Danh mục: Cây Hoa Hồng – Rose Plant
ROSE SPRING DWARF DISEASE
ROSE SPRING DWARF DISEASE
CAUSAL ORGANISM:
A virus is suspected in causing this disease.
SYMPTOMS:
Rose mosaic usually appears in spring as a distortion of growing tips or expanding leaves. Later the leaves can appear to be wavy and have yellow lightening patterns, oak leaf patterns or simply gold to yellow veins. Plants infected with virus usually are slower to develop in spring than healthy plants and usually produce fewer good quality blooms. During the warm summer typical symptoms can disappear only to come back as fall and cooler temperatures arrive.
CONTROL:
Since there is no cure for the virus diseases it is important to purchase only quality materials which have no symptoms of the disease. Some pathologists suspect that mosaic may be pollen transmitted which could prompt removal if other roses in the garden are valuable and not already infected. In some exhibition gardens the disease can actually be very common. Propagation of buds from infected roses will probably result in transmission of the disease if the buds actually take.
ACKNOWLEDGEMENTS:
I would like to thank the following plant pathologists with the California Department of Food and Agriculture’s Plant Pests Diagnostic Centre: Dan Opgenorth and Dennis Mayhew. They have given me invaluable advice in preparing this article. All the above pictures were taken by Baldo Villegas.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp. 26-27.
ROSE MOSAIC
ROSE MOSAIC ON ROSE PLANT
CAUSAL ORGANISM:
Prunus Necrotic Ringspot Virus: Mosaic is probably the most commonly found virus on roses but many other virus diseases also exist. While mosaic is transmitted by propagation other viruses can be transmitted by pollen, insect feeding or simply by mechanical contact. Symptoms of virus are usually dramatic manifestations of coloration, spotting or irregular distorted growth of leaves, flowers or growing points.
SYMPTOMS:
Rose mosaic usually appears in spring as a distortion of growing tips or expanding leaves. Later the leaves can appear to be wavy and have yellow lightening patterns, oak leaf patterns or simply gold to yellow veins. Plants infected with virus usually are slower to develop in spring than healthy plants and usually produce fewer good quality blooms. During the warm summer typical symptoms can disappear only to come back as fall and cooler temperatures arrive.
CONTROL:
Since there is no cure for the virus diseases it is important to purchase only quality materials which have no symptoms of the disease. Some pathologists suspect that mosaic may be pollen transmitted which could prompt removal if other roses in the garden are valuable and not already infected. In some exhibition gardens the disease can actually be very common. Propagation of buds from infected roses will probably result in transmission of the disease if the buds actually take.
ACKNOWLEDGEMENTS: I would like to thank the following plant pathologists with the California Department of Food and Agriculture’s Plant Pests Diagnostic Centre: Dan Opgenorth and Dennis Mayhew. They have given me invaluable advice in preparing this article. All the above pictures were taken by Baldo Villegas.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp. 26-27.
Contact: +84.933.067.033
BACTERIAL CROWN GALL
BACTERIAL CROWN GALL ON ROSE PLANT
CAUSAL ORGANISM:
Agrobacterium spp: This is really the only serious bacterial disease of Rose. The bacteria is found world wide wherever roses are grown and is especially severe in loose sandy or sandy loam soils.
SYMPTOMS:
On roses the symptoms of overgrowths can occur at the crown, bud union or on the roots. Galls are usually round to irregular in appearance and may have a rough exterior. Upon cutting across a gall, a disorganized callus type of tissue is commonly found. The portions closest to the exterior usually contain the actively growing bacteria. However, once the tumor inducing plasmid is introduced into a plant disease can occur without the presence of the vectoring bacteria.
DISEASE CYCLE:
The bacteria causing the disease are soil born and can survive in soils for many years. When roses are planted in infested soil any wound sites on the roots or crown offer points of entry for the bacteria. Once in the host the tumor inducing principle carried on a small circular portion of DNA is incorporated into the plant cell and a overgrowth begins to form. In some plants the bacteria can be systemic and galls may begin to form at many sites on the plant. As the galls develop callus tissue is laid down which is susceptible to other types of breakdown, decay or sloughing. In this way the soil around a plant can become infested with the bacteria. The bacteria survives many years in the soil and can be moved with water or other infected plant parts.
CONTROL:
Always inspect new plants thoroughly before placing them in your garden. Since wounds can be infected at the time of digging some plants may have latent infections which could become evident several years after they were planted. If crown gall is detected the plant may survive many years but could serve as a reservoir for the bacteria. Thus, removal of the plant as well as adjacent soil is recommended. In some cases soil fumigation is used to kill the bacteria in the soil, but this is only effective where relatively porous and dry soils are involved. Plant surgery is also an option on specimen roses but precautions should be taken to sterilize cutting equipment before and after use. These plants should probably be removed from the garden and watched closely for further development of disease. Any plants propagated from infected material should also be watched for the development of galls resulting from systemic contamination.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp. 23-26 and Color Plates 39-42.
RUST ROSE
RUST ON ROSE PLANT
CAUSAL ORGANISM:
Phragmidium spp: The rust of rose is one of the most commonly found and easily identified diseases of rose. Severe outbreaks occur where cool temperatures and high moisture are found during the prime growing season. Where foliage is heavy, the first symptoms usually are found close to the ground and on the insides of plants. Nine species of the rust fungus are known to occur. The fungus is complex having up to five different spore stages in its life cycle. The resistance of various cultivars is usually well documented because rust is a very common disease in some parts of the country.
SYMPTOMS:
In early spring powdery pustules of light orange to yellow spores appear on the under side of leaves. Soon after these aecieospores can be found on the upper side of leaves where they are more obvious. As we move into summer the uredial stage usually is predominate forming the typical red brown to orange spores. This stage can repeat several times during the growing season usually in 10 to 14 day intervals. Finally as fall approaches and evenings become cool the over wintering telial stage develops black teliospores. Leaves, succulent canes and flower parts are all susceptible to the rust fungus.
DISEASE CYCLE:
The fungus over winters as teliospores on fallen leaves or on infected canes. The spores are wind borne and germinate to infect leaves through the stomata. Rust fungi are obligate parasites and can not be cultured. As the infection proceeds the various spore stages develop on rose, there is no alternate host for rose rust. Reinfection and spread occurs through aeciospores and urediospores. Spore germination requires cool summer temperatures and continuous moisture for at least two hours so the germ tubes can enter the leaf stomates. Teliospores serve as a means of over wintering on leaves and infected canes.
CONTROL:
In areas where Rust is severe, sanitation should be practiced to reduce inoculum and prevent early season infections. Infected canes should also be spring pruned to reduce the initial inoculum levels. Pruning very dense bushes will help to reduce the moisture levels inside of plants and prevent some infections. Preventative fungicidal sprays should be applied every 7 to 10 days when conditions are favorable for rust development.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp 11-12 and Color Plates 12-19.
ROSE CANKERS
ROSE CANKERS ON ROSE PLANT
CAUSAL ORGANISM:
Coniothyrium spp: After a long cold wet winter, roses can be expected to have some dead and cankered canes. While these pathogenic fungi are not very sophisticated, they can cause considerable damage. The problems can be especially acute on old established roses that have lost some vigor and on young bare root roses emerging from cold storage.
SYMPTOMS:
In early spring, pruned stems provide wound sites which can be colonized by canker causing fungi. The stems will yellow, often have red spots and later become brown or black. Black erumpent spots can often be found in the discolored tissue which are the fruiting structures of the fungus containing spores.
DISEASE CYCLE:
The canker fungus is most active during the cold time of the year when roses are not actively growing. Pruning cuts or wounds on stems provide sites of entry for germinating spores. The fungi are not high level pathogens and can not produce the disease when conditions are favorable for plant growth. During the dormant months, fungi colonize the tissues, sporulate and are spread to other pruning or wound sites. The disease can be extensive and severe under the ideal conditions for development.
CONTROL:
Promoting vigorous growth and removal of dead canes and stubs will help to reduce the primary source of inoculum. When pruning before winter always make an angular cut close to an active bud so the callus can form a protective layer before winter. A dormant spray could be used to protect pruning cuts and wounds during the cold and wet winter. In spring, removal of infected canes and a general spray program for fungal diseases should reduce canker problems and protect the plants until they can become vigorous growers once again.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp 14-17.
CONTACT: +84.933.067.033
BOTRYTIS BLIGHT
BOTRYTIS BLIGHT ON ROSE PLANT
CAUSAL ORGANISM:
Botrytis cinerea: Botrytis blight is common in all parts of the world. This fungus is not a specific pathogen and can take advantage of many situations to produce a blight or rot condition on many hosts. It is an opportunist on cut or pruned rose canes and will infect flowers and buds.
SYMPTOMS:
The most common symptoms usually are seen on young flower buds which droop, turn black at the base and later produce the cottony grey-black mycelium of the fungus. Flowers can also be affected in the same way and cut ends will have the black canker like symptoms with presence of mycelium. Any time conditions are cool and wet a grey-black mycelial growth will indicate Botrytis.
DISEASE CYCLE:
This fungus is not specific to roses, but will grow on many different plants and plant debris. Under cool wet conditions profuse sporulation results and spores are moved to roses by air currents or blowing rain. A minor wound in a bud or flower, or perhaps a pruning cut will provide the initial point of entry. As the infection progresses more sporulation results and additional sites become infected. The fungus is a low level parasite and will colonize wound sites as well as dead plant materials.
CONTROL:
Prevention is the best means of control. This can be accomplished through intense sanitation procedures. By elimination of opportunistic colonization on dead plant material the amount of sporulation can be reduced. Good ventilation is also essential in reducing disease incidence. Some sprays may give short term relief but the fungus usually becomes quickly resistant. In greenhouse conditions special covers are used to reduce the levels of ultraviolet light required by the fungus for sporulation. In most cases, removal of infected plant parts and protection of wounds by chemicals is all that can be done until warmer and dryer conditions prove too unfavorable for continuing disease.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp. 18-19 and Color Plates 30-35.
ANTHRACNOSE
ANTHRACNOSE ON ROSE PLANT
CAUSAL ORGANISM:
Sphaceloma rosarum: Not much is known about this disease, however, it can be severe under cool moist spring conditions. Wild rose, climbers and ramblers seem most susceptible but hybrid tea and bush roses also get the disease.
SYMPTOMS:
Initially leaf spots are about .5 cm diam and black, which makes them easily confused with blackspot. As the development progresses the spots become purple to brown and finally light brown or tan with a red or purple margin. Stems, hips and pedicles can also be infected and as lesions mature small black dots will appear in the papery tan centers. These black dots are the spore producing acervuli of the fungus. Spotting, yellowing and severe defoliation and shot hole can result under moist spring conditions.
DISEASE CYCLE:
The fungus over winters in old lesions on leaves and canes. Warm spring conditions promote the development and release of spores from the acervuli in old lesions. The spores are believed to be carried by water or rain to newly expending leaves and stems. Not much is known about the sexual stage of the fungus or conditions favorable for spore germination. It seems that cool moist conditions are favorable for this disease as for Black Spot.
CONTROL:
Removal of old leaves from around the base of plants and pruning out canes that have infections will do much to reduce the inoculum levels in spring. Generally, the same spray program that is used for Black Spot should work for Anthracnose also.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp. 20-21.
BLACKSPOT
BLACKSPOT ON ROSE PLANT
CAUSAL ORGANISM:
Diplocarpon rosae: This disease may also be called leaf spot, leaf blotch, star sooty mold and several other names. It is the most important disease of outdoor roses on a world wide basis. The fungus has probably been widely distributed with the cultivated rose and no really complete resistance is believed to exist.
SYMPTOMS:
Small black spots of 2 mm diameter can be found on upper leaf surfaces as well as immature canes. These spots are black and sooty enlarging to 12 mm with generally circular appearance but having a feathery edge. Further development involves the appearance of yellow margins around the spot and a yellow condition that can extend into the entire leaf. Late in the growing season defoliation can occur along with purple red, raised irregular blotches on immature wood.
DISEASE CYCLE:
The fungus usually over winters on infected leaves and canes as a mycelial mat rarely producing the perfect or sexual stage. As temperatures rise in the spring the fungus produces conidia which are moved by air currents or splashing water to new developing and expanding leaves which are very susceptible. Conidia germinate under conditions of free moister and need free water conditions for at least seven hours in order for infection to occur. The fungus is considered an obligate parasite producing haustoria in the host cell. As the infection develops, the leaf spot expands taking on the characteristic black appearance and producing conidia as secondary inoculum. Usually the lower and inside areas of the plant are more likely to be infected because these areas have longer time periods when free water is available on leaf surfaces allowing the germination and penetration of the fungus. Several cycles of infection and production of secondary inoculum can occur throughout a growing season.
CONTROL:
Dormant pruning, removal of attached leaves and cleaning up old leaves under the bushes can do much to reduce the over wintering inoculum. A well aerated site will do much to reduce disease incidence by preventing the occurrence of free water on the foliage for long time periods. Pruning to allow air movement and watering without wetting the foliage could also be important means of prevention. Some roses may be more resistant than others, but specialized races of the fungus quickly arise. When conditions are favorable in early spring, protectant sprays can be used on a one week interval or after periods of rain to prevent infection. Surfactants may allow the active materials to spread more evenly on plant surfaces and persist longer during periods of precipitation.
REFERENCES:
Horst, R. K. 1983. Compendium of Rose Diseases. The American Phytopathological Society, St. Paul, Minnesota. Pp.7-11 and Color Plates 8-11.
BỆNH ĐỐM LÁ PHYLLOSTICTA
BỆNH ĐỐM LÁ PHYLLOSTICTA TRÊN HOA HỒNG
(phyllosticta leaf spot disease)
Bệnh đốm lá Phyllosticta phổ biến hơn bệnh đốm đen và thán thư đối với cây hồng, bệnh đốm lá thường bẳt đầu xuất hiện và gây hại phố biến ở phần chóp lá hoặc rìa lá hồng, sau đó vết bệnh sẽ lan dẩn vào trong phiến lá.
Các dấu hiệu nhận biết bệnh đốm lá do nấm Phyllosticta trên cây hồng
Khi bệnh xuất hiện bắt đầu từ chóp lá, vết bệnh thường có dạng hình chữ V ngược, màu nâu nhạt hoặc nâu đậm tùy theo giai đoạn phát triển của vết bệnh, phần tiếp giáp giữa mô bệnh và mô khỏe xuất hiện đường viền dày, màu tím nhưng không đều, đôi khi đường viền không thế hiện rõ rệt.
