What is Swiss needle cast?  Swiss needle cast is a fungal disease of Douglas-fir.  This tree is native to the Rocky Mountains and the Pacific Coast but has been grown in Wisconsin as a landscape ornamental and as a Christmas tree.  Swiss needle cast can limit the aesthetic appeal of Douglas-fir grown in landscape settings, as well as the marketability of Douglas-fir grown in Christmas tree production.

What does Swiss needle cast look like?  Infected needles become discolored (blotchy yellow-green or completely yellow) and then brown from the tips.  Older needles are more severely affected than younger needles.  Brown needles drop prematurely, leaving twigs with only the newest growth.  Using a hand lens, small, black reproductive structures of the Swiss needle cast fungus can be seen in two diffuse bands on the undersurface of infected needles.

Where does Swiss needle cast come from?  Swiss needle cast is caused by the fungus Nothophaeocryptopus gaeumannii.  Spore production, needle infection, and symptom development are favored by wet environmental conditions (e.g., rainy weather).  Infections primarily occur on new needles as they emerge and expand in the spring.  Fully expanded needles are less susceptible to infection.  Once infection has occurred, fruiting bodies (i.e., reproductive structures) form and produce spores on both discolored and green needles.  Spores may be produced for several seasons before needles drop.

How can I save a tree with Swiss needle cast?  Infected needles cannot be cured.  However, fungicide sprays containing chlorothalonil or mancozeb may help prevent additional infections on small trees where complete, uniform coverage is possible.  Fungicide treatments are not recommended for large trees.  For plantation and landscape trees, apply two fungicide applications, the first when buds are ½ to two inches long, and the second about three weeks later.  In the more stressful environment of nurseries, trees may require sprays every two weeks through mid-August.  Using preventive treatments, infected trees may regain their lush, full look within two years.  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 can I prevent Swiss needle cast in the future?  Use Douglas-firs grown from seed originating in Pacific Coast areas rather than those grown from seed originating in the Rocky Mountains.  Pacific Coast trees appear to be less susceptible to Swiss needle cast.  Also, use resistant and tolerant varieties where available.  Purchase stock from a reputable nursery; Nothophaeocryptopus gaeumannii is often spread through infected nursery stock.  When planting Douglas-firs, choose a site that has well-drained, but moist soil with a neutral to slightly acidic pH and allow adequate spacing between trees to promote increased airflow and quicker drying of needles.  This drier environment is less favorable for infection and disease development.  Make sure trees have sufficient water and are fertilized properly (based on soil and needle nutrient tests) to reduce stress that may increase trees’ susceptibility to Swiss needle cast.

For more information on Swiss needle cast:  Contact your county Extension agent.

What is Phytophthora root rot?  Phytophthora root rot is a common disease of Christmas trees including Douglas-fir, true firs (e.g., Fraser, balsam and Canaan), spruces, and pines.  The disease has caused significant problems in Christmas tree production in several states.  In Wisconsin, losses due to Phytophthora root rot have been particularly high in Fraser fir Christmas tree production.

What does Phytophthora root rot look like?  Symptoms of Phytophthora root rot are often not observed until the disease is quite advanced.  Above ground, affected trees initially have single branches (typically low on the tree) with needles that turn from green to yellow to red-brown, and remain on the tree.  Soft, sunken areas (i.e., cankers) may also form on trunks near the soil line.  As the disease progresses, trees wilt and die.  Below ground, affected trees have root systems with a reduced number of fine, water-absorbing roots.  What roots remain are often black and lack white growing points.  The outer tissue of these roots easily sloughs off and the interior root tissue is also typically discolored.  Discolored roots may, but oftentimes do not, have a foul odor.

Where does Phytophthora root rot come from?  Phytophthora root rot is caused by several species of the water mold (i.e., fungus-like organism) Phytophthora.  WI DATCP staff have recently identified six Phytophthora species (P. cactorum, P. europaea, P. megasperma, P. plurivora, P. sansomeana, and P. sp. ‘kelmania’) that can be involved in Christmas tree root rot in Wisconsin.  These organisms can survive for many years in soil and plant debris as thick-walled resting spores (called oospores) that can eventually germinate and directly infect trees.  Alternatively during wet periods, certain of these oospores can germinate to produce swimming spores that are attracted to the roots of Christmas trees and other host plants.  Oospores can be moved from field to field on seedlings and transplants, on soil clinging to field equipment and hand tools, in irrigation or flood water, and even on boots and shoes.

How do I save a plant with Phytophthora root rot?  If you have trees that you suspect are suffering from Phytophthora root rot, have them examined by a professional plant disease diagnostician.  If the diagnostician confirms Phytophthora root rot, dig up and burn any symptomatic trees and limit access to the area of the field where the trees were grown.  Quarantining the area can help limit spread of contaminated soil to other areas of the field.  Fungicide treatments will NOT cure trees suffering from Phytophthora root rot.  However, fungicide treatments in the last year of production may be useful in limiting development of visible root rot symptoms on trees growing near a Phytophthora-infested area so that these trees can be successfully marketed.  Fungicides containing mono- and di- potassium salts of phosphorous acid, metalaxyl (mefenoxam) and etridiazole are registered for Phytophthora management in Christmas tree production in Wisconsin.  DO NOT use the same active ingredient for all treatments.  Alternate the use of at least two active ingredients with different modes of action to help minimize problems with fungicide-resistant strains of Phytophthora.  Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use them in the safest and most effective manner possible.

How do I avoid problems with Phytophthora root rot in the future?  Choose sites with well-drained soils and avoid planting in low areas where water drains and pools.  DO NOT plant Christmas trees in sites that may have had a history of Phytophthora root rot including nurseries, orchards and soybean fields.  Phytophthora species that cause problems on shrubs, trees and even soybeans can also cause problems on Christmas trees.  Buy healthy Christmas tree seedlings from a reputable grower.  Carefully plant seedlings making sure that planting holes are large enough for roots to spread in all directions.  This will reduce the likelihood of girdling or J-roots that may make trees more prone to infection.  Also, minimize root wounding at planting, and avoid soil compaction by heavy equipment.  Water trees adequately, but DO NOT overwater.  Use well water for irrigation, if possible.  Avoid using water from ponds, rivers and streams as this water may be contaminated with Phytophthora.  Routinely inspect Christmas tree plantings for symptoms of Phytophthora root rot and follow the recommendations outlined above if you notice symptoms of the disease.

For more information on Phytophthora root rot of Christmas trees:  Contact your county Extension agent.

What is Phomopsis tip blight?  Phomopsis tip blight is one of the most common fungal diseases of conifers in Wisconsin.  It is most severely affects junipers (e.g., Eastern red cedar, creeping and Rocky Mountain junipers) but can also cause issues on arborvitae, Douglas-fir, true firs, larch, pines and spruces.

What does Phomopsis tip blight look like?  On junipers, small gray lesion (spots) first form on the terminal four to six inches of new shoots in early spring.  Infected branches typically initially turn dull red or brown, and then ash-gray as lesions girdle and kill branch tips.  Small, black pycnidia (the reproductive structures of the causal fungus) can easily be seen on dead branches with the unaided eye or with a hand lens.  Severe infections may result in death of an entire juniper.  Phomopsis tip blight rarely kills other conifer hosts, although branch dieback is a typical symptom.

Where does Phomopsis tip blight come from?  Phomopsis tip blight is caused by several fungi currently or formerly classified in the genus Phomopsis.  These fungi survive in diseased and dead branches.  Spores of these fungi are produced throughout the growing season, and are spread by wind and rain.  Infections can occur whenever new foliage is produced, and moisture or humidity is high.  Most infections occur in the spring, but late summer infections can occur if over-watering or over-fertilization stimulates new growth.

How do I save a juniper with Phomopsis tip blight?  Prune out and destroy diseased branches as they appear.  Always prune in dry weather, and cut four to six inches below obviously diseased areas on each branch.  Decontaminate pruning tools after each cut by treating them for at least 30 seconds with a 10% bleach solution or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants).  For particularly susceptible junipers, combine pruning with use of copper or mancozeb-containing fungicides.  Make applications at seven to 21 day intervals during rapid growth in the spring.  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 Phomopsis tip blight in the future?  Plant only resistant juniper species, varieties, and cultivars.  DO NOT plant conifers in poorly drained sites or heavily shaded areas.  DO NOT overcrowd trees and shrubs in new plantings.  Provide adequate space between plants to promote good air circulation and rapid drying of foliage.  DO NOT prune or shear conifers excessively as this stimulates excessive new, susceptible growth.  If possible, DO NOT use overhead sprinklers for watering.  Use a soaker or drip hose instead.  If you must overhead water, water early in the day to allow for fast drying of plants.

For more information on Phomopsis tip blight:  Contact your county Extension agent.

What is Dothistroma needle blight?  Dothistroma needle blight is a common needle disease that can affect over thirty species of pine trees.  In Wisconsin, Austrian pines are most commonly and severely affected by this disease.

What does Dothistroma needle blight look like?  Dothistroma needle blight first appears as dark green, water-soaked spots on the needles.  The spots become tan, yellow, or reddish-brown, and may encircle the needles to form bands.  The tip of the needle beyond the band eventually dies, leaving the base of the needle alive and green.  Young trees are more likely to suffer damage than older trees.  Seedlings (< 1 yr. old) can be killed within a year after infection.

Where does Dothistroma needle blight come from?  Dothistroma needle blight is caused by the fungus Dothistroma pini, which survives in diseased needles.  Watch for tiny, black reproductive structures of the fungus (called pycnidia) that can be found erupting from the surface of infected needles.  Spores are produced in these structures throughout the growing season, and infection by spores can occur at any time, but particularly during periods of wet weather.  Symptoms appear from five weeks to six months after infection.

How do I save a tree with Dothistroma needle blight?  Copper-containing fungicides (e.g., Bordeaux mix) can help prevent new infections, but will not cure diseased needles.  Typically a single fungicide application in early June is sufficient to provide protection of new foliage.  However, a second application three to four weeks later will provide more complete control.  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.  Several years of treatments may be needed to completely rid a tree of all infected needles (through natural needle loss).

How do I avoid problems with Dothistroma needle blight in the future?  DO NOT plant Austrian pines as they are extremely susceptible to Dothistroma needle blight.  Consider using other conifers instead.  If you decide to plant susceptible trees, make sure the trees are disease-free at the time of planting.  Also, be sure to provide adequate spacing between the trees to ensure good airflow and promote rapid needle drying.  If you have established trees that are suffering from Dothistroma needle blight, remove fallen needles from around the base of these trees as these can serve as a source of fungal spores.

For more information on Dothistroma needle blight:  See UW Bulletin A2620, Pine Disorder:  Dothistroma Needle Blight (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.

What is Cytospora canker?  Cytospora canker is one of the most common fungal diseases of Colorado blue spruce.  This disease can also affect Engelmann, Norway and white spruce, as well as balsam fir, Douglas-fir, European larch, tamarack, and white pine.  Trees that are 15 years old or older and are at least 20 feet high often show symptoms of Cytospora canker.  Cytospora canker can kill trees, but more often simply makes trees so unsightly that owners opt to remove the trees.

What does Cytospora canker look like?  Cytospora canker usually first appears on lower branches and progresses up the tree, although individual upper branches may show symptoms as well.  Needles on infected branches turn purple, then brown.  Diseased needles eventually fall off, and infected branches die.  Infected branches often ooze a bluish-white sap somewhere along their length.

Where does Cytospora canker come from?  Cytospora canker is caused by the fungus Cytospora kunzei (also sometimes referred to as Leucocytospora kunzei or Leucostoma kunzei).  The fungus survives in infected branches and spores are spread by wind, rain splash, insects, birds, and mammals.

How do I save a tree with Cytospora canker?  Immediately remove and destroy any diseased branches by pruning them using the three-point method of pruning (see University of Wisconsin Garden Facts XHT1014, How to Properly Prune Deciduous Trees, for details).  Prune only in dry weather.  Between cuts, decontaminate pruning tools by treating them for at least 30 seconds in 10% bleach or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).  Decontaminating tools will help prevent movement of Cytospora kunzei from branch to branch and from tree to tree during pruning.  If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

How do I avoid problems with Cytospora canker in the future?  Perhaps the easiest way to avoid Cytospora canker is through proper tree selection, planting and maintenance.  Avoid planting full-sized varieties of trees susceptible to Cytospora canker, particularly full-sized varieties of blue spruce.  Instead plant dwarf tree varieties.  Smaller trees will have canopies where air will more easily penetrate into the interior, thus drying branches and needles more rapidly.  In general, a drier environment is less favorable for disease development.  If you choose to plant a full-sized tree, leave adequate space between the tree and other trees in your landscape.  Proper spacing will provide good air flow and again promote drier conditions that are less favorable for disease.  Optimally, when trees are full sized, they should be far enough apart so that branches do not overlap.  As a tree becomes well established, selectively prune branches to open up the tree’s canopy to further promote a drier environment.

Also minimize environmental stresses to any tree susceptible to Cytospora canker.  Prevent water stress by avoiding soil compaction and by ensuring adequate soil drainage.  During dry periods, make sure your tree receives approximately one inch of water per week either from natural rain or by applying supplemental water at the drip line of the tree (i.e., the edge of where tree branches extend) and beyond using a soaker or drip hose.  To help maintain proper soil moisture, mulch out to at least the drip line of the tree.  Use one to two inches of mulch on a heavier, clay soil; use three to four inches of mulch on a lighter, sandy soil.  DO NOT pile mulch against the trunk of the tree; keep mulch approximately four inches from the trunk.  Prevent nutrient stress by properly fertilizing your tree based on a soil fertility test provided by an accredited lab.

DO NOT use fungicide treatments for Cytospora canker control; fungicide treatments are not effective.

For more information on Cytospora canker:  See UW Bulletin A2639, Colorado Blue Spruce and Other Spruce Disorder:  Cytospora Canker (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.