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Combining store hygiene and grain management practice with physical control of moulds and pests to maintain quality - CE0314

Project Code: CE0314

Funded By Department for Environment, Food and Rural Affairs

Lead Research Centre
Central Science Laboratory,
Sand Hutton

Abstract of Research Proposal
Projects CE0309-13 in the MAFF grain storage programme focus strategically on particular topics addressing improvements in storage practice and reductions in pesticide use. There is also a need to combine emerging ‘best practices’ from these areas and with applications under test by HCGA and the industry to keep overall grain storage strategies up-to-date. This project is designed to provide this integration and the basis of improved decision support for transfer to the industry in conjunction with HGCA.
The evolution and validation of cost-effective strategies for protection of grain should permit reduction of pesticide use and substitution of organophosphates while maintaining and increasing market quality. To accomplish this, good technology transfer is necessary. Much of the research is aimed at improving the decision making in stores directly or by, e.g. the ‘Integrated Grain Store Manager (IGSM) decision support system.
Results and feedback from MAFF and related work will form the basis for updating strategies and decision support for grain storage and encouraging use of cooling and drying with modified atmospheres to reduce pesticide use.

Summary of Objectives
1) To devise means of laboratory and farm-scale experiments, options for storage strategies which reduce pesticide usage, by combining controlled atmospheres, cooling and drying, for instance by determining the feasibility of reducing drying costs by storage grain at elevated moistures under controlled atmospheres.
2) To integrate information from MAFF projects and feedback from HGCA funded applied work into an evolving storage strategy based on validating grain storage strategies in commercial scale experiments. The validated information will be incorporated into updates of current decision support software.

Summary of progress from 98/99 annual report:
A farm scale experiment was set up to show differences in pest populations developing in grain cooled to the old recommendation of about 10-15oC, and grain cooled to 0-5oC, which is the current recommendation.

Mite and insect numbers in six cooled 3m deep bins of feed wheat at about 15% m.c. The grain was delivered at 16-18oC so three of the bins were left uncooled. The other three were continuously cooled, using 0.03kW fans, connected to a differential thermostat set at 6oC. Monitoring of insect numbers will be carried out using 9 surface - placed PC traps, and 5 probe traps at each of 1m and 2m depths. Mite numbers will be estimated by examining sievings from five 200g spear samples at each depth and temperatures will be measured by thermocouples at 3 depths, attached to hourly-recording data loggers. Initial populations of S. granarius, O. surinamensis, A.siro and L.destructor at 0.8kg, 0.5kg, 0.9kg and 1.7/kg respectively were achieved by introduction into each bin at 3 depths and 9 columns.

The initial grain temperatures was 14-16oC. By the first trapping/sampling exercise in December the cooled bins were 6-7oC, but the other bins had cooled naturally to 9-12oC. By the next sampling in January, the cooled bins were 6oC but the other bins were only 2-3oC warmer. By February there was no difference and all bins were about 6oC. Mean moisture contents at the surface of all bins peaked in January at just over 17% and fell to 15.6% in April. Beneath the surface, mean moistures were between 1.5 and 15.0% Acarus peaked at a mean of 174kg at the surface of the warmer bins in March and about 18kg in the warmer, but were usually less than 10kg at 1 and 2m. Lepidogyphus rose from a mean of about 3kg to 33kg in the warmer bins but fell from 133kg to 3kg in the cooler bins. Elsewhere, numbers were usually less than 20kg. Oryzaephilus trapped at the surface peaked at 18 in February in the warmer bins and 70 in January in the cooler bins but by April, none were found. At 1m numbers fell from 187 to 0 by March in the warm bins and from 97 to 0 by February in the cooler bins. At 2m, numbers fell from 23 to zero in the warmer bins by March and from 58 to zero by February in the cooler. Sitophilus trapped fell from 42 to 2 between November and February in the warmer bins and from 23 to 2 in the cooler. At 1m and 2m, average catches in the traps were usually less than 3.

A commercial scale experiment was designed to establish whether surface mite populations can be prevented by a top-dressing of a silcaceous dust under fluctuating UK winter conditions as well as to determine the fate of insects moving away from a cooling front.

Mite and insect numbers were compared in four quadrants of a cooled 3m deep floor store, approx. 9.9 x 8.75 holding 250 tonnes of feed wheat at about 14%m.c. Two will be top-dressed with ‘Protect-it’ a silicaceous dust at 2g/kg, raked in to 0.3m. Monitoring of insect numbers was carried out using 12 surface PC traps, and 12 probe traps at 1m. Mite numbers were estimated from nine 200g spear samples at each of 1m and 2m depths and temperatures were to be measured by two rows of thermocouples in each quadrant at the surface, 1m and 3, depths, attached to hourly-recording data loggers. The grain was cooled under the existing underfloor aeration system. Initial populations of S. granarius, A.siro and L.destrictor at 0.8kg, 0.3kg and 0.4kg were achieved by introduction at 3 depths and 10 columns in each quadrant.

Grain temperatures started at 13-16oC at the start of November, were already below 10oC one month later and 4-6oC in January Mean numbers of Sitophilus in the treated quadrants were one-fifth to one-tenth those in the untreated, except for the initial sampling when they were about 40x higher!

Surface moistures only peaked at about 16% in February, too low and too late to permit significant mite infestations, so samples of the surface treated grain were used for laboratory bioassays.

Five 1.5kg samples were scooped from the surface of each treated and untreated quadrant and used to set up 50g insect and mite bioassays, with the remainder used to determine dose variability and grain percentage dockage. Each sample provided one of five replicates for each species. Bioassays were carried out at temperatures of 10, 15 and 25oC and moisture contents of 16-17% for 4 species but only if they were able to complete life-cycle development. Bioassays results were used to calibrate mean percentage population inhibition. For the mite tests to date, treatment achieved 100% inhibition for both Acarus siro and Lepidoglyphus destructor at all temperatures with the exception of the latter at 25oC, where a few mites survived treatment giving 99.999% inhibition. For the insects, 100% inhibition was achieved for Oryzaephilus surinamensis but developing stages of Sitophilus granarius escaped treatment resulting in inhibition of 73.2%. However this reduction in population compared to the controls showed that the treatment clearly affected the number of eggs laid. Further studies showed that the mean percentage dockage for all quadrants was high at 6.63% and very variable, ranging from 3.16-17.57%. Mean ‘Protect-it’ doses for the treated quadrants was 2.01 g/kg with no significant difference between the two quadrants. However doses across the surface were very variable and were estimated to range between 0.55 and 3.46 g/kg. Although treatment was very uneven there was no indication that this affected efficacy.

Storage under ‘modified atmospheres (MA)’ might offer an alternative to drying of grain or be used as a method of dealing with ‘harvest backlogs’. An experiment therefore compared the growth of natural inocula of grain storage fungi on five replicates of each of 40g wheat at 75, 85 and 90% equilibrium relative humidity (16, 17.5 and 18.5% m.c.) under 0.5% oxygen (MA) and aerobic conditions. The r.h. was maintained by conditioning the stream or standing air using saturated salts of KOH solutions. Fungal growth was monitored visually and when growth became apparent under aerobic conditions, dilution plate assessments were carried out to provide quantifiable comparison of the fungal numbers. The fungi were incubated at 25oC on 2 media: 2% malt + chloramphenicol for yeasts and moulds: DG18 + chloramphenicol for the more xerophilic fungi. The experiment was carried out once and then been repeated because of problems maintaining the required e.r.h. in the MA grain. Mould counts were lower in MA grain but the fungi were not completely inhibited. For instance, at 85% e.r.h. total (log) storage counts were 5.6 under aerobic conditions but only 2.8 under MA. The predominant fungus was the xerophilic Wallemia sebi. More conventional fungi such as Penicillium spp and members of the Aspergillus glaucus group were just one power of ten lower in MA than aerobic conditions.

The observations on surface moisture content in the farm and commercial test contribute to HGCA Project 0075/01/97/01A on limiting uptake to prevent mites.

Added value is being provided into this project by EU project, FAIR CT97 3648, ‘Building a decision support system for malting barley storage’. The activities include modelling pesticide residue and efficacy decline at 10 and 35oC and carrying out farm and commercial-scale validation trails of malting barley storage strategies. This allows additional data and conclusions to be incorporated into this project.


Start date: 01/04/98
Completion date: 01/04/02

Project Documents
• Final Report : Combining store hygiene and grain management practice with physical control of moulds and pests to maintain quality   (1673k)
Time-Scale and Cost
From: 1998

To: 2002

Cost: £379,523
Contractor / Funded Organisations
Central Science Laboratory
Grain Pests              
Pest and Weed Control              
Pest Control              
Plants and Animals              
Fields of Study
Arable Crops