plant issue 1 plant protection directorate july 2017 of ... for the plant disease... ·...

PLANT DISEASE AND PEST CLINIC NEWS

Plant Protection Directorate Department of Agriculture, Ministry of Agricultural Development June 2017

For more information visit: www.ppdnepal.gov.np For questions contact: Shalik Ram Adhikari Email: [email protected]

Issue 1

July 2017

Welcome!

.

A field visit was organized by the Plant Protection Directorate to Bista Gaun, Godavari Municipality with Dr.

Jim Correll, Winrock Farmer‐to‐Farmer volunteer, on 18 June, 2017.

This bulletin from the Plant Protection Directorate is an update about diseases and other problems observed in the Plant Disease Clinic and regional clinics to communicate disease diagnosis information throughout Nepal.

Winrock International/ USAID hosted a workshop involving the plant disease clinics. The purpose of the workshop was to establish a laboratory to do plant disease identification and diagnostics. The workshop involved collecting plant samples, isolating and identifying plant pathogens associated with samples and identifying disease management options. The program was funded by the USAID Winrock International Asia Farmer‐to‐Farmer (F2F) Program conducted by volunteer Dr. James Correll.

Introductory newsletter compiled by Juniper Kiss, Anglia Ruskin University ([email protected]).

The Newsletter contains information on plant diseases and pests identified in Nepal for the preceding month.

For additional details on individual diseases in Nepal visit:

http://www.plantwise.org/KnowledgeBank/CountryHome.aspx




Issue 1

July 2017

Alternaria leaf spot is the most common fungal disease of crucifers in Nepal. Mainly two species in the genus Alternaria cause this disease: Alternaria brassicae and Alternaria brassicicola. It is commonly found in cabbage, cauliflower, broccoli, turnip, radish, broad leaf mustard etc. Symptoms can be appeared on young seedlings in seed beds. The first symptoms of the disease are minute yellow specks on the oldest leaves and stems. The spots darken and enlarge into circular, tan to dark brown spots causing concentric circles and mature lesions have a bull's eye type appearance. Symptoms caused by A. brassicicola are generally similar to those caused by A. brassicae except that the lesions are sooty black in colour. These two species can be identified by their conidia structure under microscope.

The disease is seed, soil and wind borne. Spores on the seed surface can remain for up to two years and if the infection is internal, the fungal mycelium can remain viable for more than twelve years. This fungus survives also in infested crucifer debris in the soil, cull piles or on cruciferous weeds. Spores can be spread by winds, water splash, insects, people and equipment. The disease is favoured by moist and warm weather. Several disease cycles can be completed under favorable conditions.

Management of this disease begins with using disease free seeds. Treat the seed with fungicide or hot water. Do not grow varieties which have shown susceptible to the disease. Reduce inoculums source by destroying cull piles, plant debris and alternate hosts. Apply Trichoderma in the soil in seed bed as well as in the field. At least two year crop rotation with non cruciferous crops is recommended. Avoid excessive irrigation and overhead irrigation.

Scout the seedbed and field regularly for the disease development. Apply fungicide when

disease is becoming severe and weather is favourable for disease development.

http://www.plantwise.org/knowledgebank/datasheet.aspx?dsid=4482

Disease caused by Exserohilum turcicum

(previously classified as Helminthosporium

turcicum), a fungus found in humid climates

wherever corn is grown. The pathogen

survives in corn debris and builds up over time

in residue and continuous corn cropping

systems. The disease is favored by heavy

dews, frequent showers, high humidity and

moderate temperatures. Spores are spread by

rain splash and air currents to the leaves of

new crop plants in spring and early summer.

Spores may be carried long distances by the

wind. Infection occurs when free water is

present on the leaf surface for 6 to 18 hours

and temperatures are 65 to 80 F. Infections

generally begin on lower leaves and progress

up the plant, but infections may begin in the

upper plant canopy when spore loads are

high. New NCLB lesions can produce spores in

as little as 1 week, allowing NCLB to spread

much faster than many other corn leaf

diseases.

The pathogen was first identified in the

country in1964 .The disease is widely

distributed throughout the country; however

Alternaria Leaf Spot of Crucifers R.D. Rajbhandari

Northern Leaf Blight (NLB)

Drona Budathoki




Issue 1

July 2017

it is more prevalent in the cool and humid

conditions of the foothills. It was not

considered a the major disease of maize in

Nepal until 1985. It is also common in the

winter maize of the terai region. The disease

usually appears before tasseling. Maize late

sown in the season is most affected by this

disease in hills. The lesions of northern leaf

blight can be observed together with other

diseases on the same or on different leaves of

the plants.

Symptoms

Northern corn leaf blight lesions are

gray‐green and elliptical, beginning 1

to 2 weeks after infection.

In a susceptible reaction, fungal

sporulation will begin within a few

days.

Distinct cigar‐shaped lesions

unrestricted by leaf veins make

northern corn leaf blight (NCLB) one

of the easiest diseases to identify.

Under moist conditions, lesions

produce dark gray spores, usually on

the lower leaf surface, giving the

lesions a "dirty" appearance.

As many lesions enlarge and coalesce,

entire leaves areas may be covered.

Heavy blighting and lesion

coalescence give leaves a gray/burned

appearance.

Disease Cycle

Management

Crop rotation to reduce previous corn

residues and disease inoculum

Tillage to help break down crop debris

and reduce inoculum load

Registered fungicide sprays may be

necessary .

Powdery mildew is a common disease of

vegetable crops. It attacks cucumber,

pumpkin, chilly etc. This disease can

significantly reduce the yield. The pathogen

found in the tomato of Bista Gaun was

Leveillula taurica (Oidiopsis taurica) and chilly

and pumpkin were infected with Erysiphe sp.

Powdery mildew appears as superficial growth

on leaves which is white powdery spots and

blotches. The infected plants are seen to be

sprinkled with powder. Later on, severely

infected leaves turn yellow and can become

necrotic during the growing season. The

disease is more pronounced when the

Powdery Mildew Diseases

Surendra Pokharel

Northern Leaf Blight




Issue 1

July 2017

environment is cool with high humidity,

although, it is seen in warm and dry conditions

as well. The plant part affected by Leveillula is

the leaves and petioles, stalks, and flowers are

rarely affected.

Powdery mildew on pumpkin leaf infected by

Erysiphe

During the winter, the fungus can survive as

cleistothecium. In spring, the cleistothecium

ruptures and release spores that are spread by

wind. After releasing, it starts to infect the

succulent new growth of the plants.

Throughout the growing season, more spores

are produced and spread by wind. These

spores start new leaf spots on the plant and

neighboring plants.

If available, growing of disease resistant

varieties is the best practice of disease

management. Planting at close spacing should

be avoided which lead to the development of

wetness that promote infection. Transplanting

of disease free seedlings can reduce the

infection level at the plants. Weeds should be

controlled nearby planting sites because the

fungus has a wide range of hosts. Irrigation of

crops through drip is a good method as

overhead irrigation splash up spores and

creates humid environment to favor

development of powdery mildew disease.

Conventional approved fungicides can be

applied to control the powdery mildew.

Abstract

This short study was conducted to identify the

causal organism of bean root rot disease from

june 16 to june 20, 2017. The samples were

collected from Sinamangal, Kathmandu and

were inoculated in water agar and potato

dextrose agar (PDA). Fungal colonies were

isolated from disease samples. Based on

morphological characterization and disease

symptoms, the fungal isolates found in this

study was Rhizoctonia solani Kuhn.

Keywords: causal organism, Fungal colonies,

isolates, Rhizoctonia solani.

Introduction

Rhizoctonia solani Kuhn is a anamorphic form

of Thanatephorus cucumeris (Frank), causes

many plant diseases. It is one of the most

important and widespread fungal diseases of

beans in Nepal. It causes greater losses in the

temperate and sub‐tropical areas. It is a

common inhabitant of most soils survives as

actively growing mycelium, resting mycelium

or sclerotia. Spread occurs by soil movement

with water and on contaminated tools and

plant parts. Basidiospores are only rarely

produced and are generally of minor

significance in disease dissemination.

On bean, germinating seeds and seedlings are

attacked by this pathogen. Reddish spots,

which can be sunken, expand to kill the plants.

Isolation and identification of

Rhizoctonia root rot (Rhizoctonia

solani Kuhn in Phaseolus vulgaris

Naba Raj Bhandari

Powdery Mildew on Cucumber




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July 2017

Reddish‐brown to brown collar rots are

common on young plants. These rots inhibit

normal growth and cause stunting or plants

with poor vigor. Callus formation and

thickening of the collar area also occurs. Root

rots form at any time. Extensive root rots

cause plants to decline and yields are reduced.

Materials and Methods

This study is aimed at identifying causal

organism of root rot of bean. The sample was

brought by Senior Plant protection officer Mr.

Dinesh Babu Tiwari from his kitchen garden,

Sinamangal Kathmandu in June 16, 2017. The

variety of bean was malepatan. The root

samples were inoculated into culture plates of

water agar and Potato dextrose agar and were

left for 72 hours in room temperature. After

72 hours of inoculation, Inoculated petriplates

were observed in stereoscope microscope,

fungal colony and mycelial growth were

examined. After then, actively growing on PDA

plates, mycelium‐agar plugs were excised

from the margin of the fungal colony and was

observed in compound microscope.

Results and Discussion

Observation of Infected roots

Reddish‐brown to brown rots were observed

on roots and collar region of bean plants

Observation of fungal colony

Observing excised fungal colony in compound

microscope, Colorless mycelium in young

cultures and brownish in old cultures were

observed. After staining with lactophenol,

Typically branched hypha at 45° or 90° angles,

with constrictions at the point of origin of

hyphal branches were also examined. This is

the main typical morphological character of

Rhizoctonia solani.

Fungal Identification

Based on culture morphology and morphology

of mycelium Rhizoctonia solani was

confirmed.

Rhizoctonia root rot on beans Taking margin of the fungal colony for

microscopic observation




Issue 1

July 2017

Conclusion

Mycelia of Rhizoctonia solani in culture look

hyaline, septate, branched hypha at 45° or 90°

angles, with constrictions at the point of origin

of hyphal branches. Taking all visual and

morphological developmental characters

together, we confirmed that the fungus

isolated from naturally infected Phaseolus

vulgaris plants is a Rhizoctonia solani Kuhn.

Cucumber plant gets affected by many

diseases, among them downy mildew is an

important one. This disease is caused by

Pseudoperonospora cubensis, an oomycete

fungus‐like organism. High humidity and warm

temperatures favor downy mildew, so the

chance of infection from this disease is high.

Farmers should be aware of these favorable

environmental conditions for this disease.

Once these environment got by the pathogens

with susceptible variety of cucumber,

infection takes place and few days later light

yellow spots with water soaked appearance

on the topside of older leaves can be

observed. Some angular spots, not passing

through the main vein, may also be seen.

During prolonged wet periods, the disease

grows rapidly with downy growth on

underside of leaves and ultimately whole

plant look burnt. The result of this disease is

reduced yield, misshapen fruits and fruits with

sunscald.

The pathogen isolated from the collected

samples of downy mildew had produced large

number of sporangia on the underside of

infected leaves. Usually sporangia are released

into the environment and move to other

plants with air current. These biotroph

pathogens can survive on their collateral hosts

where there is not hard frost. Lemon shaped

sporangia were seen on the tip of branched

sporangiophores.

Disease Management

Resistant varieties should be planted when

possible. Clean cultivation, maintaining the

plant density to avoid the micro‐climatic favor

to the pathogens is a good idea to prevent

pathogen to grow rapidly. Farmers have to

always keep in mind that fungicides have

limited effectiveness after infection. So it is

always advisable to use systemic fungicides

like Cymoxanil alternate with protectants for

example Mancozeb at the early stage of

disease development or prior to the infection.

Downy Mildew of Cucumber

Shalik Ram Adhikari

Note : Farmers should always read the label provided

and use the personal protective equipment while

using the chemical fungicides. Pre‐harvest interval

should be strictly followed.

Fig. Angular yellow leaf spot and downy growth on topside and underside, from left to right.




Issue 1

July 2017

Sporangiophore and sporangia

Certification of workshop trainees at the Plant Protection Directorate

If you are interested in contributing any information about plant

diseases or pests in the newsletter, please contact the clinic!

plant issue 1 plant protection directorate july 2017 of ... for the plant disease... ·...

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