Tree Pathologies and Management Options
For now this page is just a table of tree diseases, symptoms, and management options. It’s a work in progress (as is everything on this website, heh). I’ll add pictures at a later date when the list is more fleshed-out. At some point I plan to add lists of insect pests and nutrient deficiencies.
This list is far from exhaustive. It is not organized, it is rather verbose, the formatting makes me cringe, and there are no pictures yet so it may be difficult to use as a resource if that’s what you’re looking for.
Some of the pathologies aren’t relevant to the work I do at Thirty Pines (e.g. damping off of seedlings), and some do not affect trees in our area of upstate NY (e.g. little leaf disease). I’ve included things like these because I’m approaching this as a learning exercise for myself; diseases that aren’t applicable to our region can teach us about the diseases and symptomatologies that do exist here. Also, disease ranges are changing (mostly expanding northward) so it seems short-sighted to stick to the status-quo. Also also, this stuff is fascinating and I know you want the full story because you clicked the link. Either that or you got lost and are now trapped in tree nerd purgatory.
Best viewed on a desktop or large screen!
Sources include UMN extension, UMass extension, UC IPM, PNW Pest Management Handbook, and Dr. Enrico Bonello’s tree pathology course.
| Disease | Symptoms | Species Affected | Pathogen Type | Treatment | Spread | Mechanism | Notes |
|---|---|---|---|---|---|---|---|
| Fire blight | Young leaves and twigs die, forming a characteristic hook shape that resembles fire damage. Fruit turns black and dries. Sunken cankers on branches/twigs. Cream/yellow colored ooze near infected/dead areas | pear, quince, apple, crabapple, hawthorne, mountain ash, serviceberry, raspberry, cotoneaster (+ many others in the Rosaceae familiy) | Bacteria - Erwinia amylovora | Remove all infected tissues. Pesticides can be effective to save blossoms and prevent infection in new wounds. Pesticides are ineffective for infections established inside the tree (i.e. cankers, wilted twigs). Some very susceptible plants likely cannot be saved | Insects, pruning tools, splashing water | Killing of tissues via toxins | Some fruit varieties are resistant, giving the grower time to prune infected tissue, but no plants have been found that are immune. |
| Bacterial leaf scorch | Premature browning of leaves starting from the outer edges. Disease progresses slowly over a matter of years in mature trees | Many | Bacteria - many | No treatment. May kill the tree, or the tree may recover | Insects, pruning tools | Blocking of water vessel elements (either by pathogen itself or by plant response to pathogen) | This disease can be mistaken for oak wilt or Dutch elm disease. However, leaf scorch progresses much more slowly, leaf browning happens from the outside edge of the leaf and progresses inward, and there is no staining of sapwood |
| Crown gall | Swollen, disfigured areas throughout tree (roots, stem, twigs). Galls range from barely noticeable up to 1 foot in diameter. | Many. Mostly willows, poplars, fruit trees, and roses | Bacteria | Difiicult to eradicate once the infection is established. Avoid planting new plants that have galls. New plantings can be protected by treating roots in Galltrol or similar (contains beneficial bacteria).. | Bacteria invade roots from infected soil; wounds near ground, pruning tools | Integration of bacterial DNA into host plant genome | Established trees/plants can usually survive with the bacteria. Not lethal but can appear (very) unsightly and/or concerning. |
| Elm yellows | Yellowing and wilting of leaves. Can occur rapidly with little warning or progress slowly over time (usual timeframe is ~1 month). Inner bark is speckled with small tan patches in infected trees. | Elms | Phytoplasma - Candidatus Phytoplasyma ulmi | No treatment. As spreading mechanism is not fully understood, it's advised to remove infected tree. | Root grafts(?)/insects(?)/unclear | - | the inner bark of infected American and winged elms smells like wintergreen. The inner bark of infected slippery elm smells like maple syrup. |
| Ash yellows | Chlorotic foliage together with stunted grow results in yellow, tufted appearance of new growth. Gradual dieback throughout crown (usually entire branches at a time).Witches' broom near base of tree is diagnostic but does not occur in all infected trees. | Ashes | Phytoplasma - Candidatus Phytoplasma fraxinii | No treatment | Insects(?)/unclear | - | If you see a declining ash tree it is likely dying due to the emerald ash borer, not ash yellows. The phytoplasma that causes ash yellows also causes lilac witches broom. |
| Cedar-apple rust | Broadleaved trees: orange, powdery horns on fruits, yellow/orange spots on leaves. Junipers: round woody galls and gelatinous orange "tentacles" on leaves/twigs | apple, crabapple, hawthorn, serviceberry, Eastern red cedar, various junipers | Fungus - Gymnosporangium juniperi-virginianae | Remove and dispose of infected fruits/leaves; remove nearby junipers, fungicide spray | Airborne spores | - | The fungus that causes this disease needs to alternate between plants in the Rosaceae family and plants in the Cupressaceae family. Removing the alternate host in an area will prevent the disease from spreading |
| Damping off | Seeds fail to grow after germination; seedlings wilt and die quickly after germinating | Many | Fungus | Improve drainage/reduce standing water; soil fumigation; antifungal seed coatings | Spores in standing water/saturated soils; transport of infested soils | Tissue death (usually roots/lower stem) | This disease is really only a problem for new seedlings in nursery settings. It exists in natural areas but treatment is extremely expensive and generally unnecessary. |
| Little leaf disease | Yellowing/small needles. Premature loss of older needles (liontailing). General tree decline | Shortleaf pine, loblolly pine | Fungus | No treatment | Spores in standing water/saturated soils; transport of infested soils | Root rot | This disease generally affects trees 20+ years old. It is typically only a problem in the Southern US/Piedmont region. |
| Oak wilt | Scorching mostly around leaf margins. Often discoloration of xylem. Can kill mature red oaks within weeks, white oaks generally hold out for longer, up to a few years. | Oaks (chinkapin and tanoak to a lesser extent) | Fungus | No treatment for infected trees. Trenching (mechanical or chemical) around infected trees can stop spread to neighboring trees. Remove infected red oak material ASAP, or sterilize by tarping in an open, sunny area. | Mostly through root grafts. Can be spread by beetles to wounded oak trees. | Blocking of water transport mostly by tyloses formed by tree in response to infection | Not very prevalent in our area but widespread just to the west. Avoid pruning oaks during growing season as beetles that vector the disease are attracted to wounds during the spring and summer. |
| Dutch Elm disease | Leaves on scattered branches become yellow and wilt. Sporadic dieback in upper crown quickly spreads until entire canopy is affected. There is usually sapwood staining and/or xylem discoloration. Mature trees die within months to years after infection. | Elms | Fungus | Prune out all infected branches as soon as possible (5-10 feet below sapwood staining). Dispose of infected wood. | Insects. Some spread through root grafts, but this is less common | Blocking of water transport mostly by tyloses formed by tree in response to infection | Beetles infect trees by feeding in small twigs in upper canopy - if caught quickly the infection can be excised and the tree saved. However, if a tree is infected once it is likely to be infected again in the coming years. |
| Verticillium wilt | Scorched, browned leaves often persisting on branches after they die. Usually accompanied by discoloration of xylem. | Maples and redbuds are most susceptible, but many species are affected. Conifers are resistant/immune. | Fungus | Prevention is best - maintain the hatlh and vigor of trees to enable them to fight off infection. No treatment once a tree is infected but water and fertilization *may* help. | Soilborne. Can persist in soil for up to 25 years. | Blocking of water transport mostly by tyloses formed by tree in response to infection | Vegetables in the nightshade family (tomato, potato, pepper), cucurbits (melons, squash, cucumber), as well as strawberries are highly susceptible to verticillium wilt. Avoid planting vegetables in an area where the soil harbors verticillium. |
| Diplodia tip blight | Branch tips die back. Can cause cankers, usually on smaller twigs and branches, cankers typically have whitish dried resin on them. | Red pines, mostly Austrian, Scots, mugo, red, jack, and ponderosa | Fungus | Relieve drought stress (water and/or mulch). Fungicide can be applied to very valuable trees but needs to be applied every couple weeks so can be cost-prohibitive | Rain splash, there are likely insect vectors as well | - | This disease mostly disfigures trees but it can kill them if the infection is persistent or if it moves into the main stem. Sometimes the pathogen can exist inside the tree without the tree showing any symptoms and then explode when the tree is stressed by lack of water, storm damage, etc. |
| Brown spot | Brown spots on needles or necrotic bands, often with a pronounced and clearly defined border to the dead area. | Pines. Most damaging to grass-stage longleaf pine, Austrian pine, Scots pine, ponderosa pine | Fungus | Controlled burns, foliar sprays, improve air circulation through pruning, avoid planting trees too close together | Wind, rain splash, pruning tools | - | Brown spot thrives in wet, warm conditions. Once the disease becomes established, it will remain until environmental conditions become drier and/or cooler. This disease is likely to spread to new areas given climate change. |
| Powdery mildews | Whitish powdery coating on leaves | Many trees and other plants | Fungus | Foliar sprays very effective but generally treatment is not needed | Wind | - | Powdery mildews needs high humidity and temperatures, and usually occurs from mid-summer onwards. It is not very damaging to trees and is mostly an aesthetic problem. |
| Walnut anthracnose | Dark leaf spots in spring/early summer. Leaves turn yellow mid summer and the tree can be entirely defoliated if the infection is severe. Fruit damage ranges from small superficial spots to wasting of almost entire husk and nutmeat | Black walnut, occasionally on English walnut | Fungus | Remove infected leaves and fruit after they've dropped. Foliar sprays sometimes used in agricultural settings. | Wind | - | This disease can be very damaging in agricultural/monoculture settings. One or two years of severe infection likely won't kill a tree but repeated infections can weaken a tree so that it becomes susceptible to other diseases, water stress, etc. |
| Sycamore anthracnose | Sparse crown, dried/dead leaves, necrotic areas on leaves often following veins, cankers on twigs. An angular branching pattern can arise from repeated infections year-after-year | Sycamore | Fungus | Dispose of leaves after they fall. Fungicide and trunk injections can be helpful but usually not necessary. Pruning can be a palliative but does not help significantly | Rain splash, wind | - | This disease is essentially a constant problem for sycamores. Long, cool (55-65 F), wet springs can promote development/spread of this disease. Infections can cause extensive defoliation. Anthracnose itself usually won't kill a mature tree, but many years of disease can weaken it to the point where it succumbs to other stresses. |
| Dogwood anthracnose | Brown to reddish dead patches on leaves, often with distinct edges. Cankers on twigs, branches, and stems. Prolific epicormic sprouting mostly near unions of dead branches (sprouting near pruning wounds is not a symptom) | Can be lethal on flowering dogwood and Pacific dogwood. Kousa, Tatarian and redosier dogwood are more resistant. | Fungus | Shade and moisture promote disease; plant trees in open areas and prune for light and airflow. Dispose of fallen leaves. Remove as many infected interior shoots as possible. Foliar sprays are effective on high-value trees, may also be worthwhile on smaller trees with canopies that are easier to access. | Rain splash, wind | - | Pathogen is native to Asia, so native dogwoods have no defense mechanisms. It can become a serious problem but I have not seen many cases in upstate NY so I'm not sure that it's very prevalent around here. |
| Other anthracnoses | Symptoms vary between species. Usually symptoms include brownish dead patches on leaves. New leaves are often cupped or distorted. It is not a major threat to most other trees. | Ash, maple, oak, birch, butternut, elm, hornbeam, and others. See other entries for sycamore, black walnut, and dogwood - anthracnose can be more serious in those species. | Fungus | Prevention is best: when possible, plant trees in open locations with sun and airflow, prune to increase sun and airflow throughout canopy. Remove infected leaves after they drop throughout the season. Fungicide spray may be warranted on high-value trees, but must be timed correctly to correspond with environmental conditions and tree phenology. | Airborne spores | - | Wet, cool spring weather with little wind can promote development of this disease. |
| White pine blister rust | Swelling on smaller branches, often with yellowish pustules, blister, and oozing. Flagging throughout the canopy that progresses to larger branch dieback and can lead to tree death. On currants there are small, orange protrusions on the underside of leaves that produce an orange powder (these are the spores). | Highly susceptible: Western white pine, sugar pine, limber pine, white bark pine. Moderately susceptible - Eastern white pine, foxtail pine | Fungus | Prune infected branches back at least 18" from the last canker. No treatment for trees with cankers near or on main stems. | Mostly wind, possibly insects | - | This disease is decimating white bark pine in western mountainous areas and may lead to extinction of the species. It is not as serious on Eastern white pines in our area but can weaken trees significantly. This rust alternates between pines and currants and requires but can travel long distances between host species (>300 miles). It was introduced to North America from Europe on Eastern white pine nursery stock. Why would someone grow a North American tree in Europe and then sell it back to North America...? Mysteries of the universe... |
| Fusiform rust | Symptoms similar to white pine blister rust (see above). Can be differentiated based on geography and host species. | Mostly slash pine and loblolly pine; does infect other pines. Oaks in the red oak group (doesn't damage most oaks at all). | Fungus | In agricultural settings foliar sprays are effective. Minimize fertilization and wait until trees are at least 8-10 years old before fertilizing. Remove branches with galls closer than ~12" to main stem. In landscape settings, pruning larger branches with galls will reduce the chance of breakage. | Wind | - | Fusiform rust is really only a problem in the southern US. It requires proactive management there on pulp plantations. Upwards of 60% of trees were infected in some areas during the 1970s but genetic programs have increased rust resistance in most/all trees currently being planted. This fungus alternates between pine and oak trees - both must be present for widespread disease development but it does not impact oak health appreciably. |
| Western gall rust | Spherical galls, sometimes spread throughout significant portions of tree canopy. Galls may be orange or yellow when the rust is sporulating or the same color as the rest of the bark. | Monterey, Jeffrey, lodgepole, jack, Scots, Austrian, mugo pines (also other 2-needled pines) | Fungus | Consider pruning larger branches with galls to reduce chance of breakage. Fungicide applications may be warranted in Christmas tree plantations. | Wind, rain splash | - | The only potential impact this disease has in upstate NY is on Christmas tree plantations. It is unlikely (but not impossible) for it to occur on landscape trees because there is very low pathogen pressure here. Otherwise it is generally confined to the Western US (where I don't believe it's a serious problem). |
Please ignore the rest of this page, these are notes for myself on stuff to add later.
Pics of galls, bacterial ooze, cankers, witches broom, flagging, leaf scorch vs leaf spot, etc. for general symptom examples
Pics representative of different disease families (include lists of diseases from table for ease of reference???)
Rusts
Wilts
Anthracnoses
Pics of decay types, description of structural compromise involved and mechanism (i.e. cellulose vs lignin degradation, etc) - white rot, brown rot, sap rot
Pics of diseases of concern in upstate NY