What Is Cytospora Canker – Control Of Cytospora Canker Disease
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By: Teo Spengler
Cytospora canker disease generally attacks spruces, especially Colorado blue and Norway varieties, as well as peach trees, Douglas firs or hemlock trees. What is cytospora canker? It is a destructive disease caused by the fungus Leucostoma kunzei that disfigures and can even kill vulnerable trees. Read on for more information about symptoms of cytospora canker as well as cytospora canker treatment.
What is Cytospora Canker?
You may not have heard of cytospora canker until after a tree in your backyard is infected. If you notice that the lower limbs on your tree are dying, the tree might have cytospora canker disease. It attacks older trees, stressed trees and those with shallow roots or planted in inappropriate sites.
One of the first symptoms of cytospora canker disease on spruce is the browning of needles on the tree’s lower limbs. When they fall, you may notice light patches of resin on the dead bark of the branches. Over several years, symptoms of cytospora canker spread and upper branches brown and die. Dead areas of bark appear, known as cankers.
On trees without needles, like peach trees, look for cankers on branches around pruning wounds. They may be present for several years, extending along the branch, before they kill it.
Control of Cytospora Canker
You may look to fungicidal sprays as a cytospora canker treatment, but these are not effective and are not recommended by experts. Instead, try using organic methods for control of cytospora canker.
Prevention is easier than cytospora canker treatment. Take care not to wound trees susceptible to this disease. Wounds, like those from weed whackers and saws, serve as entry points for the fungus.
Crowded trees are more likely to get and pass along the fungus. Plant yours with lots of room and good air circulation.
Take every precaution to keep the trees healthy and strong. Water them during dry periods and fertilize them annually to provide nutrients. Vigorous trees are less likely to get attacked.
Prune out any infected branches and burn them, since the fungus overwinters in cankered bark. Use bleach to disinfect the pruners before and after each use. The best time for pruning is late winter or early spring in dry, sunny weather.
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Cytospora canker in Colorado spruce.
Photo credit: Joseph O'Brien, USDA Forest Service, Bugwood.org
Cytospora canker is caused by a fungal pathogen which attacks many species of conifer, including Colorado, white, Norway, and Engelmann spruce and Douglas-fir, with Colorado spruce more susceptible than any other species. Spores are released from cankered branches throughout the growing season and spread by rain, wind, insects, birds or man to other branches on the same or other trees. Infection typically occurs through wounds, first infecting and killing the bark and eventually spreading to kill the entire branch. Cytospora can also be opportunistic, growing in bark killed by other pathogens. Damage is usually seen on older, larger trees.
Brian Hudelson, UW-Madison Plant Pathology, UW-Extension
Item number: XHT1003
What is Cytospora canker? Cytospora canker is one of the most common fungal diseases of Colorado blue spruce. This disease can also affect Norway spruce (and less frequently other spruces) as well as Douglas-fir and balsam fir. Trees that are 15 years old or older and are at least 20 feet high most typically show symptoms of this disease.
What does Cytospora canker look like? Cytospora canker usually first appears on lower branches and progresses up the tree. Individual upper branches may show symptoms as well. Needles on infected branches turn purple, then brown and die. Diseased needles eventually fall off and the infected branches die. Infected branches often produce a bluish-white sap that oozes somewhere along their length.
Where does Cytospora canker come from? Cytospora canker is caused by the fungus Leucocytospora kunzei (also referred to as Leucostoma kunzei), which survives in infected branches. Spores of the fungus are spread by wind, rain splash, insects, birds and mammals.
How do I save a tree or shrub with Cytospora canker? Immediately remove and destroy any diseased branches, by pruning them using the 3-point method of pruning (see University of Wisconsin Garden Facts XHT1014 for details). Prune only in dry weather. Between cuts, be sure to clean your pruning shears by dipping them for at least 30 seconds in a 10% bleach solution or 70% alcohol (spray disinfectants that contain at least 70% alcohol can be used). This will prevent movement of the fungus from branch to branch, or from tree to tree during pruning. DO NOT attempt to use fungicide treatments to control this disease.
How do I avoid problems with Cytospora canker in the future? Perhaps the easiest way to avoid Cytospora canker is to avoid planting Colorado blue spruce. If you do plant blue spruce, allow adequate spacing between trees in new plantings. For established trees, judiciously prune branches to open the trees’ canopies. Proper spacing and pruning promote increased airflow, which leads to a less favorable environment for infection and disease development. In addition, minimize any stress to your trees. Prevent water stress by avoiding soil compaction, and by making sure there is adequate soil drainage. During dry periods, water your trees adequately (approximately one inch of water per week) using a soaker or drip hose. Proper mulching (one to two inches on a heavier, clay soil three to four inches on a lighter, sandy soil) can help moderate your trees’ moisture levels. Prevent nutrient stress by properly fertilizing your conifers based on a soil fertility test. The University of Wisconsin Soil Testing Laboratories (http://uwlab.soils.wisc.edu/) can assist with soil and plant tissue fertility testing.
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Pathogen: Cytospora leucostoma
(Reviewed 11/09 , updated 11/09 )
Symptoms and Signs
The first noticeable symptom of a Cytospora infection is usually wilting or flagging of a branch. A close look at the branch reveals a dark-colored bark canker with a depressed center. Amber-colored gumming can occur at the edges of the canker. The canker eventually girdles the branch, causing it to die dead limbs become evident in mid- to late summer.
Cytospora canker can be distinguished from other cankers by the presence of pycnidia, which are pimplelike structures that form on the outer bark of the canker. Pycnidia are initially black, but turn white. In humid, but not excessively wet conditions, amber tendrils containing spores exude from the pycnidia.
If pycnidia are not present, Cytospora canker can be differentiated from bacterial canker by the difference in the canker margins. Removing the bark from a Cytospora canker reveals abrupt margins that frequently exhibit a zonate (bathtub-ring) pattern whereas bacterial cankers have irregular margins. The zonate pattern is created when established Cytospora cankers overwinter and resume growth the following year.
Comments on the Disease
Cytospora leucostoma is a relatively weak pathogen. Its spores are spread from cankered branches by rain and wind and can infect any type of bark wound, such as those caused by sunburn, old bacterial cankers, boring insects or other damage it cannot infect healthy, undamaged bark. Damage is usually limited to bark tissue. Shothole borers may also vector this disease.
Cytospora canker tends to be most serious in weak orchards where infections often develop into cankers and continue to grow for several years, killing major limbs and causing significant economic loss. Generally this disease is of little consequence in vigorous orchard blocks.
Water stress, potassium deficiency, overcropping, and high ring nematode pressure increase tree susceptibility to the spread of infection (canker development). Trees planted on shallow or heavy textured (clay) soils are generally more likely to suffer economic damage from Cytospora, because water and potassium management on these soils can be challenging.
Cytospora canker is a warm-season (summer) disease with peak fungal growth occurring just above 90 o F. Canker growth potential is highest when temperatures are high and prune tree growth activity is low (July-September).
There is no known chemical control for Cytospora. Manage infection and spread of the disease by avoiding tree stress, and by removing and destroying cankered wood from the orchard.
Avoid stress factors such as potassium deficiency, sunburn, high ring-nematode (Criconemella xenoplax) populations, trunk borers, and soil moisture stress that specifically predispose prune trees to the spread of the disease. Prune trees to minimize sunburn potential, and paint exposed trunks and scaffold crotches with white interior latex paint to further protect them from sunburn. Avoid, where possible, planting on marginal soils, especially shallow or clay soils. Maintain adequate orchard water status, especially after harvest. Avoid defoliation (sunburn potential) caused by prune rust infections. Pruning cuts and leaf scars are not important infection sites. Thin heavily cropped trees.
During the growing season, remove (cut out) cankers and destroy dead or damaged wood. Pruning during the growing season allows you to better identify branches with cankers. To ensure that all the disease is removed, cut several inches to one foot below any canker symptoms into healthy wood. Check the cut surface of damaged limbs to ensure that all the disease has been removed. Incomplete canker removal wastes time and money with little to no benefit in disease management.
In stressed orchards where infected wood (cankers) are allowed to remain on the tree, continued canker growth and scaffold death can occur. Growers must decide, on a block-by-block basis, whether cutting out cankers or replacing the orchard or portion of the orchard is the best economic decision. Trees or limbs killed by Cytospora canker and left in the orchard or adjacent to living trees provide inoculum for further infection and should be removed or destroyed.
UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
J. E. Adaskaveg, Plant Pathology, UC Riverside
J. L. Caprile, UC Cooperative Extension, Contra Costa County
Acknowledgment for contributions to Diseases:
Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California
4. Cytospora Canker
Cherry Trees Affected: This disease is one of the most destructive diseases to sweet and sour cherries.
Symptoms: Cherry tree branches develop dark, depressed cankers that cause the tree branch to wilt. An amber-colored gum may appear at the edge of the canker. The canker will eventually girdle the limb and cause it to die.
Causes: Black pycnidia, spore-producing structures, appear on the canker. These black pycnidia will turn white over time. In humid conditions, spore masses expel from the pycnidia. Rain and wind carry the spores to infect any bark wound. These wounds may be the result of sunburn, old cankers, or wood boring insects. This disease cannot attack healthy, undamaged bark. A cherry tree’s susceptibility to Cytospora canker increases when it’s stressed from drought, potassium deficiency, overcropping, and ring nematodes.
Treatment: There is no chemical control for Cytospora canker. Control infection by limiting tree stress. Prune your infected cherry tree during the growing season when it’s easier to identify the cankers.
Season: Cytospora canker thrives in the summer when temperatures are above 90 degrees. Dead limbs girdled by cankers appear in mid to late summer.
Risk: Formed cankers will kill parts of your cherry tree.
Rhizosphaera Needle Cast
Blue spruce trees are susceptible to an infectious needle disease caused by the fungus Rhizosphaera. The disease, referred to as Rhizosphaera needle cast, is the most common problem seen on blue spruce samples that are submitted to the Plant Disease Clinic. White spruce are classified as intermediate in susceptibility to the disease and Norway spruce are relatively resistant.
Symptoms - The disease is usually first evident on lower branches and then works upward gradually. Second-year needles turn a purple or brown color and eventually fall from the tree. After several successive years of needle loss branches may die. In general, trees appear to die from the bottom upward. In some cases, however, infections start higher on the tree, giving the appearance of scattered dead areas.
The disease can be diagnosed by looking at the discolored needles with a magnifying glass or hand lens. Small black spots (fruiting structures of the fungus) appear in rows in the infected needles. The fungus is actually emerging from the stomata (natural pore-like openings) that occur in lines on all sides of a spruce needle. Green needles may show these small black fruiting structures.
Keep in mind that environmental or site-related stresses can also cause discoloration and loss of needles on spruce trees. The extended wet weather of 1993, for instance, has been responsible for needle browning and even tree death in some cases. (Fruiting structures of the fungus are not evident on these trees.)
Spread - Rhizosphaera over winters in infected needles on the tree and on needles that have fallen to the ground. The fungus is spread by splashing and dripping water beginning in spring and continuing into the fall. Newly emerging needles can become infected during wet spring weather.
Control - If symptoms appear, diseased trees should be sprayed with a fungicide in the last 2 weeks of May and again 4 to 6 weeks later. Be sure to read the product label for specific rate and timing instructions. Good coverage and proper timing of applications are critical for successful disease control. Fungicides labeled for Rhizosphaera needle cast include Daconil 2787, Daconil Ultrex, Terranil 90, Thalonil 4L, Thalonil 90, Manicure Flowable, and Twosome Flowable.
In addition to fungicide sprays, other control measures include spacing trees adequately to promote good air circulation, improving tree vigor through mulching and watering when needed, and not shearing trees when the foliage is wet.
Rhizosphaera needle cast is pictured and discussed in Pm-1528 "Common Diseases of Conifers in Iowa .” Copies of this publication are can be purchased at the Harrison Count Extension Office for $2.40.