Major Pest and Plant Diseases of Rice (PDF)

MAJOR PEST AND PLANT DISEASES OF RICE AND THEIR MANAGEMENT AGR. VIRGILIO M. VERO Any disturbance that interferes with the normal structure (e.g., height, tiller, leaves), functions (e.g., reduced vigor, early death), and economic value (e.g., reduced yield, poo...

MAJOR PEST AND PLANT DISEASES OF RICE AND THEIR MANAGEMENT AGR. VIRGILIO M. VERO Any disturbance that interferes with the normal structure (e.g., height, tiller, leaves), functions (e.g., reduced vigor, early death), and economic value (e.g., reduced yield, poor quality, produce) of plant (HOST) is a DISEASES. A plant disease can identify (DIAGNOSE) through the characteristic manifestation of diseased conditions (SYMPTOMS) and the presence of visible structures (SIGNS) produced by the pathogens. The causal agent (PATHOGEN) may be either a living (BIOTIC) or nonliving (ABIOTIC) agent. Biotic agents have the ability to enter and colonize plant parts and other plants (INFECTIOUS). When a disease increases rapidly in a large plant population overtime, a serious outbreak occurs (EPIDEMIC).  HOST A host is a plant that can become infected by a pathogen.  PATHOGENS Infectious plant diseases are caused by living (biotic) agents, or pathogens. These pathogens can be spread from an infected plant or plant debris to a healthy plant.  ENVIRONMENT This is the most complex of the three, but can also be manipulated to reduce root disease issues, Any environment that cause plant stress can make a plant more susceptible to plant disease. FIELD GUIDE ON MAJOR RICE PEST, DISEASE AND THEIR MANAGEMENT MAJOR PLANT DISEASES OF RICE (Oryza sativa) BLAST (Magnaporthe grisea) FUNGAL DISEASE  WHERE TO FIND? ON LEAVES (LEAF BLAST) ON NODES OF SYMPTOMS: Small to spindle- TILLERING (NODE shaped spots with brown BLAST) border and gray center; spots SYMPTOMS: Black, join resulting in drying and rotten node that later death of leaves breaks. SUSCEPTIBLE STAGE: SUSCEPTIBLE STAGE: Seedling to tillering. Tillering  WHERE TO FIND? ON BASED OF THE ON NODES OF PANICLE (PANICLE BLAST) TILLERING (NODE BLAST) SYMPTOMS: Black node SYMPTOMS: Black, panicle and later breaks; rotten node that later unfilled panicle breaks SUSCEPTIBLE STAGE: SUSCEPTIBLE STAGE: Tillering Booting to heading  WHERE TO FIND? ON SEEDS: (usually found at the basal portion of the grain); has very low seed transmission rate. SYMPTOMS: Sterile lemma and a rachilla discolored with fungal growth. SUSCEPTIBLE STAGE: Maturity  SHEATH BLIGHT (Thanatephorus cucumeris) FUNGAL DISEASE  WHERE TO FIND? ON LEAF SHEATH: Leaf sheaths above the water line (sclerotia may be present on affected areas). SYMPTOMS: Oval gray spots that later enlarge; with black brown margins and gray center. SUSCEPTIBLE STAGE: Tillering to heading  WHERE TO FIND? ON LEAVES: Basal portion of the leaves SYMPTOMS: lesions are irregular, banded with green-brown coloration; center is grayish white; leaf withers; panicle exertion affected when flag leaf is infected. SUSCEPTIBLE STAGE: heading and at maturity  BROWN SPOT (Cochliobolus miyabeanus) FUNGAL DISEASE  WHERE TO FIND? ON LEAVES LEAVES: (common in plants in the shaded area, in potash deficient and saline fields) SYMPTOMS: small, circular, oval spots fairly scattered on the leaves with gray center; spots fuse and leaf withers SUSCEPTIBLE STAGE: tillering  WHERE TO FIND? ON SEEDLINGS: leaf coleoptile and roots (seedborne; seedling infection arises from infected seeds). SYMPTOMS: brown spots on leaf coleoptile; roots with black lesions. SUSCEPTIBLE STAGE: seedlings on seedbed  WHERE TO FIND? ON GRAINS: fungus enters the glume and infects the seed. SYMPTOMS: black spots on glumes and covered with dark brown velvety mat of fungal spores; seeds become discolored and shriveled. SUSCEPTIBLE STAGE: maturity STEM ROT (Magnaporthe salvinii) FUNGAL DISEASE  WHERE TO FIND? LEAF SHEATHS: near water line; split open affected stem to see fungal mycelium and black sclerotia inside. SYMPTOMS: small, black irregular lesions on outer leaf sheaths near the water line; lesions enlarge and infect inner leaf sheaths and stem; leaf sheaths rot and many sclerotia are embedded in decaying tissues. SUSCEPTIBLE STAGE: late tillering to maturity.  SHEATH ROT (Acrocylindrium oryzae) FUNGAL DISEASE  WHERE TO FIND? At the uppermost leaf sheath that encloses emerging panicle (white powdery fungal mass inside infected sheath) SYMPTOMS: irregular lesions with gray center and brown margins; on the sheath, panicle emerged partially; and mostly unfilled seeds SUSCEPTIBLE STAGE: from tillering to panicle initiation  WHERE TO FIND? On grains SYMPTOMS: brown discoloration, chaffy, and covered with white to light pink fungal growth SUSCEPTIBLE STAGE: maturity (the pathogen can survive for 10 months on seeds while in storage)  BACTERIAL LEAF BLIGHT (Xanthomonas oryzae) BACTERIAL DISEASE  WHERE TO FIND? KRESEK: usually found in seedbed and newly planted seedlings. SYMPTOMS: tiny water-soaked spots on lower leaves; spots enlarged, turn yellow and dry rapidly; seedling wilts. SUSCEPTIBLE STAGE: seedling  WHERE TO FIND? ON LEAF (LEAF BLIGHT): leaves (presence of opaque dew drops on the surface of lesions in the morning). SYMPTOMS: water-soaked stripes that later cover a large area of leaf blade; lesions are grayish white with wavy light brown margin. SUSCEPTIBLE STAGE: reproductive to maturity.  BACTERIAL LEAF STREAK (Xanthomonas oryzae) BACTERIAL DISEASE  WHERE TO FIND? On leaves SYMPTOMS: fine translucent streaks that enlarge lengthwise; coalesce (‘merging lesions’) form large brown affected leaves; later stage, entire leaf turns brown and withers SUSCEPTIBLE STAGE: tillering to maturity NOTE: wind-borne, present in lowland and upland fields  TUNGRO VIRAL DISEASE  NOTICE CHANGE ON Plant height and leaves SYMPTOMS: mottled young leaves; older leaves are yellow to yellow-orange; stunted with slight reduction in tiller number. SUSCEPTIBLE STAGE: seedling to tillering. NOTE: spread only by the green leafhopper (GLH); widespread occurrence. GRASSY AND RAGGED STUNT VIRAL DISEASE  GRASSY STUNT NOTICE CHANGES ON: plant height and leaves. SYMPTOMS: severe stunting; profuse tillering; erect growth habit; leaves are short, narrow, pale green to yellow with numerous small dark brown spots. SUSCEPTIBLE STAGE: from seedling to tillering  RAGGED STUNT NOTICE CHANGES ON: plant height and leaves. SYMPTOMS: stunted plant; torn or ragged leaves with twisted tip; vein swellings on leaves and near leaf collar; plant remains green. SUSCEPTIBLE STAGE: from seedling to tillering. MAJOR HARMFUL INSECTS OF RICE (Oryza sativa) MOLE CRICKET (Gryllotalpa orientalis) IDENTIFYING MARKS The insect is light brown, the wings are folded and do not cover the full length of the abdomen. The forelegs are broad, curved, with strong teeth-like structures for digging soil. The hind legs, eyes, and antennae are small and almost invisible. The adult is 25-35 millimeters (mm) long.  WHERE TO FIND? They live in all rice environments but are most prevalent in non-flooded upland rice fields with damp soil. They are usually found in burrows along the levees or shelter in seedbeds during daytime. Heaps of soil mark the entrances to extensive burrows in the soil. They prefer moist soils with high organic matter. In areas where the dry season is short, they can multiply in unusually large numbers. They cannot survive in the rice fields after flooding.  DAMAGE Mole cricket damage is greater near the field borders where they relocate after tillage operations. Susceptible growth stages are from seedling to tillering. At night, adults and nymphs feed on sown seeds and roots of rice plants either in the seedbed or of young seedlings, causing bare patches in the field. In older plants, tillers near the soil surface may be chewed on, but the damage can generally be tolerated. Young and newly planted seedlings are most commonly attacked in the early part of the season before fields are flooded. LIFE CYCLE  LIFE CYCLE Females burrow bunds and construct hardened cells in which eggs are laid. Each cell contains 30-50 eggs. Depending on the temperature, eggs hatch in 15-40 days. Their capacity to migrate is limited. They also eat each other. Nymphs become adults in 3-4 months. Adults are attracted to light traps. MANAGEMENT OPTION CULTURAL CONTROL Bund shaving and plastering with fresh wet soil kills their eggs. Levelling fields provides better water control, which can limit mole cricket invasions. Collecting nymphs and adults during land preparation, bund repairs, and seedling pulling in nursery beds reduce their population. CULTURAL CONTROL Maintaining standing water in the field prevents their damage. After rains, they are attracted to light sources during nighttime. They can then be collected, destroyed, and even eaten. Varieties with long and dense fibrous root systems like many of the modern varieties tolerate damage better. BIOLOGICAL CONTROL They eat each other when they are together. Hence, they regulate their own numbers. Nymphs and adults have many natural enemies such as big wasps and nematodes CHEMICAL CONTROL Poisoned baits made by mixing moistened rice bran and insecticide, placed along rice bunds or drier areas of the field, kill night-foraging mole crickets. Foliar insecticides are ineffective while granular insecticides are effective but expensive. LEAF FOLDER (Cnaphalocrocis medinalis) IDENTIFYING MARKS The adults are light brown moths with a wingspan of 12-20 mm. A dark terminal band characterizes the outer margins of the wings. Larvae are transparent green and measure up to 2.5 centimeters (cm) in length. Adults are attracted to light at night; at daytime, they are mostly found in shaded or grassy areas.  WHERE TO FIND? Leaffolders live in all environments but are abundant during the rainy season. High humidity, shady areas of the field, and excessive use of nitrogenous fertilizers favor their rapid multiplication.  DAMAGE Leaffolders inflict damage in the larva stage. Plants are susceptible to attack up to 10 weeks after transplanting (i.e., from seeding to flowering). Infestation usually occurs during late growth stages of the rice crop. The larvae infest the leaves of young plants; they fasten the edges of a leaf together and live inside the rolled leaf. Heavy infestation makes the plant look burnt, sickly, and twig-like. LIFE CYCLE  LIFE CYCLE The eggs are laid singly or in pairs on the young leaves. They are flat, oval, and whitish yellow. Eggs hatch to larvae in 4-7 days. The transparent green, slender larvae feed inside the folded leaves for 15-25 days before pupation. Adults emerge 6-8 days from pupa. Total life cycle takes 25-52 days. For adult moths, the potential sugar source in the field is the honeydew excreted by planthoppers. MANAGEMENT OPTION  CULTURAL Clipping tops of bundled seedlings before transplanting removes eggs. Removing weeds prevents its buildup. Reducing amount of nitrogenous fertilizer and splitting the application make rice plants less favorable for egg laying and leaffolder attack. Potassium makes cell walls thicker because of greater silica uptake, making the plant more tolerant to leaffolders.  CULTURAL Higher infestation occurs in shady places. Wider spacing reduces infestation. Early planting enables plants to escape a high degree of defoliation. Most modern rice varieties can compensate for leaffolder defoliation, making insecticides no longer necessary for control. Varieties with narrow leaves are more resistant to leaffolders than varieties with wider leaves.  BIOLOGICAL Small wasps and crickets kill the eggs. Big wasps, damselflies, ants, and carabid (guitar) beetles prey on larvae. During the wet season, frequent moderate rainfall enables pathogens to wipe out the entire larval population. Fungi and nuclear polyhydrosis virus (NPV) kill the larvae. Spiders eat adults CASEWORM (Parapoynx stagnalis) IDENTIFYING MARKS The adults are small, delicate, snowy-white moths with pale brown or black spots on the wings. They have a wingspan of 15-25 mm. Larvae are pale translucent green, with a pale orange head. There are easy early detection methods to know the pest activity in the area. Moths are attracted to light traps, which also indicates whether there is pest activity in the area.  WHERE TO FIND? Caseworm is found in irrigated and wetland areas where standing water in the field is a prerequisite for larval survival. The infestation is severe on dwarf, compact, heavy-tillering, and high-yielding varieties during the rainy season. Defoliation occurs before maximum tillering of rice  DAMAGE The larva is the damaging stage. The larvae cut the tip of the leaves as though by scissors, to make floating cases. They use these cases as a reservoir of water, for breathing, and to protect themselves against predators. The cases also facilitate their dispersal through flowing water and wind. During the day, the larvae remain inside the case and float on the water surface.  DAMAGE At night, they feed on the lower side of leaves lying flat on the water, or on submerged leaves. In general, a young vigorously growing crop recovers from defoliation, but maturity may be delayed by 7-10 days. In heavily infested crops, however, the loss of photosynthetic tissue can be critical and seedlings may die. Older plants are generally more tolerant to damage, and mature plants are seldom attacked. Susceptible growth stages are from seedling to tillering. LIFE CYCLE  LIFE CYCLE The eggs are laid singly on the undersurface of the lower leaves touching the water surface. The eggs are pale, yellowish green, and laid in one or two long rows. They hatch to larvae in 2-6 days. After a few days, the first instar larvae construct floating cases. Their cases are replaced as the larvae grow. Larvae are semiaquatic and can withstand prolonged immersion as they have slender gills along their sides.  LIFE CYCLE The fully developed larva is 13-20 mm long. Pupation takes place inside the last larval case, which is fastened Caseworm damage. Note the cut leaf cases and standing water. Life cycle of a caseworm adult 4-7 days 2-6 days pupa egg larva 6 to the base of the stem. The adult emerges in 4-7 days from the pupa. Adults can live up to 3 weeks, and are attracted to light traps. MANAGEMENT OPTION  CULTURAL Transplanting older seedlings limits the period of larval attack. Draining the field for several days kills caseworm larvae. Sparse planting reduces damage.  BIOLOGICAL Big wasps and water beetles kill larvae. Spiders, dragonflies, and birds prey on the adults.  CHEMICAL Caseworm larvae are highly susceptible to foliar and granular insecticides. Apply insecticides only to fields with standing water and only when larvae are present. RICE SKIPPER (Pelopidas mathias) IDENTIFYING MARKS The adult is a stout brown butterfly with small white spots on the wings. Adults are active during the day, making darting, erratic movements from which the name skipper was coined. Adults rest in the shade during the day. Larvae are elongated with a constriction behind the head accentuating their flattened shape.  WHERE TO FIND? Occurs in all rice environments, but prevalent in rainfed rice. Upland environments with their diverse microhabitats can provide more favorable sites than lowland rice plains. In some cases, upland rice is most affected. Droughts, downpours, floods, or misuse of pesticides can cause their outbreaks because useful organisms regulating them get depleted.  DAMAGE Defoliation is the first sign of the presence of skipper larvae. The larvae are difficult to see because they hide in the leaf tubes and feed mostly at night. Damage occurs in patches or clusters, around where females lay their eggs. Damage is not uniformly dispersed across a field. The larvae feed on leaves from the margins inwards and then parallel to the midrib.  DAMAGE In addition, the larvae tie with silken threads the two edges of the same leaf or two adjacent leaves to form a tube in which they live. Generally one larva is found in a fold. Damage is severe in young transplanted rice seedlings and the attack may continue until the plant matures. In severe cases, the plant does not recover. This pest adversely affects grain quality. LIFE CYCLE  LIFE CYCLE Eggs are smooth and creamy white, laid singly on the upper surface of leaves. They are semispherical with a flat base, and hatch in 3-6 days. Larvae are pale green with a vertical streak on either side of the head. Full-grown larvae measure 30-35 mm in length and covered with powdery white wax.  LIFE CYCLE They become pupae in 13-26 days. Pupae that stay in the leaf are fold spun by the larvae. The adult butterfly emerges in 7-12 days after pupation. The adults mate in the morning. MANAGEMENT OPTION  CULTURAL Dense cropping and good fertilization are important. Do not overuse or underuse nitrogen fertilizer. The experience of progressive farmers in the area can provide guidelines on the amount and number of fertilizer applications. Life cycle of a skipper adult pupa 7-12 days 13-26 days 3-6 days egg larva 8. Early plantings will normally escape colonization and significant damage.  CULTURAL Larvae and pupae can also be hand-collected. Hitting the foliage with bamboo sticks will dislodge larvae to drown in the water. Modern rice varieties can normally tolerate relatively high levels of leaf loss.  BIOLOGICAL Small wasps kill eggs. Big wasps and tachinid flies kill larvae. Orb spiders (web spinners) capture and eat the adults in flight.  CHEMICAL Same as green-horned caterpillar. Application of contact insecticides in late afternoon gives high efficacy. This is because most larvae come out at this time of day to feed on foliage. SHORT-HORNED GRASSHOPPER (Schistocerca gregaria) IDENTIFYING MARKS The adults are small, yellow and brown, about 3 cm in body length, with conspicuous, broad, brown stripes running laterally through the eyes and extending posteriorly along the wings. The antennae are short, much less than the length of the body. When in swarms, they are in their migratory phase and are called locusts.  WHERE TO FIND? They are found in all rice environments but are prevalent in rainfed areas. They tend to localize in dry areas and rice fields adjacent to grasslands where they breed. They cannot be found along rice field margins during early hours of the morning and after sunset. Pampanga and Mindanao are areas where they have caused havoc to cultivated crops, including rice.  DAMAGE Grasshoppers can damage rice at all stages of crop growth. Nymphs eat newly germinated rice seedlings and cause them to wither. Adults feed on the leaves and shoots, and may eat the base of the panicle causing it to wither and die.  DAMAGE If the emerging flowers are attacked, the resulting grains become chaffy. Swarming locusts can remove most of the foliage in a rice field leaving only the base of tillers. LIFE CYCLE  LIFE CYCLE They lay their eggs on the rice foliage or inside the soil and their nymphs are semiaquatic. MANAGEMENT OPTION  CULTURAL Flooding the stubble drowns grasshoppers. Shaving of bunds kills egg pods. Sweeping along the bunds reduces their numbers. Adults are sluggish at night, and can be picked directly from the foliage.  BIOLOGICAL Small wasps attack eggs. Parasitic flies, nematodes, and fungal and bacterial pathogens kill nymphs and adults. Birds (house sparrow), frogs, and web-spinning spiders are major predators of nymphs and adults. ARMY WORM (Spodoptera frugiperda) IDENTIFYING MARKS The adult moth has dark purplish brown forewings with numerous spots and lightcolored lines. The hind wings are whitish, narrowly banded along the outer margin. The wingspan is about 30 mm. Larvae are soil-dwelling or hide underground to avoid predation by birds. They become active at night and emerge from the ground. Larvae come in various colors, ranging from creamy white to green or dark purple, with or without stripes.  WHERE TO FIND? They live in all rice environments, but are serious in upland rice as they need dry soil for pupation. Lowland fields also occasionally Locust in gregarious stage Note armyworm larva feeding on flag leaf, when rice is at its maturity 11 suffer damage when the larvae move from one field to another. Armyworms are usually abundant in rice crops grown after a long dry spell.  DAMAGE Larva is the damaging stage. Young rice plants are often cut at ground level while older plants are only defoliated. Newly hatched larvae usually feed together on the leaf surface. The older larvae are night-feeders and are usually found in the soil around the base of the plants. Susceptible growth stages are from seedling to ripening.  LIFE CYCLE Eggs are laid in clusters of several hundreds, usually on the leaves. These egg masses, which measure about 4 x 7 mm, appear golden brown because they are covered with the body scales of the female. The eggs take 3-4 days to hatch; the larvae disperse quickly from the egg batch. Young larvae are light green. The later instars are dark green to brown on their backs, lighter underneath, and have prominent black spots on the thorax. There are often thin, light-colored lines along the body.  LIFE CYCLE There are black crescent spots next to the stripes. The head is black to dull brown with a yellow V- shaped marking. Larvae can be 50 mm long before they pupate. Larval duration is 20- 26 days. The pupae are reddish brown and are found in the soil in individual earthen cells under upland conditions. In wetland fields, larvae pupate in the rice plants or in grassy areas along the field borders. Adults are attracted to light traps WHORL MAGGOT (Hydrellia philippina ) IDENTIFYING MARKS Adult flies are dull grey. Females are 1.8-2.3 mm long. Males are slightly shorter.  WHERE TO FIND? It is a pest of rice seedlings only under irrigated and rainfed conditions. Adults prefer ponds, streams, lakes, and irrigated rice fields for their breeding. This is because the adults locate rice fields by reflected sunlight from the water surface. Hence, direct-seeded fields or seedbeds are not seriously damaged. Rice crop with a mat of azolla on the water surface repels egg laying of adult flies.  DAMAGE The larva that causes damage is called the maggot. It feeds on unopened leaves, nibbling the inner margins. When the leaves emerge from the whorl, damage can be seen as pinhole feeding areas on the leaves, with conspicuous white and yellowish linear patches near the edge of leaves. Severely damaged leaves become distorted and may break from the wind. Infested plants are stunted with few tillers.  DAMAGE Susceptible growth stages are seedling to tillering. However, the pest can cause damage to the boot leaf and developing panicles, which can lead to only partial filling of the grains. Crop maturation may be delayed up to 2 weeks, thereby increasing the risk of crop exposure to typhoons and other stresses.  LIFE CYCLE The white elongated, cigar-shaped eggs are laid singly on either surface of the leaves. Eggs hatch into maggots after 2-6 days. The maggot is transparent to light cream and moves down the leaf into the whorl on a film of water or dew, and feed within the developing leaf whorl. Larval period is 8- 17 days. Maggots pupate between leaf sheaths. Pupal period is 5-9 days. There are overlapping generations under field conditions. MANAGEMENT OPTION  CULTURAL Densely planted seedbeds do not attract adult flies. Transplanting older seedlings (25-30 days) avoids damage. Draining the field at 3-4 day intervals during the first 30 days after transplanting reduces egg laying. Adults are not attracted to light traps, and they feed on decaying matter. Direct seeding discourages its buildup because the plant covers the water surface more rapidly.  CULTURAL Dense planting decreases egg laying. Plants that cover the water surface such as azolla help prevent infestation. Increased potassium increases plant tolerance to maggots, as cell walls get thicker because of greater silica uptake. Adult flies are strongly attracted to fishmeal baits. High-tillering varieties are more tolerant than low- tillering varieties.  BIOLOGICAL Small wasps and field crickets kill eggs. Big wasps kill maggots. Water-borne and aerial-borne spiders eat adults.  CHEMICAL Control of pest in seedbed is less expensive. Treat the seedlings by soaking them overnight in a slurry of systemic insecticide and zinc oxide (ZnO2) powder solution before transplanting. Broadcast granules or mix systemic granules during the last harrowing before transplanting. Foliar sprays are effective only at 1-2 weeks after transplanting. YELLOW STEMBORER (Scirpophaga incertulas) IDENTIFYING MARKS The male and female adults are two different forms, and with distinct sexual characteristics. The female moth has one dark spot at the center of its bright yellowish forewings, while spots on the forewings of the male are not clearly seen. The wingspan is 22–30 mm. The males are smaller than the females, and do not have yellowish hairs at the end of the abdomen.  WHERE TO FIND? Yellow stem borer is a notorious pest of deepwater rice. It is abundant in aquatic habitats where flooding occurs and where multiple rice crops are grown annually. Rice plants at the vegetative and early heading stages are preferred for egg laying. Plants receiving high nitrogenous fertilizers are also favorable to larval survival.  WHERE TO FIND? Only one larva can be found in a stem. To detect the presence of moth, flush the borders of the field. To monitor larval densities, dissect tillers at tiller elongation and panicle initiation stages. For eggmasses, check seedbed or newly established crop at weekly intervals starting 3 weeks after transplanting up to 9 weeks after transplanting. Egg- laying can peak at 3.5 eggmass/m2.  DAMAGE The larvae bore into the rice stems and hollow out the stem completely. In young plants, the central leaf whorl does not unfold, turns brownish, and dries up, although lower leaves remain green and healthy. Such symptom is referred to as deadheart. In older plants, the panicles dry up with unfilled grains and turn white. Such symptom is referred to as whitehead. Both deadheart and whitehead can easily be pulled out by hand. Older plants often break where the stem was hollowed out causing lodging.  LIFE CYCLE Eggmasses are laid in batches of 80-150 near leaf tips or on the leaf sheath, and covered with the brown anal hairs of the female moth. Eggs hatch in 4-9 days. All eggs in one eggmass hatch simultaneously. The newly hatched larvae crawl toward the tip of the plant and have silken threads, and are usually dispersed by wind to adjacent rice plants.  LIFE CYCLE Then they descend toward the base and crawl between leaf sheaths and enter the stems. Larvae are hairless, pale or yellowish, and 18-25 mm long when mature. The larvae have small orange heads. One larva can be found in a stem. Larval period is 30-40 days. Before pupation, the larva makes an exit hole through which the adult moth later escapes. Pupation takes place inside the stem, often below the soil.  LIFE CYCLE Larvae seal entrance holes with silk to make stems watertight. Adult moth emerges from pupa within 7- 11 days. The adults can survive for 4-10 days without food. Adults are attracted to light traps. WHITE STEMBORER (Scirpophaga innotata) IDENTIFYING MARKS The adult of this species looks similar to the YSB except that it does not have any dark spot on the forewings, in either sex. Hence, the white stem borer (WSB) sexes look similar. Orange hairs are present at the end of the female white stem borer’s abdomen, while in yellow stem borer they are yellowish. The wingspan of the adult female is 26-30 mm, with males being smaller.  WHERE TO FIND? Predominant in rainfed areas where there is only one wet season crop per year, and where stubble are left undisturbed during the dry season. Upland rice is susceptible to WSB species, as the larvae cannot survive extremely wet situations.  WHERE TO FIND? Thus, this insect does not occur in areas with high rainfall. Early in the season, deadhearts are caused in the nurseries and in the young crop, while later in the cropping season subsequent generations cause whiteheads. WSB is presently found in the Visayas and Mindanao.  DAMAGE The larvae bore into the rice stems and hollow out the stem nodes and internodes. Young plants exhibit deadhearts while older plants develop whiteheads. Older plants often break where the stem is hollowed out causing lodging.  LIFE CYCLE Eggmasses are laid in batches of 80-150 on the leaf sheath, and covered with the brown anal hairs of the female moth. Eggs hatch in 4-9 days. Larvae are milky white and 18-25 mm long when mature. They are more white-colored than those of yellow stem borer. Head capsule is black. Larval period ranges from 19 to 31 days. Larvae remain dormant at the base of the plants during the dry season.  LIFE CYCLE Pupation takes place inside the stem. Adult moth emerges from pupa within 7-11 days. After the crop is harvested, the larvae sleep in the lowest internodes of the stubble. With the first rains, the larvae become active, pupate, and the moths emerge. Moths are especially seen in the early stages of the crop. Adults are attracted to light traps. PINK STEMBORER (Sesamia inferens) IDENTIFYING MARKS The adult moth is fawn-colored with brown streaks on the forewings and white hindwings. There is a cluster of hairs on the neck. The wingspan of female moths is 30-35 mm. The male and female moths can be distinguished by their antennae; they are comblike in the male and threadlike in the female. The males are smaller than the females. IDENTIFYING MARKS The larva is purplish pink on the back and white on the abdomen. The head capsule is orange-red. The body is distinctly segmented with no stripes, and tapers toward the abdominal tips. Larvae are found at ground level inside the stem. The eggs are beadlike, and laid in rows within the leaf sheath and the stem. They are creamy white to dark and are not covered with hairs.  WHERE TO FIND? They are abundant in upland rice grown near sugarcane or related grasses. They are also seen in upland rice fields of Claveria, Misamis Oriental (Northern Mindanao).  DAMAGE Young plants typically show deadheart symptoms. The older plants have extensive parts of the stem hollowed out, with consequent physical weakening of the stem and a reduction of crop yield.  LIFE CYCLE Eggs are laid within the leaf sheath. Eggs hatch into larvae in 7 days. Larval duration lasts for 36 days before pupation. Larvae feed on many cultivated as well as uncultivated crops, which makes them capable to move to adjacent fields or border areas to complete their development even after the rice has been harvested.  LIFE CYCLE A single larva can damage many tillers, as they can come in and out of the rice tillers. They pupate either inside the larval tunnel within the stem or outside the stem between the leaf sheath and the stem. Adult moths emerge from pupae within 10 days. Adult survives for 4-6 days. Total life cycle takes 46-83 days. MANAGEMENT OPTION  CULTURAL Before sowing: Plowing/harrowing the rice field immediately after harvest turns under stubble harboring larvae and pupae. They are either preyed upon by useful organisms or get dried up under the heat of sun. This is effective for managing yellow, white, and striped stem borers. If the population in stubble is high, flooding the field before land preparation for the next crop and keeping it submerged up to a week can kill resident larvae. Spreading straw under the sun kills resident larvae in it.  CULTURAL Delaying seedbed planting until moth’s emergence to avoid egg-laying. Choosing right planting time minimizes stem borer population growth, as well as using seedbed trap crops to manually collect eggmasses, and also to know stem borer activity. Conserving and enhancing the action of indigenous useful organisms such as small and big wasps, carabid beetles, and spiders regulate stem borer buildup. Collecting eggmasses, larvae, and pupae of stem borers in containers with minute holes so that once the wasps emerge, they will disperse in the field.  CULTURAL At seedling stage: Monitoring seedbeds for eggmasses every after 5 days helps in effective pest management decision-making. Changing the method of seedling cultivation. For instance, using a plastic covering at the nursery stage reduces the possibility for adults to lay eggs. Periodically raising the level of irrigation water drowns the eggs, which are deposited at the base of tillers and in leaf sheaths.  CULTURAL Cutting the tops of bundled seedlings before transplanting to remove eggmasses. This prevents eggmass carry-over from seedbed to transplanted field. Planting a trap crop. It is done by planting a susceptible rice variety ahead of the main planting time, applying N fertilizer, and installing light traps to attract moths for egg laying. This should be done community-wide. Spraying pesticide when natural control is low helps bring down pest level.  CULTURAL After transplanting: Rouging infested plants to kill the larvae. This should be done for several years over a large area. Early and late plantings to avoid crop continuity and buildup of the borer population. This is location-specific. Asynchronous planting creates many oviposition periods with overlapping generations, as there is continuous supply of food. It also increases larval development. Encourage synchronous plantings (3-4 weeks duration) in the dispersal range of the moth (10-20 km). Crops that are established within a month from the first planting date are considered as regular-planted.  CULTURAL Use of light traps to arrest the moths flying in the night. Peaks in the light traps depend on major planting seasons rather than environmental conditions. Removal of eggmasses from the field. It is more effectively done if timed based on light trap collections (10 days after a peak moth flight) or timed to coincide with susceptible growth stages—stem elongation and panicle exsertion (1 week before panicle exsertion). For a hectare, it takes approximately 4 days for a skilled person to remove eggmasses.  CULTURAL Transplanted rice is more susceptible to damage than direct-seeded rice because transplanted rice is planted later, has lower plant density, proportionally lower flooding period, and longer maturity. In directseeded rice, there is vigorous growth, no standing water during vegetative stage, shorter time to mature, and it has narrow stems that are more hard, hence more first instar larvae die. Thus, plant at a higher range of crop density. High amount of potash reduces stem borer incidence. Increased K reduces stem borer susceptibility as cell walls get thicker because of greater silica uptake.  CULTURAL Incorporation of ash enriches the plant with silicon that affects stem borer development. Increased use of N and P favors stem borer attack. High nitrogen application increases crop duration and stem borer’s survival, feeding rate, and larval size. Harvesting at the ground level removes majority of larvae of all species.  CROP ROTATION Vigorous and well-nourished crop tolerates stem borers more than a stressed crop. Spot application of pesticide (bio-pesticides or systemic insecticides) helps in judicious use of pesticides.  VARIETIES Select varieties that have moderate resistance to stem borer. Modern cultivars mature early so they are less attacked.  BIOLOGICAL High parasitization of eggmasses by small wasps can be known by rearing field-collected eggmasses. Long-horned grasshoppers, fire ants, and crickets are egg predators. Long-horned grasshopper prefers yellow and white stem borer eggmasses. Crickets and mirids feed on other stem borer species. They prefer naked eggs. Carabid beetles, lady beetles, fire ants, water beetle larvae, water striders, spiders, and fish prey on newly hatched larvae that fall on the water surface.  BIOLOGICAL Spiders, dragonflies, and damselflies prey on adults. Big predators of moths are frogs, ducks, and owls. Provide more perching places for owls in the field. They capture moths at night. The rice stubble decays with high moisture. It also encourages white fungal growth on the larvae and pupae residing in the stem. Bacteria (Bacillus thuringiensis) also infect the larvae. Both naturally occurring Bt and commercial Bt formulations infect larvae.  CHEMICAL Insecticide use is often difficult after stem borer larvae have entered the tillers. At tillering stage, sprays and granules are equally effective in flooded areas. From panicle initiation to flowering stages, granules are not effective and only spray formulations should be used. BROWN PLANTHOPPERS (Nilaparvata lugens) IDENTIFYING MARKS Adults are 2.5-3.0 mm long, brown, winged, or without wings. The legs are hairless and the hind leg has a large, mobile outgrowth.  WHERE TO FIND Rainfed and irrigated wetland fields are preferred. It is rare in upland rice. Directsown fields are more prone to heavy damage than transplanted fields. All plant growth stages can be attacked, but the most susceptible growth stages are from early tillering to flowering. Increasing nitrogen levels, closer plant spacing, and higher relative humidity increase their numbers.  DAMAGE Adults and nymphs cause direct damage by sucking the sap at the base of the tillers. Plants turn yellow and dry up rapidly. Heavy infestation creates brown patches of dried plants known as hopperburn. They also transmit virus diseases: ragged stunt, grassy stunt, and wilted stunt. Excreted honeydew on infested plants may also become a medium for sooty mold fungus.  LIFE CYCLE Eggs are laid in batches inside the leaf sheaths and on the leaf midrib. Nymphs are brown. Nymphs molt five times before turning to adult. Adults with long wings are attracted to light traps. WHITE-BACKED PLANTHOPPERS (Sogatella furcifera) IDENTIFYING MARKS Adults are 3-4 mm long, with a white marking on the back. They are either winged or wingless. The legs are not covered with hairs. They feed at the base of the rice plants. Adults may be collected by hand or by using sweep nets or sticky traps.  WHERE TO FIND? Rainfed and irrigated wetland fields are preferred. It is rare in upland rice. Excessive nitrogen use, continuous submerged conditions in the field, closed canopy, and succulent rice plants favor their buildup.  DAMAGE Adults and nymphs cause direct damage by sucking the sap from young leaves. Heavy infestations make leaves dry and become brown patches of dried plants, referred to as hopperburn. The honeydew produced by hopper serves as a medium for mold growth, which imparts a smoky hue to the paddy field. They are not known to transmit any virus disease.  LIFE CYCLE Eggs are laid in batches inside the leaf sheaths. Nymphs are pale brown. Nymphs develop to adult in 11-12 days. The adults live for 18-30 days, with females living a little longer than the males. Adults are attracted to light traps. MANAGEMENT OPTION  CULTURAL 20 days before transplanting: By changing planting distance, microclimate modification in the field is possible. Dense planting increases number of planthoppers. Seedbeds must be far from light sources to discourage hopper attack and virus infection by virus-infected hoppers. Plant early-maturing varieties to create a rice-free period in the year.  CULTURAL Practice balanced fertilization. High nitrogen use increases planthopper attack. Split nitrogen into three applications during crop growth to reduce BPH buildup. Adult of WBPH (winged form). Note white line on the back. Increased potassium reduces planthopper susceptibility as cell walls get thicker because of greater silica uptake. Grow no more than two rice crops per year and use early-maturing varieties to reduce their continuous breeding.  CULTURAL Plow under volunteer ratoons after harvest. Raise the level of irrigation water periodically to drown the eggs, which are deposited at the base of tillers and in leaf sheaths. Drain the field for 3-4 days to reduce planthopper numbers at initial infestation levels. Intensify weeding to reduce hopper density.  CULTURAL At tillering stage: Keep water level low to enhance growth of useful organisms. Intensify forecasting. At this stage, they tend to buildup rapidly.  CULTURAL At milk stage: Drying and flooding the paddy alternately reduces their growth. To spare beneficial organisms, use selective insecticides only if pest infestation is high. There are new varieties that are resistant to white- backed planthoppers.  BIOLOGICAL Avoid early application of pesticides and establishment of refuge areas that encourage buildup of useful organisms. Small wasps attack eggs. Mirid bugs prey on eggs.  BIOLOGICAL Dragonflies and damselflies prey on moving adults. Similarly, spiders, water bugs, and lady beetles prey on mobile stages (nymphs and adults). Dryinid kills nymphs. Fungus kills nymphs and adults.  CHEMICAL Application of insecticides when long-winged adults are numerous kills useful organisms and not the eggs. Varieties with built-in resistance need not be sprayed. Young nymphs can be effectively controlled by useful organisms.  CHEMICAL At heading stage, use entomophagous fungus and botanical insecticides. Selective insecticides can also be used. Avoid‘preventive’ and calendar-based use of pesticides as they cause pest resurgence. GREEN LEAFHOPPER (Nephotettix virescence) IDENTIFYING MARKS They are slender insects, usually narrowing at the back. They have thin tapering antennae. The hind legs are covered with hairs. Adults are 3.2-5.3 mm long, opaque green, with black markings on the head, face, wings, and wing tips.  WHERE TO FIND? Grasses found near irrigation canals and levees, and rice ratoons are favorable for feeding and egg-laying. Tillering and panicle initiation stages are most favorable for their multiplication, although seedling to booting stages are also susceptible. They jump readily when disturbed.  WHERE TO FIND? They are active in summer and become sluggish during cold weather. Thus, their numbers decline drastically. To quickly detect them, either tap vigorously several plants, stopping now and then as one walks through a field, or sweep rice foliage with an insect net.  DAMAGE Adults and nymphs cause direct damage to the rice plant by sucking the sap from leaf sheaths and leaf blades. They also cause indirect damage by injecting toxic chemicals and transmitting viruses (tungro, dwarf, transitory yellowing, and yellow-orange leaf) and a mycoplasma disease (yellow dwarf).  DAMAGE They mostly confine themselves and feed on the leaf and leaf sheath of rice. Mild infestations reduce plant vigor and number of productive tillers. Heavy infestations cause withering and complete drying of the crop.  LIFE CYCLE Eggs are laid in small slits made in the soft parts of the leaf sheaths. Newly laid eggs are oblong, bent, pale yellow, and barely visible. The eggs hatch into nymphs in 6-12 days. Nymphs have varied color patterns on their back.  LIFE CYCLE The first instar nymphs are numerous on the lower surface of older leaf blades, but from second instar onwards, they distribute themselves evenly on all the leaves. There are five instars before they become adult. Adults are attracted to light traps. On full moon, catches are more. ZIGZAG LEAFHOPPER (Recilia dorsalis) IDENTIFYING MARKS They are slender, small insects, usually tapering posteriorly with thin tapering antennae. They jump readily when disturbed. The hind legs are covered with hairs. They have white forewings with pale brown bands forming the shape of a W giving the zigzagged pattern. They can be found either on leaves in the upper parts of the rice plant or on tillers near the base.  WHERE TO FIND? They are present in all rice ecosystems but only transmits virus diseases to wetland rice. They are highly mobile and colonize rice fields in the early growth stages. Sometimes, they are the most abundant leafhopper species on rice seedbeds and weed-covered levees between planting seasons.  DAMAGE They are present in all rice ecosystems but only transmits virus diseases to wetland rice. They are highly mobile and colonize rice fields in the early growth stages. Sometimes, they are the most abundant Adults and nymphs cause direct damage by removing sap from young rice leaves. They also transmit orange leaf, tungro, and dwarf viruses. Leaf tips dry and leaf margins become orange.  DAMAGE Later, the entire leaf becomes orange and leaf margins curl. Damage appears first on older leaves. Nymphs and adults excrete honeydew, which causes sooty molds.leafhopper species on rice seedbeds and weed-covered levees between planting seasons.  LIFE CYCLE Eggs are laid in rows within the leaf sheaths. Eggs hatch to nymphs in 7-9 days. Nymphs are yellowish brown. There are five instars lasting for 16 days, before they become adult. Adults are 3.5-4.0 mm long and live for 10-14 days. MANAGEMENT OPTION  CULTURAL Seedbeds should be raised, far from light sources, and covered with mesh cloth to limit virus infection and early damage by leafhoppers. Mobile nurseries planted to a set of different susceptible and resistant varieties can be used to detect the percentage of virus infection before transplanting. The nursery boxes can be set under lights to attract leafhoppers. The percentage of infected seedling can be determined by the iodine diagnostic test.  CULTURAL Transplant older seedlings to shorten the susceptible vegetative period in the field. Early plantings in the dry season reduce the risk of insect-transmitted diseases. Remove grassy weeds and volunteer rice in fallow fields as they help reduce leafhopper numbers.  CULTURAL Increased N increases their attack, but it also promotes tillering and plant vigor necessary to boost the crop’s ability to compensate for pest damage. Therefore, optimal and timely use of nitrogen is important. Increased K increases resistance of the rice plant as cell walls get thicker because of greater silica uptake.  CULTURAL Crop rotation with a non-rice crop during the dry season will remove weeds and volunteer rice plants. Similarly, in the uplands, if rice is intercropped with soybean, it will reduce green leafhopper incidence compared with rice followed by rice. Dense planting increases the number of leafhoppers.  CULTURAL Observing ratoon and volunteer rice for leafhopper numbers indicates their density. Draining water from the field reduces their numbers. Many varieties resistant to green leafhoppers are commercially available. There are few varieties with resistance to virus diseases, but widespread planting of GLH-resistant varieties helps suppress the incidence of viruses.  BIOLOGICAL Small wasps kill eggs. Dryinids, water bugs, dragonflies, damselflies, spiders, and nematodes attack nymphs and adults.  CHEMICAL A systemic insecticide will be more effective. Granules incorporated in the soil are more effective than broadcasted granules or sprays in seedbed. Apply insecticide if GLH is prevalent in the area. SEED BUG/PADDY BUG/RICE BUG (Leptocorisa oratorius) IDENTIFYING MARKS Young nymphs are green while adults are greenish- brown. The adults are slender and about 15 mm long. When the temperature is high and the insects are not feeding, they camouflage themselves on the plant by taking up a particular posture. The first and second instars often raise their abdomen when on the panicle, but when on the leaves, their whole body is straightened. IDENTIFYING MARKS The older nymphs and adults lower their abdomen flat against the panicle or leaf, draw the antennae and front legs together anteriorly against the substrate, and extend the middle and hind pairs of legs against the abdomen. When the plant is disturbed, nymphs drop to the lower parts of the plant while the adults fly a short distance. When handled or threatened, both nymphs and adults secrete an odorous substance that leaves an orange stain on the fingers.  WHERE TO FIND? They are found in all environments but are prevalent in rainfed wetland or upland rice. They are destructive in areas where rainfall is evenly distributed throughout the year, and also in irrigated crops. Extensive weedy areas of rice fields, wild grasses near canals, staggered rice planting, rice fields adjacent to woodlands, and coconut plantations favor bug multiplication. Susceptible growth stages are from flowering to milky stage.  DAMAGE Adults and nymphs appear in the young crop with the early rains. They suck sap from the developing grains at the milky stage. All soft milky grains are susceptible to attack. Panicles in heavily infested fields remain erect. Insect attack results in discolored or shriveled grains; off- smell of raw and cooked rice, and off-flavor of straws, which is unattractive to cattle. Before grain formation, the bugs feed on succulent shoots and leaves. Nymphs cause more damage than adults.  LIFE CYCLE Eggs are laid in rows on dead or dry parts of the leaves or stem. Occasionally, they are laid on living leaves. They are red and flat. Eggs hatching to nymphs are dependent on high relative humidity. The egg stage lasts for 6-9 days. The nymphs are green. Nymphs turn to adults in 17-27 days after the fifth molt. Adults live up to 65 days under favorable conditions. MANAGEMENT OPTION  CULTURAL Eliminate grassy weeds from rice fields, levees, and surrounding areas either by cutting or burning to reduce habitats for egg-laying. Avoid staggered planting of fields to break continuous food source. Passing baskets or bags coated on the inside with sticky material are promising in repelling/capturing them.  CULTURAL Net and handpick bugs to reduce their numbers. Put attractants such as arasan or anything having bad odor like dead snails or rats. The bugs attracted can be burned or sprayed with chemicals to reduce their numbers.  CULTURAL Awned (bearded) varieties are resistant. Varieties with panicles enclosed in the leaf sheath for longer time offer some mechanical resistance to feeding  BIOLOGICAL Small wasps and long-horned grasshoppers kill eggs. Fungal pathogens infect nymphs and adults. Spiders, crickets, lady beetles, and long-horned grasshoppers feed on nymphs and adults.  CHEMICAL Foliar sprays or dust formulations are effective. Spray or dust at flowering stage in the early morning or evening on calm days. Granular insecticides are ineffective. RICE BLACK BUG (Scotinophara coarctata) IDENTIFYING MARKS Adults are 8-9 mm long and are brownish-black with a few distinct yellowish spots on the thorax that bears spines below the anterior angles. They are called shield bugs because of their shield-like appearance. They produce an offensive odor when disturbed. Young nymphs are brown with a green abdomen.  WHERE TO FIND? They prefer rainfed wetland and irrigated rice to upland rice. They also favor continuously cropped irrigated rice areas and poorly drained fields. They are usually found in large numbers between tillers at the soil level after the heading stage of the rice when irrigation has been stopped during the ripening stage.  WHERE TO FIND? In flooded fields, they are always found on the rice canopy above the water level. Dry season rice crop is prone to damage than the wet season crop. Presently, rice crops in Palawan and Mindanao are seriously affected. However, its distribution is rapidly spreading to other areas of the Philippine archipelago.  DAMAGE Susceptible growth stages are from seedling to flowering. During the day, the adults and nymphs suck plant sap at the base of stems, often just above water level. At night, they move up the rice plant and suck sap from the tillers. The adults prefer the stem nodes as feeding sites owing to the reservoirs of sap. Infestation at the tillering stage results in dead-hearts, but continued feeding turns leaves reddish brown, reduces tillering, and causes stunting.  DAMAGE When infestation is at the booting stage, the panicles fail to develop grains, which mimics the damage done by stem borers (whitehead). They can also feed on panicles during milky stage causing brown spots in injured grains. Their saliva is toxic. During severe infestations, young plants often die and the whole field appears burnt. Such damage is referred to as bug burn, which is similar to hopper burn caused by planthoppers.  LIFE CYCLE Round and greenish-pink eggs are deposited in batches of 40-50 on the basal parts of rice plants near the water surface. They are well-guarded by the female until they hatch. The nymphs develop to adults by 1 month, after changing their skin 4-5 times. Adults can live for up to 7 months. They are strongly attracted to light and often appear in swarms.  LIFE CYCLE They are carried to large distances by strong winds. Adults and older nymphs can survive under adverse conditions. They hide in cracks in soil, bunds or adjacent higher grounds to a depth of 30 cm when there is acute water shortage, temperatures fall abruptly, and crop is harvested. Total life cycle takes 32-42 days. Adults are attracted to strong light. MANAGEMENT OPTION  CULTURAL Removing weeds reduces their breeding sites and allows sunlight to penetrate to the base of the rice plants. Early-maturing varieties evade the damaging population of the pest and break its life cycle. Plowing immediately after harvest destroys their breeding sites Flooding the field drowns eggmasses. Eggs submerged in water for 24 hours do not hatch.  CULTURAL Light traps using mercury bulbs are effective in reducing egg-laying adults. Kerosene light traps are not bright enough to attract black bugs. Practice direct seeding. There are no commercially available resistant varieties but there is a tolerant variety, IR44526. IR1314 is a recommended tolerant variety but it cannot be grown in areas where tungro is a problem.  BIOLOGICAL Small wasps (Telenomus triptus) kill eggs. Frogs and ducks prey on nymphs and adults. Carabid beetles feed on eggs, nymphs, and adults. Green muscardine (Metarhizium anisopliae) attacks the nymphs and adults  YEAR AND SECTION: CROP SCIENCE 2A CROP SCIENCE 2B HORTICULTURE 2B ANIMAL SCIENCE 2G VIRGILIO M. VERO INSTRUCTOR CRPT 110 THANK YOU!  REFERENCE Tiongco, E. R., Duque, U. G., Troung, H. X., Aragon, M.L., Joshi, R. C., Tagubase, J. J. (2011). Field Guide on Major Disorder of the Rice Plant in the Philippines – Disease and Nutritional Deficiencies. Philippine Rice Research Institute. Philippine Rice Research Institute(2012). Field Guide on Harmful and Useful Organisms in Philippine Rice Field – (Insects and Non-Insects). Maligaya, Science City, Munoz, Nueva Ecija.