Category Archives: Disease – Conifer

Cedar-Apple Rust – Juniper

What is cedar-apple rust? Cedar-apple rust is the name of a group of closely related diseases caused by fungi that infect both junipers and woody rosaceous plants such as apple, crabapple, hawthorn and quince.

Cedar-apple rusts form slimy, orange  fruiting body on junipers in early spring.
Cedar-apple rusts form slimy, orange
fruiting body on junipers in early spring.

What does cedar-apple rust look like? On junipers, the cedar-apple rust fungus causes formation of irregularly-shaped brown galls (roughly 1∕2 to two inches in diameter). During moist periods in spring, these galls produce a distinctive orange, gelatinous slime. Symptoms on rosaceous hosts appear in late May as circular, yellow-orange areas on leaves. The undersurfaces of these diseased areas often have a fringed appearance.

Where does cedar-apple rust come from? Several fungi in the genus Gymnosporangium cause cedar-apple rust. These fungi overwinter as galls on junipers.

How do I save a tree or shrub with cedar-apple rust? Junipers can easily be treated for cedar-apple rust by pruning branches about four to six inches below the galls. Clean
pruning shears between cuts by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). This will prevent movement of the fungus from branch to branch, or from plant to plan during pruning. To prevent future infections, you can apply fungicides containing triadimefon or ferbam every seven to 21 days from early July through August. You can control cedar-apple rust on rosaceous hosts using fungicides containing chlorothalonil, ferbam, dithiocarbamates, mancozeb, metiram, sulfur, thiram, triadimefon, triforine, or zineb. Apply treatments when flower buds first show color, when half of the flowers are open, at petal-fall, seven to 10 days after petal fall and again 10 to 14 days later. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

How do I avoid problems with cedar-apple rust in the future?  The best way to avoid cedar-apple rust is to plant trees and shrubs that are resistant to the disease. Check at your local nursery for resistant varieties of juniper, apple, crabapple, hawthorn, and quince that are available in your area and that will satisfy your landscaping needs.

For more information on cedar-apple rust:  See UW-Extension Bulletins A2598 and A8KS711 or contact your county Extension agent.

Winter Burn

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.

Browning due to winter burn on dwarf Alberta spruce.
Browning due to winter burn on dwarf Alberta spruce.

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 deice 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 “How to Properly Prune 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 three 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.

White Pine Blister Rust

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 (not 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.

White pine blister rust cankers on branches and stems often have a cracked or blistered appearance and may bear yellow to orange spores in fruiting bodies of Cronartium ribicola.
White pine blister rust cankers on branches and stems often have a cracked or blistered appearance and may bear yellow to orange spores in fruiting bodies of Cronartium ribicola.

Where does white pine blister rust come from? The white pine blister rust fungus Cronartium ribicola 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 infection. 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 (main stems) of trees. A canker is a localized diseased area, which may be 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 portions beyond the canker are killed. Dead white pine branches may temporarily retain 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 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 in proximity to diseased gooseberries or currants. Therefore, removal of these alternate hosts (especially within 200 feet) can greatly reduce 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 in the presence of gooseberries or currants and where moisture conditions favor infection.

Use of protectant fungicides may be a management practice in white pine production nurseries. Nursery stock should be carefully inspected, 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.



Weir’s Cushion Rust of Spruces

What is Weir’s cushion rust? Weir’s cushion rust is a needle disease that disfigures and reduces growth of spruce trees (Picea spp.) of all ages. This disease has been known in both eastern and western regions of the United States, but was recognized in Wisconsin for the first time in 2002.

Yellow spots and bands in winter on spruce shoots affected by Weir's cushion rust.
Yellow spots and bands in winter on spruce shoots affected by Weir’s cushion rust.

What does Weir’s cushion rust look like? Needles on current year’s shoots affected by Weir’s cushion rust may develop yellow spots or bands in summer and fall. These spots and bands may intensify to give needles a bright “green and gold” appearance during the following spring, when tiny blister-like pustules also may develop in the yellow areas. Microscopic examination of these pustules is required for diagnosis of this disease. Affected one-year-old needles continue to yellow, turn brown, and fall off as spring and summer progress. Trees badly damaged by Weir’s cushion rust will have thin crowns due to repeated loss of the previous year’s needles.

Where does Weir’s cushion rust come from? Weir’s cushion rust results from colonization of spruce needles by the fungus Chrysomyxa weirii. This fungus overwinters in needles infected during the previous growing season. In late summer, or more typically the next spring, Chrysomyxa weirii produces spores in tiny, blister-like pustules that develop on these needles. These spores can be blown by wind or splashed by rain to newly emerging needles on the same tree or other trees. Spore germination is followed by infection of young needles.

Can I save a tree affected by Weir’s cushion rust? Fungicides containing chlorothalonil may be applied to trees affected by Weir’s cushion rust to prevent new needle infections. The first application should be made when 10% of the buds have broken and two additional applications should be made at seven to 10 day intervals thereafter. Fungicide applications do not kill the fungus in needles that are already infected, so it is important to begin applications promptly and to complete the spray program, to ensure thorough coverage of foliage. Please be sure to read and follow all fungicide label instructions to ensure that the fungicide is used in the safest and most effective manner. Needles infected by Chrysomyxa weirii the previous year will die, and the fungus will not continue to live or produce spores on dead needles. Therefore, destruction of dead needles is not necessary.

How do I avoid Weir’s cushion rust in the future? Growers and homeowners should be careful not to accept nursery stock affected by Weir’s cushion rust, which may be present in wholesale or retail nurseries. Spruces in nurseries and the landscape should be carefully inspected in late summer and fall for yellow spots and bands on current year’s needles and in spring for these symptoms and pustules on the previous year’s needles. Affected trees should not be moved to areas where the disease is not already present. Preventative application of fungicides may prevent establishment of the fungus on new trees or in previously unaffected nurseries.

For more information on Weir’s cushion rust: Contact your county Extension agent.



Swiss Needle Cast

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 traditionally 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.

Fruiting bodies of the Swiss needle cast fungus on the undersides of needles.
Fruiting bodies of the Swiss needle cast fungus on the undersides of needles.

What does Swiss needle cast look like? Infected needles become discolored, turning a blotchy yellow-green or yellow, and then browning 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 Phaeocryptopus gaeumannii. This fungus tends to produce spores, infect needles, and cause more severe disease during rainy weather. Infections occur primarily on new shoots as they expand in the spring. Fully expanded needles are less susceptible to infection. Once infection has occurred, fruiting bodies form and produce spores even on 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, two spray applications are recommended, the first when buds are 1/2 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 insure that you use the fungicide 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; Phaeocryptopus 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, which is less favorable for infection and disease development. Make sure trees have sufficient water and are fertilized properly (based on a soil and tissue nutrient test) to reduce stress that may increase trees’ susceptibility to Swiss needle cast.

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

Thanks to Diana Alfuth, Thad Kohlenberg, and Judy Reith-Rozelle for reviewing this document.

Sudden Oak Death

Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.
Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.

What is sudden oak death? Sudden oak death (also called ramorum leaf blight or ramorum dieback) is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California. The disease has also been reported in Oregon, as well as in Europe. Currently 60 species of plants have been reported to be susceptible to the disease. Twenty-eight of these plants are confirmed hosts. In addition to the trees listed above, the following trees fall into this group:

  • bigleaf maple (Acer macrophyllum)
  • Bodnant viburnum (Viburnum X bodnantense)
  • ‘Brouwer’s Beauty’ pieris (Pieris floribunda X japonica)
  • California bay laurel (Umbellularia californica)
  • California buckeye (Aesculus californica)
  • California coffeeberry (Rhamnus californica)
  • California honeysuckle (Lonicera hispidula)
  • canyon live oak (Quercus chrysolepis)
  • coast redwood (Sequoia sempervirens)
  • doublefile viburnum (Viburnum plicatum var. tomentosum)
  • douglas-fir (Pseudotsuga menziesii var. menziesii)
  • evergreen huckleberry (Vaccinium ovatum)
  • Formosa firethorn (Pyracantha koidsumii)
  • ‘Forest Flame’ pieris (Pieris formosa X japonica)
  • Himalaya pieris (Pieris formosa)
  • Japanese camellia (Camellia japonica)
  • Japanese pieris (Pieris japonica)
  • laurustinus (Viburnum tinus)
  • madrone (Arbutus menziesii)
  • manzanita (Arctostaphylos manzanita)
  • rhododendron (Rhododendron spp.)
  • Sasanqua camellia (Camellia sasanqua)
  • toyon (Heteromeles arbutifolia)
  • western starflower (Trientalis latifolia)
  • witch hazel (Hamamelis virginiana)

An additional 31 species including the following are suspected hosts, although tests to verify their susceptibility have not yet been completed:

  • Burkwood viburnum (Viburnum X burkwoodii)
  • California hazelnut (Corylus cornuta)
  • Camellia X williamsii
  • cascara (Rhamnus purshiana)
  • Chinese pieris (Pieris formosa var. forrestii)
  • common lilac (Syringa vulgaris)
  • David viburnum (Viburnum davidii)
  • drooping leucothoe (Leucothoe fontanesiana)
  • European beech (Fagus sylvatica)
  • European cranberrybush viburnum (Viburnum opulus)
  • European turkey oak (Quercus cerris)
  • European yew (Taxus baccata)
  • fragrant viburnum (Viburnum farreri)
  • grand fir (Abies grandis)
  • Holm oak (Quercus ilex)
  • horse-chestnut (Aesculus hippocastanum)
  • lingonberry (Vaccinium vitis-ideae)
  • mountain laurel (Kalmia latifolia)
  • Northern red oak (Quercus rubra)
  • Pieris formosa var. forrestii X Pieris japonica
  • poison oak (Toxicodendron diversiloba)
  • Prague viburnum (Viburnum X pragense)
  • reticulate camellia (Camellia reticulata)
  • salmonberry (Rubus spectabilis)
  • Southern red oak (Quercus falcata)
  • strawberry tree (Arbutus unedo)
  • sweet chestnut (Castanea sativa)
  • Viburnum X carlcephalum X Viburnum utile
  • Victorian box (Pittosporum undulatum)
  • wayfaringtree viburnum (Viburnum lantana)
  • wood rose (Rosa gymnocarpa)

At this time, sudden oak death has not been reported in Wisconsin. However, the disease was recently found at a large nursery near Los Angeles, CA that ships plants throughout much of the United States, including Wisconsin. Thus, the disease may be present in Wisconsin, but not yet detected.

Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.
Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.

What does sudden oak death look like? Symptoms of sudden oak death vary depending upon the plant species infected. On some hosts, infections occur primarily on leaves leading to light brown leaf spots and blotches. These leaf symptoms may be indistinguishable from other, more common, leaf spots and blights, or may mimic sunburn or leaf scorch symptoms. Twigs and branches that become infected often wilt, forming a “shepherd’s-crook”, and subsequently die back. Infection of tree trunks leads to cankers (i.e., sore-like areas) that produce copious amounts of an amber to black colored ooze. This ooze can dry to form a stained area on the bark. Removing the bark over the affected area will reveal discolored wood beneath that sometimes (but not always) has a black border. Cankers can eventually expand to girdle trunks, thus resulting in the death of the tree or shrub. Trunk infections appear not to extend into the root system of the plant. Once sudden oak death cankers develop, other pathogens may invade the infected areas, accelerating tree or shrub death and complicating the diagnosis of the disease.

Where does sudden oak death come from? Sudden oak death is caused by the fungus Phytophthora ramorum, which was first recognized as a pathogen in 1995. Phytophthora ramorum can be spread over long distances through movement of infected plants or infested plant parts. The fungus can also be moved with contaminated soil (e.g., on vehicle tires, tools, or shoes), or in contaminated water. Once established on plants in a given location, the fungus produces reproductive structures (called sporangia) that can be moved from plant to plant by rain splash, or wind. Phytophthora ramorum has currently been documented as occurring in California, Oregon and Europe, but the recent discovery of the pathogen in a large nursery in California that ships plants throughout the United States raises the possibility that this pathogen may have been spread to other areas.

How do I save a plant with sudden oak death? If you believe you have seen a plant that has sudden oak death, IMMEDIATELY call the Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 to make arrangements for an appropriate diagnosis. Because Phytophthora ramorum is a regulated, quarantined pathogen, DO NOT remove the affected plant (or parts thereof) or take the plant from the site where it is located. PDDC staff will make arrangements for sample collection and testing. If your plant tests positive for Phytophthora ramorum, it will be removed and destroyed to help prevent further spread of the pathogen.

How do I avoid problems with sudden oak death in the future? Carefully inspect any new nursery stock upon delivery (or prior to purchase, if possible) for symptoms of sudden oak death. Keep new stock isolated from older stock as long as possible, to minimize possible movement of the pathogen should the disease develop after plants have arrived. If you see any suspect symptoms, alert the PDDC so that arrangements can be made for proper testing for Phytophthora ramorum.

For more information or help in diagnosing sudden oak death: Contact Brian Hudelson, Plant Disease Diagnostic Clinic, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706-1598, phone: (608) 262-2863, fax: (608) 263-2626, email:, see the USDA APHIS sudden oak death website, or contact your County Extension agent.

Root and Crown Rots

What is root/crown rot? Root/crown rot is a general term that describes any disease of woody ornamentals where the pathogen (causal organism) attacks and leads to the deterioration of a plant’s root system and/or lower trunk or branches near the soil line. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

Discoloration of maple crown and roots typical of Phytophthora root/crown rot.
Discoloration of maple crown and roots typical of Phytophthora root/crown rot.

How do you know if your tree or shrub has a root or crown rot? Gardeners often become aware of a root/crown rot when they see above ground symptoms of the diseases. Affected plants are often slow-growing or stunted and may show signs of wilting. Often the canopy of an affected tree or shrub is thin, with foliage that is yellow or red, suggesting a nutrient deficiency. Careful examination of the roots/crowns of these plants reveals tissue that is soft and brown.

Where does root/crown rot come from? Several soil-borne fungi can cause root/crown rots, including (most frequently) Phytophthora spp., Pythium spp., Rhizoctonia solani, and Fusarium spp. These fungi have wide host ranges, and prefer wet soil conditions. Some root rot fungi such as Pythium and Phytophtora produce spores that can survive for long periods in soil.

How do I save a plant with root/crown rot? REDUCE SOIL MOISTURE! Provide enough water to fulfill a plant’s growth needs and prevent drought stress, but DO NOT over-water. Remove excess mulch (greater than four inches) that can lead to overly wet soils. Chemical fungicides (PCNB, mefenoxam, metalaxyl, etridiazole, thiophanate-methyl and propiconazole) and biological control agents (Gliocladium, Streptomyces, and Trichoderma) are labeled for root/crown rot control. However, DO NOT use these products unless you know exactly which root/crown rot pathogen is affecting your tree or shrub. Contact your county Extension agent for details on obtaining an accurate root/crown rot diagnosis and for advice on which, if any, fungicides you should consider using.

How do I avoid problems with root/crown rots? Buy plants from a reputable source and make sure they are root/crown rot-free prior to purchase. Establish healthy plants in a well-drained site, and when planting, place the root collar just at the soil surface. Moderate soil moisture. Add organic material (e.g., leaf litter or compost) to heavy soils to increase soil drainage and DO NOT over-water. Also, DO NOT apply more than three inches of mulch around trees and shrubs, and keep mulch from directly contacting the base of trunks and stems. Prevent physical damage (e.g., lawnmower injury) that can provide entry points for root/crown rot pathogens. Finally, minimize movement of root/crown rot fungi in your garden. DO NOT move soil or plants from areas where plants are having root/crown rot problems. DO NOT water plants with water contaminated with soil (and thus potentially with root/crown rot fungi). After working with plants with root/crown rot, disinfest tools and footwear with a 10% bleach solution, a detergent solution, or alcohol.

For more information on root/crown rots: See UW-Extension Bulletin A2532, or contact your county Extension agent.

Rhizosphaera Needle Cast

What is Rhizosphaera needle cast? Rhizosphaeara needle cast is one of the most common fungal diseases of Colorado blue spruce. This disease can also affect other conifers including Engelmann, black, Serbian and Sitka spruce; Austrian, mugo and eastern white pine; Douglas fir; and western hemlock.

Browning of interior spruce needles caused by Rhizosphaera needle blight.
Browning of interior spruce needles caused by Rhizosphaera needle blight.

What does Rhizosphaera needle cast look like? The first noticeable sign of Rhizosphaera needle cast is a loss of the innermost needles on the lower branches of spruce trees. Often the youngest needles remain healthy. If your tree has this pattern of needle loss, use a 10X hand lens to observe the shed needles. If Rhizosphaera needle cast is the problem, you should be able to see rows of small black dots erupting through the surface of the needle. These black dots are fruiting bodies of the fungus that causes the disease, and are diagnostic.

Where does Rhizosphaera needle cast come from? Rhizosphaera needle cast is caused by the fungus Rhizosphaera kalkhoffii. 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 branches or trees.

How do I save a tree or shrub with Rhizosphaera needle cast? You can treat infected trees with fungicides containing copper (e.g., Bordeaux mixture) or chlorothalonil. These treatments will not cure existing infections, but can prevent additional infections. Apply treatments every three to four weeks during periods of wet weather. DO NOT use the same active ingredient for all treatments. Instead, alternate the use of copper and chlorothalonil to help minimize problems with fungicide-resistant strains of Rhizosphaera kalkhoffii. For fungicide treatments to be effective, you must thoroughly cover all susceptible needles. This is often difficult in large trees. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the fungicide(s) in the safest and most effective manner possible.

How do I avoid problems with Rhizosphaera needle cast in the future? Perhaps the easiest way to avoid Rhizosphaera needle cast is to avoid planting Colorado blue spruce. If you do plant blue spruce, check existing spruce trees for disease. Remove and destroy any diseased branches. Also, allow adequate spacing between trees in new plantings. This promotes increased airflow and quicker drying of needles, which is less favorable for infection and disease development.

For more information on Rhizosphaera needle cast: See UW-Extension Bulletin A2640 (available at or contact your county Extension agent.

Phytophthora Root Rot of Christmas Trees

Phytophthora root rot can cause severe losses in commercial Christmas tree production. (Photo courtesy of Sara Ott)
Phytophthora root rot can cause severe losses in commercial Christmas tree production. (Photo courtesy of Sara Ott)

What is Phytophthora root rot? Phytophthora root rot is a common disease of Christmas trees including Douglas-fir, balsam and as well as 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 fungus-like organism (i.e., water-mold) 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 that can eventually germinate and directly infect trees. Alternatively during wet periods, certain of these resting spores can germinate to produce swimming spores that are attracted to the roots of Christmas trees and other host plants. Resting spores 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.

Extensive external and internal darkening of root tissue is typical of Phytophthora root rot.
Extensive external and internal darkening of root tissue is typical of Phytophthora root rot.

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: See the WI DATCP Plant Industry Laboratory Report 2014 “Christmas Tree Survey for New Root Rot Diseases” (available in the “Ornamentals” section at or contact your county Extension agent.

Phomopsis Tip Blight

What is Phomopsis tip blight? Phomopsis tip blight is one of the most common fungal diseases of conifers in Wisconsin. Eastern red cedar, creeping and Rocky Mountain junipers, arborvitae, Douglas-fir, true firs, larch and jack pine are most commonly affected by the disease.

Die-back of juniper branch tips caused by Phomopsis tip blight.
Die-back of juniper branch tips caused by Phomopsis tip blight.

What does Phomopsis tip blight look like? Initially, small gray lesions (spots) form on the terminal four to six inches of new shoots in early spring. Infected branches typically first turn dull red or brown, and finally ash-gray as lesions expand to 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 plant.

Where does Phomopsis tip blight come from? Phomopsis tip blight is caused by the fungus Phomopsis juniperovora, which survives in diseased branches. Spores of the fungus 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 when 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. Disinfest pruning shears after each cut by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). Use of copper-based fungicides or mancozeb may be needed for susceptible junipers. Make applications at seven to 21 day intervals during rapid plant growth in the spring. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide 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. DO NOT prune or shear conifers excessively as this stimulates overproduction of new, susceptible growth. If possible, DO NOT use overhead sprinklers for watering. Use a soaker 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: See UW-Extension Bulletin A8KS711, or contact your county Extension agent.