Fabraea Leaf Spot

Overview

  • Fabraea leaf spot is a fungus (Diplocarpon mespili) that infects primarily leaves and fruit of pear and quince. Infections can result in significant leaf spotting, defoliation, and unmarketable fruit.
  • Fabraea leaf spot infection occurs from spring to summer, and like apple scab, spores are released and spread during periods of rainfall.
  • Sanitation by flail mowing leaves and brush may help reduce Fabraea leaf spot spores, however, chemical control is still usually necessary.
  • Chemical control using contact fungicides beginning in the spring and continuing into the summer in wet years are necessary to control Fabraea leaf spot.

Symptoms & Signs

Fabraea most noticeably first manifests itself as small, purple-black spots on leaves and fruit. Spots gradually enlarge into brown lesions 1/8 to ¼ inch in diameter. When the infection is severe, defoliation can occur and fruit will become deformed and not sellable and/or drop off the tree. Fabraea may also infect shoots, again appearing initially as purplish spots, becoming lesions/cankers which may persist into the next growing season. Leaf and fruit infections are most notable in the Northeast and Midwest, but in the Southeast , shoot infection can be significant. Severe infections can result in reduced flower bud formation for the following season.

Disease Cycle

Similar to apple scab, much Fabraea overwinters in leaves on the orchard floor. Farther south, overwintering is also likely to occur in shoot cankers. Spores are released from leaves with rain from mid-May to July (in the Northeast and Midwest) and result in primary infection on fruit and foliage. Shoot cankers spread Fabraea from late-April through May (in the Southeast) with more driving rains. Length of wetting for infection to occur can range from 12 hours at 50 degrees F. to as little as 8 hours from 68 to 77 degrees F. Infections take about 7 days to become visible. Once primary infection occurs, secondary infection can spread rapidly with rain and wind during the summer, particularly during wet seasons.

Chemical Control

Contact/protectant fungicides are necessary to control Fabraea leaf spot. EBDC fungicides (Manzate, Penncozeb, Dithane) and Ziram give good control. (But EBDC’s have a 77 day Pre-Harvest Interval.) Early season fungicide application(s) for pear scab (as long as EBDC’s or Ziram are included) will prevent initial infection by Fabraea. Where disease pressure is high, however, summer-long fungicide applications (once the pear scab season has passed) will be required, particularly in wet summers. Late-maturing varieties may even need fungicide sprays into the early fall to prevent Fabraea from infecting fruit.

Fungicide Resistance in the Eastern U.S.

None known because contact fungicides are necessary for control.

Non-Chemical Control

Biological Control

Other than sanitation, there is no known biological control of Fabraea leaf spot.

Cultural Control

Flail mowing/chopping leaves and brush and removing obvious cankers on the tree may help to control Fabraea leaf spot and is recommended.

Resistant Varieties

Although there are some variety differences in susceptibility to Fabraea leaf spot, generally just consider the fact all European pear varieties are susceptible such that the disease will need to be controlled. Bosc and Seckel, however, appear to be especially susceptible to Fabraea.

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Pear scab

Note Number: AG0159
W.S. Washington and Oscar Villalta, Knoxfield
Updated: January 2006

Pear scab, or black spot, is caused by the fungus Venturia pirina. It infects leaves, shoots, blossoms and fruit, and can cause serious crop loss especially in wet seasons when control measures are inadequate. The disease is found world-wide, wherever pears are grown. The fungus is closely related to apple scab, but although many similarities exist, cross-infection from one host to the other cannot occur.

Symptoms

The symptoms of pear scab are very similar to those of apple scab. Fruit infections appear as olive-green to black spots. Early infections cause large spots that distort the fruit while later infections cause smaller, more superficial spotting. As with apple scab, infections immediately before harvest may produce storage scab i.e. very small black spots that develop on fruit during storage. Leaf infections, which are less common than in apple scab, frequently occur on the underside of leaves. Twig infections, by contrast, are more common than on apple, and appear as small oval blisters on the affected shoot .

Figure 1. Winter Nelis fruit infected with pear scab, showing spotting and fruit distortion

Economic importance

Pear scab is the most serious and widespread fungal disease of pears. Losses from the disease are similar to those caused by apple scab on apples, and control depends mainly on costly spraying programs

Disease cycle

Figure 2. Pear scab lesions on underside of leaf

The disease cycle of pear scab is similar to that described for apple scab. The main difference is that under Victorian conditions shoot infections on pears are more common than on apples. These shoot infections can provide the fungus with another means of overwintering, although overwintering as ascospores in dead leaves under trees is still the most important source of primary inoculum. Shoot infections are common on Winter Nelis and Beurre Bosc, but are less common on Williams’ Bon Chretien and Packham’s Triumph.

Infection periods (the time that leaves or fruit must remain wet for infection to occur) of pear scab are similar to those described for apple scab, although few detailed studies have been carried out to confirm this.

Control measures

Principles of control are very similar to those for apple scab. Control is based on a protectant spray program, supplemented by post-infection and autumn eradicant sprays. The period from delayed green tip to petal fall is most important in preventing infection. This corresponds with the period of greatest discharge of ascospores. Apply the first spray when one-third of buds reach the stage of delayed green tip. Apply the second spray about five to seven days later, and the third spray about 10 to 14 days after the first. A fourth spray should be applied at petal fall. Growing plant tissues could become exposed during infection periods in showery weather, and a fifth spray may be needed between delayed green tip and petal fall. Alternatively a post-infection spray may be needed.

Cover sprays applied at 10-14 day intervals after petal fall may be necessary if primary infection has occurred, and if wet weather favourable to infection persists. During dry summer weather no further sprays are necessary. However, if an infection period does occur, the use of an appropriate protectant spray before the wet period, or a post-infection spray shortly after it, should prevent development of summer scab.

Similarly, infection periods immediately before harvest may make sprays necessary in order to prevent the development of scab in storage.

Note that post-infection sprays must be applied within several days of an infection period. For maximum effect they should be applied as soon as the weather clears after such a period.

When scab has been difficult to control, use sanitation practices after harvest to reduce the carryover of the fungus into the next season. Some practical sanitation practices are:

  • treating leaves on the tree immediately before leaf fall with a nitrogenous fertiliser to hasten leaf breakdown
  • mulching the leaf litter after leaf fall by sweeping and then using a mechanical shredder, slasher or flail mower to chop leaves into small pieces which then break down more rapidly
  • combining leaf mulching with a ground application of a nitrogenous fertiliser.

When planning your scab spray program, it is wise to include at least two fungicides with different modes of action. This minimises the risk of development of resistance to fungicide. Consult with chemical resellers for the fungicides and spray timing that is most appropriate in your situation.

Monitoring potential overwintering scab

Check levels of leaf infection in all blocks after harvest to estimate the potential level of scab which may overwinter and initiate primary infection in the following spring.

For effective pest and disease control, correct diagnosis is essential. Phone Crop Health Services on (03) 9032 7515 or fax (03) 9032 7604.

The previous version of this note was published in December 1999.

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

Pear Diseases & Disorders

Pear > Deficiencies & Pests > Diseases & Disorders

The two most common diseases affecting pear trees in California are fire blight and pear scab. Blossom blast and oak root fungus also occur in some pear orchards, but are limited geographically.

Fire blight, caused by the bacterium Erwinia amylovora, is most common in the Delta Region of California. The bacteria overwinter in pear trees in “holdover cankers”. In the spring infected trees have dead flower clusters and shoots, along with oozing in young tissues. Pear trees are susceptible to fire blight infection in open flowers during bloom. Fire blight susceptibility persists longer into the season in Bartlett and Starkrimson cultivars due to their extended bloom period. The disease is prevented primarily by the use of bactericide sprays that contain copper, spreptomycin or terramycin. Infected plant parts are periodically cut well below the infection zone. Cuttings should be removed and burned to prevent bacterial spores from spreading throughout the tree and orchard (UC IPM website, 2013).

Pear scab, caused by the fungus Venturia pirina (Aderh.), is most common during the early growing season in the North Coast region and occasionally in the Sacramento River district. The fungus can affect several parts of the tree, including blossoms, leaves, fruit and young twigs. Early infections cause scab-like lesions on the fruit and can alter fruit shape. Fungicides are typically used during high humidity conditions to prevent the growth and spread of pear scab (UC IPM website, 2013; Gubler et al., 2007).

For detailed information, including the Year-round IPM Program for pear, and University of California’s official guidelines for pest monitoring techniques, pesticides, and nonpesticide alternatives for managing pests, see the UC Statewide IPM Program: How to Manage Pests: Pears

Pear Photo Gallery

These photos are accessed from the UC ANR Repository, are available courtesy of University of California research and extension personnel and programs, including the UC Statewide IPM Project. Photo information, including the photographer, is displayed when the larger image is viewed.

Deficiencies | Insects, Mites & Nematode Pests | Diseases & Disorders | Vertebrates

Bacterial ooze due to fire blight. Photo by JKClark, UC Statewide IPM Project © UC Regents Flower clusters infected with fire blight bacteria. Photo by JKClark, UC Statewide IPM Project © UC Regents Pear scab lesions. Photo by JKClark, UC Statewide IPM Project © UC Regents Papery bark and dead blossom buds on pear caused by bacterial blast. Photo by JK Clark, UC Statewide IPM Project © UC Regents Pear decline. Photo by JK Clark © UC Regents

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Pyrus calleryana ‘Aristocrat’: ‘Aristocrat’ Callery Pear1

Edward F. Gilman and Dennis G. Watson2

Introduction

`Aristocrat’ Callery Pear quickly grows 35 to 45 feet high and 30 to 35 feet wide, with widely-spaced, upright-spreading, thornless branches. The more dominant trunk and open form of `Aristocrat’ Callery Pear helps to make it less susceptible to wind and ice damage than `Bradford’. Branch angles are wider and lateral branches grow at a slower rate than on `Bradford’, therefore the branches are better attached to the trunk. In spring before the new leaves unfold, the tree puts on a brilliant display of pure white flowers which, unfortunately, do not have a pleasant fragrance. The leaves emerge as red/purple, then become 1.5 to 3 inches long, glossy green with wavy margins and a red blush. They turn red again in fall before dropping. The small, pea-sized, red/brown fruits which form are quite attractive to birds and other wildlife, and mummify on the tree persisting for several months to a year. Planting two or more cultivars of Callery Pear together could increase fruit set.

Figure 1.

Young Pyrus calleryana ‘Aristocrat’: ‘Aristocrat’ Callery Pear

General Information

Scientific name: Pyrus calleryana Pronunciation: PIE-rus kal-ler-ee-AY-nuh Common name(s): ‘Aristocrat’ Callery Pear Family: Rosaceae USDA hardiness zones: 5A through 9A (Fig. 2) Origin: not native to North America Invasive potential: little invasive potential Uses: shade; street without sidewalk; container or planter; screen; specimen; parking lot island < 100 sq ft; parking lot island 100-200 sq ft; parking lot island > 200 sq ft; sidewalk cutout (tree pit); tree lawn 3-4 feet wide; tree lawn 4-6 feet wide; tree lawn > 6 ft wide; urban tolerant; highway median Availability: not native to North America Figure 2.

Range

Description

Height: 35 to 45 feet Spread: 25 to 35 feet Crown uniformity: irregular Crown shape: pyramidal Crown density: moderate Growth rate: fast Texture: medium

Foliage

Leaf arrangement: alternate (Fig. 3) Leaf type: simple Leaf margin: undulate, sinuate/undulate, crenate Leaf shape: ovate Leaf venation: pinnate, reticulate Leaf type and persistence: deciduous Leaf blade length: less than 2 inches, 2 to 4 inches Leaf color: green Fall color: red Fall characteristic: showy Figure 3.

Foliage

Flower

Flower color: white/cream/gray Flower characteristics: very showy

Fruit

Fruit shape: round Fruit length: less than .5 inch Fruit covering: dry or hard Fruit color: brown, tan Fruit characteristics: attracts birds; not showy; fruit/leaves not a litter problem

Trunk and Branches

Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns Pruning requirement: needed for strong structure Breakage: resistant Current year twig color: brown Current year twig thickness: thick Wood specific gravity: unknown

Culture

Light requirement: full sun Soil tolerances: clay; sand; loam; alkaline; acidic; occasionally wet; well-drained Drought tolerance: high Aerosol salt tolerance: moderate

Other

Roots: not a problem Winter interest: no Outstanding tree: no Ozone sensitivity: tolerant Verticillium wilt susceptibility: resistant Pest resistance: sensitive to pests/diseases

Use and Management

Planted commonly as a street tree or in parking lot islands, it is also quite suited for downtown tree pits due to its urban tolerance. Like `Bradford’ pear, it is able to tolerate small soil spaces. It looks great located along a street on 20 to 25-foot-centers and creates a `corridor’ for traffic flow.

The major problem with the `Bradford’ pears has been too many upright branches growing too closely together on the trunk which leads to branch breakage and splitting. `Aristocrat’ appears to be mostly free of this problem, but has been shown to be more susceptible to fire blight than `Bradford’, particularly in evaluations conducted in the south. Pruning the trees early in their life to space lateral branches along a central trunk should be all that is needed to ensure a strong, well-structured tree. Only buy trees with well-spaced branches.

Callery Pear trees are shallow-rooted and will tolerate most soil types including alkaline and clay, are pollution-resistant and tolerate drought and wet soil well. `Aristocrat’ is a very adaptable tree suited for downtown and other restricted soil spaces.

Pests

Aphids cause distorted growth and deposits of honeydew.

Scales occasionally affect pears.

Several borers may attack pear. Keep trees healthy to prevent attacks.

Diseases

`Aristocrat’ pear is very susceptible to fire blight. This disease can devastate a planting. Tips of infected branches appear scorched and burnt. The leaves droop, turn brown, but remain hanging on the tree. The bacteria wash down the branch and form cankers. Bark inside the canker often shreds and peels. When a canker girdles a branch, that branch dies. Prune out infected branches well below the infected area.

Footnotes

This document is ENH-694, one of a series of the Environmental Horticulture, UF/IFAS Extension. Original publication date November 1993. Revised December 2006. Reviewed February 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

Edward F. Gilman, professor, Environmental Horticulture Department; Dennis G. Watson, former associate professor, Agricultural Engineering Department, UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office.
U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.

The European pear, Pyrus communis, is a perennial deciduous tree in the family Rosaceae, grown for its fruit. The tree is a short deciduous tree with a tall and narrow crown and alternately arranged, simple leaves. The leaves are elliptical with finely serrated margins and defined tips and can reach 2–12 cm (0.7–4.7 in) in length. The tree produces white flowers which are 2.5 cm (1 in) in diameter and a fleshy green pyriform fruit. Pear trees can reach 9 m (30ft) and will produce fruit for about 20 years . The European pear may be referred to by name of its cultivars which include the Bartlett, d’Anjou, Kaiser Alexander and Comice pears. The European pear occurs only as cultivated trees and does not grow wild in nature. It is descendant of wild European and Asian pear trees.
Pear fruits
Pear blossoms
Pear trees in blossom
Pear buds
Pear blossoms
Young pears ‹ ×

Uses

The pear fruit is eaten fresh or can be cooked in a range of sweet dishes. The fruit may also be pressed for juice. The leaves of the tree can be used to produce dyes and the wood can be used in carpentry and is very durable.

Propagation

Basic requirements Pears grow very well in areas that have a late frost and a cool, dry summer and will grow at temperatures between -26 and 45°C (-14.8–133°F). Pear trees have a chilling requirement of between 1000 and 1500 hours between 0 and 7°C (32–44.6°F) to break dormancy depending on the particular variety being grown. Generally, trees must cross pollinate with a different variety in order to successfully set fruit. Pear trees require a deep, well draining soil with a pH of 6–7 and will grow in sandy, medium or heavy soil. Pear trees are the most tolerant of all fruit trees of wet soils but roots should not be waterlogged for more than a few days at a time. Propagation Pear trees are propagated by budding onto suitable rootstocks. Rootstocks are usually also pear but quince is also used in warmer growing regions. Pear trees are usually acquired from the nursery as bare-rooted seedlings. They are planted by digging a whole which is large enough to accommodate the outstretched roots of the tree without bending. The graft union should be at least 10–15 cm (4–6 in) above the soil line.Trees should be spaced 4.8 m (16 ft) apart, leaving 7.5 m (25 ft) between rows. The best time for planting is in early Spring or Fall while the trees are still dormant. Young trees are susceptible to wind damage and should be provided with a wind break. Training and pruning Pear trees are usually trained in the same way is apple trees and often they follow a central leader system. The central leader system encourages earlier fruiting and is recommended for European pear varieties. The system consists of one main trunk which gives rise to 12 t0 16 primary scaffold branches. The tree becomes conical in shape, being wider at the bottom and narrower at the top. The shape is achieved through selective pruning of the branches in the years after planting. At time of planting, the tree is headed back by cutting the leader at a height of approximately 90 cm (36 in) from the ground. All branched lower than 76 cm (30 in) from the ground should also be removed at this time alongside and damaged or broken branches and those with narrow crotch angles. In the first winter following planting, the longest, most vigorous, vertical shoot should be selected as the leader and other vigorous shoots with narrow crotch angles removed. Branches with wide crotch angles (>40°) can be left on the tree and corrected with spacers (lengths of wire secured around the branch to correct the growth angle). Each year, while the tree is dormant, the central leader should be headed back by about 1/3 of its length and any vigorous, competing branches with narrow crotch angles removed. After the tree has fruited for two years, some branches will need removed to open up the canopy. General care and maintenance The amount of fertilizer that should be supplied to pear trees depends on the soil type and composition and should be checked with the aid of a soil test. Less nitrogen is supplied to pear trees than to apple as it promotes vigorous growth, increasing susceptibility to fire blight. in the first year of growth, phosphorous and potassium may be required but in subsequent years, only nitrogen is generally added to the soil. The area around the base of the pear tree should be kept free from weeds which compete for water and nutrients. In commercial plantations, appropriate herbicides may be used for weed control. In the home garden, weeds can be removed by hand. Pear trees may require fruit to be thinned to prevent over production which can lead to reduced yields in subsequent years or cause damage to the tree through excess weight. fruits should be thinned early in the season to a final density of approximately 1 fruit every 15 cm (6 in). Harvesting Pear fruits are usually harvested when mature, but are are ripened off of the tree. Pear allowed to ripen on the tree tend to ripen from the core outwards, resulting in fruit with mushy centers. It can be difficult to determine the correct time to harvest pears and so a variety of factors should be taken into consideration prior to picking. One of the most common indicators of maturity is the firmness of the fruit. Commercial plantations use devices called penetrometers to determine fruit firmness. Pears should be harvested when the reading is between 16 and 19 pounds.
CABI Crop Protection Compendium. (2010). Pyrus communis (European pear) datasheet. Available at: http://www.cabi.org/cpc/datasheet/46190. . Paid subscription required. Lord, W. G. & Ouellette, A. (2013). Growing pears in the home garden. University of New Hampshire Cooperative Extension. Available at: https://extension.unh.edu/resources/files/Resource000587_Rep609.pdf. . Free to access. Marina, R. Growing pears in Virginia. Virginia Cooperative Extension. Available at: https://pubs.ext.vt.edu/422/422-017/422-017_pdf.pdf. . Free to access. Sutton, T. B., Aldwinckle, H. S., Agnello, A. M. & Walgenbach, J. F. (eds.) (2014). Compendium of Apple and Pear Diseases and Pests. 2nd Edition. American Phytopathological Society. APS Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/44303.aspx Available for purchase from APS Press.

Pear Varieties: What Are Some Common Types Of Pear Trees

Pears are a terrific tree to grow in the garden or landscape. Less prone to pests than apples, they provide beautiful spring flowers and bountiful fruit for years. But pear is a broad term – what are the different varieties of pear and what are their differences? Which ones taste the best, and which will grow in your area? Keep reading to learn about the different types of pear trees.

Different Pear Varieties

So what are some common types of pear trees? There are three main varieties of pear tree: European, Asian, and hybrid.

European pear varieties are the most classic examples of the pears you buy in the store. They have a sweet, juicy quality and include:

  • Bartlett
  • D’Anjou
  • Bosc

They’re picked hard on the vine then ripened in storage. They are also, unfortunately, very vulnerable to fire blight, a bacterial disease that’s especially prevalent in the southeastern United States.

Other parts of the world have more success growing European pears, but they’re still always somewhat vulnerable. If you’re worried about fire blight, you should consider Asian pear and other hybrid pear tree types.

Asian and hybrid pear varieties are much hardier against fire blight. The texture is somewhat different, though. An Asian pear is shaped like an apple and has a crisper texture than a European pear. It’s even sometimes called an apple pear. Unlike with European pears, the fruit ripens on the tree and can be eaten immediately. Some common varieties are:

  • Twentieth Century
  • Olympic
  • New Century

Hybrids, also called Oriental hybrids, are hard, gritty fruits that ripen after they’re picked, like European pears. They’re usually used more for cooking and preserving than eating fresh. Some popular hybrids are:

  • Orient
  • Kieffer
  • Comice
  • Seckel

Flowering Pear Tree Varieties

In addition to these fruiting pear varieties, there are also flowering pear tree varieties. Unlike their fruiting cousins, these trees are grown for their attractive ornamental qualities rather than the fruit.

The most common ornamental pear tree variety grown in landscapes is the Bradford pear.

How to Manage Pests

Pests in Gardens and Landscapes

Apple and Pear Scab

Revised 1/11

In this Guideline:

  • Identification
  • Life cycle
  • Damage
  • Management
  • About Pest Notes
  • Publication
  • Glossary

Leaf infected with apple scab.

Pear scab appears as velvety, dark olive to black spots on leaves and leaf stems.

Apple scab lesions on the undersurface of a leaf.

Apple scab infecting flower stems.

Fruit scabs caused by apple scab infection.

Fruit damaged by pear scab.

Apple and pear scab are two different diseases that look very similar and are controlled in similar manners in home gardens and landscapes. Both cause spotting and scabbing of fruit, especially during wet springs but different fungi cause them.

The fungus Venturia inaequalis causes apple scab. Apple scab is a serious disease of apples in California, resulting in loss due to severe surface blemishing of fruit. It is most severe in coastal and foothill areas where spring and early summer weather is cool and moist. However, it can be a problem wherever apples grow when conditions are favorable for pathogen development. Apple scab also is a problem on ornamental crabapple.

Pear scab, which the fungus V. pirina causes, results in similar blemishes on pear fruit.The disease is most prevalent in the North Coast production area. However, V. pirina won’t affect apples nor can the apple scab fungus cause problems on pears. Both have quite limited host ranges.

IDENTIFICATION

Scab first appears as yellow, or chlorotic, spots on leaves. As the disease progresses, dark, olive-colored spots form on leaves, fruit, and—in severe cases—stems. Spots on the undersurface of leaves sometimes look velvety due to fungal growth. Affected leaves might twist or pucker; in minor cases, this will affect only a few, irregularly scattered leaves, but if the disease is severe, all foliage could show symptoms. Severely affected leaves often turn yellow and drop.

When scab affects flower stems, it can cause flowers to drop. Scabby spots can appear on fruit later in the season. These begin as velvety or sooty, gray-black (and sometimes greasy looking) lesions that sometimes have a red halo. The lesions later become sunken and tan and can have areas of olive-colored spores around their margins. Severely infected fruit becomes distorted and usually drops from the tree. Fruit also can crack, which allows entry of secondary organisms.

LIFE CYCLE

Both apple and pear scab pathogens overwinter primarily in infected leaves on the ground. Rainfall or sprinkler irrigation is necessary to release the spores. In spring, air currents or splashing water carry these primary spores (ascospores) from the infected leaves to flowers, leaves, or fruit where they germinate and cause primary infections. Pear scab also can overwinter in lesions on pear twigs in high rainfall areas.

Secondary spores, or conidia, are produced on infected leaf or fruit surfaces 8 to 17 days following primary infection. In the case of pears, this process also occurs on twig lesions. The disease continues to spread until conditions become dry or the plant tissue becomes more resistant to infection.

Infection occurs most rapidly between 55° and 75°F, and leaves or fruit must remain wet continuously for a minimum of 9 hours for initial infection to occur at these temperatures. If spring weather is dry from the green tip stage of bloom (when flowers are still green and petals aren’t showing yet) through fruit set, scab usually won’t be a problem.

DAMAGE

Scab can destroy an apple or pear crop. Young, infected flowers or fruit can drop, or the fruit can become malformed, cracked, and unsightly, rendering it unusable. Defoliation follows severe, early leaf infection. Late-season infections generally can be tolerated in backyard trees, because peeling the fruit will remove the pinpoint-sized scab lesions.

MANAGEMENT

Several techniques are available for controlling scab. Advantages of one method over another depend on the number of trees you are managing and whether conditions are ideal for disease development.

For a single, backyard tree, removing—then composting or destroying—its dropped leaves in autumn or winter can limit the disease to tolerable levels. In plantings of several trees, additional steps might be necessary to effectively control this disease, especially in cool, moist coastal areas. These include applying zinc and fertilizer-grade urea (or some other nitrogen source) to leaves in autumn to hasten leaf fall and adding lime to leaf piles beneath the tree. In pears, apply urea by itself, because zinc can be phytotoxic.

If you are using sprinklers that wet any of the tree’s foliage, irrigate between sunrise and noon to allow adequate drying time, or reduce the angle of the sprinkler.

Disease-resistant Cultivars

Table 1 lists the relative susceptibility of different apple varieties to apple scab. Major breeding efforts for disease resistance are ongoing in New York, where Enterprise, Liberty, Prima, Priscilla, and many newer varieties appear to be resistant to scab. Scab-resistant crabapples also are available.

European pear cultivars with negligible scab risk include Arganche, Barnett Perry, Batjarka, Brandy, Erabasma, Harrow Delight, Muscat, Orcas, and Passe Crassane. Because Asian pears (Pyrus pyrifolia) are a different species, they are less susceptible to scab than European pears (P. communis).

TABLE 1. Susceptibility of Apple Varieties to Apple Scab.

Susceptible Highly resistant
Bellflower Easy-Gro
Blushing Gold Enterprise
Fuji Florina
Gala Freedom
Golden Delicious Goldrush
Granny Smith Jon Grimes
Gravenstein Jonafree
Grimes Liberty
Ida Red Mac-free
Jonathan Prima
Monroe Priscilla
Mutsu Pristine
Paula Red Redfree
Red Delicious Sir Prize
Rome Beauty Spigold
Stayman Winesap Williams Pride
Winesap
Yellow Newtown
York Imperial

Fungicide sprays are necessary only if the weather is rainy and leaves are likely to remain wet for 9 or more hours. Fungicide applications require careful attention to timing, as preventing early infection is the most important step toward successfully controlling later fruit infections. It is difficult to prevent secondary fruit infections once primary infections occur.

Unlike peach leaf curl, treatments for scab made when trees are completely dormant aren’t effective and aren’t recommended. If treatments are needed, the generally recommended time is between when buds begin to break and a month after petal fall.

If rain threatens, it is important to apply a fungicide as soon as you see the tips of the leaves emerge. A second application might be needed 10 to 14 days later if it is still rainy, once you can see blossom clusters but before they have opened. If rainy weather continues, apply a third spray toward the end of the bloom period, when most of the petals have fallen.

The surfaces of the fruit and foliage become more resistant to infection as the season progresses, although extended wet, foggy weather can lead to an infection period due to secondary spores that develop on leaves and fruit. If no scab infections are evident 1 month after petal fall, secondary infections probably won’t be a problem, and fungicide sprays can stop. However, continue to watch for pinpoint scab symptoms, especially if late rains occur.

Several fungicides are available for controlling apple and pear scab. These include fixed copper, Bordeaux mixtures, copper soaps (copper octanoate), sulfur, mineral or neem oils, and myclobutanil. All these products except myclobutanil are considered organically acceptable.

Generally copper or Bordeaux sprays should be used only from green tip to full bloom. Later applications increase the risk of fruit russetting, a chemical burning of the fruit skin, although in some years this occurs even if you’ve used these materials only before full bloom. Fixed copper products include Lilly Miller Kop-R-Spray concentrate and Monterey Liqui-Cop. Bordeaux mixture is a combination of copper sulfate and hydrated lime that must be mixed just before application. For more information about how to prepare this fungicide, see Pest Notes: Bordeaux Mixture.

You can apply wettable sulfur through bloom and early fruit set. When using sulfur-containing compounds such as wettable sulfur, never apply them within 3 weeks of an oil application or when temperatures are near or higher than 90°F. Bordeaux has a narrower application time frame than other sulfur-containing products, because it contains copper, and shouldn’t be applied after full bloom.

Myclobutanil (Spectracide Immunox Multipurpose Fungicide Spray Concentrate) is a synthetic fungicide that is effective against apple scab. You can apply it any time from green tip until after petal fall.

WARNING ON THE USE OF PESTICIDES

Broome, J. C., and C. A. Ingels. Dec. 2008. Pest Notes: Peach Leaf Curl. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7426.

Giraud, D. D. 1989. Apple Scab Control for the Home Orchardist. Univ. Calif. Coop. Exten. Publ., Humboldt Co.

Ohlendorf, B. L. 1999. Integrated Pest Management for Apples and Pears, 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3340.

Postman, J. D., R. A. Spotts, and J. Calabro. 2005. Scab resistance in Pyrus germplasm. Acta Hort. 671:601–608.

Swezey, S., P. Vossen, and J. Caprile. 2000. Organic Apple Production Guide. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3403.

UC Statewide IPM Program. Nov. 2000. Pest Notes: Bordeaux Mixture. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7481.

PUBLICATION INFORMATION

Pest Notes: Apple and Pear Scab (formerly titled Apple Scab)
UC ANR Publication 7413

Produced by UC Statewide IPM Program, University of California, Davis, CA 95616

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Spraying Fruit Trees

Dormant sprays can help reduce pests & disease in home orchards.

Prevention is the first step in controlling diseases and insect pests in home orchards. Many problems can be avoided by choosing resistant fruit tree varieties and providing them with proper care. That care includes removing all dropped fruit and leaves that might be harboring pests.

But even the most vigilant gardeners may need to spray their trees during the dormant season to reduce over-wintering pest and disease organisms.

Spraying fruit trees during the cool seasons, November through March, can help control pests that take up residence in the cracks and crevices, according to Ross Penhallegon, horticulturist with the Oregon State University Extension Service. Such dormant spraying is more effective than waiting until the weather warms and pests become active.

Below are some least toxic sprays and treatments for fruit trees. These products are widely available at garden centers. Always follow label directions.

Dormant Oil: Apply when trees are dormant, November through March, after all the leaves have fallen. Mix with water as directed and spray to all surfaces of the trunk, branches and twigs. Apply when the temperature is expected to rise during the day; temperatures below 35 degrees can damage the bark. Dormant oil controls aphids, scale, spider mites, and many other insects by desiccating or smothering eggs and larvae.

Lime-Sulfur: Spray to control fungal and bacterial diseases such as peach leaf curl, fire blight, scab and anthracnose. Do NOT apply sulfur sprays to apricots.

Fixed Copper: Spray on apples, pears, cherries, peaches, and plums to control canker. Allow two weeks between applications of copper and any sprays containing sulfur. Add a spreader-sticker product to help copper adhere to the tree surface.

Latex paint: Coat the trunks of young trees with white latex paint mixed half-and-half with water. The paint reflects strong sunlight that, once the leaves fall, can cause cracking, a favorite place for pests to overwinter and can cause substantial winter damage.

Here are some tips for specific fruit trees:

Apples: Spray copper before fall rains; dormant oil once or twice from January through March; lime-sulfur in January or February (just before buds open) and wettable sulfur just after petal fall.

Apricots: Spray copper before the fall rains and dormant oil in February.

Cherries: Use wettable sulfur or lime-sulfur applied weekly during blooming for brown rot. Information on synthetic sprays to control cherry fruit fly is available at your local county office of the OSU Extension Service.

Pears: Spray copper before the fall rains; spray lime-sulfur two to three times beginning in fall, again during winter, and finally in March just before buds open; spray dormant oil in early spring before buds open and wettable sulfur just after petal fall.

Peaches: Spray copper or a good dormant fungicide three to four times between December and bud break. Spray copper or lime-sulfur before fall rains and in spring just before bud break; apply sulfur weekly during blooming and again after all petals have fallen.

Author: Peg Herring
Source: Ross Penhallegon / University of Oregon Extension Service

In the Garden

Q: Is there an environmentally friendly way to prevent rust on my pear trees?

A: Pear rust has become a major problem in our region the past few years. The fungus disease can be easily identified by bright yellow to orange spots that form on leaves, twigs, branches and fruit.

There are two rusts affecting pears in our area. The symptoms of Pacific Coast pear rust usually show up soon after flowering is over. Yellowish spots appear on developing fruit, which become malformed and often drop from the tree. In severe cases, the yellow spots also form on leaves and twigs. In addition to pears, this disease also affects hawthorn, apple, crabapple, serviceberry, quince and mountain ash.

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Trellis rust is identifiable by bright yellow or orange spots that are evident on both surfaces of the leaves. The spots also can show up on twigs, branches and fruit. Often, heavily infected fruit mummify in place rather than falling from the tree.

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Over three feverish days, Bob Lilly and his team of Arboretum Foundation volunteers struggle to transform their plot inside the Washington State Convention Center into an award-winning garden. Read more. (Lauren Frohne / The Seattle Times)

Both of these diseases require an alternate host within about a 1,000-foot radius for the disease to occur. The alternate host of Pacific Coast pear rust is a conifer species, incense cedar (Calocedrus decurrens). The alternate host for trellis rust is juniper.

There are no chemical sprays registered for homeowner use that will control pear rust, and the only truly effective control is removal of the alternate host. Obviously that isn’t likely to happen if you live in a heavily populated urban setting. Hence, the only option left is to remove affected leaves and twigs to try to limit the severity of the disease. Then keep your fingers crossed that someone will come up with an environmentally friendly spray that will prevent the disease in the near future.

Q: Is it true that citrus peels will keep cats out of my garden?

A: There’s nothing worse than when a cat decides to use your garden for a litter box, especially if it’s your vegetable garden. From many comments I’ve received, it appears the often-recommended use of citrus peels is rarely, if ever, successful.

The majority of commercial deterrents haven’t proved to be very reliable, either. If you decide to try one, check the label. Not all of them are suitable for use in a veggie garden. Moth balls, also often recommended, should never be used because they contain toxic substances inappropriate for use around edible plants, and are attractive to children who think they are candy.

Fortunately there are two methods that really do work. The first is to pound 8-inch-long sticks or bamboo stakes into the soil at 4-inch intervals. You need to get them deep enough into the ground so the cat can’t easily knock them down. If there isn’t room to scratch, the cat will look for another area with open unencumbered soil. The obvious disadvantage to this method is that it takes forever to pound in all those stakes, and they’re a pain to work around.

The other method is more expensive, but much less intrusive. Battery operated devices exist that attach to your hose and contain heat and motion detectors. When the device detects an intruder, it blasts it with a powerful spray of water, reloads and gets ready to fire again. I’ve used one successfully to prevent raccoons from getting into and tearing up my fountains. The key is to place them where they have a sight line into most areas of the garden, yet don’t look directly into the sun. If you have a large garden, more than one might be needed. By the way, if your significant other is a gardener, don’t forget to tell him or her these devices are out there. If you hear a “yeeeeow,” instead of a “meeeeow,” your spouse probably just got a big surprise!

Pear Trellis Rust

The fungus causes conspicuous yellow to orange leaf spots and can also infect small twigs and fruit, causing fruit to mummify. Fruiting bodies called “aecia” form on lower leaf surfaces. They are similar to aecia of the more familiar cedar-apple rust fungus, but the aecia of pear trellis rust have conspicuous acorn-like swellings at the base and can produce spores for two years in a row. Like many other rust fungi, pear trellis rust requires two alternate hosts to complete its life cycle. Many species of juniper are alternate hosts for pear trellis rust. Spindle-shaped galls form on branches of the juniper host, followed by development of orange, gelatinous spore masses the second spring after infection. Galls can produce spores for several years in a row. The spores are wind-blown to pear in the spring where they initiate new infections.

Pruning galls from junipers in early spring before production of the orange, gelatinous spore masses helps to prevent new infections. When planting new junipers near pear trees, choose resistant species, such as Juniperus horizontalis, J. communis, and J. squamata. Immunox fungicide (active ingredient = myclobutanil) is registered for preventative control of rusts on ornamental pears, but it may not be used on fruit-producing pears.

(Answer)

Pear Trellis Rust is a relatively new fungal disease in Ontario, first recorded in 2007. Unfortunately, can be difficult to treat in urban settings, simply due to population density. It’s caused by the fungus Gymnosporangium sabinae that, as you know, hosts in winter on junipers (although some junipers are resistant). In spring, the orange, gelatinous fruiting bodies (telia) emerge – usually after a rain – and mature to spread wind-borne spores over many kilometers. Some sources suggest the spores can carry for as much as 2-6 km. The spores alight on pear leaves, including those of ornamental pears, and then complete their spring and summer lifecycle – in their turn infecting or reinfecting junipers. And the cycle begins anew.

Advice is often to remove either the pear or the juniper, if they are spaced closer than 150 m (450 feet). In fact, the recommendation is to keep the two alternate hosts at least 1 km apart. You can see why pruning your neighbour’s juniper might not be the solution if other neighbours within a 1-km radius also have infected junipers. However, if you do see galls or telial fruiting bodies on the tree, it would be best practice to prune them out. Depending on the weather, this is best done in March.

The Ontario Ministry of Agriculture and Rural Affairs (OMAFRA) has an excellent fact sheet on Pear Trellis Rust.

On the pear trees, it’s the leaves rather than the wood that play a role in the lifecycle of this fungus, so there’s no need to disfigure your trees by pruning. However, do try to gather up and dispose of any fallen pear foliage and fruit; do not add them to your compost. One suggestion is to pluck them off the tree before they fall, but this is impractical for widespread infection.

While there are no fungicides specifically approved for Pear Trellis Rust, OMAFRA suggests that other fungicides might help minimize the impact on your trees. Look for those used to treat other Gymnosporangium rusts, such as cedar-apple rust.

If ever in doubt about a tree problem, it’s always wise to seek out a certified arborist for an on-site consultation. You can find an arborist near you through the International Society of Arboriculture (ISA) website here.

The very best of luck with your pear trees.

Yellow Pear Leaves: What To Do When A Pear Tree Has Yellow Leaves

Pear trees are a great investment. With their stunning blossoms, delicious fruit, and brilliant fall foliage, they’re hard to beat. So when you notice your pear tree leaves turning yellow, panic sets in. What could be causing this? The truth is, a lot of things. Keep reading to learn more about what brings about yellowing leaves on flowering pear and how to treat it.

Why A Pear Tree Has Yellow Leaves

The most obvious cause of pear tree leaves turning yellow is, of course, autumn. If your days are getting shorter and nights are getting colder, that may be all there is to it. There are plenty of more troublesome causes, though.

Your tree could be suffering from pear scab, a bacterial disease that manifests itself in the

spring with yellow spots that darken to brown or olive green. The disease spreads through splashed moisture, so remove and destroy all affected foliage and water your tree in the morning when excess water will dry the fastest.

Pear Psyllas, a small flying insect, may also be the culprit. These bugs lay their eggs on pear leaves and the babies, when hatched, inject the leaves with yellowing toxins. Spray petroleum oil on the leaves in late winter to deter egg laying.

Your yellow pear leaves might also be caused by the stress of over or under watering. Pear trees like infrequent, but deep, waterings down to 24 inches. Dig a foot or two down in an area near your tree to get a sense of just how deep the moisture goes after a rainfall or heavy watering.

Yellow Pear Leaves Due to Nutrient Deficiency

Yellow pear leaves can also be a sign of a number of nutrient deficiencies.

  • If your new leaves are yellow to white with green veins, your tree might have an iron deficiency.
  • Nitrogen deficiency brings on small new leaves and dropped yellow mature leaves.
  • Manganese deficiency causes new yellow leaves with green bands and dead spots.
  • Zinc deficiency sees long, narrow stems with clusters of small, narrow, yellow leaves on the ends.
  • Potassium deficiency causes yellowing between the veins on mature leaves that can eventually wither and die.

All of these deficiencies can be treated by the spread of fertilizers fortified in your missing nutrient.

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