Presentation on theme: "Mitchie & John Moe ARS Master Rosarians Pacific Northwest District"— Presentation transcript:
1 Mitchie & John Moe ARS Master Rosarians Pacific Northwest District Diseases of RosesMitchie & John MoeARS Master RosariansPacific Northwest DistrictMay 25, 2012
2 Acknowledgements Most photos used in this program are copyrighted. Permission was received to use the copyrighted photos for this educational program! Please do not copy or reproduce for any other uses.An excellent source – the ARS Consulting Rosarian ManualAnother excellent source -Baldo’s Bugs & Roses, the website of Baldo Villegas, known to rosarians as “The Bugman”Please – no commercial use of this program!
3 IntroductionThere are many diseases of roses that have described in various books, but there are three that seem to afflict the rose garden at one time or another:MildewBlackspotRustIf these three can be controlled, the rose garden will be generally disease free. They often be managed by following these recommendations:Buy certified stock free of diseasesKeep free of weeds, fallen leaves, and disease-infested plants or canesUse regular spray programs, and practice good cultural methodsNote: This program deals primarily with identification of diseases, and does not get into specific chemical controls, which is a subject by itself.
4 Powdery MildewSphaerotheca pannosaOne of the most prevalent and serious diseases of roses – some more susceptible than others!Starts on leaves, but spreads to buds and young shootsCommon in crowded plantings where air circulation is poorThe fungus can over winter on infected canes, and leaves left on the bush"Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”Photo by Jack Kelly Clark
5 Powdery Mildew (cont.)Relative humidity must be quite high for spore germinationOptimum conditions for this are 71°F and 98 percent relative humidityProduces mycelium (fungal threads shown here) that grow only on the surfacePhoto by Jack Kelly Clark"Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”
6 Powdery Mildew Control Disease over-winters on canes and leaves, and spores move to new growth foliage in spring to begin disease cycleAggressive spring pruning will remove a large source of fungusFungicides work best at onset of disease, not after massive infection has occurredA regular fungicide spray program is generally necessary to control itPhoto credit - used with permission, by David Hughes, Gardenseeker.comDavid Hughes, Gardenseeker.comThis is why the first fungicide spray is so important!
7 Black Spot One of the most common diseases of roses Diplocarpon rosaeOne of the most common diseases of rosesDisease cycle typically begins on leaves or canes infected the previous seasonLeaves less than two weeks old are the most susceptible"Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”Photo by Jack Kelly ClarkSmall 2 mm black spots enlarging to 12 mm with generally circular appearance, but having a feathery edge found on the upper leaf surfaces as well as immature canes
8 Blackspot (cont.)Lower areas are more likely to be infected as spores are splashed up on new foliage during rains or irrigation– will continue up the stem - as disease spreads, leaves go from green to yellow and then dropBecomes active in a wet environment with temps between °F – needs about 7 hours to germinate, symptoms appear in 3 to 10 days, and produce new spores that can spread to and infect to infect additional leaves and canes within 10 daysCredit -Clemson University - USDA Cooperative Extension Slide Series, Bugwood.orgClemson University - USDA Cooperative Extension Slide Series, Bugwood.org
9 Blackspot ControlSpores can over winter on canes and leaves, and the entire cycle will repeat itself the following season if a fungicide spray program is not started early!Good sanitation will reduce the chance of infection– remove diseased leavesAggressive spring pruning will remove a large source of fungusPrune to allow air circulation, and water without wetting the foliage"Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”Photo by Jack Kelly Clark
10 Blackspot Control (cont.) Maintain a regular fungicide spray program throughout the growing seasonAs an option, a small amount (1/2 tsp/gal) of household detergent added to the spray may allow the active ingredients to spread more evenly, and remain longer when leaves are wetOne way to minimize - buy disease resistant varieties of rosesCredit -Clemson University - USDA Cooperative Extension Slide Series, Bugwood.orgClemson Univ - USDA Coop Extension Slide Series, Bugwood.org
11 Downy Mildew A very serious disease that can affect all roses! Peronospora sparsaA very serious disease that can affect all roses!May appear only when favorable conditions of humidity over 85% and temps of ° FUnder cool and moist spring conditions, young leaves, stems and flowers may show purple to red or brown irregular blotches that tend to follow the leaf veinsAdvanced infections will have yellowing of leavesPhoto credit – Gail TrimbleGail Trimble
12 Downy Mildew (cont.)White to grayish fungal threads containing spores coat the undersides of leavesSpores may germinate in as little as 4 hours, and appear on leaf surfaces in 3 daysCan defoliate a plant in a day or soFungus can winter-over in plant parts"Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”Photo by Jack Kelly Clark
13 Treating Downy MildewOnce seen, it is generally too late to prevent severe leaf dropTreating generally requires using some very potent and costly fungicidesOnce treated, severely prune heavily infected and defoliated plants to encourage new growthDestroy all cut material, spores can live for a monthPhoto credit – Gail TrimbleGail Trimble
14 AnthracnoseSphaceloma rosarumInitially spots are small and black - easily confused with blackspotSpores believed to be carried by water or rain to new leaves and stemsAs disease progresses, spots become purple to brown and centers turn gray or white with dark marginThis light-colored center best defines the difference with blackspotCan be severe under cool, moist spring conditionsPhoto credit – Baldo VillegasBaldo Villegas
15 Anthracnose (cont.)Tissue may drop out of the center of the spots, giving infected leaves its other name of “Shot Hole Fungus”Fungus overwinters on leaves and canesCan cause leaf drop that weakens the plantIn extreme cases, it can result in complete defoliationCredit – Gail TrimbleGail Trimble
16 Anthracnose ControlSanitation is best means of control – remove diseased leaves, and dispose in trashPlant spacing, use of drip lines or soaker hoses rather than sprinklers should helpPrune out canes that have infections in fall – dispose in trash, not in compost pileFungicide used for black spot is usually effectiveCredit - Paul Bachi, University of Kentucky Research and Education Center, Bugwood.orgPaul Bachi
17 Botrytis BlightWhen the weather is cool and wet, the conditions are right for this fungusMost common symptom - young flower buds droop, turn black at the baseLater producethe cottonygrey-blackmycelium ofthe fungusBotrytis cinereaGail TrimblePhoto credit – Both by Gail TrimbleGail Trimble
18 Botrytis Blight (cont.) Spores are moved to other plants by wind or blowing rainCan affect any part of a plant except rootsNote the grayish fuzzy growth on the cane that indicates botrytisWet or very humid weather may be highly favorable for the spread of the diseaseGood ventilation is also essential in reducing disease incidenceFungus may overwinter in dead plant tissuePhoto credit – The University of Georgia College of Agricultural and Environmental SciencesUniv of GA
19 Botrytis Blight Control Prevention is the best means of controlGood sanitation is a must!Remove faded or blighted flowers, leaves, or entire plants if infected at the baseDiscard in trash! Not in compost!Fungus becomes quickly resistant, so alternate use of fungicidesPhoto credit – Gail TrimbleGail Trimble
20 Rose CankerConiothyrium sppA fungal disease that can affect any part of the plant, but most common on stems and canesAfter a cold wet winter, pruned stems provide wound sites for canker causing fungiCanker can also enter thru leaf scars – do NOT tear off leaves during fall pruning!The stems will yellow, often have red spots and later become brown or blackPhoto by John MoeJohn Moe
21 Rose Canker (cont.)May eventually girdle the cane as disease progresses – if it does, growth will dieTissue within the canker begins to dry out and shrink, giving it a shriveled lookCan be acute on old roses that have lost vigor, and on new bare root roses emerging from cold storagePhoto by John MoeJohn Moe
22 Rose Canker ControlTime fall prune so tips will dry and harden before winterDormant spray can protect pruning cutsDisinfect pruners before moving to another bushIn spring, remove infected canes and spray for fungal diseaseFungicides that control black spot on ornamentals will also help to control cankerPhoto credit – John MoeJohn Moe
23 Rust A fungal disease common in many areas, easily identified Appears on the underside of the foliage as red-orange spotsThrives in cool, moist weatherThe summer stage is cyclic, and may repeat every 10 to 14 days in favorable weatherFungus overwinters on infected leaves and canesSpores are wind borneCan defoliate the plantPhragmidium sppPhoto Credit – Clair Martin, Huntington Botanical GardensClair Martin
24 Rust ControlGood sanitation will help to prevent early season infectionsRemove affected leaves and dispose in trashDon’t water in the evening so that the leaf surface is wet over nightFungicide you use for powdery mildew or black spot is usually effectivePhoto credit - The University of Georgia College of Agricultural and Environmental SciencesUniv of GA
25 Bacterial Crown GallAgrobacterium tumefaciensBacterial disease usually seen on bud union, or on the trunkThrives in warm, sunny weather; not active in cold weatherCork-like substance that will turn brown and harden as it agesPlants will usually be stunted in their growth habitsPhoto by John MoeJohn Moe
26 Bacterial Crown Gall (cont.) Can persist in the soil in a dormant state for yearsThe growth can be removed, however, chances are it will eventually returnIf you do cut out galls, use a sharp knife or pruning shears, brush on full strength bleachDestroy the galls; disinfect cutting tools with a strong bleach solution after each cutPhoto by John MoeJohn MoeThis cut was most likely made with infected pruners!
27 Bacterial Crown Gall Control Avoid injury to canes and stems when planting or cultivatingMaintain good garden sanitation and cultural practicesIf heavily infected, remove and discard the plantIf you can, replace soil where rose was growing with new soil, or saturate the soil well with a 10% bleach solution before replantingDisease is un-treatablePhoto credit – Baldo Villegas
28 Rose Mosaic Probably the most commonly found virus in roses Prunus Necrotic Ringspot VirusProbably the most commonly found virus in rosesMosaic is primarily transmitted by propagationUsually appears in spring as a distortion of growing tips and leavesSymptoms include coloration patterns (shown), distorted leaf growth, slow to develop, and fewer quality bloomsPhoto credit - The University of Georgia College of Agricultural and Environmental SciencesUniv of Georgia
29 Rose Mosaic (cont.)No cure – buy quality plants showing no symptoms of the diseaseCommercial rose growers purchase rootstock that has been “virus indexed”, which means it has been lab tested to confirm the absence of the virus in the plants tissueOverall damage from the disease may be mostly cosmetic with little reduction of plant vigorUniv of GATop photo credit - The University of Georgia College of Agricultural and Environmental SciencesBottom photo credit - "Used with permission from the University of California Statewide IPM Program, photo by Jack Kelly Clark”Jack Kelly Clark
30 Rose Rosette Disease (RRD) Exact cause unknownThe distinctive red stems, misshapen leaves are symptomsThe main host is R. multifloraNew growth appears unusually soft and pliableRRD is suspected to be carried from plant to plant by mitesCan be confused with plant damage from chemicals like Roundup®Photo credit - James W. Amrine Jr., West Virginia University, Bugwood.orgPhoto by James W. Amrine Jr.
31 Rose Rosette DiseaseIf you are sure that it is this disease, you need to act fast!Very serious disease – no cure, fatal to plant!Photo credit - James W. Amrine Jr., West Virginia University, Bugwood.orgPhoto by James W. Amrine Jr.Remove the diseased plant as soon as possible (including the entire root system) and destroy it!
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