DISEASES OF RICE and their MANAGEMENT Part 1: Understanding the PalayCheck System

What is a disease? A disease is an impairment of the normal physiological functioning of a plant/or plant part. It interferes with its normal structure, condition, and economic value. Reduced vigor, early death Reduced yield, poor quality produce Nodes, leaves, tillers, plant height

? How do we diagnose diseases? Through the characteristic manifestation of diseased conditions (symptoms) and the presence of visible structures (signs) produced by the causal agent (pathogen). What will you do if you see these symptoms ?

Chicken pox? Insect bite? Allergy? Measles? Can you identify the disease? Chicken pox? Insect bite? Allergy? Measles? So, we probe more. Is it itchy? Do you have fever? What did you last eat? ….?

To diagnose rice diseases, PrObE. Previous and current season management practices investigation (field history) Observation of field symptoms for any pattern of occurrence Examination of affected individual plants on whole basis in comparison to healthy plants from the same fields CONSIDER: disease distribution, spread, occurrence, condition of the field, presence of other organisms, toxic substances, disease symptoms. Ask the farmer, too.

Bacterial Fungal Viral Bacterial leaf blight (BLB) Bacterial leaf streak (BLS) Fungal Sheath blight Rice blast Viral Click on buttons. They are hyperlinked to the respective slides. Tungro

Bacterial leaf blight BLB is prevalent in both irrigated and rainfed conditions particularly during the wet season. BLB is characterized by yellow symptoms

Bacterial leaf blight ‘Pale yellow’ leaf ‘Kresek’ or wilting

Bacterial leaf blight Causal organism: Xanthomonas oryzae pv. oryzae Able to survive in seed, plant residues, in perennial hosts, or in paddy soil and water. May survive in infected rice stubble or plant debris in or on soil as long as the host tissue is not decomposed. Alternate hosts: Leersia oryzoides, Zizania latifolia

Bacterial leaf blight Economic importance Reduction in photosynthetic area Reduction in 1000 grain weight Empty grains 20 – 50% yield loss reported

Bacterial leaf blight Endemic sites Bicol Region Calauan, Laguna Leyte Isabela Source: IRRI

Bacterial leaf blight Pr Ob E Pr Ob E Recall if nitrogen fertilizer rate was high (<120kg/ha) , if field was continuously flooded, and variety is susceptible. Pr Closely observe the rice plants early in the morning before the dew on the plant leaves dries up. Look for opaque-yellowish dew beads (bacterial ooze) on the leaf surface. Ob Examine with healthy plants if leaf turns pale yellow and small water-soaked lesions appear on the leafblades that later cover most of the leaf surface. E

Bacterial leaf blight Take these immediate actions! 1. Pull out diseased plants. Do not bury them in the paddy soil since the bacteria can survive and spread in irrigation water. 2. Drain and saturate the soil to reduce humidity. 3. Apply minimal amount of nitrogen fertilizer or withhold further application.

Bacterial leaf blight When seen in neighboring fields Avoid the movement of irrigation water to your field. Generally, initial infection occurs at the bunds opening for irrigation water. Clean the farm implement used in affected field before operating in other areas. Click on black button. It is hyperlinked back to the slide on classification of diseases. Other options: Fallow the field after harvest and allow it to dry Plant resistant variety. Practice field sanitation, perform regular weeding Chemical control of BB is not economical and effective

Bacterial leaf streak BLS is prevalent in continuously submerged plants. Yellow lines manifest at the leaf tip then run downward creating streaks that turn dark brown on entire leaf. Without intervention, the canopy of the infected field becomes rusted and later burns severely.

BLB and BLS are almost the same in symptoms and management options. Pr Ob E Bacterial leaf streak Recall if nitrogen fertilizer rate was high and if seeds planted were not of good quality. Pr Observe if huge part of paddy has yellow canopy. Ob Check plants closely if leaf tips are yellow running downward forming streaks. E BLB and BLS are almost the same in symptoms and management options.

Sheath blight Sheath blight occurs in very populated irrigated or rainfed lowland fields with high N rate in soils. Caused by Rhizoctonia solani, it manifests first in the sheaths of the plant.

Sheath blight On leaf sheath: oval gray spots with black brown margins that later enlarge On leaves: gray irregular lesions banded with green brown coloration and grayish center; panicle exertion affected when flag leaf is infected.

Sheath blight Primary inoculum sources are soil-borne sclerotia (infection bodies) and mycelia in plant debris. Sclerotia float and infect sheaths near water line. They can be spread by irrigation water and soil movement during land preparation which lead to reoccurrence of disease.

Sheath blight first observed in the field after plants reach the maximum tillering stage. Incidence of the disease increases as the plants grow older.

Sheath blight Economic importance Yield loss is caused by unfilled grains, lodging, or death of tillers. Grain weight, panicle length, and milling quality are affected. Yield loss can reach : 50% with susceptible cultivars especially when disease develops at booting stage. 20-25% if disease develops up to the flag leaves 20-42% in plots with high nitrogen

Sheath blight Pr Ob E Pr Ob E Were plants infected with sheath blight in the previous season? Resting fungal mass from crop residues may not be decomposed. What variety was planted? What was the seeding rate used? Is N rate too high? Pr Observe if white leaf patterns. Check field if there are sclerotia bodies floating in water. Ob Check leaf sheaths at early stage of plant if there are gray spots that are powdery. Gray powder is a sign of fungus development. E

Sheath blight Take these actions! Sanitation – control weeds in the paddy and on the bunds plow deeply to bury infected stubble and weeds Expose soil to intense sunlight Reduce seeding rate or provide wider plant spacing Efficient use of nitrogen fertilizer Drain the field at maximum tillering for a few days Biological control –fungal antagonist: Trichodermma harzianum;

Rice blast Blast, a fungal disease, is found in both upland and lowland environments severed by water deficiency accompanied by high night humidity and low night temperature.

Rice blast Magnaporthe grisea, the causal organism, can cause lesions. Foliar blast Sheath blast Neck blast Rice blast Magnaporthe grisea, the causal organism, can cause lesions. Blast occurs in all phases of the plant’s growth.

Rice blast Economic importance Yield losses can reach to more than 50%. A 10% neck rot causes yield loss of 6% and 5% increase in chalky kernels.

Pr Ob E Rice blast How was field water managed? Was the field too wet? What was the variety planted? Was the N rate too high? Pr Observe if there are lesion patterns in the field. The earliest is during 17 DAS in seedbed. Ob Examine plant if there are leaf blast manifestations . Initial lesions are green and diamond-shaped which turn dark yellow in leaves. E

Rice blast Take these actions! Use of resistant cultivars Early sowing of disease-free seeds after the onset of the rainy season. Water seeding is better than drill seeding. Efficient use of nitrogen fertilizer. Nitrogen should be applied in small increments at any time. Nitrate nitrogen is more conducive to disease development than ammonium nitrogen. Soil amendment with silica. Silica is known to increase the resistance of varieties to blast. Amend soils with calcium silicate slag if soils is low in plant-available silicon.

Rice blast Take these actions! Water management practices in rainfed areas. Flooding the field, when possible, can reduce the severity of blast. Destruction of diseased crop residue by burning. Avoid farm activities when plants are wet. Chemical control. Fungicides such as benomyl, pyroquilon and tricyclazone can possibly control disease. Two applications is recommended: one at early heading; second will be a few days later when the heads are most of the way out of the boot.

Tungro Virus prevalent in irrigated lowlands with staggered-planted fields. Efficiently vectored by green leafhopper (GLH) Rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV) cause Tungro. RTBV cannot be transmitted unless RTSV is present.

Tungro Plants are susceptible from seedling to tillering. Symptoms: mottled young leaves; older leaves are yellow to yellow-orange; stunted with slight reduction in tiller number

Tungro Similar symptoms Yellow-type symptom caused by nutrient deficiencies (Zn, K, S) and water stress Zn S K Uneven standing crop and orange canopy due to insect pest infestation and rat damage

Tungro Generally healthy and GLH-free GLH with viruses move into field Newly transplanted Few days later More GLH move into, lay eggs and develop to nymphs 1-2 weeks later; infection starts, symptoms not clearly manifested Source: IRRI, 2003

Tungro GLH adults move out Nymphs and adults spread within the field More than 4 weeks later; infection is widespread 3-4 weeks; infection increases rapidly; symptoms clearly discernible

Pr Ob E Tungro Was the variety planted susceptible to the virus? Is the field staggered-planted or planted asynchronously? What practices done that favor population growth of GLH? Pr Inspect fields; critical time is 6 weeks after transplanting. Observe neighboring fields for uneven standing crop, ratoons, and presence of tungro; examine distribution of diseased plants; assess GLH population; Ob Examine plant if there are yellow and orange color in topmost leaves; stunted growth; and reduced tillering E

Tungro Take these actions! Observe a fallow period Plant resistant varieties – most economical means. IR 36, IR42, IR54, and IR64 were resistant to GLH, but these are now susceptible. Rotate resistant Matatag lines (10, 11, 12,32,33,51). Plant in synchrony Destroy stubbles right after harvest by plowing and harrowing to eradicate GLH and tungro hosts Use insecticides only when needed – do not spray when: a. in seedbed b. in plants more than 60 days old after transplanting c. when no tungro and few GLHs are present

Illustrated guide to disease diagnosis BACTERIAL LEAF BLIGHT Gray to brown, uneven lesions progressing downwards. ‘BLIGHT’ –rapid and extensive discoloration and wilting SHEATH BLIGHT Large, irregular lesions with dark brown margin and gray center. BACTERIAL LEAF STREAK Linear, water-soaked, yellowish streaks between the veins.

Illustrated guide to disease diagnosis RICE BLAST Green and diamond-shaped lesions then enlarge and turn dark yellow. TUNGRO Yellow to yellow orange leaves. Young leaf is mottled.

For bacterial and fungal diseases sanitation and right cultural practices (water and fertilizer management) should be primarily considered. For viral diseases Consider variety, and control of virus carrier (GLH)

In sum, these will help: Monitor field from time to time. PrObE to properly diagnose disease. Observe one month fallow period to minimize disease occurrence. Avoid too much fertilizer especially N. Avoid applying unnecessary pesticides. To prevent significant yield loss due to pests. [Key Check 7]

CREDITS Dr. Fe Dela Pena Note: Instructional presentation designer: Ms. Ella Lois Bestil Sources of technical content/reviewers of presentation: Dr. Fe Dela Pena Note: Adapted from a powerpoint presentation developed by: Mr. Glenn Ilar, Mrs. Marissa Reyes You may use, remix, tweak, For more information, visit: & build upon this presentation non-commercially. However, always use with acknowledgment. Unless otherwise stated, the names listed are PhilRice staffers. Produced in 2011 Text: 0920-911-1398