Management of storage pests in Sweet Sorghum

Management of insect-pests in bulk storage is a challenge in handling the post-harvest farm produce. Improper management, inadequate storage facilities and procedures may contribute to the loss of grain quality and decrease in the value of stored grain in the market. The loss of grain quality can occur from spoilage caused by molds, insects, rodents and other storage pests. The storage insect-pests not only consume grain but also cause heating, spoilage and reduction in grade if measures are not taken to manage them. It is possible to manage these insects in bulk storage by reducing storage temperatures or frequent inspections and by fumigations. Since insect infestation is a cycling problem, repeated use of chemical fumigants may cause problems more severe than insect contaminated grain. Enough care should be exercised in using fumigants since some can create serious residue hazards. Most of the fumtgants are lethal or acutely toxic to human beings at concentrations effective against insects and elaborative safety precautions must be observed at all times.

Amongst the different methods of insect-pest management, the following are the important methods that can help in safe storage of food grains at farmer’s level.

1. Preventive management measures

2. Curative management measures

1. Preventive Management Measures

The following preventive management measures are very important in overcoming the problems associated with insect-pest attack on the stored grains.

(i) Hygiene or sanitation:

Hygiene or sanitation is the first and foremost aspect in preventive management. To ensure proper hygiene, the following steps need to be considered.

• Threshing floor/ yard should be clean, free from insect infestation.

• It should be away from the vicinity of villages/ granaries.

• The harvesting and threshing machines need to be thoroughly cleaned before use.

• Trucks, trolleys or bullock carts, used for transportation of food grains, need to be cleaned and made free from insect infestation.

• The storage structures/godowns need to be cleaned properly before storage of newly harvested produce.

• All dirt, dust, rubbish, sweepings and webbings etc. should be removed from the dryers, stores and dumped/ destroyed.

• All the cracks, crevices, holes existing in the floors, walls, ceiling should be neatly and permanently plastered with mud or cement .

• Rat burrows, if existing, need to be closed with a mixture of broken glass pieces and mud and then plastered neatly with mud/ cement.

• White wash of the storage structure prior to the storage of food grains is very useful.

• The food grains should be stored in godowns, which are rat and moisture proof.

Proper stacking of bags also helps in grain protection.

(ii) Disinfestation of storage structures/ godowns:

Disinfection of the storage structures is yet another important preventive mode of managing insectpests.

There are traditional and scientific methods of doing it.

• Before use, the godown/ storage structure should be disinfected with approved residual insecticides preferably by spraying malathion 50% EC, with dilution of 1: 100 and applied at the rate of 3 lit/ 100m^2•

Curative Management Measures

These methods are followed when the infestation has occurred in the stored grains. The infestation of stored grain insect-pest can be managed by the following methods.

1. Non-chemical management measures.

2. Chemical management measures.

1. Non-chemical management measures:

Measures that do not use chemicals for the management of insect-pests of stored grains are:

a. Ecological measures:

The safety of stored grains from insect-pests largely depends on the following three factors viz.

i. Management of temperature

ii. Management of moisture content of grain

iii. Availability of oxygen

Temperature, moisture content in grain and oxygen are required for rapid development and multiplication of insects. By proper manipulation and management of these factors through design and construction of storage structures/ godowns and proper storage practices, ecological conditions unfavorable for attack by various insects can be created.

i. Management of temperature:

Temperature ranging from 20°C to 40°C accelerates the development of insects but above 42°C and below 15°C retards reproduction and development, while prolonged temperature above 45°C and below l0°C may kill the insects. Heating of grains to 50°C will be lethal for insects.

ii. Management of moisture content of grain:

Moisture is another critical factor in safe storage of food grains. Grains stored at around 10 per cent moisture content escape from the attack of insects.

iii. Availability of oxygen:

In storage, grains and insects consume oxygen during respiration and carbondioxide is produced. Insects respire at the rate of 20,000 to 1,30,000 times than that of the same weight of the grains. Thus oxygen level will reduce below 1% and carbondioxide level will automatically increase which will be lethal to all the stages of insects.

a. Mechanical management measures:

Amongst various methods of insect-pest management, mechanical methods are quite practicable.

i. Screening of grain:

Broken and cracked grains promote attack by stored grain pests. Hence, screening/ sieving out of such grains reduces the insect infestation and gives a better appearance to the lot. Of course the grain does not become free from insect. Following points help in making the screening more effective.

• Screening should be done regularly and away from the stores to avoid any re-infestation.

• Immediate destruction of screenings.

• Bags used for carrying the screenings should not be used again without disinfestation.

ii. Engineering control measures:

In grains having moisture content below 10%, most of the insect species do not survive/ multiply. In villages the grain are dried by spreading a thin layer in the Sun or by dryers.

2. Chemical measures of insect-pest management:

Amongst the present methods of insect management, usage of chemicals is the most popular and perhaps the most effective one. The term insecticide may be applied to all these chemicals, which are used to kill or control or manage the insects. They may be used for both types of treatments:

a. Prophylactic treatment

b. Curative treatment

a. Prophylactic treatment:

Prophylactic treatment methods are used to prevent insect infestation and cross infestation by spraying insecticides. These insecticides should not, however, be sprayed on food grains directly.

b. Curative treatment:

In spite of regular prophylactic treatment, infestation develops due to hidden infestation or cross infestation. It can be managed by the use of following insecticides and fumigants.

i. Knockdown chemicals:

Those insecticides which are capable of immobilizing or killing insects quickly are called as knockdown chemicals. They are usually aimed against flying insects but may kill the insects on surfaces as well as in cracks and crevices. Such chemicals are Pyrethrum spray, lindane smoke generator or fumigant strips.

ii. Grain protectants:

Mixing of chemical dusts with the food grains meant for human consumption is not recommended. However, they can be mixed with the grains meant for seed purposes only. Pyrethrum dust, DDT and BHC dusts etc. are normally used as seed protectants.

iii. Fumigants:

A fumigant is a chemical which at required temperature and pressure can exist in the gaseous state in sufficient concentrations to be lethal to a given pest organism. Nowadays a good number of fumigants are used for the control of insects. One of the effective fumigants is given below.

• Aluminum phosphide:

This is a solid fumigant available in the market in the form of tablets of 3 gm each packed in sealed tubes. Of course, it is one of the very potent fumigants and can be used practically on all food grains, milled products etc. The active ingredient is phosphide gas, which is an acute toxic poison.

When the tablet comes in contact with the moisture of the atmosphere, it liberates ammonia, carbon dioxide, and phosphide. Phosphide gas being highly toxic, it should be handled with great care and by trained staff only. However, tri-laminated envelope packaging of aluminum-phosphide, which is comparatively tamper proof, is permitted for manufacture, stocking, open sale and use in India.

Procedure:

The fumigatorium or storage structure with grain in bulk is made sufficiently airtight by plastering cracks, crevices etc., leaving one or two openings for application of the fumigant. It is applied at the rate of 2 tablets (3 gm each)/ tonne or Tri-laminated envelope packaging at the rate of 6 gm/ tonne to the food grains. In case of bagged storage, 1/z of the required quantity of the fumigant is distributed at top layers of bags and the remaining 1/z on peripheral bags. The stack is then immediately covered with gas proof cover. The edges are plastered with mud or weighed down by sand snakes.