Rice

Diseases of Rice

( Oryza Sativa )

1
- Bacterial Diseases

1 - Bacterial Blight
The causal organism            
Xanthomonas oryzae pv . oryzae
- Favorable conditions for the pathogen
- Combination of rainy weather, dull windy and temperature 20 - 26?C
- High doses of N
- Close planting

Symptoms
- 5 . 10mm long green - Yellow spot at tip of leaves
- These spots enlarge and turn to Yellow
- Drop of  bacterial exudates may be observed on young lesions

Control
- Avoid excess of nitrogen
- Avoid Heavy plantation

2 - Bacterial Leaf streak

The causal organism             Xanthomonas oryzae   pv . Oryzicola
Symptoms
- Lesion begins as small, intervene, water –soaked (dark -green ) , streaks which later become translucent
- The translucent   streaks enlarge and coalesce turning into light brown then grayish - whit until the whole leaf dries -up

Control
- Good rotation
- Resistant verities

2 - Fungal  DiseasesOf Rice

1 - Aggregate Sheath Spot

The causal organism             Rhizoctonia   oryzae - sativae
Symptoms
- The spot lesions first appear on the lower leaf sheaths at the water line
- Lesions are circular to elliptical with gray -green surrounded by brown margin
- By the developing  of plant growth, frequently, additional margins from around the initial lesion
-  Later in the season, secondary infections frequently occur well above the water line
Control
            MonCut                      300g /Fadden
or        Fuji one                      400cm
/Fadden

2 - Rice kernel Smut

The causal organism             Tilletia     barclayana
Symptoms
- The symptoms appears as a black mass of chlamydospores that replace all or part of individual kernels near maturity stage
- Completely smutted kernels may be slightly swollen while others may break open exposing the dark spores
- These black spores make the disease easy to recognize
- In case of epidemic, a dark cloud of spores may be observed
Control
- Avoid excessive rates of nitrogen fertilizer
- Plant short grain varieties
- Plant certified rice seed

3 - Blast of rice

The causal organism Pyricularia    Oryzae    Cavara
Symptoms
- The disease can infect paddy at all growth stages and all aerial parts of plant(Leaf, neck and node)
- On the leaves and neck infections are more severe
- The symptoms appear as small spots on leaves and after short period enlarge into spindle shaped
- By the disease developed, several spots coalesce and appear as irregular shape

Control

- Use seed from a disease - free crop
- Destruction of middle hosts
- remove the  weed hosts
- Avoid excess of  N - fertilizer
- Use of tolerant varieties
- Seed treatment with fungicides

4 - Brown Spot

The causal organism Helminthosporium    oryzae
Symptoms
- Diseased seed is primary source of inoculation
- The symptoms  Occur in nursery as well as field
- Leaf spotting is very common Causes blight of seedlings
-  50 % yield reduction in severe cases
Control
- Use disease free seed
- Treat the seed with fungiesides
- Avoid excesses of  N -application

5
- False Smut

The causal organism             Ustilaginoidea    viridis
Symptoms
- The disease occurs on ear heads
- Ovaries are transformed  into large, velvety green masses
- Round to oval, irregular sclerotial bodies are formed 
- Few spikelet affected
Control
- Use certified seed
- Collect and destroy diseased grains in order to reducing inoculum for the next year
- Use                Cobox             250g / 100L .W

3
- Insects on Rice

1
- Aphids

The causal organism             Aphis     gossypii
Damage
- The insects have piercing -sucking mouthparts and feed on plant sap, and input toxins  inside the infected plants
- The toxin causes yellowing of leaves, and small plants may die
- Rice plants with one to two leaves have been killed with only two or three green bugs present per plant
Control
Use
Perfekthion                500cm
/Fadden
Or       Aphox             50g
/ 100L .W
Or       Mospilan                    12
. 5g / 100L .W

2 - Rice water weevil

The causal organism Lissorhoptrus oryzophilis
Damage
- The damage from rice water weevil is caused by larval feeding on the root system of rice plants
- The economic loss occurs when adults move into field soon after flood
- The leaves on the infected plant become narrow and wilted
Control
Use
Peleo               100cm /Fadden          
NoMolt           50cm
/ 100L .W

3 - Rice stink bug

The causal organism Oebalus    pugnax      
Damage
- The life cycle of the insect from October -April
- The adult stage spent winter in the wild grasses
- In April and early May, the adults  migrate from wild grasses to rice plants when plants begins to develop kernels
- Nymphal and adult feeding removes contents  from developing seed (milk and soft dough stages ) and results in an empty seed coat
-  In the feeding sites, Yellow to black spots formed and are often associated with microorganisms
- The  insect causes  reducing head yield and increased percent broken kernels
Control
NoMolt           50cm / 100L .W

3 - Green Rice leafhopper

The causal organism Nephotettix virescens 
Damage
- Although leafhoppers can be present in fields during most of the growing season, the heaviest populations usually occur from early July –August
- The insects feed on rice plants by sucking up plant sap
- The symptoms usually occur on older leaves first
-  The insects are very mobile Thus, infestations are rarely localized
Control
- Early and effective weed control program is an important way to control the insects
Use
NoMolt           50cm
/ 100L .W

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