Connecticut State The Connecticut Agricultural Experiment Station

Common Diseases of Crabapple

There are a number of diseases that commonly occur on crabapples in home plantings. Scab, cedar-apple rust, and cedar-hawthorn rust are diseases that are usually encountered every year, whereas fire blight is an occasional problem. Many factors contribute to both the occurrence and severity of these diseases. Some of these include severity of the infection the previous year, weather at the time of budbreak, cultural practices, and type of crabapple variety planted.


Crabapple diseases can be effectively controlled through the combined use of culture, sanitation, resistance, and fungicide sprays. This integrated approach to disease control minimizes the reliance upon one type of control over the others and usually results in effective disease control.
Culture: Cultural methods include maintaining tree vigor by proper planting, fertilizing, and pruning and by following general practices that help to minimize tree stress.
Sanitation: Sanitation involves pruning and removing affected or dead portions of the tree and removing diseased foliage or fruit, which are often important sources of inoculum for the next season.
Resistance: Resistance involves selection and planting of varieties with genetic resistance to specific diseases. This effectively reduces or eliminates occurrence of the disease in question.
Fungicide Sprays: Proper selection, timing, and application of these sprays are important. Thorough coverage of all parts of the tree is necessary and sprays should be applied until runoff. The fungicide label will contain information on plant hosts and diseases, dosage rates, and safety precautions.


Scab, caused by the fungus Venturia inaequalis, is the most common and one of the most devastating diseases of crabapple in Connecticut. Defoliation of trees as a result of this disease is not only unsightly, but also reduces the vigor of the tree, making it more susceptible to environmental stress and other opportunistic pests. Scab is usually most severe in wet weather. The fungus causes circular, olive-black spots on the leaves, fruit, and young fruit stems. As the spots develop, the leaves may turn yellow and drop prematurely. Symptoms typically first appear on the leaves in May or early June. Heavy infections can result in defoliation by June.
The fungus overwinters on dead, fallen leaves and produces spores (primary) in the spring that can infect sepals, young leaves, and young fruit during periods of rain. Infection from these primary spores can take place anytime after growth begins until mid to late June if suitable weather conditions exist. During the summer, a different spore (secondary) is produced by the fungus that is capable of inciting more new infections when splashed onto leaves and fruits by rain.
Scab is most effectively controlled by planting resistant varieties. A partial list of resistant crabapples includes: Adams, Baskatong, Brandywine, Callaway, David, Dolgo, Donald Wyman, Malus floribunda, Henry Kohankie, Henningi, Jewelberry, Ormiston Roy, Professor Sprenger, Malus seiboldi var. zumi cultivars Calocarpa, Silver Moon, Sugartyme, Malus tschonoski, Weeping Candy Apple, White Angel, and White Cascade. A good sanitation program in which diseased leaves and fruit are removed from the vicinity of the tree will also help to eliminate sources of inoculum in the spring. Scab can also be controlled with properly selected and timed fungicide sprays. Among the fungicides registered for use in Connecticut are thiophanate methyl, mancozeb, chlorothalonil, chlorothalonil plus fenarimol, and copper sulphate pentahydrate. Applications can be made at budbreak and repeated at label intervals until mid-June. More frequent sprays may be necessary in wet weather.
Cedar-Apple Rust:
Cedar-apple rust, caused by the fungus Gymnosporangium juniperi-virginianae, is a problem when crabapple and certain species of juniper and red cedar grow in close proximity. This rust requires two different hosts to complete its life cycle. The fungus causes brilliant yellow-orange spots or lesions on crabapple leaves and occasional lesions on the calyx end of the fruit. On cedar, the fungus produces brown to reddish-brown galls, ¼-2″ in diameter. During rainy periods in the spring, distinctive bright orange, gelatinous spore-horns protrude from the surface of these galls. The spores are blown by the wind to crabapple trees where they infect and produce their characteristic lesions.
Removal of unwanted junipers or cedars located in close proximity to the crabapple tree usually reduces the number of spores capable of infecting, although this is often not practical. Galls can also be removed from juniper branches during dormancy. However, selection and planting of resistant varieties are the most important and effective methods of control. Examples of rust-resistant varieties are: Ellwangerina, Henry Kohankie, Ormiston Roy, and Red Baron. Where the disease seldom occurs or few leaves are infected, no control is necessary. Where disease is frequent and severe, fungicide sprays can be applied to the rosaceous hosts. Among the fungicides registered for use in Connecticut are chlorothalonil, ferbam, mancozeb, triadimefon, triforine, and myclobutanil. Applications can be made at budbreak and repeated at label intervals as necessary. More frequent sprays may be necessary in wet weather. Fungicide control for Juniperus hosts is usually not practical since it often requires a season-long spray program.
Cedar-Hawthorn Rust:
Cedar-hawthorn rust is caused by Gymnosporangium globosum, a fungus that is related to the cedar-apple rust fungus. Because these fungi are so closely related, the diseases caused by them are very similar. Cedar-hawthorn rust also requires two different hosts in order to complete its life cycle—these include Juniperus species (e.g., eastern red cedar), as well as many rosaceous species. However, cedar-hawthorn rust has a wider rosaceous host range than cedar-apple rust, which includes apple, crabapple, many hawthorns, pear, quince, and serviceberry. Mountain ash and medlar have also been experimental hosts of this fungus. The disease cycle is essentially the same as previously described for cedar-apple rust. Cedar-hawthorn rust usually infects leaves but can also produce symptoms on fruit and green stems, resulting in deformity. Cedar-hawthorn rust can be distinguished from cedar-apple rust by several attributes of the aecia on the undersurface of the leaves of the rosaceous host. For example, the fingerlike projections of the aecia of cedar-hawthorn rust are substantially longer than those of cedar-apple rust. Additionally, cedar-hawthorn rust produces slightly smaller, more flattened galls on the juniper hosts.
Control strategies are essentially the same as for cedar-apple rust. Hawthorns with reported resistance include English hawthorn, Cockspur thorn, yellow-fruited thorn, Crataegus intricata, and C. pruinosa.
Fire Blight:
Fire blight, caused by the bacterium Erwinia amylovora, is the most devastating disease of crabapple. Fortunately, this disease is only an occasional problem and, when it does occur, it is often isolated to specific geographical locations. However, when infection occurs, the disease can develop quite rapidly and can destroy individual trees in a single season. The bacteria survive the winter in old cankers on crabapples and other plant hosts and in healthy buds. As the weather becomes favorable for growth in the spring, the bacteria begin to multiply rapidly and can be seen oozing out of tissues. This creamy, bacterial ooze is attractive to insects and they pick it up and carry it to open flower buds where infection occurs. The bacteria are also carried by wind and rain to open blossoms. Infected tissues are characterized by their blackened, “burned” appearance, hence the name “fire blight.”
The most effective method for control of this disease is to select and plant crabapple varieties that are resistant to fire blight. These include: Adams, Callaway, David, Dolgo, Harvest Gold, Indian Summer, Jewelberry, Liset, Profusion, Red Baron, Selkirk, and Sentinel. Sanitation is also a very important aspect of control. Any cankered or infected branches or twigs should be cut back to healthy wood during the dormant season. All pruning cuts should be made at least 8-12″ below visible symptoms. All tools should be disinfested with 10% household bleach (1 part bleach: 9 parts water) or 70% alcohol. Prunings should be removed from the vicinity of the tree. The effects of this disease can also be minimized by maintaining overall tree health by following proper cultural practices that avoid excessive vigor. It is especially important to avoid heavy applications of nitrogen in the spring.


Several diseases commonly occur in home and landscape plantings of crabapples every year. These are scab, cedar-apple rust, cedar-hawthorn rust, and occasionally fire blight. This fact sheet discusses the symptoms, factors that contribute to the severity of these diseases, and control or management options.

Apple scab

Apple scab is one of the more serious diseases of ornamental crabapples. It is caused by the fungus Venturia inaequalis. Apple scab mainly affects members of the rose family, including nearly all commercial cultivars of apple (Malus spp.), crabapple (Malus spp.), hawthorn (Crataegus spp.), mountain-ash (Sorbus spp.), cotoneaster (Cotoneaster spp.), firethorn (Pyracantha spp.), and common pear (Pyrus spp.).


Apple scab can be observed on leaves, blossoms, fruit, and, less frequently, on young succulent shoots. The most obvious symptoms occur on leaves and fruit in the spring and summer, and look like small velvety brown to olive-green spots that enlarge and darken to become more or less circular. Lesions are superficial with feathery, indistinct margins. When infections are numerous, young leaves become curled and distorted. Severely infected leaves and fruit fall prematurely. Scab lesions on remaining fruit and twigs become corky, cracked, and rough. Symptoms on mountain-ash and other hosts are similar to those on crabapple, with emphasis on foliar lesions and premature leaf fall.


Apple scab is most severe during spring and early summer when the humidity is high and the temperature is moderate. Overwintering fungal spores (ascospores) are produced in the diseased leaves on the ground. In most years, the first fungal spores (primary inoculum) mature and are capable of causing infections in the spring at about the time of budbreak (leaf expansion). Fungal spores are expelled into the air following rainfall and continue to be discharged over a period of 1-3 months. The peak period of spore dispersal often occurs near the end of bloom (pink to full-bloom stages). Whether infection occurs or not depends on the period of wetness and the temperature. Fewer hours of wetness are required for infection at high temperatures than at low. For example, at 43 degrees F, a 25-hour period of wetness is required for infection; whereas only a 9-hour wetness period is needed between 61 degrees and 75 degrees F. The severity of disease increases with the duration of wetting. According to Mill’s Chart (W.D. Mills, Cornell University), 9-14 hours of wetness are needed for initial infection to occur in the typical northern Illinois spring temperature range of 50-60 degrees F.

Once the fungus has become established on the host, it produces secondary spores (conidia) which help to re-infect new leaves throughout the summer. Conidia are disseminated by splashing rain or irrigation and wind to new leaf or fruit surfaces, and give rise to new lesions. Several “secondary” cycles may occur during the growing season if wet weather prevails during the summer.


Plant Resistance
The best way to prevent apple scab is to plant resistant crabapples. Many species, cultivars, and varieties of Malus are resistant to the scab fungus. Some crabapples especially resistant to apple scab include M. ‘Adirondack’, M. baccata ‘Jackii’, M. ‘Beverly’, M. ‘Dolgo’, M. ‘Donald Wyman’, M. ‘Mary Potter’, M. ‘Molazam’ (Molten Lava), M. ‘Prairifire’, M. ‘Red Jewel’. M. ‘Sutyram’ (Sugar Tyme), M. ‘White Angel’, and M. ‘Zumi Wooster’

The Morton Arboretum publication Crabapples for the Home Landscape provides information on selecting crabapples.

The apple scab fungus overwinters on fallen leaves and infected twigs so collecting and removing or composting these leaves and twigs will reduce the source of infection. Sanitation practices, such as leaf litter removal and pruning, should be done in the fall or winter before bud break occurs. Earthworms and litterdecomposing microorganisms degrade fallen leaves and help reduce the overwintering population of the scab fungus. Natural leaf decomposition can be accelerated by composting leaves (piles must be mixed regularly and reach temperatures of at least 120 degrees F throughout) and applying nitrogen fertilizer (e.g., urea) to the leaves in the fall.

Fungicide control programs for scab should be integrated with sanitation and other cultural management practices. Apple scab can be effectively managed with fungicides by controlling primary infections. It is important that sprays are applied according to plant development, with the first spray at bud swell and additional sprays at 10-to-14-day intervals. The number of fungicide spray applications required varies with many factors, including weather conditions (rainfall), the susceptibility of the plant, the rate of plant growth development, the fungicide used, and the amount of fungal inoculum present.

Call The Morton Arboretum Plant Clinic at 630-719-2424 or refer to “Pest Management for the Home Landscape” (University of Illinois Extension) for a complete listing of chemical recommendations. Use pesticides safely and wisely; read and follow label directions

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used.

The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

Crabapple (Malus spp.)-Scab


Apple (Malus spp.)-Scab

Crabapple Cultivar Susceptibility

Cause Venturia inaequalis, the fungus that causes scab on commercial cultivars of apple. This is the most serious disease of crabapple and can defoliate susceptible trees. Wet, cool spring weather favors the disease, which affects leaves and fruit. Trees that lose many leaves due to scab may become weak and more susceptible to other pests and environmental problems.

The fungus overwinters in diseased leaf debris on the ground. Ascospores on leaves are produced in wet spring weather. Wind carries spores to young leaves and flowers where they initiate primary infections. Infections eventually produce millions of conidia, which splashing rain and wind spread to new leaf or fruit surfaces in the tree. Spores germinate to cause new lesions. Several secondary cycles of conidial germination, infection, and sporulation may occur during a growing season.

Symptoms The first visible leaf symptoms in spring are pale, chlorotic, water-soaked spots the size of a pinhead. These enlarge, becoming darker and smoky in appearance, later taking on an olive shade and ultimately a brownish black color. Spots may be any shape but frequently are circular. Young infections often show a radiating spread of fungus tissue through the leaf; such areas later appear as irregular, brown infections. Diseased leaves can be curled and distorted and often drop early, thus defoliating and weakening the tree.

Bud or blossom infection often leads to shedding of blossoms and no fruit production.

Cultural control

  • New plantings:
    • If possible, plant disease-resistant trees (see Crabapple Cultivar Susceptibility). The following types did not develop scab over a 33 year evaluation period at Wooster, Ohio: M. sargentii ‘Sargent’, M. baccata ‘Jackii’, M. x ‘Beverly’, M. x ‘Silver Moon’, and M. x ‘White Angel’.
    • Plant trees in full sun and/or avoid too much shade.
  • Existing plantings:
    • Avoid wetting the leaves when irrigating.
    • When possible, rake and destroy fallen leaves before they become dry and brittle.

Chemical control Do not apply if fruit is to be consumed. Apply fungicides early and thoroughly to protect new growth. The first susceptible tissues exposed in opening cluster buds are the tips of the leaves and sepals. The most critical period for scab development is from the breaking of the cluster buds until leaves are fully expanded. Use only one fungicide from any single fungicide group once a year. Always tank-mix and/or alternate products to prevent buildup of resistant pathogens.

An interesting study from Indiana found apple orchard isolates of this fungus resistant to Group 1 fungicides (such as the thiophanate-methyl-based products below) but not isolates from ornamental crabapples.

  • Affirm WDG at 0.5 lb/100 gal water. Group 19 fungicide. 4-hr reentry.
  • Aprovia at 5.5 to 7 fl oz/A plus another fungicide and an adjuvant. Do not use within 30 days of harvest. Group 7 fungicide. 12-hr reentry.
  • Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. For nonbearing fruit trees only. Group 3 + 11 fungicide. 12-hr reentry.
  • Bayer Advanced Disease Control at 0.75 fl oz/gal water. H
  • Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. H
  • Broadform at 4 to 8 fl oz/100 gal water. For nonbearing fruit trees only. Group 7 + 11 fungicide. 12-hr reentry.
  • Concert at 9 to 17 fl oz/100 gal water. May cause injury to buds, blooms or tender new growth. Landscape use only. Group 3 + M5 fungicide. 12-hr reentry.
  • Daconil Weather Stik at 1.4 pints/100 gal water every 7 to 14 days. Treated fruit must not be eaten. Group M5 fungicide. 12-hr reentry.
  • Eagle 20 EW at 6 to 12 fl oz/100 gal water. Do not use treated fruit for food. Group 3 fungicide. 24-hr reentry.
  • Flint at 2 to 2.5 oz/A for edible types or Compass O 50 WDG at 2 to 4 oz/100 gal water for ornamentals. When using Compass do not use with an organosilicate surfactant. Use as a protectant fungicides and not curatively. Do not use within 14 days of harvest. Group 11 fungicide. 12-hr reentry.
  • Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Do not apply to ‘Flame’, ‘Brandywine’, or ‘Novamac’. Phytotoxicity can be extreme on sensitive cultivars. Group 11 fungicide. 4-hr reentry.
  • Insignia SC at 3 to 6 fl oz/100 gal water. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
  • Inspire Super at 12 fl oz/A. Do not apply within 14 days of harvest. Group 3 + 9 fungicide. 12-hr reentry.
  • Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
    • Dithane M45 at 3 or 6 lb/A.
    • Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
    • Manzate Pro-Stick at 3 or 6 lb/A.
    • Penncozeb 75 DF at 3 or 6 lb/A.
    • Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Do not use treated fruit for food.
  • Merivon at 4 to 5.5 fl oz/A. Do not use with EC or oil-based products. May be used day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
  • Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
  • Orkestra at 4 to 8 fl oz/100 gal water plus an adjuvant. Group 7 + 11 fungicide. 12-hr reentry.
  • Pageant at 6 to 12 oz/100 gal water. The addition of a silicone-based surfactant has improved control. Group 7 + 11 fungicide. 12-hr reentry.
  • Phospho-Jet is registered as a basal bark spray at 62.4 fl oz in 62.4 fl oz water plus 3 fl oz of Pentra-Bark. Spray first 5 feet of trunk including scaffold limbs until runoff. Group P7 fungicide. 4-hr reentry.
  • Phyton 27 at 4 fl oz/10 gal water. Group M1 fungicide. 48-hr reentry.
  • Pristine at 14.5 to 18.5 oz/A. The addition of a silicone-based surfactant has improved control. Can be used day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
  • Propiconazole-based products. Group 3 fungicides.
    • Alamo is registered for trunk injection, see label for details. Group 3 fungicide.
    • Banner MAXX at 2 to 4 fl oz/100 gal water. For nonbearing fruit trees only. 12-hr reentry.
    • Infuse Systemic Disease Control at 0.5 Tbsp/gal water. H
    • ProCon-Z at 2 to 4 oz/100 gal water. 24-hr reentry.
    • ProPensity 1.3 ME at 2 to 4 fl oz/100 gal water. 24-hr reentry.
    • Propizol is registered for trunk injection, see label for details. 24-hr reentry.
    • Strider at 2 to 4 fl oz/100 gal water. Also registered for trunk injection, see label for details. Group 3 fungicide. 24-hr reentry.
    • Systemic Fungicide (ferti-lome) at 0.25 fl oz/gal water. H
  • Sovran at 3.2 to 6.4 oz/A. Use as a protectant fungicides and not curatively. Some sweet cherries, such as ‘Van’, may be injured if accidentally sprayed. Group 11 fungicide. 12-hr reentry.
  • Spectracide Immunox at 1 fl oz/gal water. H
  • Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
  • Tebuconazole-based fungicides are registered. Do not use within 75 days of harvest. Group 3 fungicides. 5-day reentry.
    • Tebucon 45 DF at 4 to 8 oz/A.
    • Tebuzol 3.6F at 4 to 10 fl oz/100 gal water. Not for food. No reentry interval listed.
    • Torque at 4 to 10 fl oz/100 gal water. 12-hr reentry.
    • Unicorn DF at 2 to 3 lb/A. Includes sulfur in the formulation. 5-day reentry.
  • Tebuject is registered for tree injection as a preventative treatment. Do not inject trees less than 2 inches in diameter or unless trees are suffering from various stresses.
  • Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Thiophanate-methyl-based products. These materials will kill earthworms, which help decompose scab infected leaves. Use in a tank-mix with other products. Group 1 fungicides. 12-hr reentry.
    • Cleary’s 3336 EG at 12 to 16 oz/100 gal water. Do not use after fruit set if applied to fruiting trees.
    • OHP 6672 4.5 F at 10.75 to 20 fl oz/100 gal water. Do not use treated fruit for food.
    • Systec 1998 FL at 20 fl oz/100 gal water.
    • Tee-Off 4.5 F at 10.75 to 20 fl oz/100 gal water plus a surfactant.
  • Topguard at 13 fl oz/A plus another fungicide. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
  • Tourney 50 WDG at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Trionic 4 SC at 8 to 16 fl oz/A. Do not apply within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
  • Vangard WG at 5 oz/A alone or at 3 to 5 oz/A when tank-mixed with another fungicide. May be applied day of harvest. Shorten intervals between applications when weather is warm. Group 9 fungicide. 12-hr reentry.
  • Zyban WSB at 24 oz/100 gal water. Not to be confused with the smoking cessation drug. Group 1 + M3 fungicide. 24-hr reentry.

Notes Some registered products offer only suppression of this disease and thus are not recommended for use. These products include DoubleNickel 55, Ph-D, Oso, and Regalia.

Early freezes or severe cold can damage apple trees, a possible cause of later, rapid deaths. The decline is more common among densely planted trellised orchards (above right).


Six years ago, an unpleasant surprise greeted plant pathologist Kari Peter as she inspected a research orchard in Pennsylvania. Young apple trees were dying—and rapidly. At first, she suspected a common pathogen, but chemical treatments didn’t help. The next year, she began to hear reports of sudden deaths from across the United States and Canada. In North Carolina, up to 80% of orchards have shown suspicious symptoms. “Rows of trees collapse for what seems like no reason,” says Peter, who works at the Pennsylvania State University Fruit Research and Extension Center in Biglerville.

Now, as their trees prepare to blossom, North America’s apple producers are bracing for new losses, and scientists are probing possible causes. Apples are one of the continent’s most valuable fruit crops, worth some $4 billion last year in the United States alone. Growers are eager to understand whether rapid or sudden apple decline, as it is known, poses a serious new threat to the industry.

Weather-related stress—drought and severe cold—could be an underlying cause, researchers reported this month in PLOS ONE. Early freezes are becoming more common across the eastern United States, for example. But that doesn’t appear to be the whole story, and scientists are examining an array of other factors, including pests, pathogens, and the growing use of high-density orchards. “There are a number of things going on that are going to be really difficult to sort out,” says David Rosenberger, a retired plant pathologist who worked at Cornell University.

One common symptom in trees struck by rapid decline is dead tissue at the graft union, the part of the trunk where the fruit-bearing budwood of an apple variety is joined to hardy rootstock to create new trees. The union is vulnerable to late-season freezes because the tissue is the last to go dormant.

A team led by plant pathologist Awais Khan of Cornell found dead tissue just below the graft union in trees from an affected orchard in New York. They suspect the cause was the extremely cold winter of 2014–15, which was followed by a drought. The dying tissue could have weakened the trees, allowing pests or pathogens to invade. But Khan and colleagues could not locate any known culprits in the affected trees or nearby soil, they reported in PLOS ONE.

Observations from other apple-growing regions suggest extreme weather isn’t entirely to blame. In Canada, rapid decline “exploded” in British Columbia in the summer of 2018, after a string of unusually mild winters, says Tom Forge, a soil ecologist with Agriculture and Agri-Food Canada in Summerland. These orchards are irrigated, suggesting drought was not a factor.

Some scientists wonder whether certain rootstocks or exposure to herbicides might make trees more susceptible. Decline seems to be more common in trees with a popular rootstock, called M9, which can be slower to go dormant in fall, Peter says. Rosenberger has noticed that decline appears to be more common in orchards with fewer weeds, leading him to suspect herbicides play a role.

Young apple trees died rapidly in this high-density orchard in Pennsylvania.

Kari Peter

Meanwhile, the search for new pathogens is accelerating. Last year, a team that included Peter and plant pathologist Ruhui Li of the U.S. Department of Agriculture in Beltsville, Maryland, reported in Virology Journal that they had found a previously undescribed luteovirus infecting dead trees. Scott Harper, a plant pathologist at Washington State University in Prosser, has also found undescribed viruses in dead trees. Li’s group has already infected young trees to see whether its virus is harmful, and Harper is planning similar greenhouse experiments. But getting an answer could take up to 5 years. “In the meantime, people are biting their nails,” Rosenberger says.

In hard-hit North Carolina, researchers have found ambrosia beetles infesting the graft union of dying trees. These stubby insects burrow into weakened trees and cultivate fungus for their larvae to eat. Those fungi or stowaway fungi might harm the trees, an idea that Sara Villani, a plant pathologist at North Carolina State University in Mills River, and colleagues, will start to test in June. Researchers there will also test way of boosting the trees’ immune systems.

Modern apple farming methods could also be a factor. Rapid decline is most common in dense orchards, which are increasingly planted because they are efficient to manage. Instead of about 250 trees per hectare, high-density orchards can have 1200 or more. Tightly packed trees must compete for nutrition and moisture. They also have shallow roots, which make them easier to trellis but more vulnerable to drought. “I’m not criticizing the system,” Khan says, “but it’s not robust for these kinds of fluctuations.”

As studies proceed, researchers remain vigilant. “It wouldn’t surprise me,” Villani says, “if we get more reports of apple decline.”

Apple tree appears dead on top but sprouting from bottom

For the most part, plants decline and die in situations where the amount of food/energy they’re able to create (with the help of the sun) is less than they are expending to drive their metabolic processes. It doesn’t LOOK like your tree is in any immediate danger of expiring, but symptoms made manifest by ongoing limitations commonly lag the cause by weeks to months. Necrotic leaf tips and margins are far more often than not a symptom of over-watering and/or a high level of dissolved solids (salt) in the soil solution. Occasionally it can be traced entirely to growers watering with their own version of enhanced frequency; more often, it’s the result of a poor soil that simply does not allow the grower to water correctly w/o the plant paying a tax in the form of diminished root health because the soil remains saturated long enough to have attained the age of majority. Curing the effects of too much water in the soil starts by using a soil that doesn’t hold too much water, and by default, not enough air. Then, using a ‘tell’ as an indicator of when it’s appropriate to water to put a polish on what you practice. I use soils that hold no (or nearly no) excess (perched) water. That means I’d have to work very hard at over-watering. That scenario makes things easy for the grower and easy on the plant. If you’ve been forever in battle with your chosen soil for control of your plants’ vitality, the change that occurs when you switch to a good soil (one that allows you to water correctly , will make it seem like you have somehow done something magic. Too, where a poor soil makes fertilizing something of a helter skelter proposition, good soils make it monkey easy. Your job, as chief grower, is figuring out what is most limiting to your plant and fixing it. This represents the difference between a plant surviving at the outer limits of what it’s programmed (genetically) to tolerate and one that’s growing in its ‘sweet spot’. understanding how soils work, followed by understanding how plants work, are representative of the largest steps forward you’ll likely make as a container gardener. There are several links I can suggest if you have interest? Low light and cool temps can cause plants to stall in sort of a consequential dormancy, but nutritional issues and root congestion can do the same; as can the cyclic death and subsequent regeneration of roots as the root mass wobbles back and forth between just right and too wet. Soggy soils kill roots. Before the top can/will grow, the root system has to be able to support new growth, so dead roots have to be replaced. The energy it takes to regenerate roots might have been put toward an increase in the plant’s mass. The difference between what a plant is and what it could be is described as lost potential. Even plants that LOOK good can be losing out on an extreme measure of potential; and in plants, lost potential can never be regained under ANY circumstances. If your plant has a droopy or hang-dog look, it’s likely from a lack of turgidity (internal water pressure), brought about by too little water, too much water, and/or a high level of dissolved solids in the soil. Unfortunately, after wilting the leaves of F lyrata often don’t recover to occupy their former spatial positions. IOW, once they wilt, their attitude usually changes at least partially so that droopy appearance becomes a permanent thing. Try reading this. Al


The most valuable part of any living, growing landscape are the trees that provide a protective border around your property, that offer shade during the “dog” days of summer, and that act as an all-season wind break.

Strong, healthy trees perform countless other chores; the emphasis is on the word “healthy.” Trees have a number of enemies including wind, temperature extremes, lightning, hail, snow, and ice. They can suffer from disease and pest damage and we humans can also unintentionally stunt their growth and contribute to their demise.

Here are a few common symptoms exhibited by unhealthy trees and what their cause may be:

Slow growth poor growth or decline in growth, This occurs when trees are planted too deep or roots are covered by adding soil over existing roots. Healthly trees should have trunks with roots flaring out from the base slightly above the soil level.

Decline in your ash tree’s crown, D-shaped exit holes in the bark, and excessive woodpecker damage. This may be an indication of EAB infestation. The Emerald Ash Borer (EAB) was discovered in Michigan in the summer of 2002 and has since killed several million ash trees throughout the Midwest.

Defoliation. Unlike the EAB, the gypsy moth will feed on several different species of trees and shrubs. The damage is caused by larvae or caterpillars when they emerge in early spring and start feeding on leaves. Most trees can survive moderate defoliation, but more excessive damage can make them vulnerable to other insects and diseases. This pest prefers leaves of deciduous hardwood trees such as maple, elm, and especially oak.

Oak leaves prematurely turning yellow. This is one of the first signs of iron deficiency. If left untreated, leaves will turn brown and the tree will die.

A yellow brown cast to your evergreen trees. This is usually an indicator of winter burn caused when trees evaporate moisture during the winter that cannot be replaced because the soil is frozen. An application of an anti-desiccant or anti-transparent will prevent winter burn.

Dead leaves versus twisted or curled leaves. Dead leaves at the tops of trees are usually the result of root damage or borer infestation versus twisted or curled leaves that may indicate viral infections, insect feeding, drought or exposure to herbicides.

Holes in the tree, oval to round darkened wounds in the bark, and large piles of sawdust around the base of a tree. Symptoms of chewing beetles.

Premature color. A few tree limbs or an entire tree that exhibits premature color in the fall is usually linked to root-related stress.

If you observe any of the above symptoms, contact your landscape professional or tree care expert. They can diagnose the problem and offer treatment options.

Photo courtesy of Davey Tree.

What is Wrong with My Tree?

Insects and diseases pose two of the most serious threats to a tree’s health. In addition to insects and diseases, many abiotic factors can negatively affect trees.

Determining, “What is Wrong With My Tree?”

As soon as you notice any abnormality in your tree’s appearance, you must begin a careful analysis to gain an understanding of the problem. By examining the specific symptoms of damage and understanding, “What is wrong with my tree?”, you can make a reasonable diagnosis of the problem and select the proper treatment. If you are uncertain about the disease, or do not know how to treat it, contact your local CSFS District office to conduct a homesite assessment of the trees on your property.

Colorado’s Common Insects and Diseases

Insects and diseases are a critical issue regarding the declining health of
Colorado’s pine and aspen forests. A few of the more common insects and diseases that affect these forests are the mountain pine beetle, the ips beetle, dwarf mistletoe, various aspen ailments, the spruce bark beetle and the western spruce budworm.

Learn more about Colorado’s common forest insects & diseases

Abiotic Factors that Affect Trees

Hail Damage

Hail can be very damaging to trees by ripping through leaves, defoliating branches, wounding bark and knocking off twigs altogether. Such damage leaves the trees more susceptible to disease, and makes it easy for harmful pathogens to invade.

Frost and Winter Exposure Damage

Frost during growing season can be detrimental to newly formed leaves and stems, which are not yet acclimated to cold temperatures.
Tissue will appear water soaked and will quickly become brown and shriveled.

What’s Wrong With That Tree?

As an arborist, I’m trained to have a discerning eye. While most people drive up to a stop sign and look to the left and to the right, I look left, right, and up. I avoid some intersections because I know what’s growing on the corner—a tree with a structural defect that needs only a strong wind or an ice storm to send it crashing to the ground. Though tree defects are easy to spot if you know what to look for, the untrained eye may have a hard time recognizing the signs of a tree in serious trouble.

Structural defects occur in trees for a number of reasons, and even though a tree may be structurally compromised, it could live on for years. One example is a tree with a hollowed-out trunk. Since fluids are conducted upward in the outer rings of wood and downward in the tissue just inside the bark, a tree can be big and green yet be mostly hollow. Physiologically, this tree is still functioning, but it may not be structurally sound. One stiff wind could send it toppling.

Sometimes solving the problem a hazardous tree may pose is as simple as moving the target that makes it a hazard. For example, if a limb is in danger of splitting from a trunk and falling on the picnic table below, moving the picnic table or cabling the limb may mitigate the hazard. In other cases, a health-care program designed to increase a tree’s vigor may help it overcome minor root damage or the stress caused by insect or disease damage.

Seven reasons to call an arborist

1. Cracks
2. Splits
3. Mushrooms
4. Hollows
5. Dead wood
6. Hangers
7. Tilting

For photos and more information on each of these conditions, continue reading.

Some splits require cabling so they won’t crack

This Kentucky coffee tree (Gymnocladus dioica) has a split trunk originating in a narrow crotch or compression fork.This red oak (Quercus rubra) suffers from a trunk crack caused by torsional stresses and internal decay.

Splits and cracks where branches meet trunks or where trunks diverge pose the most serious hazards. Once underway, these structural failures will only increase in size due to the stresses caused by wind, snow, and the natural process of leafing out. Trees like maples and ashes have growth habits that make them more prone to splits and cracks than other trees are.

Depending on the presence of a target (e.g., picnic table, garage), the size of the crack, and the aesthetics involved, some branch unions can be stabilized by using cables to support the weight of the defective area. Cabling is a process by which a seven-strand galvanized steel cable is anchored to two stems or limbs two-thirds to three-quarters of the way above the defect.

In some instances, cabling may not be effective. The only way to know is to have an arborist examine the crotch to determine if cabling will be supportive. The alternative is to remove the branch or stem to protect both the remaining tree and people or objects below it.

Mushrooms indicate root or trunk problems

Mushrooms typically grow on dead wood or on some other matter that is rotting. The author examines a mushroom growing on an old pruning scar.

Mushrooms growing on the ground at the base of a tree or even on the tree itself may be an indication of serious problems in the roots or in the trunk. Mushrooms are the fruiting structures of fungi, and many fungi are capable of damaging trees.

Some fungi are opportunistic, producing mushrooms only after damage has been done to the the tree, such as a wound caused by a lawnmower; these don’t cause the problem, but rather signal that there is one. Other fungi attack weakened or damaged roots and are able to further break down the tree’s defenses; these are pathogenic. A tree care professional can tell the difference between the two.

Tree hollows lead to loss of structural integrity

Hollows, which can range in size from small to extensive, are signs of decay caused by fungal diseases. The larger a hollow is, the less structural integrity a tree has. Holes in trunks are evidence of internal hollows.

Openings in tree trunks, such as squirrel holes, are evidence of internal hollows and the loss of structural integrity. Many times these hollows are not large enough to make a tree a hazard, but it is best to have them looked at by an arborist to be sure. Determining the structural strength of a hollow tree is as much art as science, and experience on the part of the arborist goes a long way in making the diagnosis.

The size of a cavity in a tree can be determined four ways: by visual observation, by drilling, by removing a core of wood from the tree, or by using a graphing device. The most accurate way to measure a hollow is with a Resistograph, which uses a small drill to measure wood density. The results of the test are then indicated on a graph. This tool can detect even minor changes in the density of wood due to decay. Decay or hollows near the base of the tree are often associated with decay in the roots as well and should be evaluated promptly. Hollows associated with root problems often occur after root damage or damage to the base of the tree. Root damage may, in turn, affect the vigor of the tree.

What is an arborist?

If you really want to know how others see your profession, listen to your children explain what you do for a living. In my family’s case, “My dad wanders around people’s trees, digs holes, thinks a lot, then writes them letters” means that dad is an arboricultural consultant.

While arborist, tree surgeon, tree doctor, and arboriculturist are all terms used to describe what I do, arborist is probably the term most often used.

An arborist is a tree-care professional who may offer tree-care advice but spends more time pruning, cabling, controlling insects, and fertilizing trees than just assessing a tree’s condition. An arboricultural consultant specializes in complex tree assessment but leaves the actual work of correcting a diagnosed problem to an arborist whom he may employ or recommend.

Certification by the International Society of Arboriculture accredits an arborist’s basic knowledge and understanding of trees, as does active involvement in other professional organizations.

Tilting trees may have compromised root systems

Tilting trees have root problems. Roots act to anchor a tree in place, so when roots decay, a tree tends to sway.

Although most root failure is not evident to the eye, if a tree appears to be tilted, there’s a good chance it has a root problem. Shifting or tilting of a tree, particularly after severe winds, may indicate decay in the roots.

With tilting trees, there’s often a lifting of the soil within a few feet of the trunk. If this is a recent occurrence, it is important to have the condition evaluated. A tree that has broken contact with the soil has lost a considerable part of its stability, and there is little a homeowner can do in that case other than have the tree removed.

Dead wood may signal a problem underground

When roots die, wood dies too. Root problems under the ground are manifested in dead wood at the top of a tree. Hanging branches are dangerous. It’s best to have an arborist remove large hangers before someone gets hurt or property is damaged.

All trees have some dead branches, but many dead limbs near the top of the tree may signal a problem in the root system. An arborist should be able to determine the cause of the stress, be it a fungal disease affecting the roots or compaction damage inflicted during a construction process. Once the cause of the stress is determined, your arborist will decide if a holistic approach would be useful to lessen stress on the tree and encourage the recovery process or if the tree should be removed.

In addition to dead wood, broken and hanging branches caused by ice or snow accumulation or excessive winds are obvious hazards that should be attended to quickly, as they may fall without provocation. Broken limbs can weigh hundreds of pounds and can cause severe damage to property or to people. Instead of trying to remove these branches on your own, call a qualified arborist or tree-care professional for removal; they have the machinery and equipment needed to do the job correctly. Any branch stubs left once the broken branch has been removed should be properly pruned to the branch collar or to a larger branch, not only for aesthetic reasons but also for the health of the tree.

Prevent problems by being proactive

Damaged root systems can lead to shifting trees, dead wood in the upper portion of the tree, and mushrooms living on dead or damaged roots, so minimizing damage to tree roots is a good idea. One way to do this is to involve an arborist during the planning phase of any construction project where trees could be negatively affected. Having an arborist recommend trees to be protected and methods of protection may save having to remove a mature tree from your landscape years down the road.

Lawnmowers are the cause of many problems at the base of trees, so providing a mulch area around trees to keep mowers away is important. Improper planting can lead to root rot and damage to the bark of the lower trunk, as can the application of too much mulch. Mulch should be applied no more than 2 inches thick, and it should be kept away from the trunk bark.

Trees don’t live forever. As a tree ages, chances are it will develop a condition that will affect its health. Being able to spot the signs of the some of the most common tree problems can hasten the diagnosis of a potentially life-threatening condition. Armed with this knowledge, you will be able to speak with confidence to an arborist about what’s ailing your tree.

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Do Apple Trees Lose Their Leaves in the Winter?

Michael Blann/Digital Vision/Getty Images

Each fall and into winter, apple trees lose their leaves until the following spring. In spring, the tree produces brand new leaves that will stay on the tree through the summer and into the fall.


All apple trees are deciduous, meaning they lose their leaves every year. The leaves usually turn yellow or brown right after the fruit matures and fall completely off the tree by the start of winter. The trees go into a dormant stage during winter, meaning that no new growth occurs during the cold season.


To prevent pests from overwintering on the ground under your apple trees, rake up dead, fallen leaves and properly dispose of them. Removing rotting fruit lying under the tree keeps pests from using the fruit as a place to overwinter.


In mid to late March, apple trees start producing leaf buds as they come out of the dormant stage. The buds turn into new leaves that stay on the tree the rest of the summer and into fall.

Apples haven’t lost their leaves yet.

Yes, make the laundry room a mud room / foyer feel – a happy color on the walls will make a big difference – with three boys you are going to need to have washer dryer but maybe you can stack them a la sherry and john’s last house and do a bench next to them with a top shelf and rows of hooks? Deeper color on the wall there – here is a color scheme idea In the kitchen, definitely invite friends to help you move the frig – that is a no brainer. What if you paint three walls a pale apple green – bm sweet caroline comes to mind and on the stove wall, what if you paint that all in chalkboard paint? That will make the black and white range kind of the “star” of its wall and combine black and white in the room too but give you a place for making lists and drawing signs. That will give you instant chic and a way to express yourself. Put up quotations about adventure – change is always stressful even when it is good change and you are the captain of the adventure ship. This will cheer you up every day. The light you have is sweet but I would rather see it in a living room so you can get lots of light fixtures heads – you can always install a dimmer in the kitchen – so you have plenty of light here. Look for one of the ikea multihead aim-them-where-you-want-them fixtures for the kitchen ceiling – good prices there. Then in the entry / laundry room and living room – I found this lavender gray called pigeon gray at bm – it is a compliment to the apple green tone but it also reads very neutral and soft and sophisticated – you could use the pidgeon gray in the living room and use the deeper lavender tone called wisteria in the entry hall since you will have all the white storage doors and eventually white laundry appliances and possibly a white entry mudroom bench under white shelf with hooks. These colors are not too girly, but they are fresh, pretty with white and can be combined with navy or brown or gray so your main upholstery whatever it is should work fine with them. Yellow/gold accents and natural butcherblock wood will also be terrific with these – nodding to your fixture and covering the water heater – ikea sells butcherblock countertops for a good price – you could cut one length into two elements for some of your goals / use them in the boys room as shelves if you had leftovers so long as someone will cut them for you. Entry kitchen – three walls – light and cheerful blackboard paint for wall of range living rm This kitchen is perhaps not the best place for a table for 4 to eat. If you do a corner banquette, a round pedestal table will fit and you can paint a wood handme down straight chairw/ spray paint apple green. That will get 4 of you if boys are not too big and can sit in corner or you might run a butcherblock countertop from the fridge to the corner at window ledge height so you can line up a few bar stools and set lunch up for 3 boys there or have a place to put a buffet or have them help you prepare food / more countertop (a friend having a glass of wine when they are at their dads?) I might look carefully if you would rather put a dining table for homework and all in your living room – divide it in half – table in one half, seating in other half and put this new sweet fixture over your table. Don’t forget when you have your painting party – In your bedroom – get enough wisteria so you can have a lavender bedroom – something pretty while you are embarking on this new adventure. You have to take even better care of you now . . . “put on your own oxygen mask first / sharpen the saw” . . sending my best energy to you.

We are waiting (and waiting) for the apple leaves to fall in order to begin pruning – but it just isn’t happening. If deciduous trees don’t drop their leaves as they should, we say we have a marcescent falll. Marcescent means the trees hold their leaves into winter. It is often triggered by a sudden change from warm to cold temperatures during the fall. Trees prepare for winter by absorbing nutrients from the leaves to store over winter. At the same time they to form an abscission layer at the base of the petiole or leaf stalk to enable the leaf to break away from the tree after the nutrients have been absorbed. If warm weather changes quickly to cold, it can kill green leaves before the abscission layer has formed and the leaves are “stuck” on the tree. They will eventually become unstuck, but this will take considerably more time.

These apple trees have not dropped their leaves yet as they were not able to produce an abscission layer at the base of the petiole.You can see these leaves were green when they froze and died without dropping.

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