Wednesday, September 30, 2015

Rose Fungal Infection and Diseases Control

What’s happen when your rose plant is not healthy? You love roses and grow them, but suddenly if it shows an abnormal condition you feel... thumbnail 1 summary
What’s happen when your rose plant is not healthy? You love roses and grow them, but suddenly if it shows an abnormal condition you feel sadness. Don’t worry. If you are know the reason and curing method that is not a problem. But most of the people don’t know what are the roses diseases, pest and specially to recover them. In here I am going to discuss major diseases in roses and the control methods. If you follow this guide you can keep it healthy.


Rose Diseases

Black Spot




This is happen due to Diplocarpon rosae / Marssonina rosae. It is a fungus. Symptoms are mainly show on leaves. You can see black color spots on the leaves. Spots are generally circular with irregular edge / fringed margin often with a yellow halo. Leaves may be completely defoliation in sever conditions.

Optimum Conditions to Spread

Normally fungus are favor to grow in high temperature and humidity. So 18-24Co is favor to grow them and 95% RH is very good to spread them. Therefore rapidly spread out in warm and wet summers. After 7 hours of contamination the infection is occurred. Symptoms can be seen in 3 -10 days after the fungal infection. New spores are reproduced in every 3 weeks.

Fungal Infection Symptoms

As I said before you can see black spots on the upper side of the leaves with the size of 1.5-13mm. the spots are surrounded by yellow halo. Infected leaves turn in to yellow and in sever conditions leaves are completely fallen down. Sometimes fungal infection can be seen in canes with reddish like spots.

Spreading

These spores can be spread via splashing water, insect or wind. Therefore in rainy and windy seasons the spreading is high. Spores can be overwinter on dead rose leaves. Then rise in favorable situations. 

Disease Control

Keeping sanitary is very important to prevent the disease. The fallen diseased rose leaves must be collected and burn. Canes should be prune to remove the infected area. It is helps to avoid overwintering of spores.
Suitable fungicide can be used before the rainy or summer season. So it is protect the plant like a coating by restricting the contamination of fungi spores. You can use fungicides with the chemical formula like Captan, Chlorothalonil (Daconil 2787; fungicide with Daconil; multipurpose Fungicide) or Mancozeb. Use a sprayer to apply them. You have to spray fungicide up to end of the rainy season with 7-10 days of interval. In additionally, to buy a plant use a certified stock with free of disease, keep the surrounding free of weeds. It will minimize the host plants.

Powdery mildew

Powdery mildew
Powdery mildew
This is caused by a fungus called as Sphaerotheca pannosa. This is not a huge problem. But in sever conditions; even the plant could be died. The powder like white spores are covered whole the plant. Therefore plant leaves unable to do photosynthesis. Then gradually plant is going to weak. The beauty appearance of the plant is completely destroyed. Especially fungus likes to grow on immature buds and leaves. Therefore new tissues cannot develop as mature.

Optimum Conditions to disease grow

Normally fungus is like high relative humidity and temperature. It is prefer 16Co at night time and 27Co at day time. 95-99% RH in night time and 40-70% RH is prefer for maximum disease development. High humidity is good for spore’s production and low humidity is encouraging maturation of spores and releases them. Windy condition spread out spores to healthy plants.

Fungal infection symptoms

Mostly immature buds and leaves are susceptible to this fungal infection. Infected leaves are covered with a grayish white powdery fungus spores. Mostly on the upper side of the leaves make a good surface to grow the fungus.
Upper side is covered with fungus spores. Therefore leaves are curling to expose to the sun light. Unopened flower buds may be white in color and never open. Sometimes the young infected leaves become purple.

Spreading

The spores are spread via wind. So, windy condition helps to improve the disease spreading. Normally spores are overwinter on stems, fallen leaves and inside the leaf buds.

Disease Control

Proper attention is needed on the buds and young leaves. Continuously check the growing tips and young leaves for sign of powdery mildew. Pruning of the infected part may be retarded the spreading. Destroy the fallen leaves and cutting parts. Soap water adding may be retarded the growing of the fungi in light condition. In sever stage, need to add a fungicide like Lime-Sulfur (Dormant Disease Control; Lime-sulfur spray), Sulfur dust, Triforine.

Downy mildew

This is another fungus attract caused by Peronospora sparsa. This is one of the most devastating leaf spot diseases.

Fungal infection symptoms

Purple red or dark brown spots can be seen on the leaves with irregular margin. However the spots often show angular shape. Rose plant stem, petiole and flower stalks can be split open with purple marks. Normally buds, sepal, petal and calyx can be affected and will present purple spots on it. Affected younger parts may be deformed. The spores normally can be seen under the leaves. In sever condition green patches can be seen on the leaves if not completely yellow leaves are resulted. In addition 1/3 of the upper plant may be defoliated.

Disease Control

Proper sanitation is better. Remove all the weeds plant from the field. Do necessary pruning for diseased parts. Collect and burn all the diseased laves and other parts. Need to use a proper fungicide like captan in sever stages.

Rust disease

Rust disease is another common rose disease that occurred by Phragmidium macronatum. Rose rust appears as yellow patches on the leaf surface. Orange color patches of spores underneath the leaf can be seen.
The fungus spores are spread by wind as others. Diseased leaves are fallen prior to the healthy leaves. Complete defoliation may be resulted in a sever condition.  

Treatments

Use a fungicide with Sulfur to prevent the rust disease. Do other sanitation practices as in previous diseases.

Botrytis blight

Botrytis blight
Botrytis blight

This is also a fungus disease caused by Botrytis cinerea. Mainly hybrid tea roses are vulnerable to this disease. Basically flowers and buds are susceptible to the disease.

Optimum Conditions to disease grow

Cool temperature, moisture and week plants are more susceptible to disease infection. So, rose plants under stress are highly vulnerable to this.  

Botrytis blight
Grayish brown area on leaves

Fungal infection symptoms

Open flowers are shown yellow or brown flecks. Lower petals show wilted and brown areas. The stem below the infected flower is shown brown color. Grayish brown areas can be seen in infected parts of the plant.

Control

Destroy all the infected flowers as soon as when they wilt or die. Remove dead plant material which spores are produced to stop large numbers of fungal spores. Need to use a suitable fungicide like Captain, Chlorothalonil, Sulfur, Thiophanatemethyl, Triforine.

Crown gall

The causative agent is Agrobacterium rhizogenes. Large lumps can be seen base of the plant stem and roots. Sometimes galls are seen upper part of the stem in sever conditions. These galls are soft than normal plant tissues. Affected parts are wild very rapidly and poorly grow.
The pathogen enters to the plants via wounds. If the pathogen infected at younger age plant could be died or no flowering.

Control

Protect the plants from physical damages and wounds to prevent the entrance of pathogen. Always use good plant materials to plant.

canker
Canker

Canker

This is caused by the fungus Cryptosporella umbrina. The disease is mainly found on outdoor garden roses. Fungus may attack on any plant parts and may die with the disease. Therefore this is a very danger one for roses.

Fungal infection symptoms

Red or purple color spots can be seen on the canes and these spots usually develop as gray-white lesions on the stem.
Whitish patches can be seen on the stem surface. In time, these white lesions enlarge and make cankers on the stem and resulting death. Canker may be spread base to top of the plant.

Spreading

The pathogen can only enter to the plant tissue through wounds. The fungus overwinters in infected canes. Fungus may be spread through wind, splashing water and tools.

Control

Select pathogen free good planting materials. Before do pruning, dip the tools in a chlorine water to disinfect. Sulfur treatment may help to prevent the disease.