The fi rst aim of IPM must be to use chemical pesticides at a sustainable level without causing unacceptable loss of crop yields. However, in order to keep up with the increase in global food production that will be required in the next 20 years, IPM will need to be capable of moving to the next level fairly rapidly, namely to enable yields to be increased while still keeping use of pesticides and other inputs at sustainable levels. Can IPM deliver? In a
groundbreaking study, Pretty (2008) analysed data from 62 IPM projects in 26 industrialized and developing countries, covering over 5 million farm house- holds farming 25 million ha. His analysis indicates that IPM is successful in most cases. Only one out of the 62 IPM projects resulted in an increase in pesticide use and an associated decline in yields. Over 60% of the IPM proj- ects resulted in a reduction in pesticide use (average reduction of 75%) and an increase in yields (average yield increase of 40%). An additional 15% of projects resulted in an increase of both yield (average 45% increase) and pes- ticide use (average 20% increase). These were mainly conservation farming projects that incorporated zero tillage to conserve soils and reduce water pol- lution and they tended to result in greater use of herbicides for weed man- agement. Approximately 20% of the IPM projects resulted in a slight reduction in yield (average 5% reduction) and lowered pesticide use (average 60% reduction). These mainly consisted of cereal production projects in Europe.
So if IPM is successful, are many farmers using it on the ground? Figures for the estimated area of crops currently under supervised control and IPM in Europe for different crop types are given in Table 2.6 (Bale et al., 2008).
Table 2.6. Supervised and integrated control programmes used in Europe. (From Bale et al., 2008.)
Crop Type Elements
Area under IPM in Europe/reduction in pesticides on that area Field
vegetables
Supervised Monitoring; sampling; disease-resistant crop varieties
5% of total area/ 20–80% reduction Cereals Supervised Monitoring; sampling; forecasting;
resistant crop varieties
10% of total area/ 20–50% reduction Maize Integrated Mechanical weeding; resistant crop
varieties; biological control of insects
4% of total area/ 30–50% reduction Vineyards Integrated Biological control of insects and mites;
disease-resistant crop varieties; pheromone mating disruption
20% of total area/ 30–50% reduction Olives Integrated Cultural control; biological control of
insects; disease- and insect-resistant crop varieties; monitoring; sampling; pheromones
Very limited
Orchards Supervised Monitoring; sampling; selective pesticides
15% of total area/ 30% reduction Integrated Monitoring; sampling; pheromone
mating disruption; biological control; disease-resistant crop varieties
7% of total area/ 50% reduction Greenhouse
vegetables
Integrated Monitoring; sampling; biological control of insects, mites and diseases;
disease-resistant crop varieties; selective pesticides
30% of total area/ 50–99% reduction
The data show that few farmers use IPM, although there are exceptions, such as greenhouse growers in the UK and the Netherlands. A lot of research has been done on IPM since the mid-1980s, so the fact that most farmers have yet to adopt it raises major issues about how research can be translated into farmer practice. The degree to which IPM has been adopted and is successful (i.e. leads to reductions in pesticide use and still maintains yield) varies sig- nifi cantly according to the type of crop grown. Crop protection tactics have to be chosen that are appropriate not only to the crop plant, but also to the physical area of production, the type and number of pests, and the physical, chemical and biological environments. Different tactics must also be capable of being integrated, and they must be affordable for the farmer. It is not sur- prising that IPM is most advanced in high-value glasshouse crops, such as fresh salads or ornamental plants. For these crops, growers can afford to spend comparatively large sums on crop protection (including labour-intensive methods such as spot-treating individual plants). There are also strong driv- ing forces to make IPM work in the form of a signifi cant pesticide resistance problem, extremely high quality standards from retailers, and pressure from consumers and others to use fewer pesticides. In contrast, producers of out- door broad-acre crops such as cereals, potatoes and cotton have much less to spend on pest management per unit area of crop, and have to work in a much more challenging physical and ecological environment.
Integrated pest management in greenhouse crops
The global area of crop production done in greenhouses (which include glasshouses, polythene tunnels and other forms of protective structure) is estimated at around 2.4 million ha, of which around 45,000 ha is done in glasshouses (van Lenteren, 2006). Greenhouse growers are able to produce high-value crops on a small area of land. Unfortunately, greenhouse crops also provide an excellent environment for pest insects, mites and plant patho- gens. Pesticide resistance evolved in some key glasshouse pests as long ago as the 1960s, prompting the early development of biocontrol. This was fol- lowed by the widespread adoption of bumblebees for pollination, which required growers to stop using broad-spectrum insecticides. Growers of greenhouse edible crops are also under severe pressure from retailers to deliver produce with zero detectable pesticide residues because of consumer concerns about residue safety (Pilkington et al., 2010).
Some very sophisticated and effective IPM programmes have been devel- oped for glasshouse crops (Table 2.7). These were mainly instigated through publicly funded research and involved close working between research sci- entists, growers and industry. We would class these as Level Four IPM accord- ing to the Prokopy scale (Prokopy, 1993). In Europe, IPM is used in over 90% of glasshouse tomato, cucumber and sweet pepper production in the Nether- lands (van Lenteren, 2000) and is standard practice for glasshouse crops in the UK. In Almeria, Spain, the area under IPM has increased from just 250 ha in 2005 to around 7000 ha in 2008, while the proportion of the Dutch
chrysanthemum crop grown under IPM has increased from just 1% in 2002 to 80% in 2007 (R. GreatRex, Syngenta Bioline, personal communication). Glass- house IPM uses a combination of biological and physical controls, selective pesticides and resistant varieties, with very careful monitoring of pest popu- lations to determine when they have passed the economic threshold. This system requires considerable knowledge on behalf of the grower but it has been adopted widely because it has clear benefi ts. These include reliable pest control, lack of phytotoxic effects, better fruit set and the fact that – because synthetic pesticides are used sparingly – operators do not have to be excluded from the glasshouse after spray applications so often. Unlike for synthetic pesticides, there is no statutory interval between the application of preda- tors/parasitoids and harvesting the crop, while for biopesticides the harvest interval tends to be very short. This means that these agents can be used right
Table 2.7. Integrated pest and disease management programme as applied in tomato in Europe. (From van Lenteren, 2000.)
Pest/disease
Method used to prevent or control pest/disease
Pests
Whitefl ies (Bemisia tabaci, Trialeurodes
vaporariorum)
Parasitoids: Encarsia, Eretmocerus Predators: Macrolophus
Pathogens: Lecanicillium, Paecilomyces,
Aschersonia
Spider mite (Tetranychus urticae) Predators: Phytoseiulus Leaf miners (Liriomyza bryoniae, Liriomyza
trifolii and Liriomyza huidobrensis)
Parasitoids: Dacnusa, Diglyphus, Opius, natural control
Lepidoptera (e.g. Chrysodeixis chalcites,
Lacanobia oleracea, Spodoptera littoralis)
Parasitoids: Trichogramma Pathogens: Bacillus thuringiensis Aphids (e.g. Myzus persicae, Aphis gossypii,
Macrosiphum euphorbiae)
Parasitoids: Aphidius, Aphelinus Predators: Aphidoletes, natural control Nematodes (e.g. Meloidogyne spp.) Resistant and tolerant cultivars, soil-less
culture
Diseases
Grey mould (Botrytis cinerea) Climate management, mechanical control, selective fungicides
Leaf mould (Fulvia = Cladosporium) Resistant cultivars, climate management Mildew (Oidium lycopersicon) Selective fungicides
Fusarium wilt (Fusarium oxysporum lycopersici) Resistant cultivars, soil-less cultures Fusarium foot rot (Fusarium oxysporum radicis/
lycopersici)
Resistant cultivars, soil-less culture, hygiene Verticillium wilt (Verticillium dahliae) Pathogen-free seed, tolerant cultivars,
climate control, soil-less culture Bacterial canker (Clavibacter michiganesis) Pathogen-free seed, soil-less culture
Several viral diseases Resistant cultivars, soil-less culture, hygiene, weed management, vector control
up to harvest, which is a considerable benefi t when the produce quality stan- dard demanded by retailers is so high. Most of the biological control used in glasshouses is concerned with managing insect and mite pests. Some micro- bial biopesticides are available against plant pathogens and can be integrated with selective pesticides but a greater range of products is required. Many of the main plant diseases are tackled currently using resistant crop cultivars, although an increasing number of effective microbial antagonists are becom- ing available. Typically, selective synthetic chemical insecticides and acari- cides will be used at the start of the season as a clean-up for insect and mite pests before switching to inundative applications of predators, parasitoids, parasitic nematodes and insect pathogens. Short-persistence pesticides are used on an at-need basis to knock back pest populations if they start to outstrip the ability of the biological control agents to regulate them.
Integrated pest management in fi eld vegetable crops
Retailers and consumers in the industrialized countries increasingly demand vegetables that are relatively uniform in size and shape and free from blem- ishes and pest-related debris. Field vegetables generally have a higher value than cereals, but a lower value than glasshouse crops. Because of the emphasis on quality, the risk of producing an unmarketable crop is relatively great. Vegetable growers are, therefore, generally risk averse. Pesticides remain the mainstay of crop protection for many vegetable crops. Most of the crop pro- tection is based around supervised spraying of pesticides or there may be some integration of different tactics to control an individual pest species, which we would class as Level One IPM. Other components of IPM that are in use in fi eld vegetables include crop rotation (with some exceptions), good crop management (removal of plant residues, application of fertilizers and irrigation) and adjustment of planting or harvesting dates (USDA, 2001). This may involve the use of pest or disease forecasts (Gilles et al., 2004). Growers walk their crops regularly and make decisions based on their fi nd- ings. In the USA, research-based economic thresholds are available for a range of crops; however, they are used less often in Europe (Collier and Finch, 2007). Pest- and disease-resistant cultivars are grown where available and if the cultivars meet other market requirements. For example, lettuce with resistance to downy mildew is grown widely. Use of physical methods of pest control is increasing. Mechanical weed control can be effective and cov- ers or mulches have been used to control pest insects and weeds; however, most growers still rely on chemical herbicides for weed control, especially glyphosate, which has a very good human safety and environmental profi le. Biological control with microbials or arthropods is relatively undeveloped. This is due to a combination of factors: lack of environmental control and problems of confi ning released natural enemies to the crop, the relatively high cost of biological control methods compared with the value of the crop, reduced and variable effi cacy compared with pesticides, and the limited research and development input in this area. However, there are some
exceptional examples of Level Two IPM that indicate how things could be done across much of the vegetable crops sector in the future. Notably, these IPM systems have been driven by very much the same set of conditions that has forced the development of IPM in glasshouse crops. IPM pro- grammes for the production of tomato crops in Florida, for example, were developed in response to pesticide resistance and severe secondary pest problems with Liriomyza leaf miners caused by the use of broad-spectrum insecticides sprayed against Spodoptera spp. caterpillars. The IPM system that was developed uses pest monitoring and economic thresholds to inform the application of foliar sprays of the bacterial insecticide Bacillus
thuringiensis (Bt), which is highly selective and preserves natural enemies
(Walker et al., 2003).
Integrated pest management in orchard crops
Retailers in the industrialized countries also have high quality standards for orchard crops. Up until the 1970s, pest management in orchard crops relied on calendar sprays of broad-spectrum pesticides, but pesticide resistance became common in many of the key pests. The IPM strategies currently used in orchards are a step forward from supervised pesticide spray pro- grammes developed in the 1970s and 1980s, and are largely based on stop- ping sprays of broad-spectrum pesticides and allowing natural enemies to re-establish, such as the predatory phytoseiid mite, Typhlodromus pyri, which is a key predator of the two-spotted spider mite, T. urticae, in apple orchards (Blommers, 1994). The level of sophistication of the pest manage- ment programme can vary widely from grower to grower, but in the last decade there has been an increasing awareness of the benefi ts of adopting IPM by growers in many of the main producer countries. Pesticide sprays are still essential tools for the majority of farmers, especially for the control of diseases such as scab and powdery mildew, but progressive growers are using disease forecasts in order to target spray applications better (MacHardy, 2000). The development of some sophisticated decision support tools (pest thresholds, monitoring and models) has allowed the targeted application of selective insecticides, insect pheromones for mating disrup- tion, microbial control agents and predators and parasitoids against aphids and moth pests without harming predatory mites (Solomon, 1987; Mac- Hardy, 2000; Cross and Berrie, 2006). This is combined with careful manage- ment of sites away from the tree where pests overwinter or which act as pest reservoirs, such as the soil, border areas and vegetation beneath the tree canopy. Although monitoring has costs associated with it, successful grow- ers fi nd that savings on reduced application of pesticides and other control agents offset these. There is still much work to be done. For example, effec- tive biopesticides are required for aphid pests and plant pathogens, many of the main commercial crop varieties have low levels of disease resistance, and there is a requirement for better integration of the different IPM systems used for individual pests and diseases.
Integrated pest management in broad-acre crops
There have been signifi cant problems since the 1950s with the over-use of synthetic chemical pesticides in broad-acre crops including cereals, maize and cotton. In some well-documented cases, such as cotton production in the Canete valley of Peru, this has included complete failure to control insect pests following the rapid evolution of pesticide resistance (Thacker, 2002). Broad-acre crops generally have high economic thresholds for pest manage- ment interventions, meaning that low densities of many pests can be toler- ated (the exceptions are for pre- and postharvest fungal diseases, some of which pose a serious hazard to human health). There is, therefore, good scope for IPM, but it is not yet being used widely. For example, it is estimated that only 10% of cereal production is done under IPM (van Lenteren, 2008). The majority of schemes are based on host-plant resistance and forecasting/ monitoring to guide pesticide applications, rather than on biological control. An exception is the use of the parasitoid Trichogramma to control outbreaks of the European corn borer, Ostrinia nubilalis, on maize (Burn, 1987). As we will discuss later in this book, since the beginning of the 21st century maize and cotton production has been revolutionized by the commercialization of GM varieties that express a gene from the entomopathogenic bacterium
B. thuringiensis, which codes for a selective, insecticidal protein that kills lep-
idopteran pests. This protein is safe for mammals and other vertebrates and does not affect the arthropod natural enemies that occur in maize and cotton fi elds. It has been taken up widely by farmers in many regions of the world with the exception of Europe, where there are deep-seated societal concerns about GM crops. Similarly, weed control has changed greatly since the intro- duction of GM, herbicide-resistant crops in 1996. Most of these crops have been engineered to be resistant to glyphosate. Over 80 million ha of herbicide-resistant crops were grown in 2006 (Gianessi, 2008). Most of these crops are maize, canola (oilseed rape), soybean or cotton. For example, 80% of US-grown cotton is now resistant to glyphosate. Because glyphosate is a broad-spectrum herbicide, the development of glyphosate-resistant crops has simplifi ed weed control by enabling the farmer to use just the one type of herbicide during production and lowering the number of sprays that have to be applied including the use of pre-emergence herbicides. Glyphosate has a low toxicity to mammals and other vertebrates and, because it is readily adsorbed by soil, there is little risk of it leaching into groundwater (Bayliss, 2000). Even though glyphosate-resistant crop seed is sold to farmers at a pre- mium price, this is offset by reduced costs from herbicides and mechanical weed control and higher yields due to better weed management. The global cumulative farm income benefi t from herbicide-resistant crops for the period 1996–2005 is estimated at over US$19 billion (Gianessi, 2008). Resistance to glyphosate is still relatively rare considering the extent to which it is used, and so far only 18 resistant weed species have been documented (WeedScience. com, 2010). However, given the large-scale uptake of glyphosate-resistant crops, there are concerns that there will be increased selection pressure for resistance in weed populations. Hence the recent development of glyphosate
resistance in two important weeds of soybean, Sorghum halepense and Euphor-
bia heterophylla, in glyphosate-resistant soybean fi elds in South America is
something of a worry (Vila-Aiub et al., 2008).
In Europe, the use of conservation biological control methods, such as wildfl ower headlands and beetle banks, is promoted through various agri- environment schemes but in the UK, for example, most of these have had a very low uptake (Boatman et al., 2007). There is greater use of IPM techniques within organic arable production, but even here there is limited use of bio- logical control, with the majority of integrated crop management schemes relying on improved monitoring and reduced applications of approved chemical controls (MacKerron et al., 1999). This is not to say that IPM cannot be made to work on broad-acre crops. If the correct research is fi nanced, done, and translated into practice, then IPM is possible. As an example of what can be achieved, a highly successful programme for management of the whitefl y B. tabaci was implemented on cotton in Arizona in 1995 (Naranjo and Ellsworth, 2009a,b). The programme relies on decision support tools based on pest sampling and economic thresholds for the targeted application of selective insecticides, including insect growth regulators such as bupro- fezin and pyriproxyfen. The use of these insecticides controls outbreak popu- lations of the whitefl y and preserves natural populations of arthropod predators, which typically consist of about 20 different taxa and which sup- press the whitefl y population below the economic threshold for up to a year after spraying (Naranjo and Ellsworth, 2009a,b). The system has now been integrated with the planting of GM Bt cotton for control of the principal lepidopteran pest, pink bollworm, Pectinophora gossypiella. It has resulted in a 70% reduction in the use of foliar insecticides together with control cost savings of over US$200 million in the 14 years from 1995 to 2009.
Integrated pest management in developing countries
Farmers in developing nations face different constraints and opportunities compared with their counterparts farming in industrialized countries. Sub-