Types of control measures

Physical and mechanical methods:

a) Drying and disinfestation:

Generally, all agricultural commodities need to be dried to safe moisture level, below 11-12%, prior to storage. Crops are usually harvested at high moisture content to avoid shattering losses. Solar drying of legumes can be done on cemented platform, mat, jute cloth or metal sheets. If grain temperature is increased up to 60°C and maintained for 10-15 minutes, all live stages of pulse beetle present in pulses are killed. Solar absorbance surfaces can effectively be used for disinfestations of pulse grains by raising the grain temperature.

b) Reducing intergranular Space:

Adult pulse beetles, being very weak and having a short life, cannot move in grain mass and are restricted to top 15 cm layer. Even the adults emerging out of the infected material cannot move in the inter-granular space and could die before mating. The inter grain space varies according to size of different pulses. Movement of adult pulse beetle can be prevented by placing a 7-10 cm layer of dry sand at the top of grain mass. Dry activated clay can also be used for the purpose. To prevent mixing of sand or clay with the material, a paper or polythene sheet can be placed on the top of surface of pulse grain and then sand or clay is placed.

c) Coating with clay or oil:

Small quantities of pulse produce are kept at farmers’ level for consumption or seed purpose. The quantity ranges from 10-100 kg and kept in mud container. The pulse can be treated with clay (a) 1-2% clay uniformly mixed with whole grains and kept in closed container. Vegetable oils can also be used to prevent pulse beetles. Non-drying oils, such as castor, niger, sesame etc., are preferred for the purpose. A dose of 0.5-1.0% is mixed with the whole grains to be stored. The insect stages already present before treatment, would survive. But application of oil will prevent laying of eggs and/or larvae hatching on grain surface and the insects would be killed before entry into the pulse. Neem oil has also been found effective @ 2-5 ml/kg to prevent insect activities.

d) Use of improved storage Structures:

Moisture proof, air tight, low cost and low thermal fluctuation structures have been designed as an improvement over old traditional structures. Some of such structures are Pusa bin, Pusa kothar, Pusa cubicle and improved bamboo basket. These structures were found effective for chickpea, lentil, pigeonpea and mungbean in humid and dry regions. The seed retained very high germination and insect damage was less than 1%. Use of these improved structures in keeping small bags as moisture proof facility has made them quite acceptable at farm level storage. Metal bins up to 1 tonne capacity are used for storage of seed legumes in dry regions. Bamboo basket pasted with mud and kept at high place also serves the purpose of pulse storage. Coal tar drums and biscuit tins can also be used with some modifications. The use of polythene lined bags to retain low moisture is found useful. For non-airtight structures, fumigation is often required which is usually not feasible under rural setup.

e) Air tight storage:

maculatus and C. chinensis infested mungbean subjected to air tightness results into check in insect population build-up. Accumulation of carbon dioxide and depletion of oxygen levels adversely affects the insect growth. Incorporation of eucalyptus and mint oil in airtight conditions results in quick arrest of infestation and ensure better protection in small quantity of legumes.

Chemical methods

a) Treatment of grain with contact insecticide:

Most of the physical methods suggested earlier may not give total insect control. Application of chemicals, therefore, sometimes becomes essential for complete insect mortality and prevention of insect growth. It features two broad types of treatment:

b) Treatment by contact insecticide

c) Treatment by fumigation:

This consists of covering the grain with a film of insecticide that acts on contact with insects, with effects that vary in rapidity and persistence. These products come in various forms (powders for dusting, powders to be mixed with water, liquid concentrates or fumigants) that dictate their techniques of application. For grain that is to be stored in bulk, the insecticide is incorporated directly into the grain by spraying before the silos are filled. For storage in bags, previously cleaned grain is mixed with powder or sprayed before bagging. In order to avoid re-infestation of grain stored in bags, further repeated dustings or sprayings are carried out while the bags are being stacked and during the storage period. The machinery used for dusting grain can range from the simple mechanical duster to motorized dusters, however, with this type of equipment, the grain is not treated uniformly, some areas receiving more dust than others. Spraying can be mechanical (pressure sprayer), pneumatic or thermal, and provides a better distribution of the product over the grain. In big storage centres, in order to obtain an even more regular distribution and a good coating of insecticide, the grain is fine-sprayed by a compressor equipped with a mist nozzle. Although contact systems of treatment are certainly effective on fully developed insects, they have little or no effect on the eggs or larvae. Furthermore, some residues of the product, though not highly toxic, may linger in foodstuffs.

d) Treatment of grain by fumigation

Fumigation is a treatment that rids stored grain of insects by means of a poisonous gas called a fumigant. This substance, produced and concentrated as a gas, is lethal for specific living species. Unlike contact powders, the fumigant penetrates to the interior of the grain mass and reaches the largely invisible incipient forms (eggs, larvae) developing there. Fumigants spread throughout the area where released, therefore, used in totally sealed enclosure. Thus, when grain stored in bulk is fumigated, the bins must be perfectly airtight. For grain stored in bags, the usual method is to cover the bags with a tarpaulin whose edges are sealed to the ground or the walls. The effectiveness of fumigation depends, on the one hand, on the actual concentration of the gas and, on the other, on the length of time during which the grain is fumigated.