Rice Production: Chapter 14 - Diseases of rice

Introduction

Like many countries in the humid tropics, Sierra Leone has a climate particularly conducive to the development and spread of plant diseases. High humidity, rain, and heavy dew are associated with increased activity of disease-causing organisms. As a result, virtually every crop of rice grown in Sierra Leone is subject to at least mild disease infection. In some instances, infection becomes severe, leading to heavy crop losses. This chapter describes several of the most common diseases of rice found in Sierra Leone and touches upon management practices which may help to prevent them.

I. Disease Considerations

The three "ingredients" of plant disease are 1) the host plant, 2) the pathogen, or disease organism, and 3) the environment. Taken together, these comprise the components of the so-called disease triangle.

It is important to recognize that the three components are interdependent. Presence of the host plant and the pathogen does not imply occurrence of the disease. The environment plays a crucial role as well: it must be conducive for the two biological systems (the plant and the pathogen) to interact in a way that infection may take place and disease follow. Consequently, disease control can involve manipulation of any one, or all three, of these components.

Disease infection can be divided into stages: 1) entry of the organism into the plant, and 2) spread of the infection through the plant. Pathogens can enter through weak or injured roots, through mechanically or insect-damaged stems or leaves, through weak outer cell walls, through dead tissue, or through succulent and easily bruised leaves.

II. Diseases Common in Sierra Leone

Listed below are several of the diseases of rice occurring most frequently in Sierra Leone in irrigated crops:

1. Blast (including Neck Blast and Leaf Blast)

Pathogen: Pyricularia oryzae (fungus)

Infection takes place at any stage of growth. Lesions are typically oval or spindle-shaped, with a grayish center and a brown halo. When several lesions join, the infected leaf appears blighted. Mild infections of blast occur regularly in Sierra Leone. Although in most cases the disease fails to kill the affected plants, farmers should realize that lesions on the leaf surface inhibit the plant's ability to photosynthesize and thus reduce yields. Blast is often associated with nutritional imbalances. Note: some varieties (e.g. CCA) are particularly susceptible to neck blast; crop losses of up to 100% have been recorded in some instances.

2. Brown Spot

Pathogen: Drechdleria pryzaae (fungus) 

Brown Spot

Brown spot can affect the crop at any stage of growth and often appears as early as the seedling stage. Brown spot starts as small, circular to oval, dark brown lesions with a light yellow halo around their outer edge. (Brown spot can be distinguished from blast by the absence of a grayish center in the lesions.) Infection can spread to cover the entire leaf surface, particularly in stands of upland rice. The disease is often associated with nutritional deficiency and/or drought stress.

3. Narrows Brown Leaf Spot

Pathogen: Sphaerulina oryzae (fungus) 

Narrows Brown Leaf Spot

Narrow brown leaf spot resembles brown spot, except -that the lesions are shorter and distinctly more linear. Some lesions have slightly broadened centers. They occur most commonly on the upper leaves and often increase in numbers d ring the latter stages of growth.

4. Sheath Blight

Pathogen: Rhizoctonia solanii (fungus) 

Sheath Blight

Initial symptoms of sheath blight infection appear as grayish-green lesions on the leaf sheath between the surface of irrigation water and the leaf blade. Adjoining lesions often merge, weakening the entire stem and causing it to topple and break. The lesions may also extend to the leaf blades, especially among susceptible varieties.

5. False Smut

Pathogen: Ustinaginoidea virens (fungus) 

False Smut

Infection by false smut occurs after heading and effects the ripening grains. Infection results in the transformation of the individual grains into greenish spore ball of velvety appearance. The balls are slightly flattened, smooth and yellow, and covered by a membrane. With growth the membrane swells and bursts, exposing the orange content of the ball. Infected grains are rendered inedible.

6. Leaf Scald

Pathogen: rhynehosporium oryaze (fungus) 

Leaf Scald

Leaf scald is quite common on mature leaves. The infection forms oblong or diamond shaped blotches. These increase into large ellipsoid olive areas which ultimately dry but and turn gray. Often the entire leaf tip succumbs to the scald, which can be recognized by its characteristic banded pattern of alternating light and dark grays.

III. Management for Disease Control

Because strong plants and a healthy environment can rule out disease even in the presence of pathogens, it is easy to see why management practices play an important role in combating plant diseases. Encourage farmers to adopt as many as possible of the following management practices to decrease the incidence of disease in their crops:

a) Selection of Resistant Varieties

As a method of rice disease control, the selection of resistant varieties is often the most practiced method. The reasons are obvious when one considers the simplicity of the practice. It represents the most economical and sensible approach, and it appeals best to farmers because it is cheap, effective, and within the reach of their means and technical skills. Work with farmers to keep track of which varieties seem most disease-free under local conditions and suggest that they be planted exclusively.

b) Balanced Fertilization

Nutritional imbalances - both deficiencies of nutrients and excesses - render rice plants much more susceptible to attack by pathogens. Deficiencies result in a general decline in the plant's health, while excesses can cause a sudden growth spurt leading to a weakening of cell walls. Either condition invites attack, as evidenced by the clear relationship between diseases such as blast and brown spot and nutritional imbalances. Balance fertilizer applications (i.e. apply fertilizer in several splits instead of all at once) to minimize the risk of nutrition-related disease.

c) Crop Rotation

Crop rotation can disrupt the life cycle of some pathogens (e.g., fungi) by removing from the environment the necessary host plant. Crop rotation can also discourage multiplication of soil-borne organisms which live among the roots of the rice plant.

d) During of Crop Residues

Disease organisms do not die when rice is harvested; they either produce spores which linger on in the paddies to infect subsequent crops, or they seek alternate hosts among nearby weeds. Encourage farmers to burn residues left over after the harvest (chaff, stubble, refuse) to kill disease-causing organisms and to destroy alternate hosts.

Rice Production: Chapter 13 - Pesticide calibration

Introduction

Most pesticide application in Sierra Leone is done with backpack, pump-type sprayers. The main function of a sprayer is to break the liquid pesticide solution into droplets of effective size and distribute them uniformly over the surface or space to be protected. Another function is to regulate the amount of pesticide to avoid excessive application (which might prove harmful, wasteful, and costly) or insufficient application (which would fail to give effective control). This chapter describes the common formulations of locally available pesticides and explains step by step how to dilute them to obtain the desired concentration for field application.

I. Pesticide Formulations

Most common pesticides are available commercially in one or more of the following forms: dust, wettable powder, emulsifiable concentrate, or granules.

1. Dusts

Dusts are widely used in agriculture, especially where it is difficult to obtain large volumes c' water for diluting sprays. The toxicant mixed or dilated with a carrier such as, talc, and mechanically blended by the manufacturer. A low concentration of the toxicant is helpful in making an even application.

Dusts are applied dry with hand dusters, ground dusting equipment, or aerial equipment and are not intended to be mixed with water or oil. In order to avoid drift it is best to use dusts when there is little or no wind, and the crops are wet from dew or rain. Because they contain a minimum of solvents and no emulsifiers, dusts are least likely to harm delicate plants.

2. Emulsifiable Concentrates

An emulsifiable concentrate is an oil-based liquid compound containing a high concentration of the toxicant. These concentrates contain emulsifiers (agents which facilitate mixing with water), as well as wetting and sticking agents to make them readily emulsifiable in water and liable to adhere to plants. Before ´:se, they must be diluted in water. They can be applied as ground sprays, or with aerial spray equipment.

3. Wettable Powders

Wettable powders, although similar in appearance to dusts, contain a wetting agent which permits them to become dispersed and suspended when mixed with water and applied as a liquid spray. Since powders do not dissolve but rather stay in suspension, spray tanks must be equipped with agitators to keep the particles in suspension. Wettable powders contain no oil or solvent, and they are consequently safer than some emulsifiable concentrates for use on plants with delicate foliage.

4. Granules

Granular pesticide formulations consist of free-flowing grains or inert materials either mixed or impregnated with a toxicant. Granules offer these advantages they do not need any further mixing or dilating they present no drift problem during applications: and they can be broadcast directly by hand without expensive equipment (since almost invariably they are made up of compounds showing low toxicity to humans).

All of these different forms of pesticides have their place in insect control because of differences in weathering properties, uptake characteristics, life cycles of insect pests, and/or growth characteristics of crops.

II. Pesticides Available in Sierra Leone

MALATHION - ID₅₀ Values Oral: 1375 Dermal: 4444

Organophosphate (contact insecticide)

Formulation: emulsifiable concentrate, wettable powder Active Ingredient: 25% or 50%

Use: Insect control in rice, vegetables

GAMA-BHC - ID₅₀ Values Oral: 600 Dermal:

Chlorinated hydrocarbon (systemic insecticide)

Formulation: wettable powder Active Ingredient: 25% uSE: Insect control in rice, vegetables

PHOSDRIN - ID₅₀ Values Oral: 6 Dermal: 4.7

Organophosphate (contact, systemic insecticide)

Formulation: emulsifiable concentrate Active Ingredient: 24%

Use: Insect control in rice, vegetables EXTREMELY Dangerous - NOT Recommended

BIDRIN ID50 Values Orals 21 Dermal: 43

Organophosphate (contact, systemic insecticide) Formulation: emulsifiable concentrate Active Ingredient: 24%

Use: Insect control in rice, vegetables EXTREMELY DANGEROUS - NOT RECOMMENDED

KOCIDE 101 ID₅₀ Values Orals Dermal:

Active Ingredient copper (contact fungicide) Formulation: wettable powder Active Ingredient: 54%

Use Control of black pod disease in cacao

III. Sprayer Calibration

If and when it becomes necessary to apply pesticides it is likely that application will be made with a pump-type backpack sprayer. These sprayers are relatively inexpensive, simple, and easy to operate. It is important that the extension agent be well versed in the use and calibration (calculation of the rate of spraying) of the backpack sprayer. Even if the extension agent does not actively encourage farmers to apply pesticides, it is quite possible that s/he will be approached by farmers owning their own equipment for instruction in the use of the sprayer. One of the best ways to help decrease pesticide abuse is to provide accurate information about the proper calibration and safe use of spraying equipment.

Before each application of pesticide, it is necessary to calibrate the sprayer to determine the exact rate of spraying. The rate of spraying is the amount of liquid emerging from the sprayer (in normal use) to cover a given area. This differs significantly from the rate of Pesticide application, which is the amount of pesticide applied per unit area. The rate of spraying varies according to the physical characteristics of the sprayer and has nothing to do with the properties of the spray itself, but the rate of pesticide application varies according to the rate of spraying and the concentration of the mixture in the tank. (This is an important distinction and should be understood clearly.) Only once the sprayer has been calibrated (to determine the rate of spraying) will it be possible to determine how much pesticide to mix with water in the tank to achieve the desired rate of pesticide application.

The rate of spraying depends on four major factors'

1) Pressure in the spray tank

Keep the pressure in the tank as constant as possible. A pressure regulator or pressure gauge is ideal, but usually these are lacking. Smooth, even pumping will help keep the pressure relatively constant.

2) Size of nozzle orifice

The size of the nozzle orifice regulates the amount of spray passing through the nozzle. The nozzle orifice wears with use and therefore must be recalibrated regularly.

3) Spray swath

The spray swath, or "path" covered by the droplets, varies according to the height at which the tip of the nozzle is held. Keep the swath as constant as possible.

4) Walking speed of Svrayperson

Walking speed directly affects the area covered per unit time, which in turn determines the amount of spray applied per unit area. Maintain an even walking speed when spraying, to the extent possible.

When calibrating a sprayer, it is important to keep in mind that the calibration will be valid only for that Particular sprayer in that Particular swamp with that particular spray-Person, since a change in any one of these variables will afect a change in the rate of spraying.

To calibrate a sprayer, follow this procedures

1. Prepare sprayer

a) Rinse supply tank and fill with clean water.

b) Remove nozzle; check and clean if necessary.

c) Flush pump, hose, and lance with clean water.

d) Apply pressure (i.e. pump) and check sprayer for leaks.

2. Determine walking speed of spravperson

a) Fill tank with clean water.

b) In an actual paddy, mark starting point with a stake.

c) Using your wristwatch, begin 1 minute trial. Walk at a constant and normal speed, carrying the filled sprayer on your back. Pump the sprayer handle with one hand to maintain pressure and direct the nozzle with the other hand to obtain a spray swath of approximately 1m width.

d) Stop walking at the end of exactly 1 minute and mark the stopping point with a second stake.

e) Measure the distance between the starting and stopping points. Record the distance in meters. Walking speed can be expressed in terms of m/minute.

f) Repeat trial at least three times to obtain an average walking speed.

3. Calculate area sprayed in one minute

If the spray swath was kept at (approximately) 1m, the area sprayed in one minute can be calculated easily using the known walking speed:

Area sprayed in one minute = spray swath (1m) x walking speed (m/minute). The answer is expressed in terms of m²/minute.

4. Determine nozzle discharge in one minute

a) Fill sprayer with clean water and pump sprayer handle to build up pressure.

b) Dip end of nozzle into a graduated cylinder.

c) Using your wristwatch, begin 1 minute trial. Open the cut-off valve and spray into the graduated cylinder. Make sure none of the spray escapes.

d) Cut off the discharge at the end of exactly 1 minute.

e) Note the volume (in liters of liquid collected. This is the nozzle discharge, expressed in terms of liters/minute (1/min).

f) Repeat trial at least three times to obtain an average nozzle discharge.

Now you can easily compute the rate of spraying'

Rate of spraying = (nozzle discharge (1/min)) / (area sprayed (m²/min))

(1/m²)

Since most pesticide application rates are given in terms of 1/ha, the rate of spraying should be converted to the same units of measurement'

Rate of spraying = 1/m² x 10000m²/1 ha = 1/1 ha ha

i.e., simply multiply the rate calibrated for 1/m² x 10000.

Dilution - preparing solution of pesticide

IV. Pesticide Dilution

Once the sprayer has been calibrated, it is very easy to calculate the amount of pesticide which must be diluted with water to achieve the desired mixture. Since the rate of spraying has been calibrated in terms of liters (spray)/ha, and since pesticide application rates are given in terms of liters (e.c. of pesticide), the desired ratio of emulsifiable concentrate to water can be determined by simple division'

Mixture = desired rate of pesticide application (liters e.c./ha) / calibrated rate of spraying (liters water/ha)

= liters emulsifiable concentrate / liters water

Rice Production: Chapter 12 - Pesticide safety and agro-chemical use

Introduction

Tile se of chemical pesticides in developing countries is subject to considerable controversy. Pests destroy up to one third of the world's food crop every year. An even greater percentage is lost in developing countries, where safe and effective pesticide use is rare.

Fart of your Job as an agriculture extension agent will be to teach farmers and agrotechnicians how to control insect damage through a combination of preventive management practices and pesticide use This chapter provides a brief introduction to the basic safety measures which should always accompany the use of chemical pesticides.

I. Pesticide Toxicity

Pesticides are useful for keeping farm animals healthy and for killing insects, weeds, and plant diseases. When used improperly they car hurt or kill other things in the environment including you or the people you work with.

All pesticides are toxic, ranging from the most dangerous (Category I) to the least dangerous (Category IV).

The ID₅₀ rating (ID refers to lethal dose) indicates the amount of pesticide that will kill 50 % test animals (male rats) in terms of milligrams of pesticide per kilogram of body weight If the ID₅₀ of a rat poison is 148 then 149 mg of the poison will kill one of every two rats that weigh 1 kg each.

ID₅₀ values provide a fairly good measure of the relative toxicities of pesticides to humans Each type of pesticide is generally assigned two ID₅₀ values, for dermal contact through the skin) and for oral contact (ingestion through the moth).

The LD₅₀ rating gives no information on the cumulative effect of repeat exposure. Organophosphates such as Phosdrin ( mevinphos) and Parathion interfere with the transmission of nerve impulses by inhibiting the enzyme cholinesterase, and because the body cannot rid itself of these poisons, their effects can be cumulatuve. Several small nonlethal doses can add up to a lethal dose.

Even relatively "safe" pesticides such as Malathion or Sevin can cause severe poisoning if enough of the pesticide is ingested or spilled on the skin, particularly in concentrated form.

Toxicity of Common Pesticides

(ID₅₀ values in mg/kg)

Pesticide	Use*	Oral	Dermal
Category I- Most dangerous
Phosdrin ( Mevinphes )	I	6	4.7
Category II Dangerous Bidrin	I	21	43
Category III - Less Dangerous
BHC	I	600
Chlordane	I	335	690
2, 4 -D	H	650	-
Dithance D-14-	F	395	1000
Paranquat (Gramoxone)	K	120	480
Negamon	N	173	1423
Vapona (Dichlorvos)	I	90	107
Category IV - Least Dangerous
Captan	F	9000
Daconil (Bravo)	F	10000	10000
Malathion	I	1375	4444
Sevin (Carbarryl)	I	850	4000

*F = fungicide

I = insecticide

K = herbicide

N = nematocide

II. Safety Guidelines

1) Laws and Regulations

Make sure you are using, storing, and disposing of pesticides in accordance with the laws and regulations of the country in which you live and work.

2) Read and Understand the Label

All persons using pesticides should understand the directions and precautions on the label before opening the container. The label should state the name of the pesticide, amount of active ingredient, uses, suggested dosages, precautions and first aid instructions. If the label is vague or unclear try to obtain descriptive pamphlet.

Never buy or use pesticides that come in unmarked sacks or bottles. Any U.S. labels which lack the above listed information should be reported, with a copy of the label if possible to the Peace Corps Information Collection and Exchange (ICE), Washington D.C. 20525. All this information is required on the label by law, and any failures to comply will be brought to the attention of the S. Environmental Protection Agency.

3) Protect Yourself

The proper use of safety equipment and protective chloting is essential in handling and applying chemicals. Rubber gloves and boots, trousers (outside of boots) long-sleveed shirt, waterproof hat and coat, and proper measuring equipment are the minimum requirements when pesticides are applied. In many instances a respirator is necessary as well. Thoroughly wash all clothing before wearing it again. Avoid handling chemicals when wearing leather shoes, since chemicals are easily absorbed by leather arid are very difficult to remove.

4) Category I and Category II Pesticides

When working with Farmers, avoid using Category I and Category II pesticides, particularly Birdin, Phosdrin, Phosphamidon and Trithion. If you or other pesticide experts ever find i-t necessary to use pesticides in either Category I or Category II, be sure to wear the required protective clothing, regardless of how uncomfortable it many get Insist that farmers who use these pesticides (almost invariably they should not be) are trained to use protective clothing.

5 ) Exposure to Pesticides

In handling any pesticide, avoid repeated or prolonged contact with the skin or inhalation of dust or spray. Clothing should be changed and hands and face washed before eating, smoking, or going to the bathroom. Wash immediately with detergent and clean water when your hands, skin, or any port of the body become contaminated or exposed.

6) Safe Working Area

Prepare pesticide solutions in a well-lit, well-ventilated place, preferably outside. Keep livestock, pets, and people out of the mixing area. Wear proper protective clothing and read the label before opening the container. ix the solution carefully to avoid accidental splashing. If a spill occurs, soak up the spill with sawdust or soil and bury the contaminated material in a hole at least 50 cm deep in an isolated place where water supplies will not be affected. Cover the material with dirt.

7) Windy Days

Never spray or dust on windy days. Do not spray pesticide if people or animals are nearby. Avoid treating crops while bees or other pollinators are active in the field. Do not apply pesticides if apiaries (beehives) are near enough to be affected adversely; notify the beekeeper so he can move the hives if necessary.

8) Protecting Passersby

Do rot permit unprotected passersby to enter treated fields until the spray has dried or the dust has settled.

9) Pesticide Storage

Store pesticide in a dry, well-ventilated place out of the reach of children and away from food and animals, pesticides in the original, labelled containers, tightly sealed to prevent the release of harmful vapors.

10) Pesticide Containers

Make sure that pesticide containers are never put to any other use. Burn all empty bags, as well as cardboard and plastic containers Do this in an isolated place, when the wind will not cause contaminated smoke to drift among homes, people, livestock, or crops. Keep well out of the smoke Bury the ashes 50 cm deep in an isolated place where water supplies will not be contaminated. Break all class containers, crash or punch holes in metal cans, and burn and bury as above.

11) Water Source

Do not contaminate streams, swamps, or other water sources either during application or when cleaning equipment. Rinse water and leftover spray mixture should be poured into a hole in the ground, never into a stream or swamp.

III. Symptoms of Poisoning

Symptoms of pesticide poisoning vary depending on the chemical group of the pesticide and the severity of the exposure. Repeated exposure to small amounts of some pesticides, can cause sadden severe illness. Poisoning caused by synthetic organic pesticides (organophosphates, chlorinated hydrocarbons, crarbamates) may cause one or more of the following symptoms:

Wild poisoning:

- irritation of the skin, eyes, nose, throat

- weakness, dizziness

- nausea, stomach cramps or diarrhea

- excessive sweating and salivation

- chest discomfort

- blurred vision

- numbness of hands and feet

Moderate poisoning:

- difficulty talking and breathing

- poor muscle coordination

- rapid pulse, flushed skin constriction of pupils

- miscle twitching

- increased severity of earlier symptoms

Severe poisoning:

- inconsciossness

- severe constriction of pupils

- convulsions

- inability to breathe

- secretion from the mouth and nose

- death

Symptoms may be delayed several hours following exposure. Appearance of come of the symptoms does not necessarily indicate poisoning - other kinds of sickness may cause similar symptoms. Always consult a physician to be certain.

IV. First Aid Measures

1) If breathing has stopped, give artificial respiration immediately.

2) Get the victim to a doctor or hospital as soon as possible. Take the pesticide label along for the doctor's information. Do not carry the pesticide container in the passenger space of a car or truck.

3) If the pesticide has been swallowed, check the label to see if the victim should be made to vomit. Vomiting can be induced by giving the victim one tablespoon salt dissolved in half a glass of warm water. To avoid dehydration, however, the preferred method is to stick a finger or spoon down the victim's throat. Position the victim face down or kneeling forward to avoid choking and/or strangulation. After vomiting has been induced, make the victim lie down and keep warm. Never induce vomiting in a person who is unconscious or having convulsions.

4) If a pesticide gets on the skin, immediately remove all contaminated clotting and wash the affected skin with detergent and water. Don't forget hair and fingernails.

5) If a pesticide gets in the eyes, wash immediately and for at least five continuous minutes with generous amounts of water. Have them checked by a doctor.

6) If a pesticide has been inhaled, get the victim to fresh air immediately and have them lie down Lossen clothing and keep the victim warm and quiet If breathing stops, begin artificial respiration. Summon medical assistance immediately

ARTIFICIAL RESPIRATION

1) Place the victim face up.

2) Remove all foreign matter from the victim's mouth with your fingers.

3) lift up under the neck and tilt the head as far back as possible, until the chin points up. This position is important to keep the air passage open.

4) For an adult victim, pinch the nostrils shut and place your mouth tightly over the victim's mouth. For a child victim, place your mouth over the mouth and nose. A handkerchief should be placed between your lips and the victim's to prevent your coming into contact with the pesticide.

5) Take a breath and exhale into the victim until you see the victim's chest rise se shallower breaths for children.

6) Remove your mouth and release the victim's nostrils. Listen for the sound of air coming out.

7) Repeat

- every 5 seconds for adults

- every 3 seconds for children

8) Bulging of the stomach may make breathing more difficult. Turn the head of the victim to one side and press gently on the stomach. This will force air out of the stomach but may cause vomiting.

9) If vomiting occurs, quickly turn the victim on their side, wipe out the mouth and then re-position them.

10) Continue artificial respiration until the victim begins to breathe unassisted, or until a doctor pronounces the victim dead, or until the joints stiffen.

Rice Production: Chapter 11 - Pest prevention

Introduction

Irrigated rice must be protected against serious damage from permanent or sporadic pests. In many developing regions, the tendency is to rely on control of pests (through chemical pesticides), rather than on prevention of pests (through management practices). It is Up to the extension agent to make the farmer aware that pest control in its broadest sense includes everything that makes life difficult for the pest, kills it, discourages it from reproducing, or prevents it from spreading. This chapter describes some of the management practices which can help prevent pest infestation from reaching the stage where the far met will be forced to resort to chemical control.

I. Educating the Farmer

Farmers field school

The key to effective pest prevention lies in a complete and accurate understanding of the pest, its life cycle and habits. Although most farmers will usually be able to identify the pest causing damage to their crops, often they lack a detailed knowledge of the relationship between the pest and the rice growth cycle. This is hardly surprising, since most pest activity occurs at night, or in places in which it is difficult to observe (e.g. inside the stern of the plant).

Perhaps the most important contribution the extension agent can make toward pest prevention is to educate the farmer about the life cycle and habits of the pest. Teach the farmer to look for signs of crop damage. Point out as many pests as you are able to identify, and explain as much as you know about their life cycles. Ask questions which will start the farmer thinking regularly about pests.

II. Preventative Practices/Insects

Field study and identifying of insects

With one or two exceptions, it is difficult to eliminate insect pests completely simply with management practices -but there is no question that preventative practices can have a significant effect in controlling or reducing insect populations. And since crop damage occurs in direct proportion to insect population, it is important to know which management practices will help keep down the numbers of harmful insects. Preventative practices which have been effective in Sierra Leone include:

a) Flooding

Flooding

After the harvest, many species of insect pests enter into the pupating, or resting stage. Flooding the plots immediately after harvest can drown many pupating insects, especially stem borers. Flooding also effectively controls air-breathing insects, such as the mole cricket.

b) Draining

Draining

Draining the plots represents an easy, inexpensive, and effective control against caseworm. Encourage the farmer to drain the affected plot(s) dry for 7-10 days to prevent the spread of caseworm. (Note: be sure not to drain the water out of one plot and into another, since this will merely result in the spread of the infestation.)

c ) Burning

Burning off rice straw

Burning off straw and stubble after the harvest drives away any regaining insects, kills pupating insects in the soil, arid helps control disease as well.

Hand weeding in the rice paddles

d) Plawing

Removal of paddy stubbles and wild grasses after harvest by plowing them under will minimize the next generation of insect pests by killing larvae hibernating in the soil and eliminating a ratoon crop (which serves as a host environment for rice-specific pests).

e) Brushing Bunds and Peripheries

Many species of insect pest emerge from the plots during certain farming operations (e.g. brushing, burning, plowing) and seek refuge in the weeds growing on the bunds and along the edges of the swamp. Brushing the bunds and peripheries deprives many insects of a valuable habitat and can significantly reduce their numbers. 

f) Crop Rotation.

Crop Rotation.

Crop rotation can be extremely effective against certain insects, especially rice bugs. In a heavily pest infested area, encourage as many farmers as possible to plant a rice pest resistant crop (e.g. groundnuts or cowpeas). If deprived of a rice environment, many rice specific insects will move elsewhere or die. 

g) Uniformity of Planting

If sufficient labor is available, encourage the farmer to plant the entire crop at one time. Since the entire crop will subsequently undergrow the same growth stages at the same time, certain pests which attack only during certain growth stages (e.g. rice bag) will have a very short attack "window."

h) Host Plant Resistance

No rice variety has been found to be immune from insect attack, but certain varieties clearly are more susceptible to attack by certain insects. Teach the farmer to be aware of such susceptibilities (most farmers will in turn be able to teach you about such things). Advise against the continued use of varieties which local insects seem to prefer.

Rice birds

III. Preventative Practices/Birds birds represent the single greatest pest hazard to rice farmers in Sierra Leone. Bird attack during the final stages of grain ripening can cause losses of up to 90% in uguarded stands - in a matter of days. Most farmers are well aware of the bird problem and rely on traditional methods of prevention and control. These include bird-scaring apparati constructed of sticks, vines, tin cans filled with pebbles, rags etc...), slings, and snares.

Note: Some farmers attempt to poison birds by baiting them with rice treated with pesticide. Needless to say, this practice i extremely dangerous, all the more so because people have been known to eat the birds killed by the poisoned bait. Always discourage this practice, which in any case affects only a few birds.

IV. Preventative Practices/Rats

Catching Marsh rice rat

Rats also can pose a major pest problem - and they can be extremely difficult to control. Two types of rat arc common in Sierra Leone The cutting grass is a large nocturnal animal (weighing up to 40 labs) which causes extensive damage to rice by feeding on the bases of the culms. Although many farmers believe that cutting grass will not cross broad irrigation channels or enter into flooded plots, the animal in fact is an excellent swimmer. Maintaining 6"-8" of standing water on the plots will slightly discourage feeding, but the only effective control is to fence off the swamp and deny the animal entry, or hart it antoher rice pest is the smaller field rat (actually several different species). These 8"-10" animals live in nests constructed inside the bunds and attack the rice during all growth stages. They are extremely difficult to control as they make their homes inside the swamp itself. The most effective way to control their numbers is to tear apart the bands and destroy the nests.

Rice Production: Chapter 10 - Insect pests of rice

Introduction

In Sierra Leone, as in most regions in the developing world where irrigated rice is grown, insect pests can be a major problem. Tropical conditions favor the year-round proliferation of insects, and double-cropping practices provide a steady habitat for feeding and breeding. In order -to take preventative measures against insect pests, the farmer must be able to recognize crop damage and identify which insect pest is responsible. This chapter provides a brief introduction to the major insect pests of rice in Sierra Leone, grouped according to the type of crop damage they inflict.

I. Stem Borers

Rice stem borer

a) Crop Damage

Rice stem borers are one of the most destructive types of insect pests of rice, occurring regularly and afflicting plants from seedling to maturity. Stem borers are the larval stage of any one of several species of winged insects which lay their eggs on the leaves or stems of the rice plant. When the egg hatches, the larva emerges, bores into the inside of the culm, and feeds on the interior of the stem. While feeding, the borer cuts off the growing part of the plant from the base, causing the tiller to die. Farmers generally cannot see the borer unless they cut the stem open. The presence of stem borers is most often determined by signs of crop damage

To determine the presence of stem borers, look for the following signs:

- dead hearts (young tillers which have dried up and died after borers have cut off the growing part from inside)

- white heads (empty, whitish panicles resulting from stem borer attack after panicle initiation had already occurred)

- holes in the stems (indicate where the borer entered the stem)

- presence of adult insects b) Species Most Common in Sierra Leone

Name	Larva	Adult
Striped stem borer	light brown larva with 5 thin stripes length to 17 mm	dirty brown moth(dark spots on wings)
Pink stem borer	pink larva with a dark head; segmented length to 25 mm	dark brown moth(white band across wings)
White stem sorer	creamy white larva length to 17 mm	white moth
Yellow stem borer	yellowish larva length to 17 mm	straw-colored moth(pointed head)
Diopsis or Stalk-eyed fly	white larva with sets of "feet" length to 25 mm	rust-colored bug with eyes at the end of stalks

II. Leaf Cutters/Leaf Feeders

a) Crop Damage

Leaf cutters and leaf feeders include a wide variety of different species of insects Although they can attack at any point in the crop cycle, damage is generally most heavy the seedling and tillering stages, when the leaf tissues are tender and succulent.

To determine the presence of leaf cutters/leaf feeders, lock for the following signs:

- irregular holes eaten into the leaf surface

- skeletonizing of leaf blades (i.e. leaves eaten down to the midribs)

- cut-off-leaf tips

- pieces of leaves floating in the water (also cases - see note on caseworm below)

- presence of insects (many species of leaf cutters/leaf feeders are easily observed, e.g. caterpillars grasshoppers)

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Caterpillars	various sizes and markings	butterflies and moths
Crasshoppers	various sizes and markings
Army worms	black worms length, to 35 mm (appear periodically in mass concentrations)	hair:, brick-red moth
Caseworm*	pale green larva length to 25 mm	dirty white moth(nocturnal)

*Note on caseworm:

Caseworm

Caseworm is a pest specific to irrigated rice and represents the single most destructive insect pest of rice in Sierra Leone (with the possible exception of the occasional invasions of army worms). Caseworm infestation can be extremely widespread in newly transplanted rice, and crop loss can approach 100% if control measures are not taken. The worms feed on the leaves and stems and in many cases cut off the leaf tips, resulting in a "mowed" appearance of the rice.

The worm is semi-aquatic in habit and needs to live in water order to draw in oxygen through its gills carries a water supply with it by living inside a water-filled "case" which it constructs by cutting off a leaf segment and rolling itself up inside. This case serves as a portable environment. It also do doubles as a boat: when the caseworm wants to move to another rice plant, it drops into the water and floats inside the case to a new source of food. Each caseworm attacks several plants in this fashion and constructs many cases before it is fully grown. (for control measures, see next chapter)

III. Leaf Scrapers

Green Rice Leafhopper

a) Crop Damage

Leaf scrapers are generally present in moderate numbers in Sierra Leone and habitually cause relatively minor damage. However, in certain instances they can represent a really serious threat to a crop. Leaf scraper damage occurs most frequently d ring the seedling and early tillering stages, while tie vegetative tissue is still suculent and easily attacked. As the name implies, leaf scrapers damage plants by scraping off the chlorophylcontaining layers of the leaves.

To determine the presence of leaf scrapers, look for the following signs:

- pale colorless areas on the leaf surface (where the chlorophyl-containing tic sues have been scraped off)

- presence of insects

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Crasshoppers		various sizes and markings
Epilachna, or lady-bird beetle		orange, black-spotted beetle oval, length 5-6 mm

IV. Root Feeders

Mole Cricket

a) Crop Damage

Root feeders attack the roots of the rice plant and feed on the living tissues, causing eitherstunting or death. Damage generally proves serious only during the seedling establishment and early tillering stages, when the plant's root system is just beginning to develop extensively. Root feeders breathe air and consequently are found only in plots which are not flooded. Often root feeders make their homes inside the bunds venturing forth into the plots only to feed.

To determine the presence of root feeders, look for the following signs:

- dead seedlings (no other visible damage)

- tunnel tracks in the soil leading to affected plants

-presence of insects

b) Species Most Common in Sierra Leone:

Name	Larva	Adult
Mole Cricket		brown or charcoal-gray cricket (length -to 35mm) front feet developed for tunnelling

V. Grain Suckers

Rice bug

a) Crop Damage

Grain suckers have been known to cause severe crop loss in Sierra Leone, especially in areas where continuous cropping occurs. Often the damage caused by grain suckers is not immediately apparent, since many empty grains are not discovered until harvesting has taken place and winnowing begins. Grain suckers attack the rice plant during the milk stage of the ripening phase and suck oft the liquid contents of tic grain, leaving only the empty husk.

To determine the presence of &rain suckers, lock for the following signs:

- empty grains with tiny holes bored through the husk

- erect panicles (indicating empty grains that have been sucked dry)

- presence of insects

b) Species Most Common in Sierra Leone:

Name	Nymph	Adult
Rice bug	tiny green(rice colored) also sucks sap	long, slender insect greenish-brown length 14-17 mm