Roses in Mississippi
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Cercospora leaf spot (Cercospora sp.) This leaf spot can also defoliate roses, including some types that are not especially susceptible to black spot. Symptoms start as a light pink to purplish spot. As the spot enlarges, the center turns gray, but the margin of the spot remains purplish. The lesion is near circular. MAnAGeMent. Use the same management procedures as recommended for black spot. Stem Cankers and Die-Back These are among some of the most serious diseases of roses in the South. Caused by a number of fungi, these diseases work similarly in that they infect the rose canes and block the flow of water and nutrients to the upper part of the cane, which dies. Stem cankers start as a brownish to black stem lesion that may lengthen fairly rapidly. The lesion may stay on a single side of the stem, or it may girdle it. Girdling will cause the cane above the lesion to completely die-back and kill the cane. The first line of protection against these diseases is to select only disease-free plants for your garden. Practicing good san- itation, such as removing fallen leaves and decaying blooms each dormant season, is also helpful. Thirdly, it is important to prune the canker out as soon as you see it. Cut well below the canker (about 5 inches) and carefully inspect the cut wood to ensure there is no discoloration inside of the cane. Discoloration of the interior of the cane would in- dicate the disease has moved lower in the stem than you have cut. Clean and disinfect your pruners and recut lower down. Remove and destroy the cane. If your roses are grafted, do not allow the cankers to enter the graft. You will probably lose the rose if a canker disease enters the graft area. Roses on their own root stock may or may not survive pruning near the crown area of the plant. After pruning cankers, remove and destroy the diseased tis- sue. Use a fungicidal spray containing a topical active ingre- dient, such as mancozeb or chlorothalonil. Canker diseases are more prevalent on plants weakened by other problems, such as those defoliated by black spot. Stem canker outbreaks also seem to be worse in springs following winters that had frequent and large temperature swings. Thus, it is important to maintain the health of your rose plants so they can better fight off an infecting canker. The fungicide chosen may depend upon the type of canker. Powdery Mildew (Sphaerotheca pannosa) A white, powdery fungus growth on the surface of leaves, buds, or stems of roses usually indicates powdery mildew. In- fection on young leaves may cause curling and leaf distortion. A reddish to purplish coloration may be present. Badly in- fected flower buds do not open. In some situations, young canes may be killed. The disease is more common on older rose types, especially some climbers and bushes. The disease is more likely to infect these plants when they are grown in shady areas. MAnAGeMent. Most of the sanitation and management procedures for black spot are also valuable in controlling powdery mildew. During the growing season, you can hold mildew in check by spraying with various fungicides. If the plant is only somewhat susceptible to powdery mildew, the Cornell rose formula may be effective. Please see Plant Doctor: Black Spot and Powdery Mildew of Rose (IS 1667). During 27 STEM CANKERS late winter, a spray of dormant plants with a commercial lime-sul- fur 1:15 solution can be effective. Gray Mold (Botry- tis cinerea) Gray mold is a com- mon infection of old buds and blossoms. In the right conditions, it will also infect canes. Gray mold infection starts as a grayish-black lesion on the in- fected terminal and will extend down the stem of the infected cane. Infected buds may appear blasted and will droop over at or near the lesion. During warm, humid weather, a gray fungus may cover the infected parts. When you examine the affected area, you may find a powdery gray to black mold. MAnAGeMent. Prune out and destroy all infected parts as soon as they appear. Prune the infected parts at least two inches below the last sign of infection. Usually these infections will run their course in a week or two, but if they continue, fungicide applications may be needed. Water Molds - Pythium and Downy Mildew (Pythium and Peronospora sparsa) Two costly diseases to which all roses are susceptible are rots caused by water molds. As their name implies, water molds are favored by wet or damp environments. When the envi- ronment stays moist for some time, the water molds infect and rot the plant tissue. The most common water mold disease is Pythium root rot. It is the reason you should plant roses in well-drained soil. Good drainage is important to growing roses. Roots that stay wet for too long get infected by Pythium, and root rot sets in. The roots start to slough off, reducing the flow of water to the leaves. The edges of the leaves brown, and as root rot continues, the lower leaves turn yellow, then drop from the plant. The process proceeds up the plant. Symptoms of nutrient defi- ciency may be apparent, and the plant dies. Downy mildew is another water mold disease. It comes into the state on roses grown in cool, moist areas, such as the Pa- cific Northwest and northern California. Most roses will suffer from the disease only their first winter in the state, but others become permanently infected. When the weather becomes cool and damp during the late fall, winter, and early spring, the disease starts to emerge from the cane. Small red lesions form on the cane, and a day or so later, spores emerge. The spores will infect other plants, primarily leaves. Dark lesions will form between the veins of the leaves and enlarge. The leaf may take on a chevron-like appearance. Infected leaves will fall from the plant. If possible, do not allow water to contact the leaves. Water al- lows the spores to germinate and infect the leaves. If your roses are in a greenhouse, keep the heat above 65 F. Most fungicides will not work against water molds. Those that do are expensive, and repeated applications will be needed.
Crown Gall (Agrobacterium tumefaciens) Crown gall is a bacterial disease. It is very easily spread by in- fected wood or infested gardening equipment, especially pruners. It is important to clean and disinfect all equipment that comes into contact with this dis- ease.
Symptoms are gall-like growths that usually occur at or near the soil line and may be fairly large. Galls of another type of crown gall may also be found on the upper stems or on the roots, but these are usu- ally smaller, bead-like galls. Infected plants be- come stunted, and the blossoms and foliage are of low quality. Chemical control is not an option for controlling crown gall. This means that the best management technique is to remove and burn all infected plants. The crown gall bacteria can re- main viable in the soil for several years, so replanting in the same area is risky. It is best to move new plantings to a new location in the landscape. If you want to replant in the same area, try a biological protec- tant, such as Galltrol. Galltrol is a living culture of a close rel- ative of the crown gall organism (Agrobacterium radiobacter). Unlike crown gall, it does not attack plants but sticks to the 28 POWDERY MILDEW CROWN GALL plant parts and prevents the crown gall bacteria from enter- ing. To use Galltrol, you mix the bacteria in a bucket of water, then dip the host plants into the mixture immediately before transplanting. Galltrol can also be used as a spray or soil drench treatment for crown gall prevention. Viruses
Once a plant is infected with a virus, it cannot be cured. Most rose viruses do not do a great deal of harm to the plant but can weaken them so they are more likely to die in a severe winter. The exception to this is rose rosette virus. Rose Rosette Rose rosette virus causes a severe disease in most rose types and is often fatal, especially in R. multiflora. In recent years it has been a severe problem in Knock Out roses, especially along the I-40 corridor. The virus is moved from plant to plant by grafting or by a very small (eriophyid) mite, Phylocoptes fructiphylus. The mite sails on the wind on thin threads of silk, moving among plants and moving the virus with it. Symptoms of rose rosette virus differ depending upon the rose species or even rose cultivar infected. This variability makes diagnosis difficult, and laboratory testing is somewhat difficult. Several of the most diagnostic symptoms of rose rosette in- clude some reddening of the leaves and the development of closely spaced internodes that cause dense branching, also known as a witches’ broom. The witches’ broom may be an off-color green. Leaves inside the witches’ broom are often distorted and have a red cast. Flowers may abort, be con- verted to leaf-like form, or if flowers are formed, they may have fewer petals, less color or be mottled in color. Canes of infected roses may also show diverse symptoms. In- fected canes may be thicker than the older cane beneath it; they may twist or be otherwise distorted. Many infected types of rose develop dense spines that are usually flexible. You can push them from side to side with your finger. Many of the above symptoms can also be the result of an ex- posure of glyphosphate herbicide (sold under many names, including RoundUp), so careful checking on your own or your neighbors’ herbicide use is a good idea. Imazaquin has also been reported to cause herbicide damage on roses. Al- ways read the label of any herbicide before use on roses, and apply only if it specifically is labeled for use on roses. This is true for any chemical application to roses. The only remedy for rose rosette virus is to remove infected plants upon diagnosis, especially if you want to retain your other rose plantings. Other Rose Viruses A number of virus diseases attack roses, resulting in a multi- tude of symptoms such as leaf patterns, yellowing, patterns, streaking, ring spots, puckering and curling of the new leaves. Most of these viruses are transmitted by grafting. The two most common rose viruses are prunus necrotic ringspot virus and apple mosaic virus. The most common symptoms of in- fection are leaf patterns and ring spot.
The best method of control is to buy virus-free plants from a reputable dealer. Most rose viruses, with the ex- ception of rose rosette, are spread by grafting, so your other plants will most likely be safe. So when you notice infected plants, you may wish to keep them, but many rose enthusiasts remove and destroy them. If you encounter other diseases, consult your county Exten- sion office. 29 VIRUSES Austin, David. 1992. Old Roses and English Roses. Antique Collectors Club Ltd. Woodbridge: Suffolk, England. Austin, David. 1993. Shrub Roses and Climbing Roses. Antique Collectors Club Ltd. Woodbridge: Suffolk, England. Beales, Peter. 1985. Classic Roses. Holt, Rinehart and Winston. New York: New York. Beales, Peter. 1992. Roses. Henry Holt and Company, Inc. New York: New York. Collins, Pamela. Deadheading Roses: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., summer. Collins, Pamela. 2013. Notes from the Veterans Memorial Rose Garden: Old Garden Roses. Mississippi State University Extension Service, Publication, P2746, 16 pp. Collins, Pamela. Old Garden Roses: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., summer. Collins, Pamela. Pruning Hybrid-T Roses: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., spring. Collins, Pamela. Rose Varieties: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., spring. Crouse, Keith. How to take a Soil Sample: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., fall. Crouse, Keith. Interpreting Soil Test Results: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., fall.
Crouse, Keith. 2012, Soil testing for the Homeowner. Mississipppi State University Extension Service, Information Sheet, IS1294, 2 pp. Denny, Geoffrey and K. Crouse. 2013. Adjusting Soil pH in Mississippi Landscapes. Mississippi State University Extension Service, P2831, 4pp. Denny, Geoffrey. 2013. A quick Guide to Fertilizing Mississippi Landscape. Mississippi State University Extension Service, IS1977, 2pp. Denny, Geoffrey. 2012. Choosing a Disinfectant for Tools and Surfaces in Horticultural Operations. Mississippi State University Extension Service, Information Sheet, IS1955. Denny, Geoffrey and K. Crouse. 2013. Diagnosing Nutrient Deficiencies in Ornamental Plants. Mississippi State University Extension Service, Publication, P2760. For Further Reading and Viewing: 30
Denny, Geoffrey and K. Crouse. Nitrogen Fertilization of Mississippi Landscape Trees and Shrubs. Mississippi State University Extension Service, IS1978, pp2. Dobson, Beverly and P. Schneider. 2013 Combined Rose List 2013. Peter Schneider. Mantua: OH Henn, Alan. Plant Doctor: Black Spot and Powdery Mildew of Rose. Mississippi State University Extension Service, IS 1667. Henn, Alan. 2012. The Plant Doctor: How to Spray Fungicides to Protect Your Home Landscape, Garden, and Turf ( http://msucares.com/pubs/publications/p2705.pdf ). Mississippi State University Extension Service, P2705, 4 pp. Ingram, David. Black Spot on Roses Disease: Gardening through the Seasons, video, http://msucares.com/gardenvideos/index.html ., summer. Kelly, Lelia, M. Wellan, P. Collins, C. Sloan, W. Essig, B. Layton, A. Henn, D. Ingram, J. Mills Flower Gardening in Mississippi: Roses. http://msucares.com/lawn/garden/flowers/perennial/roses/ . Layton, Blake. 2011. Control Fire Ants in your Yard. Mississippi State University Extension Service, Publication 2429, 4 pp. Layton, Blake. 2008. Insect Pests of Roses. Mississippi State University Extension Service, Publication 2472, 11 pp. Quest-Ritson, Charles and B. Quest-Ritson. 2003. The American Rose Society Encyclopedia of Roses. DK Publishing. New York:New York. Sloan, Crofton. 2012. Propagating Plants for the Home Landscape. Mississippi State University Extension Service, Information Sheet 207, 4 pp. Thomas, Graham Stuart. 1991. The Art of Gardening with Roses. Henry Holt and Company. New York: New York. Warner, Christopher. 1988. Climbing Roses. The Globe Pequot Press, Chester: CT. Young, Marily and P. Schorr. 2007. Modern Roses 12. The American Rose Society. Shreveport, LA. Authors: Dr. Pamela Collins, Assistant Research/Extension Professor and Director of Gardens, Plant and Soil Sciences, Dr. Geoff Denny, Assistant Extension Professor and Nursery Specialist, Plant and Soil Sciences, Dr. Blake Layton, Extension Ento- mology Professor, Biochemistry, Molecular Biology, Entomology and Plant Pathology, Dr. Alan Henn, Extension Plant Pathology Professor, Biochemistry, Molecular Biology, Entomology and Plant Pathology 31
The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended. Publication 2835 (500-11-17)
Produced by Agricultural Communications. Mississippi State University is an equal opportunity institution. Discrimination in university employment, programs, or activities based on race, color, ethnicity, sex, pregnancy, religion, national origin, disability, age, sexual orientation, genetic information, status as a U.S. veteran, or any other status protected by applicable law is prohibited. Questions about equal opportunity programs or compliance should be directed to the Office of Compliance and Integrity, 56 Morgan Avenue, P.O. 6044, Mississippi State, MS 39762, (662) 325-5839. Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. GARY B. JACKSON, Director Yüklə 326,04 Kb. Dostları ilə paylaş:
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