Reducing Postharvest Losses
In the OIC Member Countries
25
Wheat postharvest losses
Wheat is grown under diverse climatic conditions across much of the world and has been the
staple food of the major civilisations in Europe, Asia and North Africa for 8,000 years. Wheat is
used to produce a wide variety of food products, and animal feeds, starch and ethanol.
In Pakistan, significant international development attention (e.g. by the World Bank, CIDA) was
focused on large-scale public sector grain storage of wheat and rice during the late 1970s-
1990s. During the 1980s, ~70% of the grain produced in Pakistan was retained at the farm and
market level, while the Government procured about 30% which was then stored in Provincial
Food Departments, PASSCO (Pakistan Agricultural Services and Supplies Corporation) and
RECP (Rice Export Corporation of Pakistan) (Alam & Ahmed, 1989). The dry climate during the
procurement season in Pakistan, means wheat was delivered by farmers to buying centres
sufficiently dry enough for safe storage (e.g. 8-9% moisture content) (Agroprocess, 1985).
Insect pest management in the large-scale stores typically used the fumigant aluminium
phosphide, with some residual spraying of contact insecticides such as Malathion or Actellic.
However, Alam and Ahmed (1989) confirmed the suspected widespread resistance to
phosphine, Malathion, fenitrothion and Actellic in Pakistan amongst the key storage insect pest
species Tribolium castaneum and Rhyzopertha dominica . The study recommended that urgent
improvements (e.g. use of fumigation sheets or non-leaky go-downs, correct dosage of
phosphine, fumigation to be conducted only by trained staff, monitoring of insect resistance,
improved hygiene in warehouses, research into insecticidal admixtures for use as an
alternative control strategy) were required in the phosphine fumigation practices to prevent
further resistance developing and phosphine becoming a non-toxic gas to major insect pests of
stored grain, as few alternative treatments existed. Chaudhary (1980) carried out
comprehensive studies on postharvest losses of food grain in all the four provinces of Pakistan.
PHL included losses incurred during harvesting, threshing, cleaning, drying, milling, storage,
processing, cooking and consumption. That study found through guestimates that the
aggregate PHL in Pakistan were 15.3% in wheat. Laboratory screening of botanicals such as
Azadirachta indica and Ricinus communis leaves applied at 5-8% ratio (w/w) slowed grain
weight loss during storage with insect pests, and prevented Tribolium castaneum from
multiplying as rapidly as in the control (Haq et al., 2005). Wheat varieties have been screened
for their resistance to Angoumois grain moth, Sitotroga cerealella (Shafique et al., 2006). Other
unquantified PHL are linked to millers washing grain before milling, and then not re-drying it
down to the required moisture content, which enables the miller to ship out the ‘required
content of flour’, but due to the high moisture content the keeping qualities of the flour are
reduced (CIDA, 1980). The various Pakistan wheat PHL studies report overall weight losses of
1-25%, and are presented in Table 5.