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At the end of the session, participants should be able to:
Give their own definition of plant disease
2. Know the causes of plant diseases and their characteristics
3. Know the three factors needed for the disease to occur
At the end of the session, participants should be able to: 4. Describe the specific symptoms and signs of rice diseases 5. Know the art of plant disease diagnosis and the importance of correct diagnosis 6. Explain the principle of plant disease management Objectives
Sheath Blight Causal organism : Rhizoctonia solani Symptoms: Greenish gray lesions are first observed just above the water leveling flooded field. Under favorable conditions, the lesions expand to the upper part of the sheath and extend upward to the leaves and then spread to neighboring tillers.
Sheath Blight Management Options At present, there is no resistant variety available for cultivation. The main tools that are available to minimize sheath blight are prophylactic in nature including the following: Apply recommended rate of fertilizer- that has to be adjusted according to the cropping season and the risk of sheath blight outbreak
Sheath Blight Management Options The main tools that are available to minimize sheath blight are prophylactic in nature including the following: Density of seeding/planting has to be adapted to cropping season Apply recommended fungicides at tillering and booting stage when symptoms appear.
Rice Blast Causal organism : Magnaporthe oryzae/grisea Symptoms: The disease is found throughout the whole growth stages of the rice plant. Leaf blast lesion is at first minute brown spots and expands rapidly to spindle-shaped lesions; center of the spot is usually gray or whitish with brown margin.
Rice Blast Causal organism : Magnaporthe oryzae/grisea Symptoms: Node blast has black rotten node and breaks easily. Neck blast may be confused with “white heads” caused by stemborer. Both injuries showed empty, erect white gray panicle. Unlike injury caused by stemborer, where the entire stem can be pulled readily, neck blast causes only injury at the neck and does not extend further into the leaf sheath.
Rice Blast Management Options The primary control option for blast is host-plant resistance. The disease can also be managed through the use of diverse varieties with different levels of resistance and modified cultural practices. In China, good control of panicle blast was achieved through interplanting varieties. In Japan, the use multi-lines carrying different resistance genes have successfully used to manage the disease.
Rice Blast Management Options Split application of nitrogenous fertilizer and good water management (flooding the soil) are recommended to manage the disease. Systemic fungicides are often used to control the disease in many rice growing areas
Sheath Rot Causal organism : Sarocladium oryzae Symptoms: Rot occurs in the uppermost leaf sheath enclosing the young panicle. Lesions start as oblong or irregular spots with brown margin. and gray centers. Abundant whitish powdery growth may be found inside infected sheaths.
Sheath Rot Causal organism : Sarocladium oryzae Symptoms: Rotted growing panicle are incompletely exerted with numerous empty grains Infected plants may be infested with stem borers. The disease is usually associated with virus disease infection
Sheath Rot Management Options Use resistant variety. To eradicate seed-borne pathogens causing the disease, use Mancozeb and benomyl for seed treatments. Systemic fungicide can be applied when typical symptoms are observed on emerging panicle.
Bakanae Causal organism : Gibberella fujikuroi Symptoms: The disease is commonly found throughout the whole growth stages of the rice plant. Infected seedlings elongates abnormally, becomes slender and the leaves turn pale yellow green. Infested plants develop roots at the upper nodes and the whole plant turns yellow. At booting stage, some infected plants die
Bakanae Management Options Use resistant variety. Since the causal organism is typically seed borne, seed treatment with fungicide (e.g.benomyl or thiophanate methyl) is very effective in managing the disease.
Brown Spot Causal organism : Helminthosporium oryzae Symptoms: Typical spots on the leaves are oval, about the size and shape of sesame seeds. They are relatively uniform and fairly evenly distributed over the leaf surface. Young spots are small, circular (0.05 to 0.10mm in diameter) and usually dark brown. Most spots have a light-yellow halo around their margins.
Brown Spot Management Options Since the disease is known to be associated with soil deficient in nutrients, proper fertilization, good water management and soil amendment are suggested as management option.
Narrow Brown Spot Causal organism : Cercospora oryzae Symptoms: The characteristic symptoms of the disease are usually observed during the late growth stages and are characterized by the presence of short, linear, brown lesions mainly on the leaves (although it may also occur on leaf sheaths, pedicels, and glumes).
Narrow Brown Spot Management Options Foliar fungicides such as mancozeb, benomyl, propiconazole, and iprodione effectively suppress this disease and may be economical if other diseases are also controlled along with narrow brown spot.
Bacterial Leaf Blight Causal organism : Xanthomonas oryzae pv. oryzae Symptoms: Lesions start at the edge near the tip of the leaves. The young lesion expands along the vein forming yellow streak. The edge of the lesion is usually irregular or wavy and has a yellow margin.
Bacterial Leaf Blight Causal organism : Xanthomonas oryzae pv. oryzae Symptoms: As the disease advances, the lesion covers the entire blade, turn straw colored and later become grayish from the growth of various saprophytic fungi.
Bacterial Leaf Blight Management Options Resistant variety has been the most effective and cheapest tool to manage the disease. Cultural practices (i.e. good drainage, balanced amount of plant nutrients, nitrogen in particular) clean culture (e.g. removing weed hosts and other possible sources of inoculum) and fallowing field to dry in between cropping season are some control option against the disease.
Bacterial Leaf Streak Causal organism : Xanthomonas oryzae pv. oryzicola Symptoms: Symptoms begin with fine translucent streak between veins. As the disease progresses, the streaks becomes yellowish-gray, the lesion coalesce, then eventually turn to brown to grayish white causing the leaves to die.
Bacterial Leaf Streak Management Options The use of resistant varieties is the most effective method of controlling the disease. Apply balanced level of plant nutrients, especially nitrogen. Draining the field when symptoms start to appear helps minimize the spread of the disease.
RiceTungro Causal virus : RNA virus - rice tungro spherical virus (RTSV) DNA virus - rice tungro bacilliform virus (RTBV) RTBV depends on the helper produced by RTSV for its transmission. It is the RTBV which is mainly responsible for the severe tungro symptoms.
Rice Tungro Symptoms: Rice plants infected by both RTBV and RTSV show typical tungro symptoms: stunting and yellow or orange-yellow discoloration of the leaves. Panicle exertion of infected plants is delayed and often incomplete and some panicles become short and produce sterile or partially filled grains.
Rice Tungro Symptoms: Plants that are infected with RTBV alone develop symptoms that are similar to but milder than those by both RTBV and RTSV. Plant infected with RTSV alone may be symptom less or exhibit only very mild stunting
Rice Tungro Management Options The most practical method of tungro management are: use of cultural practices (cultural control) resistant varieties (host-plant resistance) Cultural practices (cultural control) involve the following: 1. timing of planting: when both the viruliferous GLH population and tungro incidence are low
Rice Tungro Management Options Cultural practices (cultural control) involve the following: 2. synchrony of planting: establishing rice crops at about the same time to reduce the spread of tungro. 3. plowing under infected stubbles to destroy source of inoculum.
Rice Tungro Management Options Cultural practices (cultural control) involve the following: 4. direct seeding; tungro incidence is often lower in direct seeded rice; dense plant population reduce the chances for GLH to find and feed on diseased plants.
RTSV resistant and RTBV tolerant varieties in the Philippines (IRRI, 2009) Rice Tungro Resistant to RTSV Aday Sel IR77298-5-6 NSIC Rc 140 Resistant to RTSV O.barthii IR72102-159-1-3-3-3 NSIC Rc 112 Tolerant to RTBV O. rufipogon IR73885-1-4-3-2-1-6 Matatag 9 Tolerant to RTBV Balimau Putih IR 68305-18-1-2 Matatag 4 Tolerant to RTBV Balimau Putih IR 68305-18-1-1 Matatag 3 Resistant to RTSV Utri Merah IR69726-29-1-2-2-2 Matatag 2 Resistant to RTSV Utri Merah IR69726-116-1-3 Matatag 1 REACTION TO TUNGRO VIRUSES SOURCE OF RESISTANCE LINE NO. VARIETY
Ragged Stunt Causal virus : Rice ragged stunt virus (RRSV) belongs to Reoviridae family RRSV is transmitted in a persistent manner by BPH, Nilaparvata lugens
Ragged Stunt Symptoms: The primary symptoms are general stunting, ragged leaves with irregular or serrated edges, twisted leaves and leaves are darker green in color. These symptoms are generally exhibited during the tillering stage
Ragged & Grassy Stunt Management Options The use of resistant varieties for ragged stunt management is probably the most important control measure. However, BPH-resistant cultivars, which formerly had little or no ragged stunt, often showed infestations when populations of BPH became adapted to the resistant cultivars.
Ragged & Grassy Stunt Management Options Insecticides can be used to control ragged stunt by drastically reducing BPH populations, which otherwise may migrate to uninfected fields. However, the logic of this strategy implies continuous pesticide application, and local protection of a given field is in general ineffective because of the very strong mobility of the vector.
Ragged & Grassy Stunt Management Options Adjusting the timing and synchrony of crop establishment and the plowing under of infected stubbles are in general quite effective.