What is Diplodia shoot blight and canker?  Diplodia shoot blight and canker (formerly Sphaeropsis shoot blight and canker) is one of the most common fungal diseases of Austrian pine in Wisconsin.  This disease can also affect other pines including red, jack, Scots and mugo pine, as well as other conifers including cedars, cypresses, firs, junipers and spruces.

What does Diplodia shoot blight and canker look like?  Initially, affected branch tips may ooze a large amount of resin.  Eventually, these branch tips brown and die, with dead needles on these branches having varying lengths.  As the disease progresses, sunken or swollen, discolored areas (called cankers) may form on infected twigs.  Diplodia shoot blight and canker can be distinguished from damage from boring insects (where there also may be heavy resin flow) by an absence of any tunneling.

Where does Diplodia shoot blight and canker come from?  Diplodia shoot blight and canker is caused by several fungi in the genus Diplodia.  These fungi include Diplodia sapinea (formerly known as Diplodia pinea and Sphaeropsis sapinea), which has historically been cited as the cause of the disease on Austrian pine.  However, this fungus is only one of several Diplodia species that can cause problems on this host.  Diplodia fungi survive in infected shoots and pinecones where they form small, black fruiting bodies (i.e., reproductive structures) that produce brown-colored spores.

How do I save a tree with Diplodia shoot blight and canker?  Immediately remove and destroy diseased branch tips.  Also, where possible, remove and destroy pinecones that have fallen from infected trees.  Dispose of these materials by burning (where allowed by local ordinance) or burying them.

When pruning, cut branches six to eight inches below the point where they are obviously infected.  Prune only in dry weather.  Between cuts, decontaminate pruning tools by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants), or a 10% bleach solution (i.e., one part of a disinfecting bleach and nine parts water).  Decontaminating tools is important to help prevent accidental movement of Diplodia fungi from branch to branch during pruning.  If you decide to use bleach, be sure to rinse your tools thoroughly after pruning and then oil them to prevent rusting.

How do I avoid problems with Diplodia shoot blight and canker in the future?  Avoid planting Austrian pines; plant other types of evergreens instead.  Minimize any stresses on established Austrian pines.  Water trees adequately, particularly during dry periods.  Established trees should receive approximately one inch of water per week from the time that the ground thaws in the spring, through the summer and into the fall up until the ground freezes or there is a significant snowfall.  New transplants (i.e., conifers planted within three years) require approximately two inches of water per week.  During periods with insufficient rain, apply water at the drip lines of trees (i.e., the edges of where the branches extend) using a drip or soaker hose.

When planting trees, be sure to allow ample space for roots to grow, avoid compacting the soil around trees, and make sure there is adequate soil drainage.  Mulch trees to at least their drip lines with a high-quality mulch (e.g., shredded oak bark mulch, red cedar mulch).  Use one to two inches on heavier (e.g., clay) soils.  Use three to four inches on lighter (e.g., sandy) soils.  Keep mulch approximately four inches from tree trunks.  DO NOT fertilize new transplants, and fertilize established conifers only when a soil fertility test indicates that fertilization is needed.  DO NOT overfertilize, particularly with nitrogen.

Finally, you may want to apply fungicides to help prevent infections.  Apply fungicides only after you have pruned out diseased branches as described above.  Fungicides prevent infections but do not cure existing infections.  Alternate use of fungicides containing thiophanate-methyl and chlorothalonil that are labeled for use on conifers.  Start applications at bud break and continue at 14 day intervals until full shoot elongation.  DO NOT use thiophanate-methyl alone.  Overuse of thiophanate-methyl can potentially select for variants of Diplodia that will no longer be controlled by this active ingredient.  Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use the products in the safest and most effective manner possible.

For more information on Diplodia shoot blight and canker:  Contact your county Extension agent.

What is Rhizosphaera needle cast?  Rhizosphaera needle cast is the most common disease of Colorado blue spruce in Wisconsin, making Colorado blue spruce unsightly and unusable in many landscape settings.  The disease also affects other conifers including black, Engelmann, Serbian, Sitka, and white (e.g., Black Hills) spruce; Austrian, mugo and eastern white pine; Douglas-fir, balsam fir and western hemlock.

What does Rhizosphaera needle cast look like?  The first noticeable symptom of Rhizosphaera needle cast is purpling or browning and loss of the innermost needles on lower branches of spruce trees.  Often, the youngest needles at the tips of branches remain healthy.  Rows of small, black spheres form along the length of infected needles and are visible with a 10X hand lens.  These black spheres are fruiting bodies (i.e., reproductive structures) of the fungus that causes the disease and are diagnostic.

Where does Rhizosphaera needle cast come from?  Rhizosphaera needle cast is typically caused by the fungus Rhizosphaera kalkhoffii, although other species of Rhizosphaera can be involved depending on the host.  Infected needles, including those that are still attached to branches and those that have fallen to the ground, produce spores that can be blown or splashed to healthy needles.

How do I save a tree or shrub with Rhizosphaera needle cast?  Consider treating affected trees with fungicides labeled for use on evergreens and containing copper or chlorothalonil.  Treatments will not cure existing infections, but can prevent additional infections.  Apply treatments every three to four weeks starting as new needles emerge each spring.  Continue applications through periods of wet weather.  For fungicide treatments to be effective, thoroughly cover all needles.  This may be difficult on large trees.  Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with Rhizosphaera needle cast in the future?  The easiest way to avoid Rhizosphaera needle cast is to avoid planting Colorado blue spruce.  If you do plant this tree, consider using dwarf varieties, and allow adequate spacing between trees so that branches will not overlap when they are full size.  Dwarf varieties and properly spaced larger spruce varieties will have better air penetration and needles will dry more quickly.  Dry needles are less likely to be infected.  Check existing spruce trees for the disease, and remove and destroy any diseased branches and needles by burning (where allowed by local ordinance), burying or hot composting.

For more information on Rhizosphaera needle cast:  See UW Bulletin A2640, Colorado Blue Spruce and Other Conifers Disorder:  Rhizosphaera Needle Cast (available at https://learningstore.extension.wisc.edu/) or contact your county Extension agent.

What is winter burn?  Winter burn is a common problem of evergreens including those with broad leaves (e.g., boxwood, holly, rhododendron), needles (e.g., fir, hemlock, pine, spruce, yew) and scale-like leaves (e.g., arborvitae, false cypress, juniper) grown in open, unprotected locations and exposed to severe winter conditions.  Evergreen plants that are marginally hardy in a location (i.e., not well-adapted to local winter conditions) are at increased risk for winter burn.  Winter burn can be so severe that affected plants may die and/or require replacement.

What does winter burn look like?  Winter burn symptoms often become apparent as the snow melts and spring temperatures rise.  Foliage starts to brown at the tips of branches with browning progressing inward toward the center of the plant.  On broad-leaved evergreens, leaf edges typically brown first, followed by browning of entire leaves.  Foliage facing south, southwest or west is most often affected.  Symptomatic foliage often begins to drop off starting in spring and continuing through mid-summer as new foliage is produced.  In extreme cases, entire plants can brown and die.

What causes winter burn?  There are many factors that can contribute to winter burn.  In general, plants with shallow or poorly-developed root systems that do not efficiently take up water (e.g., recent transplants) are more prone to winter burn.  Warm fall temperatures that delay the onset of plant dormancy can also contribute to winter burn.  Under such conditions, plants are not prepared for the subsequent rapid onset of freezing winter temperatures, and as a result damage to foliage occurs.  Similar cold injury can occur mid-winter when temperatures drop sharply at sunset causing foliage that has warmed during the day to rapidly cool and freeze.  In addition, on sunny winter days, foliage (particularly foliage facing the sun) can begin to transpire (i.e., naturally lose water through the foliage).  Because the ground is frozen, plant roots cannot take up water and replace the water that has been lost from the foliage.  As a result, foliage dries and browns.  Foliage under snow or facing away from the sun and direct winds is usually not damaged.  Strong winter winds can lead to additional water loss making winter burn more severe.  Colder than normal winter temperatures and longer than normal winters can also be factors in the development of winter burn, especially if below normal temperatures occur into April (the time of year when plants normally come out of dormancy and are most susceptible to winter injury).  Finally, exposure of plants to salt used to de-ice roads, driveways and sideways during the winter can make plants more prone to winter burn injury.

How do I save a plant with winter burn?  For evergreens such as arborvitaes, boxwoods, junipers and yews, prune out dead, brown, damaged or dying tissue in mid-spring after new foliage is produced.  If new foliage has not yet emerged by spring, scratch the bark on affected branches and look for green tissue underneath.  Also gently peel back the bud scales to look for inner green bud tissue.  If the stem or bud tissue is green, buds on the branch may still break to form new foliage.  If the tissue is brown, the branch is most likely dead and you should prune the branch back to a live, lateral bud or branch.  Such buds and branches may be far back inside the canopy and pruning may remove a substantial amount of the plant.  Pines, spruces and firs typically produce new growth at branch tips in spring that will replace winter burn-damaged needles, and thus pruning may not be required on these evergreens.  After a couple of growing seasons, new foliage will fill in the areas that were damaged.  If an entire evergreen is brown, recovery is unlikely and the plant should be replaced with something (e.g., a deciduous shrub or tree) that is better-suited to the site.

How do I avoid problems with winter burn in the future?  Use a variety of strategies to prevent winter burn before winter arrives.

Plant the right plant in the right place.  Buy plants that are rated as cold hardy for your location and are well-adapted to local growing and soil conditions.  Plants exposed to drying winter sun and winds are more likely to be injured.  Therefore, avoid planting winter injury sensitive evergreens, particularly those that require shade or that are marginally cold-hardy, in exposed, sunny, windy areas.  Plant them on the northeast or east side of a building or in a protected courtyard.  Plant boxwoods, hemlocks, rhododendrons, and yews in partial shade to provide them added protection from winter sun and wind.

Plant evergreens at the right time of year.  Optimally, plant evergreens either in early spring (before buds break) or in late summer (i.e., August through September).   Evergreens can be planted in the summer if you provide supplemental water.  Avoid planting after early October in northern Wisconsin and after mid-October in southern Wisconsin as this will not allow sufficient time for roots to grow adequately before the ground freezes.

DO NOT prune evergreens in late summer or early fall.  Late season pruning of some non-native evergreens may encourage a flush of new growth that will not harden off properly before winter.  See University of Wisconsin Garden Facts XHT1013, Pruning Evergreens, for details on when and how to prune specific evergreen trees and shrubs.

Mulch evergreens properly.  Apply two inches (on clay soils) to four inches (on sandy soils) of loose mulch (e.g., shredded hardwood, pine, or cedar bark; leaf compost; or wood chips) around the base of evergreens out to at least the drip line (e.g., the edge of where the branches extend).  Keep mulch at least four inches away from the trunks of trees and the bases of shrubs.  Proper mulch insulates roots from severe fluctuations of soil temperatures and reduces water loss.  It also helps protect roots from injury due to heaving that occurs when soils go through cycles of freezing and thawing during the winter.  Heaving can especially be a problem for shallow-rooted and newly planted evergreens.  DO NOT mulch excessively or too close to plants as this can lead to damage by providing shelter for mice and voles (which can girdle trunks and branches) and by providing a favorable environment for disease development as well as insect activity and feeding.

Water plants properly.  Plants that are well-hydrated are less prone to winter burn.  In particular, newly planted or young evergreens, especially those planted in open, exposed sites, those planted under eaves, or those planted in dry falls may suffer severe moisture loss during the winter and consequently severe winter burn.  Established evergreens should receive approximately one inch of water per week and newly transplanted evergreens up to two inches of water per week during the growing season up until the soil freezes in the autumn or there is a significant snowfall.  If supplemental watering is needed, use a soaker or drip hose to apply water near the drip lines of plants rather than using a sprinkler.

Avoid late summer or fall fertilization.  Applying quick-release, high-nitrogen fertilizers in late summer or fall could potentially stimulate growth of new foliage (particularly on some non-native evergreens) as well as inhibit proper onset of dormancy which can lead to damage over the winter.  If you are concerned that your evergreens may need to be fertilized, submit a soil sample from around your plants to a professional soil testing lab that can provide specific information on what fertilizer to use and when to fertilize.

Protect plants during the winter.  Use burlap, canvas, snow fencing or other protective materials to create barriers that will protect plants from winter winds and sun.  Install four to five foot tall stakes approximately two feet from the drip lines of plants especially on the south and west sides (or any side exposed to wind) and wrap protective materials around the stakes to create “fenced” barriers.  Leave the top open.  These barriers will deflect the wind and protect plants from direct exposure to the sun.  Remove the barrier material promptly in spring.  DO NOT tightly wrap individual plants with burlap as this can collect ice, trap moisture and make plants more susceptible to infection by disease-causing organisms.  Use of anti-transpirant products to prevent water loss from foliage over the winter has been shown to have limited benefit.  These materials degrade rapidly, require reapplication after each significant rain or snow event, and may not be effective in preventing water loss that can lead to winter burn.

For more information on winter burn:  Contact your county Extension agent.

What is white pine blister rust?  White pine blister rust is a serious, tree-killing disease of eastern white pine and its close relatives (pines with needles in bundles of five).  This disease is caused by the exotic (non-native) fungus Cronartium ribicola, which was introduced into North America in the early 1900’s.  This pathogen is now found in most regions where pines grow in the United States, including Wisconsin.  White pine blister rust affects trees of all ages, but perhaps most frequently and severely damages seedlings and saplings.

Where does white pine blister rust come from?  White pine blister rust is caused by the fungus Cronartium ribicola, which requires two different plant hosts to complete its complex life cycle.  Spores of the fungus produced on white pine are blown to alternate host plants in the genus Ribes (gooseberries and currants).  After infecting gooseberry and currant bushes the fungus multiplies rapidly throughout the summer, repeatedly producing spores that germinate to result in additional gooseberry and currant infections.  Spores produced in late summer on gooseberries and currants are spread by the wind to white pines, where needles that are moist from rain, fog, or dew are infected.

What does white pine blister rust look like?  Infection of needles by Cronartium ribicola results in development of yellow to brown spots and bands.  The fungus slowly grows through pine needles and bark to eventually form cankers on twigs, branches, and trunks of trees.  A canker is a localized diseased area (either swollen or sunken) that is surrounded by healthy tissues.  A typical white pine blister rust canker has resinous margins, and may appear “blistered” before rupturing to expose fruiting bodies (reproductive structures) with yellow to bright orange spores of Cronartium ribicola.  As a canker expands to completely encircle stems, all parts of the plant beyond the canker are killed.  Dead white pine branches may temporarily retain their orange to red dead needles to form a bright “flag” that is a common symptom of this disease.

Can I save a tree affected by white pine blister rust?  There is no “cure” for a tree with a white pine blister rust canker on its main trunk or stem.  As the canker expands to completely encircle the trunk, all parts above the canker will die.  Branch cankers that extend to within four inches of the trunk, probably indicate that the trunk already is colonized by the fungus and future development of a main stem canker is likely.  Pruning off branches on which cankers are located farther from the trunk, however, can prevent the fungus from growing into the trunk.  These branch cankers can be removed by pruning at least six inches beyond any visible symptoms on the trunk side of the cankered branch.  Removal of branch cankers and trees with main stem cankers prevents production of spores that are spread to gooseberries and currants.  The fungus quickly dies in discarded branches and trunks and presents no further danger to either of its hosts.

How do I avoid future problems from white pine blister rust?  Infection of pine is most frequent near diseased gooseberries or currants.  Therefore, removing these plants (especially within 200 feet) can greatly reduce the incidence of white pine blister rust.  Gooseberries or currants can be killed by uprooting them or by application of herbicides in accordance with label directions.

Conditions that promote or prolong needle wetness should be avoided.  These include use of sprinklers that wet the needles of ornamental trees, dense plantings, growth of weeds surrounding young trees, or planting white pines in low-lying, chronically moist areas near water or sites that lack good air movement.  Growing white pines under a hardwood overstory that will intercept evening dew can help keep needles dry and reduce infection.

Regular inspection allows prompt detection and removal of cankered branches on young trees.  Also, because infection very often occurs on needles of low branches, pruning to remove healthy branches (if aesthetically acceptable) will reduce the likelihood of this disease.  When trees are five to seven years old, starting close to the ground, prune off all branches up to no more than one-third to one-half the height of the tree.  Branch pruning can be continued every other year until the lower eight to nine feet of trunk is free of branches.

Planting or measures to encourage natural regeneration of conifer species other than white pines (including red or jack pines, spruces, firs, arborvitae, hemlock, and junipers) might be considered, especially where gooseberries or currants are prevalent and where moisture conditions favor infection.

Application of protectant fungicides may be a useful management practice in white pine production nurseries.  Nursery stock should be carefully inspected, particularly just prior to sale, because the planting of diseased white pine seedlings is one way Cronartium ribicola has been spread into previously disease-free locations.

For more information on white pine blister rust:  Contact your county Extension agent.