Crop Pests That Cause Rice Diseases

RICE DISEASESBakanae (Fusarium fujikoroi Nirenberg)

The classic and most conspicuous symptom of the disease is the hypertrophic effect or abnormal elongation of plant. These symptoms can even be observed from a distance. The affected plants may be several inches taller than normal plants, thin, yellowish green and may produce adventitious roots at the lower nodes of the culm. Diseased plants bear few tillers and leaves dry up quickly. The affected tillers usually die before reaching maturity; when infected plants survive, they bear empty panicles.

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The fungus has micro and macroconidiophores bearing micro and macroconidia; respectively .Microconidiophores are single, lateral andformed from hyphae, while macroconidiophores consist of a basal cell bearing 2-3 apical phialides which produce macroconidia. Macroconidia are multi-celled (3 to 7 septate), slightly curved or bent at pointed ends, typically canoe-shaped and measure 25-60 x 2.5-4 µm. Microconidia are one-celled, ovoid or oblong, borne singly in chains or false head on laterally borne conidiophores and measure 5-12 x 1.5-2.5 µm. Some conidia are intermediate, with two or three cells, oblongor slightly curved.

False Smut (Ustilaginiodea virens Takahashi)

The disease occurs in the field at hard dough to mature stage of the crop. The fungus transforms individual grains of the panicle into greenish spore balls that have velvety appearance. The spore balls aresmall at first and visible in between glumes, grow gradually to reach 1 cm or more in diameter and enclose the floral parts. They are covered with a membrane that bursts as a result of further growth. Thecolor of the ball becomes orange and later yellowish green, or greenish black. At this stage, the surface of the ball cracks. The outermost layer of the ball is green and consists of mature spores together with the remaining fragments of mycelium. The outer soporiferous region is three-layered. The outermost layer is greenish black with powdery spores; the middle layer, orange; the innermost, yellowish.


Chlamydospore (a thick- or double-walled asexual spore formed directlyfrom a vegetative hyphal cell that functions as a resistant or overwintering stage) formed on the spore balls are born laterally on minute sterigmata (a small, arclike, usually pointed hyphal branch or structure supporting a spore) on radial hyphae, and are spherical to elliptical, warty, olivaceous, 3-5 x 4-6 µm; younger spores are smaller, paler, almost smooth. Chlamydospores germinate in culture bygerm tubes, which become septate and form conidiophores bearing conidia at the tapering apex. These conidia are ovoid and very minute.


Rice Blast (Pyricularia grisea Sacc.)

The fungus attacks all aboveground parts of the rice plant. Depending on the site of symptom rice blast is referred as leaf blast, collar blast, node blast and neck blast. In leaf blast, the lesions on leaf blade are elliptical or spindle shaped with brown borders and gray centers. Under favorable conditions, lesions enlarge and coalesce eventually killing the leaves. Collar blast occurs when the pathogen infects the collar that can kill the entire leaf blade. The pathogen also infects the node of the stem that turns blackish and breaks easily; this condition is called node blast. Neck of the panicle can also be infected. Infected neck is girdled by a grayish brown lesion that makes panicle fall over when infection is severe. The pathogen also causes brown lesions on the branches of panicles and on the spikelet.

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Mature conidia are usually three-celled or 2 septate, pyriform (pear-shaped), hyaline or colorless to pale olive, 19-27 x 8-10 mm in size and exhibit a basal appendage at the point of attachment to the conidiophore. Conidia usually germinate from the apical or basal cells. The conidiophores are pale brown, smooth and straight, or bending. The perfect stage is rarely found in the field.

Sheath Blight (Rhizoctonia solani Kuhn)The lesions are usually observed on the leaf sheaths although leaf blades may also be affected. The initial lesions are small, ellipsoid or ovoid, and greenish-gray and usually develop near the water line inlowland fields. Under favorable conditions, they enlarge and may coalesce forming bigger lesions with irregular outline and grayish-white center with dark brown borders. The presence of several large spots on a leaf sheath usually causes the death of the whole leaf.

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Instead of spores, the rice sheath blight fungus produces sclerotia measuring usually 1 to 3 mm in diameter and relatively spherical. Sclerotia are formed on or near the spots and can be easily detached from the plant. Under natural conditions, sclerotia usually occur singly but may sometimes coalesce to form larger masses. They are whitish when young and turn brown or dark brown when old.






Brown Spot (Bipolaris oryzae)

Brown spot may be manifested as seedling blight or as a foliar and glume disease of mature plants. On seedlings, the fungus produces small, circular, brown lesions, which may girdle the coleoptile and cause distortion of the primary and secondary leaves. In some cases, the fungus may also infect and cause a black discoloration of the roots. Infected seedlings are stunted or killed. On the leaves of older plants, the fungus produces circular to oval lesions that have alight brown to gray center surrounded by a reddish brown margin. On moderately susceptible cultivars, the fungus produces tiny, dark specks. When infection is severe, the lesions may coalesce, killing large areas of affected leaves. The fungus may also infect the glumes,causing dark brown to black oval spots, and may also infect the grain,causing a black discoloration.


The brown spot fungus produces multiseptate (three or more septae) conidiophore, singly or in bundles (generally 17), up to 600 mm long,





and 4-8 mm wide. Conidia are generally curved, boat, or club-shaped, with 6 to 14 transverse septa or cross walls, 63-153 x 14-22 mm, and often with a minute, slightly protruding hilum (dot at the point of attachment to a conidiophore).

Bacterial Blight (Xanthomonas oryzae pv. oryzae)

Water-soaked lesson usually starting at leaf margins, a few cm from the tip, and spreading towards the leaf base; affected areas increase in length and width, and become yellowish to light brown due to drying; with yellowish border between dead and green areas of the leaf. It is usually observed at maximum tillering stage and onwards. In severely diseased fields grains may also be infected. In the tropics infection may also cause withering of leaves or entire young plants (refers as kresek) and production of pale yellow leaves at a later stage of the growth.


Bacterial Blight (Xanthomonas oryzae pv. oryzicola)

Bacterial Leaf Streak first appears as short, water-soaked streaks between the veins, which become longer and translucent and turn to light brown or yellowish brown. Thus, large areas of the leaf may become dry due to numerous streaks. At the late stage the disease is indistinguishable from the bacterial leaf blight.




Tungro (Rice Tungro bacillifor virus and spherical virus)

Plants affected by tungro exhibit stunting and reduced tillering. Their leaves become yellow or orange-yellow, may also have rust-colored spots. The leaf discoloration starts from the tip and may or may not extend to the lower part of the leaf blade; often only the upper portion is discolored. Young leaves may have a mottled appearance and old leaves show rusty-colored specks of various sizes. Infected plants have delayed flowering. The panicles are small and notcompletely exerted, and bear mostly sterile or partially-filled grainsoften covered with dark brown specks. Tungro are transmitted by the green leafhoppers.






Grassy Stunt (Rice grassy stunt virus)

Plants affected by this disease, show severe stunting; excessive tillering, with short leaves that are narrow and, pale green to pale yellow in color. They may have newly-expanded leaves that maybe mottled or striped and may also have numerous small, irregular, dark brown or rust-colored spots. Brown plant hopper transmits this disease.

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Ragged Stunt (Rice ragged stunt virus)

Affected plants show stunting that may have reduced tillering. The leaves are short, dark green, and serrated along one or both edges giving a ragged appearance. The leaf blades are often twisted form a spiral. The vein swellings appear on leaf sheaths, leaf blade and culms and nodal branches are developed at later growth stages. Brown plant hopper transmits the disease

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RICE PESTSRice Leaffolder

Latin Names: Cnaphalocrocis medinalis (Guenee), Marasmia patnalis (Bradley), M. exigua (Butler)

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A larva removes the leaf tissues, folds a leaf blade together and glues it with silk. The larva, then, feeds inside the folded leaf creating longitudnal white transparent streaks on the blade. Therefore, symptoms include: longitudinal and transparent whitish streaks on damaged leaves, tubular folded leaves, leaf tips sometimesfastened to the basal part of leaf and heavily infested fields appearscorched with many folded leaves.There are three species of leaffolder and the adult moths can be distinguished by the markings on the wings. The adult is whitish yellow or golden yellow. It has three black bands on the forewings, either complete or incomplete. It has a wing span of 13 to 18 mm.The pupa is light brown or bright brown. With age, it turns reddish brown. It is 6 to 12 mm long.Neonate larvae are yellow. With age, they turn yellowish green with brown or black heads. They have distinct pinnaculae or one to two pairs of subdorsal spots on the mesonotum or metanotum. A third species lack spots on the notum. The apex of their pronotum is angulated, convex or always straight. They are from 8.5 to 25 mm long.The newly laid egg is jelly-like and transparent. It is oblong with anirregular upper surface. The mature egg is ovoid and whitish yellow. It is ventrally flattened.Feeding damage of the rice leaffolders during the vegetative stage maynot cause significant yield losses. Crops generally recover from these

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damages. Leaffolder damage at the reproductive stage may be important.Feeding damage, if it is very high, on the flag leaves may cause yieldloss.The highly visible symptoms are often the cause of farmers’ early season insecticide use. Most of these sprays have little or no economic returns. Instead, they can cause ecological disruptions in natural biological control processes, thus enhancing the development of secondary pests, such as planthoppers. In some countries, about 40%of farmers’ sprays target leaffolders. Through participatory experiments, farmers who stopped early season sprays had no yield lossand saved up to 15-30% in pesticide costs. The spray reduction also decreases farmers’ exposure to health risk posed by pesticides.

Armyworms

Latin Names: Mythimna separata (Walker), Spodoptera mauritia acronyctoides (Guenee), Spodoptera exempta (Walker)

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The armyworms damage the plants by cutting off leaf tips, leaf margins, leaves and even the plants at the base, and even the rice panicles. Symptoms include:

Fed-upon leaf tips or along leaf margins Fed-upon whole leaves leaving only midribs

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Removal of whole leaves and plants Cut on stem or plant base Cutting off rice panicles from base







The adult is either grayish black with black markings on its forewingsor pale red-brown with fewer markings on the front wings or it has pale red-brown forewings with two pale round spots. Its hindwings havetwo colors, dark red-brown on top and white underneath or the hindwings are lighter than the forewings. The insect has a body lengthof more than 15.0 mm.The pupa is 13.0 to 20.0 mm long. It is dark brown.Young larvae have two pairs of prolegs. They have brown to orange headwith an A-marking on the frons. They are grass green with gray dorsal stripes. The body of mature larva has shades of green, gray, brown, pink, or black with dorsal or subdorsal longitudinal light gray to black stripes or clear yellow stripes running along the entire length of the body. Two rows of C-shaped black spots are either present or absent along the back. They are 31.0 to 45.0 mm long.The rounded eggs are either bare or covered with a thin layer of blackish felt and are laid in oblong clusters. They are subspherical and greenish white or pearly white. They turn yellow or dark brown with age. The rice armyworm is present in all stages of the rice crop. It becomes very destructive when the population is high that it can totally devour the host plant. Mature panicles are cut off from the base of the plants.

This sporadic pest occasionally causes losses especially when an outbreak occurs. They become highly abundant and can move in large groups from field to field just so to feed and attack the crop.

Zigzag Leafhopper

Latin Names: Recilia dorsalis (Motschulsky)

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Symptoms:

Drying of leaf tips Whole leaves become orange Leaf margins become orange and curl

Adult hoppers have characteristic zigzag white and brown pattern on the front wings. The female adult is 3.5-3.8 mm long. The male is 3.1-3.4 mm long.Neonate nymphs are yellowish brown with a white abdomen, dull pink eyes, a deep brown thorax, and brown patches on the vertex. Mature nymphs are brown with darker brown markings.Individual eggs are cylindrical and white. They measure 0.9 mm long and 0.2 wide. With age, they turn to straw color. Two distinct red spots appear as eyes of the developing nymph prior to hatching.

In large numbers, these insects become important because they transmitviral diseases such as rice tungro, dwarf, and orange leaf viruses. They feed on the rice plant during all most all the stages of the cropparticularly the vegetative stage.

Zigzag leafhopper may transmit virus diseases but its low population makes the insect a minor pest of rice.

Ants

Latin Names: Solenopsis geminata (Fabricius)

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Symptoms:

Mainly occur in upland rice Missing rice seeds No plants or missing plants Loss of plant stand Patchy distribution of damage in the field Increase the incidence of diseases vectored by homoptera


Adult ants have reddish brown body with brown head. They have robust mandibles and mandibular teeth. Their pupae are whitish in color and they develop in the nests. The queen ant usually lays 75 to 125 eggs in a cluster. Aside from the rice plant, ants prefer food with high protein content, but will feed on almost anything.

Feeding damage caused by ants occur during the seedling stage of the rice crop. Ants are minor pests of rice. If damage is light, the rice crop can often recover from the loss in plant stand due to seed removal by the ants.

Stem Borers

Latin Names: Scirpophaga incertulas (Walker), S. innotata (Walker), Chilo suppressalis (Walker), C. auricilius Dudgeon, C. polychrysus (Meyrick), Sesamia inferens(Walker)

Symptoms:

Deadhearts or dead tiller that can be easily pulled from the baseduring the vegetative stages

Whiteheads during reproductive stage where the emerging panicles are whitish and unfilled or empty

Tiny holes on the stems and tillers Frass or fecal matters inside the damaged stems


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The female YSB moth has a pair of black spots at the middle of each whitish, light brown to yellowish forewing. It has a wingspan of 24-36mm. Its abdomen is wide with tufts of yellowish hairs all over. The male, gray or light brown in color, is smaller and has two rows of black spots at the tip of the forewings. It has a wingspan of about 20-30 mm. Its abdomen is slender toward its anal end and is covered with thin hairs dorsally. The YSB pupa is pale green and measures about 12 mm long. It is enclosed in a white silk cocoon. Fresh cocoon is pale brown and turns dark brown with age. The first instar YSB larva is about 1.5 mm long with yellowish green body. A full-grown larva has brown head and prothoracic shield and measures 20 mm. The egg mass of YSB is covered with brownish hairs from the anal tufts of the female. Individual eggs of are white, oval, and flattened.The male and female WSB moths are immaculately white. The male moth issmaller than the female. Both adults have a tuft of long hairs on the thorax. Its fresh pupa is whitish and soft-bodied and turns brown withage. The larva is whitish to light yellow and without body markings. Amature larva is 25 mm long. The egg mass of WSB is disc-shaped and is covered with hair. It measures 3.5 mm to 6 mm long.The SSB adults are brownish yellow with silvery scales. It has a row of 7 or 8 small black dots on the terminal margin of each forewing. The pupa is reddish brown and it measures about 11 to 13.5 mm long. Ithas two ribbed crests on the pronotal margins. The head has two short horns. The last segment of the pupa has visible spines. Neonate larvaehave large shiny brown or orange head. Their prothoracic shields have



the same color as their head. Their body is light brown or pink. Five rows of brown or pale purple longitudinal stripes run the entire length of the body. The stripes are found dorsally and laterally. Mature larvae measure 20 to 25 mm long. Newly laid eggs are glisteningwhite. They are disc-shaped. Mature eggs turn yellow. They are black when about to hatch.

The stem borer larvae bore at the base of the plants during the vegetative stage. On older plants, they bore through the upper nodes and feed toward the base. Late infestation causes whiteheads.

The yellow stem borer is an important pest of irrigated rice in South and Southeast Asia. In the Philippines, it caused about 5% to 10% yield loss. About 1% to 19% yield loss in early planted rice crops and38% to 80% yield in late-planted rice were reported in India.The white stem borer (WSB) is an important pest in rainfed wetland rice. In West Java, Indonesia, this pest has been observed in irrigated rice fields. WSB causes occasional outbreaks, especially in the Indramayu and Cirebon areas. Along the northern portion of West Java, an outbreak occurred and destroyed 15,000 ha of rice fields during the wet season of 1989-90.The striped stem borer is one of the most important insect pests in temperate Asia. During the vegetative stage, larval feeding causes deadheart. The rice plant can compensate by growing new tillers. At the reproductive stage, feeding causes whitehead. The damage could reach 100%.The gold-fringed stem borer is a major pest of sugarcane in India and Taiwan. It is a pest of maize and upland rice. Yield losses of 30% and20% due to this insect were reported in India and Bangladesh, respectivelyAmong the stem borers, the dark-headed and the pink stem borer are less important. The pink stem borer is polyphagous and prefers sugarcane to rice.

SnailsLatin Names: Pomacea canaliculata (Lamarck)

Symptoms: Missing seedlings Floating cut leaves

Cut stems Decreased plant stand Sparse or uneven stand








The golden apple snail has a muddy brown shell. The shell is lighter than the darker and smaller native snails. Its succulent flesh is creamy white to golden pinkish or orange-yellow. The male has a convexoperculum that curves out or away from the shell, whereas the female lid curves into the shell.Neonates or the newly hatched snails have soft shell. The juveniles oryoung snails are <1.5 to 1.6 cm. Medium-sized snails have a shell height of 2 to 3 cm.The eggs are bright pink or strawberry pink. With age, they lighten incolor or turn light pink when about to hatch.

The golden apple snails rasp plant tissue and cut of stems with their file-like radula or horny tongue.

It is a serious pest of young rice seedlings because it often cuts andkills growing seedlings. It also leaves large patches without rice, isparticularly a more serious problem in direct-seeded crops.

The golden apple snail is considered a major problem in direct-seeded rice.During dry periods or drought, the golden apple snails remain inactivein rice fields. They become active when fields are flooded. In the Philippines, 400,000 ha of rice were reported to be infested in 1988. In 1989, more than 16,000 ha suffered from golden apple snail damage in Japan.



The golden apple snail is now considered of quarantine importance in many countries, eg., Australia, Malaysia, and United States.

Rice Skipper

Latin Names: Pelopidas mathias (Fabricius), Parnara guttata Bremer and Grey

Symptoms: Removal of leaf tissues and veins and sometimes leaving only the

midrib Rolling down of leaf tip or folding two edges of the same leaf

or two adjacent leaves and tying them with silken threads to make a protective chamber


The adults of the two species are light brown with orange markings andwhite spots on the wings. They can be distinguished by the pattern of white spots on the wings. One adult has seven C-shaped white spots on the front wing and four white spots on the hind wing. The other one has four small spherical white spots and two elongated spots on the front wing and the hind wing lacks spots.The larval bodies of both species are green. They differ in the coloration on the head. One larva has reddish vertical bands at each lateral side of the head and the other one has brown bands that are closer together and W-shaped.The mature caterpillar measures 50 mm long.

The pupae of both species are light brown or light green. They have pointed ends.The eggs are white or pale yellow and spherical. They are pearl-like in appearance.

Rice skippers feed on rice foliage from tillering, stem elongation to panicle initiation stages of the rice crop. Feeding damage is not thatimportant as the insect is considered a minor pest.

Rice skippers are easily controlled because of the low potential severity and their low population density. They are minor pests of rice and occasions of yield loss are very rare.

Rice Caseworm

Latin Names: Nymphula depunctalis (Guenee)

Symptoms:

Leaf cases floating on water Leaves cut at right angles as with a pair of scissors Leaves with papery upper epidermis that were fed on Skeletonized leaf tissues usually appear ladder-like





The adult moth is about 5 mm long. It is bright white with light brownand black spots.First instar larva is pale cream with light yellow head. It is 1.2 mm long. With age, the larva turns greenish. It has branched and thread-like gills along the sides of the body.The pupa is cream in color and about 5.5 mm long. Mature pupa is silvery white.Individual egg is circular, flattened, and measures 0.5 mm in diameter. It is light yellow and has a smooth surface. Mature eggs aredarker and develop two purplish dots.

The larva scrapes the green tissue of the leaf with only the white epidermis remaining. The white epidermis appears ladder-like because of the back and forth motions of the larval head during feeding.

The rice caseworm feeds on rice during the seedling and tillering stages of the crop. Its damage usually starts in a flooded seedbed butdoes not occur after the maximum tillering stage.

The rice caseworm is commonly found in rice fields in low populations.It can build up and cause patches of severe defoliation that results



in stunted growth and death of plants because of pesticide use, control practices, and ecological disruptions by weather.The rice plants can recover from the damage if there are no other defoliators present. However, maturity may be delayed for 7-10 days.

Mealybugs


Latin Names: Brevennia rehi (Lindinger)

Symptoms:

Wilting Plant stunting Yellowish curled leaves Damaged spots or chakdhora or soorai disease Not uniform pattern of damage


The pale yellowish male adults have a single pair of wings and a waxy style-like process at the end of the abdomen. The first and middle legs of the male are approximately equal, whereas the last or third legs are longer. The body is 0.7-0.9 mm long.Adult females are oblong and wingless. They are reddish white and soft-bodied. Their body is covered with a distinct waxy or powdery coating. They measure about 1.2-3.0 mm long and 0.5-1.5 mm wide. They resemble woodlice in shape.The first instar nymphs or crawlers measure 0.1-0.2 mm wide and 0.3-0.5 mm long. Mature crawlers are 3-4 mm long.The elongated or oval eggs are hyaline to yellowish to pinkish. They are 0.3 by 0.5 mm. They are covered with wax. The eggs turn grayish red when about to hatch.

Both the adults and nymphs remove plant sap using their sucking mouthparts.

The rice mealybug feeds on rice during the tillering and stem elongation stages of the rice crop. Favorable conditions that cause high populations of the pest may cause yellowing and stunting of the crop.



The rice mealybug causes heavy losses to crops in Bangladesh, India, and Thailand. High density (> 100 mealybugs/hill) caused plants to wilt and die.

Green Semilooper


Latin Names: Naranga aenescens (Moore)

Symptoms:

Leaves scraped exposing the lower epidermis Leaf edges damaged






Both the male and female moths are yellow-orange. Their forewings havetwo diagonal dark red bands.The young pupa is light green and turns brown as it matures.The larval head and body are yellow-green. White lines run along the entire length of the body.The yellow eggs are spherical. Mature eggs have purple to violet markings.

Both the young and mature larvae feed on leaves. Young larvae scrape the leaf tissues of the epidermis of the leaf blade leaving only the lower white surface. Matured larvae often cut out sections of leaf blades especially in the margins.

The insect pest is found during the seedling and tillering stages of the rice crop. Its damage is not important because green semilooper isonly a minor pest of rice.

They are vectors of viruses such as tungro, yellow dwarf, yellow-orange leaf, transitory yellowing, and dwarf.

Cutworm

Latin Names: Spodoptera litura (Fabricius)

Symptoms

Seedlings cut at bases Leaf surfaces skeletonized Entire plants devoured


The adult insect is a moth with dark brown forewings having distinctive black spots and white and yellow wavy stripes. Its hindwings are whitish with gray margins and somewhat irridescent.The moth has a black or brown pupa, which measures 22.5 mm long and 9.2 mm wide.The larva is the destructive stage. The newly hatched larvae are tiny and about 1 mm long, and are greenish. The full-grown larva has a cylindrical body, brown or brownish black tinged with orange. One to two dark spots are visible on the thoracic segments near the base of the legs. The abdominal segments have two light brownish lateral lineson each side, one above and one below the spiracles. Above the top lines is a broken line composed of velvety semicrescent patches that vary in color among individuals.Individual eggs are pearly white and round and have a ridged surface.

The larva feeds on leaves and sometimes cut off the stems.

The larva attacks rice during the vegetative stages of the crop.



The cutworm is polyphagous and may become serious during the seedling stage, especially in upland rice.

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Crop Pests That Cause Rice Diseases

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