Diseases following fresh rainy spell

The Met Office on Tuesday advised farmers to ensure field sanitation and prophylactic fungicidal sprays to safeguard the standing crops from diseases following the fresh rainy spell. "Weeds are expected to shoot in excess after the rains. Farmers should control weeds growth soon after the rains," the office said in its 10-day advisory for farmers.
It said the farmers should halt irrigating their crops since the continuing rainy spell provided sufficient water and asked the growers to plan irrigation keeping in view the likely rain in agricultural plains of the country. "Wheat crop is growing at Heading/Flowering/Milk Maturity stages in most of the agricultural plains of the country," it said, adding that farmers should step up to control further weeds growth to prevent negative impact on their crops. "Weeds removing practices should be started soon after expected rains in the mentioned areas," the office said.
It says wheat crop is growing at very crucial development stages of milk maturity/ wax maturity, in Sindh and Punjab province. "Farmers of these areas are advised to irrigate the crops as per requirement keeping expected rains in mind," it adds. Rainfall/ light snowfall over the hills and over upper and central parts of Punjab is expected in the next 10 days. It forecast rainfall for Sindh at isolated places during first five days of the advisory while dry weather is likely to prevail in its most parts till March 20.
It said rainfall/light snowfall over the hills and over upper and central parts of Khyber Pakhtunkhwa is expected during the period. Rainfall is expected at isolated places of Balochistan during the first five days of the forecast period. In Gilgit-Baltistan, it said mainly cold and cloudy weather is expected in most parts. However, light to moderate rainfall (with snow over the hills) expected at isolated places during the period. In Kashmir, the office said cold and cloudy weather with rainfall/light snowfall over hills is expected in most parts.

Source: Business Recorder 

Black Spot Fungal Disease Overview

Although this fungal blight can infect many types of plants, including apple trees, tomatoes, and more, it is most often associated with roses. It’s the rose gardener’s most dreaded foe.

Host Plants

Any type of rose can become infected with black spot. Some species have been bred to be resistant to this fungus, but most of the thousands of rose species have not. Other plants related to roses, such as apples, may also be hosts – some may not show much of an infestation, in fact, and can act mainly as carriers instead.

Symptoms on Roses

The symptoms are straight-forward and well-known amongst rose gardeners. It generally manifests first on the leaves of the rose bush. It will then quickly spread, usually via water dripping from leaf-to-leaf or from leaf shaking from a breeze or animal. It quickly infests the plant’s leaves and their stems, reaching eventually for the flowers themselves. The first sign is usually a dark gray or black spot on the leaf’s underside wherever moisture might collect. It will then spread in patches across the leaf, eventually eating through it.

Life Cycle

Like most fungi, black spot needs warmth, moisture, and shade from the sun. This is usually found on the underside of leaves and inside the flowers. The fungus spreads most often through soil contamination and falling leaves and petals that have been infected. Spores will lie dormant in the ground until spring.

How This Fungal Disease Impacts the Plant

Black spot will kill leaves and, worse, destroy the roses themselves. At the very least, it will make the plant and flowers ugly and non-presentable. It can eventually kill the rose plant if it begins early enough in the season.

How to Prevent

As with most fungal infections, prevention is worth a pound of cure with black spot. Planting roses in a well-aerated spot where they receive light breezes and good air flow is a must. Proper care of the soil around them, including choosing mulches that are unable to carry black spot, is also important. Watering from the root rather than with a sprinkler system is a good idea as well. Keeping infected plants quarantined from others is vital. Many gardeners will destroy one rose bush that’s been infected in order to save the rest from possible infection. Destruction should be through bagging, removing, and burning the plant. Never compost an infected plant of any type.

Treatment of Black Spot

Less extreme treatments include fungicides, which have a high rate of success in most areas. Many of these must be hand-applied as a spray or powder. Apply before roses bud, if at all possible, but anytime the black spot has appeared is a good time. The disease’s treatment is more important than the aesthetics of the plant. Heat lamps, large fans, and other options have also been tried with limited success. The idea is to destroy the climate that the fungus thrives in.

Resources:

http://web.extension.illinois.edu/cfiv/homeowners/000805.htmlhttp://www.aaes.auburn.edu/comm/pubs/highlightsonline/summer96/blackspot.htm

Source: http://www.gardeningchannel.com

Establishing the Cause of Disease

Source: http://www.sciencemag.org/content/276/5313/726/F1.large.jpg

The correct diagnosis of a plant disease and its cause is not always an easy task. In the first instance symptoms may be ill defined which make their association with any organism problematic (Derrick and Timmer, 2000) and, secondly, plants grow in environments which are notably non-sterile. In particular, besides supporting a microflora on their aerial parts, the phylloplane, they are rooted in soil which may contain in excess of 1 million organisms per gram. The plant pathologist is therefore faced with trying to determine which, if any, of the organisms associated with the diseased plant is responsible for the symptoms. This is normally achieved by the application of the postulates of Robert Koch, a German bacteriologist of the 19th century, which for plant pathogens may be stated as follows:

1. The suspected causal organism must be constantly associated with symptoms of the disease.
2. The suspected causal organism must be isolated and grown in pure culture.
3. When healthy test plants are inoculated with pure cultures of the suspected causal organism they must reproduce at least some of the symptoms of the disease.
4. The suspected causal organism must be re isolated from the plant and shown to be identical with the organism originally isolated.

Clearly, these criteria can only be met with organisms that can be cultured, ruling out all obligate pathogens which include a number of important fungi, many phytoplasmas and all viruses and viroids. Establishing these organisms as causal agents of disease usually involves purification of the suspected agent rather than culture and the demonstration that these purified preparations reproduce at least some of the disease symptoms.
Reference: Introduction to Plant Pathology. Richard N. Strange. 2003. John Wiley and Sons Ltd.

A-Z list of Significant List of Plant Diseases and Pests

Common name	Scientific name	Organism	Affects	Biosecurity program	Emerging/ exotic/ notifiable*
African citrus psyllid	Trioza erytreae	Insect	All cultivars of Citrus. Murraya (native and ornamental forms of mock orange or orange jasmine) and a range of ornamentals.	Surveillance	Exotic2
Ash whitefly	Siphoninus phillyreae	Insect	Ornamentals and fruit crops	Surveillance	Emerging*3
Asiatic citrus psyllid	Diaphorina citri	Insect	All cultivars of Citrus. Murraya (native and ornamental forms of mock orange or orange jasmine) and Bergera koenigii (curry leaf). Also a range of ornamentals.	Surveillance	Exotic*2
Banana freckle	Phyllosticta musarum and Guignardia musae	Fungus	Severe infection results in yellowing of the leaf, which withers and dies.	Surveillance	Exotic*2
Black Sigatoka	Mycosphaerella fijiensis	Fungus	Bananas	Surveillance	Exotic*2
Branched broomrape (Australian Government DAFF website)	Orobanche ramosa	Parasitic weed	Broadleaf crops, broadleaf weeds, native plants	Surveillance	Exotic*2
Bunchy top	Banana bunchy top virus	Virus	Bananas	Surveillance	Emerging*3, notifiable*
Citrus canker	Xanthomonas axonopodis	Bacteria	Citrus	Surveillance	Exotic*2 , notifiable*
Citrus fruit borer	Citripestis sagittiferella	Insect	Citrus and other plants in the Rutaceae	Surveillance	Exotic*2
Citrus greening (Huanglongbing)	Candidatus liberobacter spp.	Bacteria	Citrus	Surveillance	Exotic*2 , notifiable*
Citrus powdery mildew	Oidium tingitaninum and O. citri	Fungus	Citrus	Surveillance	Exotic2
Citrus scab	Elsinoe australis	Fungus	Citrus	Surveillance	Exotic2
Citrus tristeza virus	Citrus tristeza closterovirus (CTV): mandarin stem pitting strains	Virus	Citrus	Surveillance	Exotic2
Cocoa pod borer	Conopomorpha cramerella	Insect of the family Gracillariidae	Cocoa, rambutan and longan	Plant Biosecurity and Product Integrity	Emerging
Electric ants	Wasmannia auropunctata	Ant	Environment	Eradication and control	Exotic*2, notifiable*
European house borer	Hylotrupes	Insect	Seasoned pine timber	Surveillance	Exotic*
Fire ants	Solenopsis invicta	Ant	Environment	Eradication and control	Exotic*2, notifiable*
Fusarium head blight	Caused by Fusarium species	In wheat mainly Fusarium graminearum andF. pseudogram- inearum	Wheat and barley	No	No; endemic and sporadic
Fusarium stalk rot	Caused by Fusarium species	Mainly Fusarium thapsinum and F. andyaze	Sorghum	No	No; endemic and common
Giant African snail	Achatina fulica	Gastropod	Environment	Surveillance	Exotic*2
Grape phylloxera	Daktulosphaira vitifoliae	Insect	Grapes	Surveillance	Exotic*2, notifiable*
Grapevine leaf rust	Phakopsora euvitis	Fungus	Grapes	Surveillance	Exotic*2, notifiable*
Mal secco	Phoma tracheiphila	Fungus	Citrus	Surveillance	Exotic*2
Mango leaf gall midge	Prontarinia spp.	Insect	Mangoes	Surveillance	Emerging
Mango leafhopper	Idioscopus nitidulus and I. clypealis	Insect	Mangoes	Surveillance	Exotic*2, notifiable*
Mango malformation disease	Fusarium mangiferae and other Fusarium spp.	Fungus	Mangoes	Surveillance	Exotic*2
Mango stem miner	Spulerina isonoma	Insect	Mangoes	Surveillance	Emerging*3
Mango weevil	Sternochetus frigidus	Insect	Mangoes	Surveillance	Exotic*2, notifiable*
Mediterranean fruit fly	Ceratitis capitata	Insect	Fruit and vegetables, esp. stone fruit	Surveillance	Exotic*2
Melon fly	Bactrocera cucurbitae	Insect	Fruit and vegetables, esp. cucurbits and beans	Surveillance	Exotic*2, notifiable*
Melon thrips	Thrips palmi	Insect	Fruit and vegetables	Surveillance	Emerging*3
Myrtle rust	Puccinia psidii	Fungus	Complete host range not known; however, it has been identified on Melaleuca, Syzygium and Eugenia sp.	Surveillance	Emerging*3
Navel orangeworm	Amyelois transitella	Insect	Citrus, English walnuts, pistachio, almonds and grapes	Surveillance	Exotic*2
Panama disease	Fusarium oxysprorum f. sp. cubense Fusarium species	Fungus	Bananas	Surveillance Control	Exotic*2, notifiable* Emerging*3
Papaya fruit fly See also: Winning the war against papaya fruit fly	Bactrocera papayae	Insect	Fruit and vegetables	Surveillance	Exotic, notifiable*
Papaya ringspot	Virus type P (PRSV-P)	Virus	Papaya and cucurbits	Control	Emerging*3
Pierce's disease and glassy winged sharpshooter	Xylella fastidiosa	Bacteria	Grapes	Surveillance	Exotic*2 , notifiable*
Plum pox (sharka)		Virus	Stonefruit	Surveillance	Exotic*2, notifiable*
Potato cyst nematode	Globodera rostochiensis (Wall.) Skarbilovich	Nematode	Potato plants and other members of the solanaceous plant family	Surveillance	Emerging*2, notifiable*
Red banded mango caterpillar	Deanolis sublimbalis	Insect	Mangoes	Surveillance and control	Exotic*2, notifiable*
Silverleaf whitefly	Bemisia tabaci biotype B	Insect	Range of ornamental and crop plants	Surveillance	Emerging*3
South African citrus thrips	Scirtothrips aurantii	Insect	Ornamental and fruit crops, esp. citrus	Surveillance	Emerging*3, notifiable*
Southern red mite	Oligonychus ilicus	Insect	Range	Surveillance	Exotic*2
Spiralling whitefly	Aleurodicus dispersus	Insect	Range	Surveillance	Emerging*3
Thrips and topovirus	Thysanoptera : Thripidae	Insect	Vegetables and fruit	Plant health pest and disease	Emerging*3
Vegetable leafminer	Liriomyza sativae	Insect	Common horticultural crops and ornamental plant species, esp. tomatoes, pumpkins and beans	Surveillance	Emerging*2
Yellow crazy ant	Anoplolepis gracilipes	Ant	Environment	Eradication and control	Exotic*2