Europe 188 Pesticide Outlook ndash; October 2001 This journal is copy; The Royal Society of Chemistry 2001 2600 6020 20790 9290 7.8 2.7 DOI 10.1039/b108605g Figure 1.A harvester demonstration ndash; over half of the UK crop is harvested by contractors using six row machines such as this (Photograph British Sugar) handash;1) in 2000 (Source British Sugar Annual Crop Surveys). This was 7 less than in the previous season. Average spend per hectare on herbicides is usually between pound;105 and pound;120 handash;1 on insecticides approximately pound;40 handash;1 whilst around pound;15 handash;1 is spent on fungicides (but usually only half the crop area requires treatment against fungal leaf diseases). Average yields are usually around 55 t handash;1 of roots at 16 sugar. It is interesting to consider the UK Ministry of Agriculture Fisheries and Food (MAFF)1 statistics for the crop (Garthwaite and Thomas 1998) which show that over the 10 years to 1996 the area treated with pesticide increased 71 but the amount of active ingredient applied decreased by 35.Between 1994 and 1996 the total area treated with herbicides increased 24 but the amount applied did not increase (608 tonnes in 1994; 604 tonnes in 1996). This is part of a general approach by growers who are willing to treat the crop more times if it means that the total amount of pesticide they use can be reduced. With weed control this is achieved by applying repeated low doses of herbicides to each weed flush when the weeds are small rather than Figure 2. Effect of weed on sugar beet yield. LEFT ndash; clean plot in which a sequence of herbicide mixtures has been used to control weeds. RIGHT ndash; Weedy plot in which yields have been severely reduced by lack of weed control.1 Now Department of Environment Food amp; Rural Affairs (DEFRA) Seed treatments and insecticides Most western European countries use pelleted seed to facilitate precision drilling but some such as Turkey still drill naked seed. Most growers aim for a final population of around 75,000 to 100,000 plants handash;1 and sow between 1.0 and 1.2 units of seed handash;1 (one unit = 100,000 seeds) in rows SUGAR BEET waiting and applying fewer but higher dose mixtures to slightly larger stage weeds. Before the 1970s multi-germ seed was used and this required hand thinning to take out the extra plants that were surplus to requirements. Up until this time most growers relied on hand labour and mechanical systems for weed control.Monogerm seed became available in the 1970s and at the same time herbicides such as phenmedipham chloridazon lenacil and ethofumesate were adopted resulting in less reliance on hand labour. Some countries such as Turkey still sow seed at close spacing and remove the surplus plants and control weeds with hand labour. Figure 3. Powdery mildew (Erysiphe betae) ndash; the main postemergence disease that affects UK sugar beet crops Pesticide Outlook ndash; October 2001 189 SUGAR BEET 45ndash;70 cm apart. Seed is purchased in the UK with a standard dressing of thiram (10.5 g kgndash;1 of raw seed) and hymexazol (5.5 g kgndash;1 of raw seed) incorporated into the pellet. These fungicides are also used in many other European countries although doses vary according to disease risks.There is an option to purchase seed treated also with imidacloprid (at 90 g unitndash;1 of pelleted seed) or tefluthrin (10 g unitndash;1). In the UK approximately 4 of seeds are treated with tefluthrin for the control of soil pests (mainly millipedes such as Blaniulus spp. and Bracydesmesdus spp. springtails Onychiurus armatus and symphilids Scutigerella immaculata). Imidacloprid is used on around 75 of the UK area. Its use in western Europe is variable generally depending on the pest risks. For instance 90 of the Belgian and 70 of the French crop is treated whilst only 40 of the German crop is sown with imidacloprid. Carbamate granules are used on approximately 10 of the sugar beet area in the UK (the largest use is of aldicarb applied in the seed furrow at drilling to control free living nematodes (Docking disorder) Ditylenchus dipsaci and other soil pests.Some such as aldicarb are effective at controlling early attacks by aphids. Post-emergence insecticides are available but owing to the widescale use of imidacloprid or carbamate granules relatively few are used in most seasons. In countries where the use of imidacloprid seed treatment or carbamate granules is low use of postemergence insecticides is generally high. Approximately 60 of the imidacloprid use in the UK is for control of both soil and foliar pests the rest for control of mainly foliar pests especially aphids. Aphids seldom damage sugar beet directly but the green aphids Myzus persicae and Macrosiphum euphorbiae are vectors of virus yellows diseases which can reduce yields by up to 50 in the worst cases of early infection.Imidacloprid gives protection against early (up to 10ndash;12 leaves stage) aphid attack. After the 12 leaves stage beet plants produce a substance that builds up in the gut of the aphid and essentially prevents it from eating so that it starves to death. Although aphid / virus forecasts are produced by IACRBroomrsquo;s Barn these are not available at the time growers order their seed (usually in July of the previous year). Therefore most growers prefer to adopt the insurance approach of ordering seed treated with imidacloprid to control soil pests and post-emergence pests such as aphids rather than wait and possibly use insecticide granules which need to be applied through special applicators on the drilling rig.Weed control The main weeds found in sugar beet in Europe include the perennial species Elymus repens and Cirsium arvense whilst common annual weeds include Chenopodium album Polygonum aviculare Matricaria chamomilla Fallopia convolvulus Sinapis arvensis and Stellaria media. Crop volunteers of potatoes and oilseed rape are present in many countries including the UK and weed beet (an annual form of Beta vulgaris) is a problem in many countries but particularly the UK where it is present in approximately 60 of sugar beet fields. 190 Pesticide Outlook ndash; October 2001 The total potential losses from weeds would be between 50 and 100 of the potential crop yield (Figure 2).Sugar beet is not competitive with emerging weeds until it has at least 8 true leaves. Weed control in sugar beet relies on a sequence of herbicide applications. Over 50 of the UK crop is treated with glyphosate or paraquat +/ndash; diquat prior to crop emergence. Much of the glyphosate is applied in the autumn or winter to control weeds present in the preceding stubble prior to ploughing with the rest applied to control weeds emerging after ploughing. Over 120 herbicide products (using 20 active ingredients ndash; CABI 2001) are approved in the UK for weed control in sugar beet. However most of these herbicides are relatively ineffective compared to those used in other crops such as cereals and most will only control weeds at the small cotyledon to first true leaves stage.Therefore a sequence of herbicides is required to control the range of weeds that emerge in sequential flushes during the early spring after beet is sown. To help timing of post-emergence sprays approximately 44 of growers use a pre-emergence herbicide (the majority apply chloridazon). This usually replaces a post-emergence spray. Post-emergence weed control uses a sequence of two or more applications. The range of weed species controlled by each herbicide is also limited and so mixtures of herbicides are applied. Weedy fields such as those on peaty soils often require 6 to 8 postemergence sprays. Typically 4 to 5 applications of herbicide treatments are used each season.The most popular postemergence active ingredients (in order of use in 2000) are phenmedipham metamitron ethofumesate desmedipham triflusulfuron-methyl lenacil clopyralid and chloridazon. To improve herbicide activity mineral or vegetable oil-based adjuvants are added to over half the post-emergence treatments. Tractor hoeing between the rows is still employed on approximately 50 of the crop mainly to control weed beet. Similar systems of low dose postemergence weed control are used in most EU countries but there are numerous small variations. A high proportion of the Belgian crop is treated with pre-emergence residual herbicides; this is to provide flexibility in timing of postemergence treatments on their heavy soils whereas few of the Dutch or Swedish crops are treated with pre-emergence residual herbicides.France and the Netherlands tend to use less herbicide active ingredient per hectare than other countries but differences between countries are usually less than 10. Post-emergence disease control In the UK post-emergence disease control is a feature from late July or early August when powdery mildew (Erysiphe betae) (Figure 3) starts to invade the crop. It usually starts in the South Eastern growing areas of Suffolk and appears later in Northern and Western beet areas. Average infestations for the last five years have been around 50 of the crop area. Forecasts based on winter and summer weather are provided for growers by IACR-Broomrsquo;s Barn. Until the advent of triazole fungicides in 1997 growers relied on sulfur for control of powdery mildew.In 2000 approximately 40 of the crop area was treated with triazole Potential changes that might result if herbicide tolerant beet introduced l More flexibility for growers in timing application of herbicides. l Herbicide costs reduced (by 70+) but total cost will depend on technology fee. l Less need to control weeds in autumn stubbles. l Reduced weed control in other crops in the rotation? (Sugar beet is once again used as lsquo;cleaning croprsquo; for the rotation?) l Weed presence at early stage of crop might reduce risk of wind or water erosion of soil. Otherwise sow cover crop such as barley which will be easier to manage than with conventional herbicides. l Facilitate use of autumn sown cover crops (e.g.for nitrate leaching). l Weed presence later in season may reduce aphid attack. l Weed presence may increase populations of beneficial invertebrates. l Approximately 30 reduction in active ingredient use in UK (more in some countries less in others). l Control of weed (volunteer) beet ndash; but will need management care to avoid herbicide tolerant volunteers. l Easier and cheaper control of perennial weeds particularly volunteer potatoes (can also reduce potato cyst nematode populations) and Cirsium arvense thistles. l High levels of weed control might reduce invertebrate populations and affect food chain for birds ndash; this is being examined in DEFRA Farm Scale Evaluations. l Increase options for direct drilling or minimal tillage systems for sugar beet establishment.fungicides (cyproconazole or fluzilazole + carbendazim) mostly applied in tank mixture with sulfur. In other European countries Cercospera leaf spot (Cercospera beticola) is a common problem with control necessitating use of resistant cultivars and a sequence of fungicide sprays during the season. The future The UK sugar beet industry has been at the forefront of reducing inputs of both pesticides and fertilisers (nitrogen SUGAR BEET ON THE WEB http://www.sugarbeet.co.uk http://www.ib.be/cefs (European Committee of Sugar Producers) http://www.britishsugar.co.uk http://www.bbro.co.uk (British Beet Research Organisation) http://hometown.aol.com/asga/sugar.htm (American Sugarbeet Growers Association) http://www.iirb.org (International Institute for Beet Research) SUGAR BEET fertiliser applications have reduced from over 150 kg handash;1 in 1970 to the current level of just over 100 kg handash;1).Disease and pest forecasts have been developed and strategies implemented to improve weed control without increasing the amount of herbicide used or the use of tractor hoes. The main problem facing the sugar industry is to remain competitive when the returns from sugar continue to fall. Biotechnology could provide a solution to some of these problems and the first of such crops which have tolerance to glyphosate (see BOX) are included in the DEFRA Farm Scale Evaluations. These will be completed in 2003 and so it is unlikely that such crops could be grown commercially until 2005 at the earliest. Acknowledgements The author is grateful to British Sugar for the use of its Annual Crop Surveys. These surveys are the source of much of the data used in this paper. References CABI (2001) The UK Pesticide Guide 2001. CABI Publishing Wallingford UK. Garthwaite D. G. and Thomas M. R. (1998) MAFF Pesticide Usage Survey Report 159 Arable Farm Crops in Great Britain 1998. Ministry of Agriculture Fisheries and Food London. Licht F. O. (1999) World Sugar and Sweetener Yearbook 1999/2000. F. O. Licht GmbH Tunbridge Wells. 114 pp. Nix J. (2000) Farm Management Notebook 31st Edition Imperial College at Wye Ashford UK. 256 pp. Mike May is Senior Liaison Officer at IACR-Broomrsquo;s Barn (http://www.iacr.bbsrc.ac.uk/broom) responsible for sugar beet technology transfer to UK sugar beet growers and advisers for the research station and the British Beet Research Organisation. Pesticide Outlook ndash; October 2001 191