Alternatives to Methyl Bromide; IPM in three typical danish flour mills 3. Results3.1 IPM in the mills 3.1 IPM in mills Although accepted as a common method (Mills & Pedersen, 1992; Kenkel et al., 1994), IPM in a flour mill is quite complicated. IPM, in the strictest sense of the term, includes the establishment of thresholds, at least the economic injury level. This is difficult to establish in a flour mill as it has neither been possible to measure the size of the pest population nor to decide the economic damage caused by an actual population size. This means that IPM strategies in flour mills may, to a much higher degree than in other stored product areas, be dependent on a strategy, which includes a number of preventive elements. Implementation of IPM Application of IPM strategies in flour mills will differ from country to country; methyl bromide is used as a fumigant in most parts of the world, and current IPM practices in flour mills also include a reliance on fumigants, especially methyl bromide (Kenkel et al., 1994). Nevertheless when the use of methyl bromide is phased out, it will be necessary to implement IPM strategies without its use. These strategies have to become much more detailed and effective, compared to previous ones, in order to constitute a pest control system that can function without any reliance on methyl bromide. Traps The population sizes of the pest species are a central question in all IPM programmes. In a flour mill it is not possible today to make a common sampling of the pest species, and other indirect measurements must be used. Concerning the two main pest species. The Mediterranean flour moth Ephestia kuehniella Z. can be caught in pheromone traps whereas the confused flour beetle Tribolium confusum Duval. is normally counted during inspections as sticky traps for this species are not normally are used in Denmark. Both methods are indirect measurements of the population size, and the measures are heavily dependent on many factors, e.g. temperature. Complaints In mills it is very difficult to estimate the economic damage caused by the insects. The actions taken against insects are normally on a preventive basis and are based upon previous experience. One measurement of damage is the number of complaints, this can be considered the most important measure for the mills. Generally complaints from larger customers, bread factories etc. do not occur because of the general quality assurance systems and the fast rate of product usage in these systems. Complaints to mills tend to come from domestic consumers who have found insects in a small bag of flour produced several months earlier. This has the consequence that an increase in numbers of complaints can be related to circumstances at the mills in the past or to circumstances at the consumer, and therefore this measure can be difficult to use, especially if pest control procedures have been altered. As the economic injury level is at present difficult to establish in flour mills, it makes further demands on the evaluation of the IPM systems. At present one way to manage insect pest infestations in flour mills without reliance on fumigants will be to establish management systems which are designed to continuously suppress the development of pests where and when problems are encountered. At the same time it is also necessary that the system works on a preventive scale. Further the actual control procedures must be as detailed as possible to prevent any problems from escalating, this being the most essential demand, which can be made on the IPM system. IPM is not a static system; new pest problems will arise, buildings and machinery are changed, and procedures are changed in order to improve the IPM system. The description of the IPM system in the following is how the systems were carried out at the mills in 1998. 3.2 General comments on the situation in Denmark The actual use of the different elements in IPM, will be a reflection on the conditions at the mills and demands and expectations put on by the surrounding community. It seems that the public in Denmark are very concerned about residues of pesticides in food, and the interest in food produced by the organic concept has increased very fast in recent years. As the number of pests in the final product can be a reflection of the amount of pesticide used in the mills, there seem to be two conflicting expectations in the public. IPM could be a way to comply with both of these expectations, although the removal of methyl bromide could increase the use of residual insecticides. As in many other countries most Danish mills are situated in older buildings, which partly explains some of the pest problems, timber structures and wooden floors with several layers and cracks, are perfect harbourages for insects, and are very difficult to clean. In Denmark the milling companies operate in a very pressurised market with low flour prices. In 1998 the price for 100 kg of flour in bulk transport would be around 190 DKK. This has the consequence that the construction of new mills is not under consideration, and further that expensive elements of IPM only are accepted if they are considered of major importance. The mills in Denmark have used pheromone traps since they became commercially available. The mills are familiar with the use of these traps and have experience in using the trap data for analysis. Chemical treatment In Denmark chemical treatment against pests in flour mills consist of general surface treatments with deltamethrine or chlorpyrifos. Pyrethrine is used against moths, and local fogging units with pyrethrine are used in areas where special problems exist. All quoted prices are in DKK. Around 15 % of the amount paid to the PCO’s is expenses for insecticides. For the time being neither heat treatments or freeze-out during winter are used in Danish flour mills as IPM components. 3.3 The mills 3.3.1 Mill 1 It has a capacity of handling 100,000 tonnes of grain per year. In 1997/98 the mill was rebuilt and most of the milling equipment was replaced. During the period 1993-97 the mill has only been partly fumigated once. Only a small fraction of the production is sold in consumer packaging. Table 1:
*) Estimate. Pest species The main pest species in this mill is T. confusum. Minor pest problems occur with E. kuehniella. Tenebrio molitor, Sitophilus granarius and psocoids can be found near the grain storage and near the grain intake at the mill. The mill is certified by the ISO 9002 system. The pest control situation has been managed by increased efforts in identifying infestation places and dealing with them. Shutdowns in production are normally for 4 hours once a week. PCO The pest control situation is placed in charge of a private PCO. The contribution from the PCO consists of eight annual inspections, during the summer time at least once a month. Further the PCO will always be consulted when pest problems are encountered. During these visits the traps are emptied, and the whole mill is inspected thoroughly. A total of 43 pheromone moth traps is used, more traps are used now and then to locate an infestation. All the relevant windows at the mill are secured with insect-proof nets. The collaboration between the PCO and the mill production manager is very detailed and can be characterised by a quick response. Sanitation The cleaning is divided into daily, weekly, monthly and quarterly cleaning procedures, these procedures are documented and to some extent also controlled. If special problems occur, hired cleaning personnel are used. If necessary the machinery is stopped for 4 hours each week dismantled and cleaned inside. Grain storage The mill has a storage capacity of 10,000 tonnes of grain. The grain store, which is situated 1 km away from the mill, is not monitored continuously. As a rule the grain inside each cell is moved every 6 weeks. The grain will be stored for at least 2 weeks, and the storage time varies greatly - up to 1 year - depending on the actual production. Flour silos The flour silos at the mill have a total capacity of 3,000 tonnes of flour, this means that the storage time in silo is very short, about a week or less. The flour silos are normally emptied and inspected once a month. The mill has had problems with flour accumulation on the sides of the silos. In order to find a solution to this problem they are altering the structure of the bottom of the silos. Final sieving The wheat flour is sieved through mesh size 280m m when leaving the mill unit. The flour meant for bags is further sieved through mesh size 280m m before it enters the packing machinery. The material from the sifters is not transported directly back to the mill machinery, it is drawn off in sacks and inspected for presence of insect pests. The control on the material from the sifters is not registered and cannot be used in an analytical way. The mill has the policy that complaints are not normally accepted. Only very rarely does the mill get complaints on its products. The mill is favoured by the small amount sold in consumer package. In one place a local fogging unit with pyrethrum is used at regular intervals, to alleviate moth problems. 3.3.2 Mill 2 This mill is the smallest of the three mills, it handles 85,000 tonnes of grain per year. It does not produce flour in domestic consumer packaging. Table 2. Five years’ statistics on economics (DKK)
of insect pest control
*) Estimate. Pest species The main pest species in this mill are T. confusum and E. kuehniella. In a small area of the mill there is an occurrence of Tenebrioides mauritanicus, and until now it has not been possible to eradicate this pest. Outside the milling area there is occurrence of Tenebrio molitor. The mill does not normally run in the weekends. In the mill buildings some old wooden silos not in use sometimes cause problems with insect pests. The IPM system is a combination of rules and procedures, some of which have been established during the quality assurance system ISO 9002. The pest control has been managed by increased cleaning efforts, including stops in production. These shutdowns in production, in which the main part of the running machinery in the mill is cleaned inside, are carried out 3-4 times annually. PCO The pest control is placed in the charge of a private PCO. The contribution from the PCO consists of eight annual inspections, plus presence at the four annual cleaning operations. During these visits the traps are emptied, and the whole mill is inspected thoroughly. A total of 47 pheromone moth traps is used. Most of the relevant windows at the mill are secured with insect-proof nets. During 1998 the mill have introduced a notice board where the staff can register any observation of pests, in order to improve the information supplied to the PCO at the time of inspection. Sanitation The cleaning routine consists mainly of cleaning on a full-time basis performed by two persons. The 3-4 annual cleaning procedures are done in 30-48 hours requiring around 150 man-hours. Grain storage The mill has a storage capacity of 10,000 tonnes of grain, separated in a number of cells, in which the largest cells are monitored continuously. The temperature reaches around 5°C during the wintertime. Flour silos The flour silos at the mill have a total capacity of 1,400 tonnes of flour, the daily storage being less, this means that the storage time is very short (about 2-3 days). The flour silos are emptied once a year, but the mill can increase the frequency of this routine. Final sieving The wheat flour is sieved through mesh size 340 m m when leaving the mill unit. The wheat flour, which is bagged in sacks, is sieved through 280 m m before entering the final silos. The material from the final sifters is tapped in sacks and inspected for insect pests. The mill will accept less than 1 complaint per 300,000 produced units. Over the years the mill has only received very few complaints, probably because it does not produce flour in consumer packaging. 3.3.3 Mill 3 It is a large modern roller-mill, handling 150,000 tonnes of grain per year. In 1998 the mills were provided with newer machinery, and a central vacuum cleaning system was also established. The last time the mill was fumigated with methyl bromide was in 1996. The main alternative to the use of methyl bromide, has been an improvement in the sanitation procedures. More resources have been allocated to sanitation procedures during recent years (Table 3). According to the mill, the expenses for pest control have further increased in 1998. During the period 1993-97, production has decreased by around 10%. Table 3. Five years’ statistics on economics (DKK) of insect pest control in mill 3.
*) Estimate. The mill is situated in old buildings containing wooden floors and old timber structures. A few old wooden flour/bran silos are also present. This creates well-known problems in many places, areas that are difficult to clean, and also a number of places, which are inaccessible, thereby causing hidden infestation of pests. Pest species The Mediterranean flour moth Ephestia kuehniella and the confused flour beetle Tribolium confusum are the two main pest species; only minor and local problems occur with other pest species, including Tribolium destructor, Plodia interpunctella and Tenebrio molitor. The IPM system is a combination of rules and procedures, some of which are established during the quality assurance system ISO 9002. The mill is also approved by the environmental management system ISO 14.001. The pest control has been managed by increased efforts in cleaning, including stops in the production. The shutdowns in production, in which the main part of the running machinery in the mill is cleaned inside, were planned to take place four times annually, but this goal was not obtained in 1998. PCO The pest control situation is managed by a private PCO. The contribution from the PCO consists of eight annual inspections, plus assistance at the four annual cleaning operations. During these visits the traps are emptied, and the whole mill is inspected thoroughly. A total of 84 pheromone moth traps is used. There are normally 1-2 traps in each room, depending on the size and equipment. All the relevant windows at the mill are secured with insect-proof nets. The catches of E.kuehniella together with the number of observations of T. confusum are evaluated against former years’ catches and observations. Sanitation The cleaning efforts consist mainly of one person who takes care of the cleaning full-time. More personnel are used when needed, especially in the four annual cleaning procedures, where hired cleaning personnel are also used. Grain storage The mill has a storage capacity of 25,000 tonnes of grain. The temperature of some of the grain silos can be monitored continuously, but more importantly, competent personnel perform the supervision of the grain stores. Heavily infested grain is rejected and the few kilograms of grain, which are inspected, possibly will not show a light infestation. In Denmark the mills do not encounter problems with insect pests in incoming grain. The grain is stored for at least 2 weeks, and the storage time is very variable - up to 1 year - depending on the actual production. Imported American wheat is the grain type, which is kept in store for the longest period. Flour silos The flour silos at the mill have a total capacity of 2,700 tonnes of flour, this means that the storage time will be very short ( a week or less). The wheat flour is sieved through mesh size 112/250 m m when leaving the mill unit. The material from the sifters is not continuously investigated for the presence of insect pest, and the material is transported directly back to the mill machinery. The wheat flour is further sieved through 224/355m m before entering the final silos. It is the goal that 100% of the wheat flour is sieved through 224m m at this stage. For the moment there are no procedures for cleaning or inspecting the flour silos, but the mill will be investigating how an effective control can take place. The mill accepts less than 1 complaint per 300,000 produced units. Flour moths in consumer products cause almost all of the complaints to the mill. In one area containing bran silos, a local fogging unit with pyrethrum is used at daily intervals, because of an inexpedient building structure causing moth problems. In the area with packing machinery a fogging unit with pyrethrum has also been used during a period with moth problems. With success the mill has tried to fill up dead ends in machinery with food grade chalk in 1998. 3.4 Possibilities of evaluating IPM programmes As it is not possible at present to establish the economic injury level for pest species in flourmills, there is a need for investigating how the effectiveness of IPM programmes can be evaluated in a sound way. With the actual procedures in the mills, the possibilities are rather limited. Within the present IPM system four parameters could be used to evaluate the effectiveness over the years. These four parameters are: Pests 1) Estimation of pest populations This estimate would be very valuable as the amount of resources allocated to pest control could be evaluated against the number of pests recorded. Considering the two main pest species, the possibility of doing this seems minimal. The best estimate is achieved through E. kuehniella, where the male moths can be caught in pheromone traps. Pheromone traps are a perfect tool in locating areas of infestation, but used as a population estimate the measure is more problematic due to its indirect nature. With regard to T.confusum the situation is even worse. The infestation by this species often occurs inside the machinery or in inaccessible places, and the numbers are normally estimated by trap catches or counts of living specimens during inspections. The commercially available traps are not considered effective in Danish mills, and the numbers counted during inspections will always be a very subjective measure. Complaints 2) Number of complaints This parameter is essential to the mills as all actions against pests are carried out in order to keep the number of complaints as low as possible. The main limitation is that the measure is related to circumstances in the past. Further, the mills agree that it is impossible to put a value on a complaint. Unfortunately the measure will also be dependent on conditions outside the mills. Insecticides 3) Amount of insecticides used If not used in a preventive way, this estimate will tell something about the demand each year for a chemical solution to pest problems. It is not a perfect measure as its size is very dependent upon the use of non-chemical solutions, and furthermore the action of the various insecticides is variable and not comparable. Amount of resources 4) Amount of resources allocated to pest control This parameter will first of all estimate on how much is considered necessary to spend on pest management in order to maintain the quality level. As it cannot be related to pest population size, it cannot be used in an analytical way. None of the objectives seems perfect, and this might be one of the most important factors objecting to the present IPM systems. The success of using IPM in flourmills will depend on the overall effectiveness in keeping pest numbers at acceptable levels. In order to achieve this, the mills are forced to increase the efforts in a continuous improvement of the different components of the IPM systems. Although the present estimations of pest populations are not perfect, they have to be used when evaluating the effectiveness of new initiatives. 3.5 Comparison of the mills Differences between mills The three mills in the present investigation are believed to be representative for Danish flour mills. Although flour mills, seem identical, differences will always be found in both production and design of the interior of the mills. Apart from their size the most pronounced difference between the three mills is that mill 3 has a much larger part of the production in consumer packaging (Table 4) and that its grain storage capacity is higher. Nearly half of the production at mill 2 consists of rye products and special flours. Further mill 2 does not make use of its full production capacity, having the effect that this mill has a much better opportunity to plan shutdowns in production. Mill 2 is also the one mill, which uses the largest amount of resources in pest control. Table 4. Overall comparison of three Danish flour mills.
During the period 1993-97 Table 1 to 3 yield an impression of the overall cost of insect pest control in the three mills - the value of production stops is not included in this estimation. Around 5-10% of the total amount spent on insect pest control has been used on fumigation. Differences in success The mills have not managed the ban against methyl bromide equally successfully. In one of the mills (Mill 1) methyl bromide has only been used once for a spot-fumigation since 1993, so for a long time the mill has managed its pest control without reliance on methyl bromide. This mill has always had a very close collaboration with its PCO, and is also the mill with the fastest response to increasing pest populations. The reconstruction of the mill in 1997/98 has further removed some inexpedient building structures, which had caused problems in the past. Mill 2 has managed removal of methyl bromide very well. It has primarily improved its sanitation programme, and until now the mill has been able to manage its pest problems in this way. One of the mills (Mill 3) has serious problems with its building structure, and so far it has not found a way to manage these problems. In table 5 selected components of the IPM systems are compared. Table 5. Selected element of IPM systems in Danish flour mills.
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