- Diplodia tip blight
- Diplodia Tip Blight of Two-Needled Pines
- Pine Tip Blight Control: Identify And Control Diplodia Tip Blight
- Pine Tip Blight Overview
- Tip Blight Fungus Symptoms
- Pine Tip Blight Control
- Pine Tree Care to Help Prevent Pine Tip Blight
- Cooperative Extension: Insect Pests, Ticks and Plant Diseases
- Diplodia Tip Blight
Diplodia tip blight
Diplodia tip blight, previously known as Sphaeropsis tip blight, is a common fungal disease of stressed conifers, especially pines with needles in bunches of 2’s and 3’s. Austrian pine (Pinus nigra) is the most susceptible host, although the following pines are also susceptible: Scots pine (Pinus sylvestris), red pine (Pinus resinosa), Mugo pine (Pinus mugo), Ponderosa pine (Pinus ponderosa) and occasionally Eastern white pine (Pinus strobus). The disease sometimes attacks other conifers such as Douglas-fir (Pseudotsuga menziesii), Norway spruce (Picea abies), Colorado blue spruce (Picea pungens), American larch (Larix laricina), noble fir (Abies procera), silver fir (Abies alba), some true cedars (Cupressus spp.), arborvitae (Thuja spp.), and junipers (Juniperus spp.). Except for young seedlings, the disease rarely attacks trees under 15 years of age and most severely damages trees that are older than 30 years. It is seldom seen in forests, but prefers ornamental trees weakened by poor sites, drought, hail or snow damage, overshading, compacted soils, root restrictions, insect activity, or other mechanical wounding. The fungus kills current year shoots and sometimes branches, and can disfigure or even kill them under severe conditions.
Diplodia kills needles at the tips of branches Symptoms often start on the lower half of the tree and progress upwards. When the new needles (candles) are expanding, they become stunted, turn yellow, and then turn tan or brown. Generally all needles on the current season’s shoot are killed.
Often resin droplets are seen on the dead shoots. During summer and fall, tiny, black fungal fruiting bodies called pycnidia, which look like black pepper, will appear at the very base of the needle under the fascicle sheath. The pycnidia may also be seen on the scales of second year seed cones and on infected bark. As lateral shoots are killed, whole branches may die back to the trunk and the tree becomes disfigured. This disease can also form perennial cankers that can cause sudden branch death.
Sometimes tip blight can be confused with damage caused by pine shoot moth larvae. However, if pine shoot moth larvae cause the damage, either the larvae or its tunnel will be found inside the shoot. Also, if shoot moth kills the tip, pycnidia will not be present on the needles.
CAUSES AND DISEASE CYCLE
A fungus called Diplodia pinea causes the disease. The fungus overwinters in pycnidia (fungal fruiting bodies) in infected shoots, bark, and seed cones. Tiny spores called conidia erupt from the pycnidia in wet weather. Although they are produced from spring to early fall, they are especially abundant in spring and early summer, when the new shoots (candles) are expanding. Candles can only be infected by the fungus while they are elongating in the spring. After the needles have fully expanded, the shoot can no longer be infected by the fungus. Wind and rain disseminate the conidia. When the conidia land on a susceptible plant part, they infect it by penetrating the plant through wounds or stomates, usually in mid- to late spring. Once the fungus penetrates the plant, it quickly spreads throughout the needles, then to the stem and into nearby needles and cones. The needles begin to die several weeks after infection. Later in fall after the needles have died, the pycnidia appear on the base of the needles or on second year seed cones.
Since cones and dead tips contain the fruiting bodies that produce millions of spores, remove and destroy all infected cones and dead and dying branches and shoots during dry weather. Pruning tools should be disinfected between cuts by dipping them in alcohol or bleach (one part bleach to nine parts of water). Maintain tree health because the disease is more severe on trees that are under stress. Keep the tree watered during dry periods. Maintain a layer of mulch under the tree to conserve moisture. Because the fungus can also infect wounded tissues, avoid pruning trees from late spring to early summer when they are most susceptible.
Registered fungicides should be sprayed at least three times beginning at budbreak, again at half candle, and third application at full candle. A spreadersticker should be applied with the fungicide.
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Diplodia Tip Blight of Two-Needled Pines
Diplodia tip blight is one of the most visible diseases in the urban environment. It affects many common landscape pines in the Midwest, including Austrian (Pinus nigra), red (P. resinosa), mugo (mugho) (P. mugo), and Scots (Scotch) (P. sylvestris) pines. It also affects ponderosa (P. ponderosa) and Monterey (P. radiata) pines. The fungus commonly attacks mature trees that have been under stress from drought, root restriction or other planting site problems. It can also be a problem in young, rapidly growing nursery or Christmas tree plantings. This disease is found throughout the Great Plains, Midwest, Northeast, and California.
Figure 1. Typical tip blight symptoms on Austrian pine.
Symptoms and Signs
This disease is characterized by the blight, or dieback of the tips of branches that can be seen easily from a distance (Figs. 1 and 2). Repeated infections over several years can lead to the majority of the tree looking brown, entire branches dying, the tree becoming deformed. If left unchecked, it can eventually kill mature trees. Upon closer examination, one can find that often this disease begins on new shoots, turning the new needles brown before they are fully formed. It also can lead to resin being exuded from the infected new shoots. The infection may expand down the branch, but the pathogen can also infect older tissues directly through wounds caused by insect activity or hail. Older cones are also susceptible to the disease and often support abundant fruiting on their scales. Occasionally, the fungus may form cankers on stems and branches of severely weakened trees.
A telltale way to determine if a tree is infected with Diplodia tip blight is to look for the signs of the pathogen, which consist of tiny black, fungal fruiting bodies (pycnidia) that are formed on the surface of infected needles (Fig. 3) and infected cones (Fig. 4). These pycnidia are the source of the fungal spores that spread the disease.
Diplodia tip blight is the most common disease on two-needled pines. Outbreaks of the pine shoot moth and European pine sawfly may lead to similar diebacks, but these can be discerned by the presence of the attackers themselves, or evidence of their feeding activities.
|Figure 2. Tip dieback caused by Diplodia pinea infection.||Figure 3. Pycnidia (fungal fruiting bodies) produced on dead needles.|
Causal Fungus and Disease Development
Diplodia tip blight is caused by the fungal pathogen Diplodia pinea (also known as Sphaeropsis sapinea). Spores of the fungus develop in the black pycnidia located at the base of infected needles and other affected plant parts from spring through fall. The fungus over winters in infected needles, bark, cones and needle litter beneath the tree.
Figure 4. Pycnidia (fungal fruiting bodies) produced on older cones.
During spring, the pycnidia produce spores that travel to newly emerging foliage during wet conditions. The spores are spread by wind-blown rain, rain splash, certain insects, and infected tools used in horticultural operations. The fungus penetrates through the stomata of new needles, which are highly susceptible at this stage, and proceeds to infect the shoot. It can spread from tree to tree anytime throughout the growing season under wet conditions. Infections often intensify within the same tree when it is exposed to water stress, particularly drought conditions. Developing cone scales are commonly infected, although they are not damaged.
- Avoid planting susceptible pines in areas that are prone to cool and wet weather in the spring followed by drought or dry soil conditions during the rest of the year. An effort should be made to keep trees in good vigor with regular maintenance, deep watering during droughts, and control of insects. Fertilization of trees with mineral fertilizer (including “deep root feeding”) to increase vigor on sites with adequate fertility, i.e. over-fertilization, will likely make trees significantly more susceptible to the pathogen. If in doubt about the nutrient status of your soil, soil nutrient analysis by a reputable lab may be warranted. Building organic soil fertility with adequate mulching, especially with composted material, would be a better way to improve the long-term health status of at-risk trees than mineral fertilization.
- When producing pine seedlings in nurseries or trees in Christmas tree plantations, ensure that there are no nearby sources of inoculum, e.g. older, infected pines in nearby windbreaks.
- Pruning of infected branches on lightly diseased trees can be an effective control measure by making the cut at least two feet below visible symptoms and if there are no infected trees nearby. Pruning should be conducted only as needed, and tools should be disinfected, e.g. with bleach or alcohol, between cuts. Pruning should be followed by sanitation (removal and destruction of infected needles and cones) to help lower the disease pressure.
- Tip blight can be partially controlled with fungicides. New spring growth must be protected from bud swell to full candle elongation. Make the first application just prior to bud break and make two additional applications at 10-day intervals. It is important to get the first application on the trees before any bud sheaths have broken. For high value trees, commercial formulations of common fungicides, such as thiophanate methyl (e.g. Cleary’s 3336, OHP 6672), propiconazole (e.g. Banner MAXX), azoxystrobin (Heritage), and others registered for use on Diplodia blight are available for application by professional arborists and landscapers. However, if bud sheaths have broken, spraying with fungicides is highly unlikely to result in control of the disease.
Pine Tip Blight Control: Identify And Control Diplodia Tip Blight
Diplodia tip blight is a disease of pine trees and no species is immune, although some are more susceptible than others. Australian pine, black pine, Mugo pine, Scotts pine and red pine are the worst afflicted species. The disease can reappear year after year and over time cause death to even large pine varieties. Sphaeropsis sapina causes tip blight of pine but it was once known as Diplodia pinea.
Pine Tip Blight Overview
Pine tip blight is a fungus which frequently attacks trees that are planted outside their natural range. The disease travels by spores, which require water as an activating substance.
Tip blight of pine overwinters on needles, cankers and two-year-old cones, which is the reason older trees are more frequently infected. Tip blight fungus can become active in a wide range of temperatures and will begin producing spores within a year of infection.
Tree nurseries are not often affected with the fungus due to the youth of the trees but older stands in forested areas can become
decimated by sphaeropsis sapina blight.
Tip Blight Fungus Symptoms
The current year’s growth is the frequent target of the tip blight fungus. The tender young needles will turn yellow and then brown before they have even emerged. The needles then curl and eventually die. A magnifying glass would reveal the presence of small black fruiting bodies at the base of the needles.
In severe infections, the tree can become girdled by cankers, preventing water and nutrient uptake. The fungus will cause death without pine tip blight control. There are many other tree problems that will mimic the symptoms of pine tip blight.
Insect injury, winter drying, moth damage and some other needle diseases look similar. Cankers are an excellent clue that the damage is due to tip blight fungus.
Pine Tip Blight Control
Good hygiene is an easy way to minimize and prevent the disease. The tip blight fungus over winters in debris, which means removal of dropped needles and leaves will limit the tree’s exposure. Any infected plant material needs to be removed so the spores cannot jump to previously healthy tissue.
When pruning out infected wood, make certain you sanitize the pruners between cuts to prevent further spread.
Fungicides have offered some control. The first application must be before bud break with at least two more applications in ten day intervals for effective pine tip blight control.
Pine Tree Care to Help Prevent Pine Tip Blight
Trees that have been well cared for and have no other stresses are less likely to acquire the fungus. Pine trees in the landscape need to receive supplemental watering in drought periods.
Apply annual fertilizer and manage any insect pests for the healthiest aspect. Vertical mulching is also beneficial, as it opens up soil and increases drainage and the formation of feeder roots. Vertical mulching is accomplished by drilling 18-inch holes near feeder roots and filling them with a mix of peat and pumice.
Cooperative Extension: Insect Pests, Ticks and Plant Diseases
Diplodia Tip Blight
Pest Management Fact Sheet #5102
Authors: Dr. Alicyn Smart, Dr. Bruce Watt, and Abigayl Novak
For information about UMaine Extension programs and resources, visit extension.umaine.edu.
Find more of our publications and books at extensionpubs.umext.maine.edu.
Other Name: Sphaeropsis sapinea and Diplodia pinea
Pathogen: Sphaeropsis sapinea
This disease can be very destructive to two- and three-needle pines and commonly infects trees planted outside of their natural range. Damage to native trees is not commonly seen.
The spores of this fungus can germinate and infect the tree over a wide range of temperatures. After the germination, the fungus infects the needle by entering the stomata. The fungus then infects the twig, and the needles become brown and form a canker on the twig (Figure 1). Although the spores require free water, as little as 12 hours of wetness is sufficient for infection. During wet springs, spores will be produced in great numbers and are readily spread by the splashing of rain. Trees that are in poor health due to environmental or cultural stress are more susceptible to infection then healthy trees.
Diplodia tip blight overwinters in diseased needles, cankers, and especially in two-year-old cones, which account for the increased incidence of the disease in older trees. The pathogen survives well on dead plant tissues and produces spores within a year after infection. These spores ooze out of a fruiting structure called pycnidia during wet weather and are carried to susceptible healthy tissue by the splashing of rain (Figure 2). Developing shoots and needles are especially vulnerable to infection.
- All species of Pine (Pinus) — Austrian Pine (Pinus nigra) severely affected
- Douglas-fir (Pseudotsuga menziesii)
- White Spruce (Picea glauca), Norway Spruce (Picea abies), and Blue Spruce (Picea pungens)
Symptoms and Signs
This fungus mostly attacks mature trees that are under stress from drought, root restriction, or other planting site problems. The most readily observed symptom is the curling and death of new shoots that have become infected in early spring. Before this, needles can turn yellow and brown before they have fully expanded. Fruiting bodies (pycnidia) of the fungus can be seen as black dots at the base of the needles, especially toward the end of the season. Pycnidia are often found under the needle sheaths and can also be found on the cone scales and the shoots. The disease tends to be most severe on older trees and is less common in nurseries. Although symptoms can be found in all parts of the crown, the lower branches tend to be more severely infected because of how the fungal spores are washed down through the tree by the rain. This fungus can also infect stems through wounds, leading to resinous cankers.
- Maintain the health of the tree by avoiding improper planting site selection and water during droughts when plants are young.
- Collect all fallen cones and dispose of them to limit the spread of the disease.
- Avoid planting too close to other plants that can limit airflow.
- Do not apply fertilizer with high amounts of nitrogen.
- Prune diseased branches to limit the spread of the disease. Avoid pruning during wet weather and sanitize pruning shears with 70% rubbing alcohol between cuts to minimize spreading the disease.
- Preventative fungicides can be used at bud break and again in two weeks.
Protective fungicides available for control of this disease must be applied during the spring just before bud break and periodically thereafter to protect new growth as it expands. Appropriate fungicides are listed below:
|Appropriate Fungicides for Diplodia Tip Blight|
|Fungicide||Application Notes||Examples of Trade Names|
|Azoxystrobin||Typical application interval 7 to 14 days. See label to verify.||Quadris, Amistar, Cabrio EG|
|Bordeaux mix||See label for timing.|
|Propiconazole||Apply when you first see symptoms on a 14-21 day schedule||Banner Maxx|
|Thiophanate-methyl||Apply at early bloom. See label.||Topsin-M|
You should check your local town ordinance for any pesticide restrictions before application.
WHEN USING PESTICIDES, ALWAYS FOLLOW LABEL DIRECTIONS!
Alicyn Smart, DPM
Plant Pathologist and Director of the Plant Disease Diagnostic Laboratory
University of Maine Cooperative Extension
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