Pre and post harvest losses in wheat
QAMAR-UL-HASSAN SIDDIQUI & MUHAMMAD SARWAR
Nuclear Institute of Agriculture (NIA) Tandojam.
Basically, Pakistan is an agricultural country and therefore, all roads to the nation’s socio-economic progress and prosperity lead through a modernizing agricultural and a concurrent effort at industrializing particularly based on the home grown raw materials. Being the dominant sector of the economy, agriculture contributes 25% to gross domestic product (GDP), employees 44% of country’s working force and contributes substantially to export earnings. Major crops such as, wheat, rice, cotton and sugarcane account for nearly 89% of value added in major crops. The value added in major crops accounts for 41% of value added in overall agriculture. Thus, these four major crops, on an average, contribute 36.5% to the value added in agriculture. While, the minor crops such as pulses, potato, vegetables, fruits etc. account for 10% of value added.
Our major objectives are to increase the production, either by increase in areas or productivity. Acreage increase has limitations like scarcity of water and precariously established balance in land allocation between equally important cash crops. Any disturbance in this balance may cause another crisis, more or less of equal severity. Hence, productivity enhancement along with pre and post harvest losses management are the only alternative and is viable meaningfully, because of the existing differential between the national average and the potential. The low national average is due to the fact, that three-fourth of the farmers do not use proper technological management in adequate quantity and proper combination of local available resources.
Wheat (Triticum aestivum L.) belongs to the Gramineae family. In Pakistan wheat is the most important food crop. The largest cropped area is devoted to wheat, which is about 8.5 million hectares and the quantity produced is more than that of 2.9% to GDP. The unprecedented drought conditions in the country have severely affected the wheat crop. Firstly, the area under the crop declined by 3.8% from 8463 thousand hectares to 8137 thousand hectares in the year 2000-2001. Secondly, according to the preliminary estimates, the size of wheat crop is 12.1% lower than the last year, declining from 21.079 to 18.535 million tons. The area, production and yield are 8306.6 thousand hectares, 18237.6 thousand tons, and 2196.0 thousand kg per hectare, respectively. On the other hand, its procurements, releases and stocks are 8582.0, 5537.0 and 3526.0 thousand tons, respectively.
Losses in wheat
Wheat is adapted to temperate regions, receiving annual rainfall of about 500-1200 mm. Higher precipitation causes lodging and diseases and interferes with field operations of planting and harvesting, so the yield is reduced. In rain fed areas, if rainfall occurs early, wheat can be planted in the last fortnight of October. Late planting of wheat can be done up to the middle of December, after which further delay in sowing reduced yield drastically. Wheat sowing however, after 20th November can cause a reduction of 15-20 kg per acre yield during each subsequent day. There are two critical periods, during which water stress reduces yield greatly; the period from the development of adventitious roots to the start of tillering, and the period from an thesis to the milk stage. According to an estimate the presence of weeds in wheat fields can reduce 14-42% of the produce. Thus, if 40 maunds of grains per acre are expected, it will reduce up to 23 maunds only. Seed rate for early, medium and late sowing varieties, should be 50, 60 & 70 kg/acre and any change in the seed rate causes substantial yield losses. Nitrogen and phosphorus fertilizers using ratio should be 1.5:1. Crops sown after rice and sugarcane or through tube well irrigated or sandy areas should be supplied with one bag of potash per acre, otherwise yield will adversely be affected.
Wheat crop is damaged by a large number of insects such as grasshoppers, crickets, aphids, army worms, while standing in the field. Grasshoppers and white ants attack plants during the seedling stage, they are more serious in rain fed areas. Aphids and army worms attack the crop in spring after heading, causing considerable losses while the crop is still standing in the field. These pests also eat away the ears, including awns, immature grains, and tillers, tender leaves in the central whorl of the plant and even the older leaves. Rodents cause little damage to the seedling and most of the damage is caused at the ripening stage. Early and late wheat crop is more liable to damage by birds. They eat the seeds before emergence or soon after emergence at planting season. Birds also damage the crop after the dough stage by eating the grain directly from the spikes and by causing some years to shatter completely.
Wheat is also attacked by a number of diseases that cause great losses to the quantity and quality of the produce. Rusts, smuts, powdery mildew and septoria are important diseases that reduce the yield of wheat in different parts of Pakistan. Powdery mildew sometimes attacks wheat in mountainous and sub- mountainous regions. Nematodes also infest wheat, in case of severe infestation, the seedlings may fail to come out of the soil, even if they grow, the infested plants remain stunted and give a shriveled unhealthy appearance. A variable number of grains in an infested ear head may produce galls, which are shorter and thicker than the healthy ones.
Although, they cause little mechanical injury to the plant root, yet their presence stimulate the formation of branched rootlets. The main root remains shorter or bunchy, bearing small galls. In areas, where termites or weevils impose economic problems, the crop should be sown after mixing granular insecticides with soil. If the attack of insects persists, the insecticides can be dusted on the crop. In certain fields, where heavy doses of N and P are applied year after year, symptoms of zinc deficiency may be noted. These symptoms appear on leaves as small white irregular patches. Rodents and birds damage can be reduced to greater extent by the presence of alternative crops, lack of shelter, scaring devices and poison baits. To avoid damage from diseases, resistant varieties of wheat should be grown; seed treatment can also be effective. Nematodes can be controlled by a suitable crop rotation. Gall nematodes can be controlled by separating the galls from the wheat seed by floating them on water in a tub.
Post harvest technology for wheat crop
A plentiful harvest of wheat is only achieved, when all necessary inputs are put together with appropriate production technology. It has been observed that majority of the farmers including progressive growers, who take keen interest in growing high yielding varieties and adopt high production technology right from selection of soil to the harvest of crop, ignore losses those occur at, and after harvesting of the crop. Both wheat grain and straw have tremendous economic value, and is consumed with great desire by men, animals and birds. Some losses at post harvest levels are discussed below:
1. Shattering: Shattering of grains from the arched occurs in the shattering susceptible varieties, before and after harvesting in the field. Substantial losses also occur during lying of wheat bundles and transportation from field to the threshing yard. The cultivation of shattering resistant varieties can be helpful in reducing these losses.
2. Over-drying: Over-drying of the harvested crops in the field, results in shattering and damage by rodents, birds, animals and sometimes by dispersing wind. It is recommended that the crops should be heaped after proper drying in the threshing yard.
3. Delayed threshing: Light to heavy losses may occur, if threshing is delayed. Untimely rains and fast winds may cause severe losses. It is recommended that threshing should be carried out without any delay. While, heaping the materials in threshing yard, it is recommended that earheads should face the centre, so as to prevent losses from periphery damage by animals etc.
4. Improper threshing yards: Improper threshing yard is also responsible for the deterioration of grain and straw quality and losses in productivity. It is recommended that the threshing yard, if not cemented should be at least clean thoroughly, even and free from soil cracks. Losses during threshing: Losses may occur during threshing, if
a) The crop at the time of heaping was not dried properly.
b) The functioning of thresher is not proper.
c) The inadequate skill of the thrasher opera to.
d) The wind velocity and direction of the thresher are not proper;
It is recommended that to avoid losses in threshing, due consideration should be given on the quality of thresher, skillness of the operator, wind velocity etc. Delayed threshing may result into, a)damage by rodents, white ants, birds and animals, b) damage by rains and wind, c) Insecurity from fire and occasional flood etc.
It is recommended that crop after harvesting should be heaped in threshing yard and the process of threshing be completed at the earliest. Losses may occur during bagging, if the quality of bags is not maintained. It is recommended that new gunny bags should be used, and if such bags are not available, then gunny bags in good conditions be used. In that condition, bags may be cleaned thoroughly for other seeds inside to avoid impurities and mixture. It is recommended that bags may be treated with some insecticides such as Malathion to get rid of residues of stored grain pests.
Wheat is to be stored by the producers, farmers and consumers in their homes and by the traders and official agencies in godowns. When this crop is harvested in the field, it is practically free from pest infestation. Grain often infested during the process of transportation, processing and storing.
As a pests of this grain, rodents (rats, mice), birds (especially sparrows) and insects are worth mentioning. Rodents including rats, mice and moles are responsible for causing enormous losses to the stored grains and besides feeding, they destroy a substantial quantity by spillage and contamination with their droppings, urine and body hairs. A rat is estimated to consume about 27 grams of grain daily; in this way they consume several million tons of wheat grain annually.
Sparrow, parakeet, crow, myna and pigeon are destructive and cause much damage by feeding and by causing the grains to shed in the storage.
They also visit the thrashing-floors to feed and use up quite large quantity of wheat. At the time of harvest, wheat grains should be dried to have their moisture contents less than 9 %, which is ideal for storage. Grains kept in damp godowns, absorb moisture from ground or atmosphere. The warm season and high moisture content of grain are highly conducive to proper development and multiplication of insect pests of stored wheat. The insects reach the grains either through the infested gunny bags, receptacles or through the storage of fresh grains in godowns already having infested grains. Within one season, they may destroy 10-15 %of the grains and contaminate the rest with undesirable odors and flavours. There are 4 insects viz., the meal moth, grain moth, rice moth and almond moth belonging to order Lepidoptera; Khapra beetle, red flour beetle, grain borer, gram dhora, mung dhora and rice weevil in the order Coleoptera and mites in the order Acarina.
The damage caused by these pests is the greatest during the monsoon season, when it is hot and humid. Only the larvae of these insects, cause damage by feeding on the grain kernels. The adults are active creatures, capable of short flights and fly about from one bin to another and spread infestation all around. Larval stages bore into the grain and feed on its contents, and about 30-50% of the contents are consumed. If infestation is severe, the devastation is completed, reducing the grain to a mere frass, the grains give out an unpleasant smell and present sickly appearance. Infested grains converted into flour have a characteristic off foul smelling odour.
As a result of destructive activities of stored grain mites, the capacity of wheat to germinate is lowered up to 54%. The most notable result is reduction in protein content. Mites raise moisture contents of the grain generating sufficient heat for the growth of infectious bacteria and fungi.
They contaminate the space between the grains with their dead bodies, cast skins and excrement, thereby hindering the circulation of air in the stock. Flour prepared from such contaminated grains has higher moisture contents, higher acidity and tends to stick together in addition to being cause of diseases. Such wheat flour has fusty smell, bitter taste and deteriorated baking quality.
Control of stored grain pests
Pakistani farmers are very hard working, they are busy all the time in growing tons of grains and fiber in adverse climatic conditions of heat and cold, but unfortunately still, we are not self sufficient in food even. Is it the fault of fortune? No. There are many factors responsible for it to which we are not paying attention. Among these factors non-availability of proper storage conditions is of prime importance.
Losses in storing: Improper storing results in losses.
It is recommended that wheat grain should not have the moisture content higher than 9-12%.
a) The wheat should be stored at some elevated place,
b) the store should have adequate air and sun light entrance,
c) the store should be cleaned and treated with some chemicals to avoid insect pest attack,
d) The store should not have the entrance place for foreign animals such as dogs, cats, birds, rodents etc. as that may spoil the quality and quantity of the stored grain,
e) Gunny bags in the store be placed systematically in lines,
f) After rainy season, the store should be fumigated and if possible, the grain may be sun dried to maintain the proper-moisture percentage.
g) And overall a continuous regular periodical examination of the store and grain is required.
h) Bhusa or straw is not less important than grain, care must be taken for its proper storage.
There are several methods to control stored grain pests, helping to check the spread of harmful insects and mites to markedly reduce their potential of infestation.
Some dangerous pests enter in the country along with seed and food grain imported from other countries. So, quarantine measures towards preventing the import of foreign pests should be very strict. The material to be imported should be subjected to laboratory test to detect any kind of pests at the point of entry.
2. Sanitation of stores
Stores should be cleaned. All cracks, holes, crevices etc. should be properly sealed. All granaries, machines and grounds of enterprises must be completely disinfected. All the post harvest wastes should be burnt or buried in soil.
3. Chemical control
Contact pesticides are commonly used on the surface of the floor of stores as dust or emulsion. Fumigants are generally used in hermetically sealed places. They are highly effective, if the necessary concentration is maintained over the required period of time. Among the various methods of controlling stored grain pests, most widely used are chemical methods.
4. Biological control
Lepidopterous pests of wheat can be controlled through natural enemies. Predaceous mites and parasites can control the stored wheat pests e.g. Trichogramma, can control the Angoumois grain moth successfully. In NIA, Tandojam, a biocontrol laboratory is rearing this parasite, but no regular experimentation has been carried out due to lack ofmanpower and facilities. Certain predatory mites, Ichneumonids, brachonid, chalcid, protozons and microbes act as predators and parasites of stored grain pests.
5. Resistant varieties
Research observations have shown that some varieties of different agricultural crops have grain resistant to insect pest attack. Such stock of resistant cultivars may be used to raise the varieties, highly resistant to the stored grain pest infestation.
6. Radiation control
Ionizing radiations have been used by the scientist to disinfest various stored items. Gamma radiation, X-rays, Cobalt and Cesium can be used to combat the storage pests.
7. Use of heat and cold environments
Temperature of 140°F, given for 10 minutes is lethal to most of the stored grain pests. Many insects are inactive below 50°F, grain stored from 40 to 50°F can escape insect infestation. Special precautionary measures should be adopted when grains are kept under temperature treatments as they are deteriorated rapidly.
For the control of bird pests of stored grain, measures should be taken to deprive them of their food and nesting places. For this purpose, covering windows and doors with wire screen, sealing holes &crevices, construction of granaries and warehouses in a way that there is no gap between walls where the birds could nest and rest, are of great importance.
Rodent pest can be exterminated by keeping the grain and grain products dry, rodents should be deprived of water and food, nesting places should be destroyed, all holes should be plugged with concrete and cement and rubbish should be removed regularly. Rats and mice can be caught by using man made traps and cages, and then be killed. Use of natural predators like cats and dogs are fatal to the rats but at the same time harmless to humans and pets. Most effectively and widely methods used to control rats is the use of rodenticides poisoned baits. Fumigation may be done in godowns and rodents burrows. Different combinations of controlling methods may be used suited to individual situation.