Cytospora Canker in Tree Fruit Crops Fact Sheet No. 2.953 Crop Series|Diseases by Ramesh Pokharel* Cytospora canker may kill the whole tree, Germany, the Cytospora cankers on sweet Quick Facts limb, or shoots resulting in partial or total cherry, are caused by L. persoonii. In Ontario loss. Even if not killed, the infected trees and western New York, C. cincta is more • Cytospora Canker, a disease start blooming later than healthier trees common whereas L. persoonii is the major of conifer and hardwoods, is which results in delay in fruit maturity and pathogen in Eastern New York, New Jersey, caused by various species production of undersized fruits. Such fruits Michigan, and Illinois. Information on of fungi, depending on the won’t reach the packing shed or will increase prevalent species in other states including host tree infected. culling percentages during the packing Colorado is not available. The symptoms, processing. Cankered areas often are covered disease cycles, and control methods are • This disease is the most by gum, produced by the tree in response similar for both species. In Colorado it is important among pests and to infection (Fig. 1). The disease name is believed that both species are present based diseases in stone fruits but attached with the fungus name and the on the infection type and existing weather is a minor problem in pome fungal names change with new taxonomic conditions; however, it is most likely that fruits in Western Colorado. research, thus there are different names for species predominance varies with the the same disease such as Leucostoma canker, location. In the U.S., the species involved • The fungus infects the bark Cytospora canker, Valsa canker or Perennial and severity of disease depend on the and causes cankers which canker. location. The disease is severe in Colorado, eventually girdles and kills Washington, Pennsylvania, New Hampshire, the tree. North Carolina (peach tree short life), Oregon and Florida. In Colorado, the disease • Peach growers in Colorado is found in all fruit growing areas with often call the disease variability in its incidence. ‘gummosis’ although this refers more to its symptom Host than the disease itself. Different species ofCytospora infect more • Cytospora Canker is than 60 genera of hardwood and conifer trees widely distributed in including aspen, green ash, Siberian elm, North and South America, alder, cottonwood, and multi- and single Asia and Europe and is stemmed willow as well as stone and pome more important in peach, Figure 1. Dark colored gummosis and fruits. Most of the stone and pome fruit nectarines and sweet canker beneath on a peach tree trunk varieties are susceptible, but the disease is (pointed by arrow a) and on tree trunk and cherries in cooler climates the branch (pointed by arrow b) indicates more important in peaches, nectarines, sweet such as in Canada and the Cytospora infection. cherries, apricots, and plums. Susceptibility northern fruit growing region differs with crops and varieties but, in of the United States. general, all are more susceptible during Distribution dormancy. The disease is widely distributed in North and South America, Asia and Europe and Importance of Disease is more important in peach, nectarines and Hard data on total losses due to this sweet cherries in cooler climates such as disease are not available, but losses in stone ©Colorado State University in Canada and the northern fruit growing fruits in Colorado are estimated to be 15-20 Extension. 9/99. Revised 7/13. region of the United States (Biggs, 1995). In percent depending upon area, management www.ext.colostate.edu practices, varieties planted and many other * Colorado State University Extension nematologist factors. However, surveys of grower’s fields and fruit pathologist, and research associate, Western Colorado Research Center. 7/2013 found that incidence and loss were several- fold higher than estimated (Pokharel and rain showers at any time of the year when Larsen, 2009a). Examples of common rainfall occurs, but they are most abundant problems among many stone fruit in late spring and early autumn. The role of producers in this area include the loss of ascospores in the disease cycle is not known. 30% of cherry trees in third year of planting or infections increasing from 15% to 70% Infection in an orchard of 700 peach trees (Fig. 2). Tree mortality is related with the age Viable Cytospora spores can be found of the tree when infected. Trees infected on the surface of peach trees all year long, in early age have higher loss rates as including during times of below-zero compared to infection in older trees. There temperatures, with peak months being is limited direct impact of the disease on July through September. Infection takes fruit quality. The disease may kill the whole place via wounds on bark and can occur tree, limb, or shoots resulting in partial or Figure 2. Increase in the incidences of from February to early April. Larger area total loss. Even if not killed, the infected Cytospora canker in a grower’s orchard colonization takes place around 36-46°F, trees start blooming later than healthier where 700 peach trees were planted in but colonization can occur at temperatures trees which results in delay in fruit maturity a year. of 50-59°F. The fungus grows in the and production of undersized fruits. Such bark during the winter whenever the temperature rises above freezing and stops fruits won’t reach the packing shed or will or cirrhi, containing thousands of conidia again in the spring when the tree’s defense increase culling percentages during the stuck together by sticky mucilage. This and growth resume. The fungus can’t infect packing processing. mucilage dissolves when wet and huge actively growing trees so new infections numbers of conidia are liberated and usually start in the late fall or early spring dispersed. These spores are produced Pathogen Life Cycle when the tree is dormant. One should throughout the year and are carried— delay pruning until late winter or early The fungi are ascomycetes in the primarily by splashing rain, pruning tools, spring greatly reduces risk of infection. The order Diaporthales, family Valsaceae. or insect—up to a distance of 40 feet from period of lowest spore availability usually is There are approximately 500 species the site of production. The distance the between March and May and corresponds in the genus Cytospora that cause the spore travel, however, depends on wind to the period of low relative humidity disease in plants. Generally imperfect speed, especially with high moisture. High and temperatures below 85°F. Increased (anamorphic) stages of two species, moisture favors spore production. There duration of wetness and length of time Cytospora cincta (Leucocytospora cinctum) are significant correlations between spore with high humidity, especially humidity and C. leucostoma (L. persoonii), are counts for L. persoonii and L. cinctum and above 90%, increases disease incidence. commonly associated with tree fruits. the number of hours that temperatures are Continuous wetting the canker with The species are closely related and can be between 50 and 60°F (10 and 15°C), the rain water or irrigation promotes spore separated only by microscopic examination duration of wetness, and the length of time formation and liberation. Injured cells at of the sexual fruiting structures and/or that relative humidity is above 90%. Conidia wounds provide the necessary food for the molecular characterization. Both species are resistant to desiccation when contained fungus spore to germinate and grow. have three subgroups. Two sub-groups of within the cirrhus; however, upon release Canker development can take place Leucocytospora cinta, a primary pathogen by water and subsequent drying, most of throughout the year, but the greatest growth of stone fruits, infect stone fruit and one them die within six hours (Biggs, 2005). occurs in the spring and the minimum infects pome fruits. In contrast, two out of Short-range dispersal of conidia indicates during the summer. Active tree growth three groups of L. persoonii infect apple and rain or wind-driven rain as dispersal agents. can create a barrier that temporarily halts one infects stone fruits. Localized splash dispersal due to sprinkler the fungus (Biggs et al., 1994). Infection of irrigation in absence of rain is the major Reproduction the tree occurs mostly through unhealed contributor of spore dispersal in arid fruit wounds and conidia are the primary source Both species and all their subgroups can production areas like Colorado. Spread of inoculum for new infections. Such reproduce asexually and sexually, but the of L. persoonii may also occur via infested conidia are most abundant under the cool sexual reproductive stage is hard to find in pruning tools, birds, and possibly by the and moist conditions of late fall and early the orchard. shot-hole borer (Scolytus rugulosus), but spring (maxima from November through these are minor compared to air, wind- March), but they are present throughout Asexual Reproduction blown rain, and local splash and washing. the year depending upon rainfall. In The infected tree/branch or twigs are irrigated orchards, conidia are potentially killed by girdling the infected part. Asexual Sexual Reproduction present whenever water is available. The fruiting bodies called pycnidia are produced The sexual reproductive structures fungus can’t infect without a wound or dead 2-3 weeks (up to 6 months) after the death (perithecia containing ascospores) are tissue including buds scars, mechanical of the bark. Under moist conditions and formed 2 to 3 years after the original injury, winter injury, sunburn, borer favorable temperatures, mature pycnidia formation of pycnidia. Ascospores are damage. In the summer and early fall the extrude flesh- to orange-colored tendrils, discharged forcibly into the air following fungus is present in phloem and xylem. In High Incidence in Colorado winter and early spring it is present in tree The problem ofCytospora canker is bark. Repeated infection occurs causing more severe in Colorado, despite semiarid multiple cankers in a branch or a tree. climatic growing condition with minimum rainfall (8”) and clay and high pH soil, and Disease Symptoms may be because: • Management practices such as The disease causes cankers at the irrigation, pruning, and nutrient infected site. The trees start oozing management practices favoring gum at or above the infection site. The Figure 3. Early infection with a mild disease incidence and spread; canker generally grows later and often is gummosis in cherry (A) and excessive • Use of minimum amount of covered by the gum. Growers consider the gummosis in peach (B) and associated canker due to Cytospora canker infection. fungicides for control of other gummosis as the only identifying symptom diseases as compared to many of the disease, but stone fruits start oozing other high rainfall states; gum whenever trees are stressed by abiotic • The importance of the disease is and/or biotitic causes. The following tips not well recognized and the lack of will help to identify the disease. effective management of chemicals. • Light brown colored gum early or Abandoned or small acreage late in the season but no canker growers are not paying attention to associated with the cause: either the disease; stress other than Cytospora canker • Despite high importance, or early infection of the fungus knowledge, research, and education • Dark brown colored gum with efforts are not sufficient; associated canker -- confirms the • Probable presence of multiple or infection by the fungus Figure 4. No gummosis but distinct canker mixed species of the fungus in • Excessive gum production growth in apricot (A) but lack of gummosis stone fruit growing area. followed by canker inside the gum and the canker is distinctly visible only by removing the upper bark apple (B; photo - commonly observed in sweet by H. Larsen). cherry (Fig. 3A) and in peach (Fig. Fertilization 3B). Light gum production is seen Imbalance (low or high) in plant which dries quickly but canker nutrients in soil and/or plants is one of symptoms on infected bark is the causes of tree stress that increases tree visible which is often damaged by susceptibility to this disease. Peach orchards woodpecker - commonly seen in sampled and tested for nutrient availability plum and apricot. (Fig. 4A) in soil and leaf tissue exhibited deficiencies • No gum and canker visible from of many different micronutrients, especially outside, but the canker is visible iron (Fe), manganese (Mn) and zinc (Zn), with the removal of outer bark - in leaf tissues despite availability in soil. generally seen in apple (Fig. 4B) Availability of these nutrients is restricted Sunken discolored areas with light and by high soil pH which is common in dark concentric circles of dead tissue often the fruit production region. Because appear as a result of small twig infections. of this, dormant trunk sprays or foliar Nodal infections are easily observed 2 to Figure 5. Cytospora canker infection, and applications may provide better tree access 4 weeks after bud break. Infected tissues a view of “flagging” symptoms due to to micronutrients like copper (Cu), iron appear dark brown with oozing from the Cytospora canker infection in a (Fe), Zn, Mn and boron (Bo). In addition, infected tissue unless the twig is killed peach orchard. some other important issues regarding entirely. One-year-old shoots that develop fertilizer application should be considered in the center of the tree are especially infected part which will ultimately kill the to manage this disease efficiently. Need susceptible to nodal infections and, if left for the nutrients should be determined untreated, rapid invasion of scaffold limbs scaffold or limbs called ‘flagging’ which are recognizable at a great distance in an by foliage tissue analysis rather than soil and large branches to which these shoots available nutrients analysis. Check foliage are attached may follow. Cankers that are infected orchard (Fig. 5). The leaves may exhibit symptoms when the branch or twig growth in late summer; the foliage should formed on the main trunk, branch crotches, have a healthy green color and terminal scaffold limbs, and older branches are the infection is severe; leaves often turn yellow, droop, and may wilt and die. growth should be about 12 inches (30 most conspicuous later. The infection on cm) on bearing trees and 18-24 inches branches or trunks enlarges, girdles the (46-61 cm) for non-bearing trees. Trees with pale, nitrogen deficient leaves are Method of Pruning flagging infected trees so that they will be more susceptible to infection by Cytospora A high incidence of disease starting visible from a distance, and pruning them canker. Balanced use of nutrients through from pruning cuts has been observed last, then treating the pruning equipment fertilizer application supplying an adequate in grower fields. We found a reduction with alcohol will save time and resources. amount of all required nutrients will help in disease incidence by more than 50% to keep trees healthy, keeping the following with the change to using proper pruning Pruning Refuse Management points in mind: methods in grower orchards. A horizontal Brush piles or dead cut trees often are • Check your plant nutrients in soil cut (Fig. 6) will retain moisture and fungal piled up near the orchards or properties and leaves each year in late June or spores more readily than a vertical or slant for a long period of time. Since this fungus early to mid-July; cut (Fig. 6 inset). Often such horizontal lives and grows in dead tissues, this refuse • Provide balanced nutrients pruning cuts are made almost flush and serves as an inoculum source especially regularly after checking the when infection takes place the infection when the rain occurs in a windy day. Rain additional needed nutrients; immediately girdles the trunk, branch or aids both sporulation and liberation of • Provide balanced N in the soil limb and kills it (as in lower right hand fungal spores and wind spreads these to the as its deficiency or excess causes picture). Avoid horizontal cuts, especially nearby areas. problems. Avoid N application in while making big cuts, and leave some late summer / early fall; that may short stubs so that infection will not Irrigation delay tree dormancy and thereby immediately girdle the limb. Do not prune induce cold susceptibility and trees when there is high humidity (such as Irrigation done to fulfill the water increase plant stress; snowy or rainy days) or other conditions requirement of the plants may trigger • Apply adequate K (provides that might provide increased opportunity disease incidences by creating higher resistance); for the fungus to establish. Despite the humidity. Thus, special precautionary • Correct yellow peach tree problem of winterized sprays, a fungicide measures are needed to reduce the disease syndrome by applications of Fe, Mn spray applied soon after the pruning helps outbreak by irrigation. and Zn as needed. to reduce the fungal infection in a freshly opened wound. Irrigation Practices and Cytospora Pruning Canker Sprinkler irrigation is considered Pruning is important and essential effective and economical as compared for tree productivity, but use of proper to furrow irrigation, but it was found pruning technique and timing is critical for that emitters (especially the hanging Cytospora canker management. Plants lack type (Fig. 7A) which are the general an active defense system during dormancy. trend in orchards) can promote disease Cuts made by pruning serve as an avenue incidence. Microjet sprinklers can create for the entry of the fungus and spore high humidity when the water they emit production continues during winter also. hits the foliage. In addition, Grove and So the timing and cut made during pruning Biggs, (2006) found that overhead and are critical for the disease management under tree sprinkler irrigations promote practices. sporulation and dispersal of this fungus. As Time of Pruning the irrigation water hits the infected trunk (Fig.7A) continually for a long period of Generally pruning is done in winter Figure 6. Severe infection started from time which is the general practice of the pruning cut which was made horizontal when the trees are dormant. Trees are growers, it soaks the dry fungal mass that close to trunk that girdled the tree, and it more susceptible during winter when initiates spore production in the infected they are dormant and are more vulnerable will kill the tree whereas in the left hand top corner (insertion) is right way of cut, tissue. The water jet exerts pressure and in March to June. The cells injured by a slant cut leaving stub (6-8”) will reduce helps to liberate and carry spores some pruning provide the necessary food for the chances of fungal spore to retain, start distance. Those spores will be picked up the fungus spore to germinate and grow at infection and kill the tree. by prevailing wind currents. Irrigation for the injury point. The common practice of a long duration, especially during a windy pruning during winter or late fall increases day, will encourage spore production and vulnerability to Cytospora. Pruning The other reason for infection spreading liberation, and carry the spores promotes de-hardening of dormant wood; from pruning cuts may be due to the greater distances. making the tree less resistant to cold injury spread of fungal spores by the pruning Inappropriate irrigation scheduling and and more susceptible to infection. Pruning implements. It can be time consuming duration can increase tree susceptibility should be delayed as late as practical for and expensive for growers to sterilize the by stressing the trees. Irrigation should be Cytospora Canker management. implements after each cut. However, by given to meet the water requirements of the tree which is determined by prevailing chemicals effectively killed the fungus and temperatures. Drip irrigation may is better controlled the disease, however, due to high choice over sprinkles to manage this disease inoculum pressure there were repeated (Fig.7 B). infections. Chemical penetration inside the tree Duration of Irrigation bark was increased by applying chemicals with carrier materials such as adjuvant, Frequent and short duration Figure 7. Use of hanging micro-jet irrigations are better than long duration sprinklers with long duration sets (A) especially the Pentabark. These are applied and long interval irrigations. The latter promotes Cytospora spore production after removal of the gum and exposing combination leads to over irrigation which and liberation. Drip irrigation (B) does not the infected wood a little bit rather than can cause yellow peach tree syndrome wet the tree branches and trunk above to the intact surface. In a previous study that is associated with deficiencies of the ground and does not promote spore chemicals were effective in excised twigs, micronutrients such as Fe, Mn, and Zn; liberation and dispersal. but not in the field. That may be because growers often assume the syndrome is the chemicals were not able to reach where the fungus is in a tree and no chemical cause by Fe deficiency alone and apply • Just before the irrigation water can penetrate and translocate within the a source of Fe alone without testing access is shut off, do one last heavy tree bark. The combination of Captan the plant tissues for nutrient content. irrigation to provide enough and thiophanate-methyl, when used for These micronutrient deficiencies and water for winter and leach the salt brown rot blossom blight control, may waterlogging create tree stress and make the accumulated in root zone during provide recent pruning cuts some degree of tree vulnerable to disease. Long duration growing season; protection against infection by L. persoonii. and long interval scheduled irrigations • Drip irrigation (Fig. 7B) may be Use of Demethylation-inhibiting (DMI) also increase tree stress by over-saturating better to avoid wetting tree trunks fungicides had very little activity against L. the soil (reducing oxygen access for the or limbs; that will reduce the spore persoonii (Biggs & Grove, 2005). root systems) and by creating a period of production in the orchard; Use 5-6 sprays of chemicals starting drought stress to the tree before irrigation. • Avoid watering Cytospora canker- immediately after prunning, early summer, Proper irrigation timing and duration will infected stone fruit blocks on mid-summer, late summer, fall and early- lessen tree stress. In those cases where windy days or nights. irrigation scheduling is at the mercy of winter. Alternate the following chemicals to water availability (some growers can only avoid developing resistance: Captan 50wp, get the water at certain times /intervals), Chemical Management 2lbs/100 gal water; Rovral 50wp, 2lb/100 the grower needs to do the best they can to Options with Regular gal water; Topsin M 85WDG, 6oz/100 gal minimize the impact. Fungicide Sprays water; Calcium propionate, 1.5 -2.3 lbs Despite grower perceptions to the anhydrous salt/100 gal. Rotation of these, According to Biggs et al., (1994) contrary, in a recent study we found especially after removing gum, may help to chemicals tested to study the efficacy of reduced irrigation had no impact on fruit manage the disease. some chemicals were effective when tested quality in peaches. The following irrigation in a laboratory condition on excised twigs. practices are recommended to reduce the However, there are no fungicides registered Non-chemical disease disease incidence and spread: specifically for control ofLeucostoma management control • Use soil moisture sensors (gypsum spp., and efficacy trials have produced block, irrometers, etc.) to assess With increasing demand for and conflicting results (Biggs & Grove, 2005). irrigation timing if possible. An production of organic fruits, there also is Similar trials in Colorado with these alternative is to take a handful of a lack of effective management options chemicals, including the combination of soil from 12” depth beneath the for organic producers. Identification of some with alcohol to evaluate anecdotal tree drip line, squeeze it in your effective non-chemical options to manage grower reports of efficacy, also produced hand and re-open your hand. If the this disease could benefit both organic inconsistent results (Pokharel, 2011). soil does not stay as a ‘balled unit’ and conventional producers. Thus, non- However, the chemical Inspire provided when poked with your finger, it is chemical disease management strategies effective control of the disease in the field time to water; were also studied. Brown mustard was for up to one year after treatment and, • Check accumulated evapo- grown in the greenhouse until flowering; at at the same time, limited re-infection transpiration losses since the last flowering the whole plant was blended in was observed in repeated experiments. irrigation and apply only as much a commercial blender with equal weight: In addition, several experiments were water as needed to replace that lost volume of water to make slurry by mixing conducted to increase fungicide efficacy in water. Frequent irrigations with with soaked (25 hours in water) mustard the field. If the chemicals are applied after small amounts of water are better and/or canola meal cake and poultices were removing the gum from the surface and than long duration irrigations; made. Poultices were applied on top of the disturbing bark and adding Pentabark, the Cytospora canker, which killed the fungus and protected the tree for at least a year; Selected References secondary infections from other infected Biggs, A. R. 1995. Canker, Blights, trees were observed during the second year and Wood Rots. Pages 28-30. In: (Pokharel, 2011). However, its practicability Compendium of Stone Fruit Diseases. was a big issue for commercial producers. (eds) J. M. Ogawa, E. I. Zehr, G. W. Bird, Thus mustard oil (which also contains some D. F. Ritchie, K. Uriu, and J K. Uyemoto. level of isothiocyanate) was tested along American Phytopathological Society, St. with several plant-derived oils. Mustard Paul. oils applied in higher concentration >50% Biggs, A.R., El Kholi, M.M., and El in water produced more consistent results Neshawy, S.M. 1994. Effect of calcium than other chemicals (Pokharel and Larsen, salts on growth, pectic enzyme activity, 2009b). However, the tree was re-infected and colonization of peach twigs by by secondary inocula after 5 months. Leucostoma persooni. Plant Dis. 78:886- 890. Cleaning Biggs, A.R. and G.G. Grove. 2005. Leucostoma canker of stone fruits. The Most growers pay attention to a Plant Health Instructor OI: 10.1094/ problem when it starts killing trees or limbs PHI 2005-1220 or when fruit production is affected. By Grove, G.G. and A.R. Biggs. 2006. that time it may be too late to manage the Production and dispersal of conidia problem easily, or the problem has become of Leucostoma cinctum in Peach and unmanageable, with Cytospora spreading Cherry orchards under irrigation in from a single infected tree to others in an Eastern Washington. Plant Disease orchard. Thus, treating the first sign of 90:587-591. infection makes it easier to manage the Pokharel, R. R. and H. J. Larsen 2009a. disease as well as requiring less resources. Incidence, severity and non-chemical When a new infection is seen in a tree management of Cytospora canker in or orchard, removing the gum from the stone fruits. Colorado State University, infected spot and applying treatments Western Colorado Research Center (chemicals or non-chemicals) will make Annual report,2008. TR 09-12:55-62. disease management easier. Often non- Pokharel, R. R. and H.J. Larsen. 2009b. chemical means may be as effective as Efficacy of plant and mineral oil chemical, especially when the disease is low against Cytospora Canker in peach. in incidence. Phytopathology 99: S103. Consider the following approaches to Pokharel, R. 2011. Cytospora canker manage the disease efficiently: management studies from 2007-2010. • Treat the first symptoms and the Annual Report of Western Colorado first tree in your orchard; Research Center, TR11-11: 43-52. • Remove the gum from the bark before applying any treatments; • When you see the disease in your orchard or your neighbor’s field, take all necessary steps to minimize the disease incidences and spread.

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