Organisation:Food and Agriculture Organization of the United Nations (FAO), AGST
Author: Danilo Mejía, PhD, AGST.
Edited by AGST/FAO: Danilo Mejía, PhD, FAO (Technical), Emanuela Parrucci (HTML transfer)

CHAPTER XXIII MAIZE: Post-Harvest Operation

4. Pest control of Storage for Maize
4.1. Characteristics of Storage Insect Pests
4.2. Nature of Insect Pest Infestations
4.3. Loss Magnitude by Insects Pests in Traditionally storage
4.4. Insect pests control strategy.
4.5. Traditional insect pest control methods.
4.6. Chemical control methods.
4.7. Rodents in storage

4. Pest control of Storage for Maize:

Insects

Rodents

4.1. Characteristics of Storage Insect Pests

Beetles and moths are the most predominant pests in the tropic causing great loss and deterioration to food grain. These pests typically have a four stage life cycle: egg, larva, pupa and finally adult as shown in the following figure 40:

Fig. 40. Cycle of life of a typical storage insect pest.
Adapted from (AGROTEC/UNDP/OPS, 1991)

The eggs are laid either on the surface of grain kernel (normally on physically damaged part of the grain or inside a tiny hole partly bored on the kernel by the parent. The eggs hatch into larvae which voraciously eat their way within the grain, and are responsible for most of the damage on crop. The larvae gradually transform into pupae, a dormant non-feeding stage. These later hatch into adults which eat their way out of the grain kernel and (if beetles) immediately start aggressive feeding on and further destruction of the grain. The Prostephanus truncatus or larger grain borer (LGB) losses in the range of 10-35 percent in 5-6 months in household storage and up 60 percent losses over a 9 month storage period. Adult moths are short-lived and do not feed, but their larvae voraciously feed and cause heavy contamination to the stored product through webbing and frass.

Insect pest damage to grain may fold into one of the following categories:

· Bored holes in the grain and disappearance of a large portion of the endosperm.

· Injury to the germ reducing the nutritive value and loss of liability of the grain.

· Heating and condensation and moulding of the grain causing reduction in nutritive value and risk to formation of toxic substances as aflatoxin.

· Contamination of stored grain with excrement and frass.

· Infested grain, specially by Sitotrogacerealella figure 41A-3,may have a sickening smell and taste that makes the grain un-palatable.

· Main insect causing significantly damage to cereal, including maize, as shown in the following figure 41A and 41B.

Fig. 41A. Common insect pests of maize.
1). Tribolium casteanum, 2). Sitophilus granaries, 3).
Sitophilus oryzae or zeamais, 4). Cryptolestes ferrugineus.
 (Source:casa Bernardo Ltda)

Fig. 41B. Common insect pests of maize.
1. Orizaephilus surinamensis, 2). Prostephanus truncatus (LGB), 3). Sitotroga cerealella, 4).Ephestia cautela.
(Source: casa Bernardo Ltda)

This list include the larger grain borer LGB introduced in Africa in 1981 (figure 41B-2). It causes severe losses on maize grain and even dry cassava in Tanzania, Kenya and Togo and threatening all neighbouring countries. Moreover, the table 24 present some properties of important grain infesting insects with emphasis for maize.

4.2. Nature of Insect Pest Infestations

Some of the maize pests have flight ability and often start the infestation in the field several weeks before the crop is harvested or when the maize is being filled dry in stalks or in shocks. The ability of the insects to fly long distances between fields and to and from maize stores as shown below can quickly spread the infestation.

The problem is aggravated by bad practice such as:

· Poorly managed storage structure to maize field

· Careless disposal of all crop or of crop residue swept from infested store

· Leaving fits and pieces of infested cob maize in unplugged fields, or lying all around the farm yard.

The infestation initially in the field often continue an intensifies in storage, reaching high proportion within 2 to 3 months of storage unless efforts are made to control the pest.

4.3. Loss Magnitude by Insects Pests in Traditionally storage

Grain must be guarded against insect infestation in the field by timely harvesting. Protection must also be availed during drying, so as to minimize drying and storage losses.

Weight loss on maize grain varies from region to region, depending on crop variety, storage condition and duration, and on pest combination in storage. Studies conducted on Zambia gave weight losses from insects pests at a small holder storage for different maize varieties to be in the following ranges:

· Local varieties weight loss ranged: 1-3 percent

· Improved varieties weight loos ranges: 5-6 percent

· Hybrid varieties weight loss: 8-9 percent

These cases were obtained in traditionally storage for 6 to 9 months, with similar work done in Kenya, Tanzania and Uganda. The low level of loss in local varieties is attributed to their resistance to insect attack because of hard kernel and to the complete and better coverage by the sheaths which protect considerably the grain in the field, during drying and in storage if in sheaths. In spite of their susceptibility short-coming , improved and hybrid varieties are normally high yielding in fast maturing compared to local varieties. These justifying their production.

4.4. Insect pests control strategy.

The control of insects for maize must start before the harvest and not only when they are detected in storage. For a better control the following point should be taken in considerations:

· The best strategy involve timely harvesting and then proper drying and cleaning of the maize prior to storage.

· Is important also to prepare in advance all storage structure and containers to be used, making them ready and safe to recieve the new crop. Some recommendations depend upon the type of containers of structures, such as:

- metal, earthware, plastic containers must be washed, desinfected with hot water and well dried before using.

- Sacks of jute, sisal and nylon should be washed and boiled in hot water to kill off insects pests or theirs eggs and larvae and dried prior to use

- Reed-woven indoor granary and out-door basket, mud-wall bins or brick-wall silos must be re-plastered using local materials (cow dung, mud, sand, wood, ash, etc) to seal off cracks, holes and crevices which could hide insects pests and their eggs

- Granaries, cribs, silos and warehouses must be cleanly swept, repaired where possible, desinfected using pests control chemicals, see table 23.

4.5. Traditional insect pest control methods.

Traditional methods used for farmers to reduce infestation of the crop may fall into three groups: 1). Special practices 2). Use of material such as ashes (for its abrasive and letal effect on the insects cuticle), mineral and oil in which physical barrier effects are responsible for the control of insects and 3).The use of whole or parts of the plants where there may be some natural insecticidal, fungicidal or repellent effect (mainly alcohols, alkaloids and terpenes). These methods include as follows:

· Storing very well dried crop or re-drying when infestation is detected

· Storage of maize in sheaths for protection by the husk

· Use of repulsive local herbs and plants to scare off the pests (Nim ground seed, leaves of acanthaceae, acardiaceas, annonaceae, myrtaceae, other plants extract, etc,

· Use of dried inert material such as, sand, crushed limestone, wood ash at 1-5 percent w/w filling up in granular space and hindering insect activity, diatomaceous earth, etc

· Use of abrasive ash from paddy husk and mixed with the grain at 0.1-0.5 percent w/w. It cause dehydrates insect pests leading to desiccation and death.

4.6. Chemical control methods.

4.6.1. Chemical methods.

Farmers some time have to turn to use chemical control methods despite some of their short-comings.

4.6.1.1. Fumigants.

Gases or vapours taken into the body of the insect through its respiratory system, resulting in death.

· Fumigants have non residual effect, but can penetrate through stacks or bulk produc killing all stage of insect life

· Fumigants do not protect against re-infestations of the grain

· They are extremely poisonous and if is not properly handled could cause death

· Use of fumigants should be done by well trained persons and they have preferently a license to carry out fumigation

4.6.1.2. Contact insecticide.

Are poisonous able to penetrate through the insect’s cuticle entering the body tissue and causing death. The use of contact insecticides by smallhoder farmers will be either in admixtures or as a surface treatment. These insecticides have long term effect, however they are specific in their effect upon insect species.

· Dusting maize cob and grain with insecticides.

· Husking and cleaning of cob maize:

Storage of maize on the cobs with or without the sheathing leaves is still common tradition among smallholder maize growers in Africa and Latin America. In countries with larger grain borer, Prostephanus truncates, storage of maize on the cob is strongly discouraged, since it favors development and spread of this pest. Therefore, the sheaths should be taken off the cobs and the dried crop well cleaned before dusting for storage.

4.6.1.3. Layer by layer dusting of maize cobs: sandwich method

The dried and well cleaned maize cobs should treated layer by layer as they are put into the store (granary). This treatment controls most traditional storage insect pests of maize, it may not be effective on the control of LGB. An overdose could be a danger to health. The following table 24 provide some recommended insecticide.

 4.6.1.4. Pest control treatment of shelled maize.

The most recommended way to store maize is in the shelled form. This practice have some advantage:

· Shelled grain is less bulky to handle and to store requiring les space of storage and less handlabour

· Facilitates control of insects and rodents and respond better to chemical treatment than maize cobs

· Reduces losses and storage is easier to manage

· LGB is easier controlled when maize is shelled and admixed with synthetic pyrethroids such as permethrin and deltametrin. The recommended insecticides are the same as table 31, and can be also recommended actellic at 0.5 percent and bromophos at 2 percent in applications rates of 100 grams per 90 kg grain and 50 grams per 90 kg grain respectively. Is important to remark that application can be made on a surface of concrete sprinkling the insecticide unformely with a shovel. Another way is to mix in a drum and shake it along with the maize.

4.7. Rodents in storage

4.7.1. Types and general characteristics.

In several tropical countries rodents (rats and mice) cause much more loss and damage to food grain than insect pests. Three species are prevalent: the brown rat (Rattus norvegicus), the house mouse (Mus musculus) and the roof rat (Rattus rattus) figure 42.

Fig. 42. Common species of rodents in storage.
(AGROTEC/UNDP/OPS, 1991)

4.7.2. Habits and characteristics of rodents:

· Usually they do same activities every day

· The follows same path over and over

· They are away of new things as for example new baits

· They can climb or jump until 60 and 90 cm

· They can swim across pools of water

· They dig and barrow holes through soil, hard structures, containers and objects

4.7.3. Rodents loss and damage to food grain:

· They damage crop in field and storage

· They eat and destroy the grain

· They foul and contaminate grain and cooked food with their feces, urine and hairs

· They can destroy buildings, structures, containers and personal clothings and bedding

· They spillage stacked bagged foods, storage structures and food containers

· They can attack young chicks and may attempt to feed on human feet, causing sores and walking difficulties to their victims

· They may cause disease to man and animals

4.8. Rodents control methods:

· By using various types of rodents traps

· By using domesticated cats

· By hunting rodents in the probably hiding places.

4.8.1. Improved rodents control methods:

· Prevent rodents entering by:

- solid walls structures

- use of metal sheets or chicken wire to structures walls which keep off rodents

- use of rat-guards as been before

· control can be achieved by baiting (poisoning). This requires training to be successful and to prevent accidents and death to humans table 25.

· all these previous methods are strongly supported by a goods standard of hygiene and storage management.

4.9. Quality and Economic Loss

Beside weight loss, which may appear small, deterioration in quality of maize due to insect attack or rats damage is also a great concern. The grain that has been damage by the insect and rats are undesirable in the market, causing great economic loss to the producer and quality loss to the consumer.

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