6.2 Diseases of Stone Fruits

• PEACH AND NECTARINE – ANTHRACNOSE – BACTERIAL SPOT Xanthomonas pruni – BROWN ROT Monilinia fructicola – FUSICOCCUM CANKER– LEAF CURL– LEUCOSTOMA CANKER– PLUM POX VIRUS (PPV) – POWDERY MILDEW – PRUNUS STEM PITTING VIRUS– RHIZOPUS FRUIT ROT– SCAB – VERTICILLIUM WILT – X-DISEASE– YELLOWS Witch's broom

CHERRY

•BACTERIAL CANKER

•BLACK KNOT

•BROWN ROT

•LEAF SPOT

•POWDERY MILDEW

•PRUNUS NECROTIC RINGSPOT VIRUS

•SILVER LEAF

PLUM

•BACTERIAL SPOT Xanthomonas pruni

•BLACK KNOT

•BROWN LINE or CONSTRICTION DISEASE

•BROWN ROT

•PLUM POX VIRUS (PPV)

•PRUNE DWARF VIRUS

6.2.1 Brown Rot of stone fruits

I. Introduction: • Brown rot is one of the most important diseases of st

one fruits in the mid-Atlantic region.• Field losses of nectarines can be extensive if conditi

ons favorable for disease development occur during the blossoming or preharvest and harvest periods. Losses of peach vary with susceptibility of the cultivar.

• Typical disease symptoms include blossom and twig blight, cankers, and a fruit rot. T

• he fungus often produces conidia profusely on sporodochia on infected areas.

• The first indication of the disease in the spring is the rapid death of blossoms which, as they turn brown, often become affixed to the twig in a gummy mass, later becoming covered with a grayish to tan( 茶色 ) spore mass.

Symptoms

• Frequently, following colonization of the blossom, the fungus enters the shoot where it causes a canker on which spores are also produced.

• Shoot blight symptoms will occur if the fungus girdles the shoot. Leaves on such shoots turn tan to brown and may remain attached for several weeks.

• Cankers formed following blossom or fruit infection appear as brownish, sunken areas, that are often covered with gum.

Symptoms

• Usually, the tree is able to restrict cankers to small oval areas at the junction of the shoot and the infected blossom or fruit. Cankers and killed shoots may be colonized by other aggressive canker-causing fungi such as Leucostoma spp.

• Brown rot on ripening or mature fruit typically develops as a rapidly spreading brown necrosis. Under optimum conditions for the fungus, entire fruit may be rotted within 48 hours of infection. The infection produces a soft dry rot, although occasionally the skin remains firm.

Symptoms

• On nectarines, brown rot sometimes occurs as qui

escent infections which can be detected as small, c

ircular, necrotic lesions on immature fruits. • Immature or mature fruit with brown rot infections w

ill sporulate profusely, shrivel, and become tough g

rayish-black mummies. • Decaying fruit in cold storage or transit may appea

r black with little or no sporulation.

Symptoms

Peach brown rot (2005.06,Meixian,Shaanxi )

Plum brown rot (2005.06,Meixian,Shaanxi )

Cup-like apothecia which produce ascospores formed on fruit mummies

Twig blight

Monilinia fructicola • overwinters in orchards as mycelium on mummies,

fruit stems, blighted blossoms and twigs, and cankers.

• Sporodochia develop under cool, wet conditions during the winter and early spring.

• Occasionally, cup-like apothecia which produce ascospores can be found on fruit mummies under the tree, but they are not usually common in mid-Atlantic commercial orchards.

Disease Cycle

• In years when apothecia were common, severe blossom blight was noted in peach and apricot orchards, but severe blossom blight also can occur in the absence of apothecia.

• Generally, conidia from mummies and cankers on stone fruit trees and other sources (for example, flowering ornamental plants of plum or quince, or wild plantings of plum) are believed to be the primary inoculum sources.

• Conidia are generally formed during late spring when temperatures range from 13-25 C.

Disease Cycle

• Conidia are disseminated by wind and rain and germinate rapidly under favorable conditions.

• Optimum temperatures for blossom infection of peach range from 22-25 C. Between 0-30 C, temperatures above or below the optimum range delay germination but do not inhibit it.

• Inoculum concentration also interacts with temperature and wetness duration to influence incubation period and disease incidence and severity.

Disease Cycle

• Although blossom blight （花腐） can be severe enough to reduce the crop, early sporulation on even a few infected blossoms provides more inoculum for later fruit infections.

• The subsequent invasion of shoots also enables the pathogen to survive in the host for long periods. In some areas, infections of flowers may result in active or quiescent infections that either cause decay of green fruit or become active prior to harvest.

Disease Cycle

• Quiescent infections of peach and nectarine have not been reported in the eastern U.S., perhaps because blossom infection is less common here than in other locations

• Under optimum temperature conditions, fruit infections can occur with only 3 hours of wetness when inoculum levels are high.

• Longer wet periods during infection result in shorter incubation periods so symptoms develop more rapidly.

Disease Cycle

• Large amounts of inoculum with highly favorable environment produces a high potential for heavy losses.

• Sporodochia of M. fructicola on infected blossoms and shoots may produce viable conidia throughout the remainder of the growing season, although sporulation from infected blossoms tends to decline over the summer.

Disease Cycle

• Insects (beetles and honey bees) also can be important as vectors of the fungus during fruit ripening, carrying conidia to injury sites produced by oriental fruit moth, beetle, and other insects that injure fruit.

• Wounded fruit are infected much more readily than nonwounded fruit.

• At harvest, apparently healthy fruit usually are contaminated with spores which, under favorable conditions, may later decay during storage and marketing.

Disease Cycle

• During or after pruning (before the pink stage), monitor a minimum of 20 sample trees per block for the presence of fruit mummies and cankers.

• A total of one to ten mummies and/or cankers, and more than ten mummies and/or cankers represents levels of moderate and high risk, respectively, for blossom infection under the appropriate environmental conditions.

Monitoring

• Before bloom, monitor the orchard floor under sample trees for the presence of apothecia of the brown rot fungus.

• These are more likely to occur in the wettest areas of the orchard on mummies partially buried in soil and/or among weeds.

• Finding any apothecia represents a potential high risk for blossom infection.

• Remove cankers surgically if possible or prune out the entire diseased area. Monitoring for and removal of cankers is best done at the same time.

Monitoring

• At shuck fall, examine ten shoots on each sample tree for the presence of blossom infection.

• A total of one to ten blossom infections and greater than ten blossom infections represents moderate and high risk, respectively, for fruit infection during the preharvest and harvest periods.

Monitoring

• Fruit susceptibility to brown rot increases rapidly as fruit begin to color.

• Monitor ten fruit on each sample tree for disease incidence. Greater than two infected fruit per ten acres (eight trees sampled) represents a high risk for a brown rot outbreak at this time.

• Monitor approximately every three to five days during the preharvest period.

• Insect, bird and hail damage to ripening fruit can result in wounds which can be quickly colonized by the rot fungus.

Monitoring

• Cultural practices. • Sanitation is essential if your orchard is to be

considered a low risk for a brown rot epidemic. The practices listed below, if followed, should minimize brown rot spore populations and limit the likelihood of an epidemic when conditions are favorable for rapid disease development.

Management

Remove all remaining fruit from the tree after the final picking.

This practice limits infection of fruit peduncles（梗） and twigs thus reducing the number of brown rot cankers.

In addition, this practice prevents the situation where overwintered mummies within the tree would be immediately adjacent to susceptible blossoms in the spring.

Management

• Furthermore, removal of remaining fruit after final picking separates the practice of removing mummies from spring pruning.

• Where these practices are separated, the grower has more latitude to selectively prune (following a severe winter with high bud mortality （死亡率） , for example) without increased risk of blossom infection.

Management

• Fruit thinning practices influence the carry over of brown rot during the summer months and into the fruit ripening season.

• In general, fruit thinned before pit hardening decompose rapidly; whereas, fruit thinned after pit hardening become infected on the orchard floor and serve as spore sources for the disease.

Management

• In spring, monitor for blossom infection and prune out any cankers and infected shoots.

• In spring, just prior to and during the blossom period, examine the orchard floor for apothecia. Their presence requires that blossoms be thoroughly protected with fungicide sprays during wet periods.

• Prune to avoid excessive overcrowding of branches to increase air circulation, promote rapid drying, and increase light and spray penetration.

Management

Fertilize to maintain optimum nitrogen/ potassium balance.

Avoid dumping rotten fruit in one location, which could become the starting point for disease and insect outbreaks in the following season.

Pick and handle fruit carefully to avoid injuries; remove field heat from the fruit promptly after harvest by hydrocooling or forced air cooling; use clean containers; keep packing areas clean.

Management

Fungicides are recommended generally in a protective program for a complex of diseases, including brown rot, scab, and powdery mildew.

Fungicides are to be applied prior to fungal infection that occurs during rain periods.

Blossom infections are controlled with two or three fungicide sprays during the bloom period, with the number of sprays often varying from year to year depending upon the weather, the susceptibility of the stone fruit species, the length of the bloom period and the type of fungicide. 

Chemical management

• 发生概况：分布？ 危害？经济损失• 轻病害识别：为害部位？发病时期？症状特点？• 病原：分类地位；形态特点• 病害发生发展规律：越冬、传播、入侵• 发病及其影响因素：寄主抗病性、气候、栽培管理、• 综合防治：清除越冬菌源；加强栽培管理，提高树

体得抗病能力；选用抗病品种；化学防治；加强贮运管理

小结

6.2.2 Peach leaf curl

• Peach leaf curl is a fungus disease that, under the right conditions, can cause severe early defoliation and crop loss on nearly all peach and nectarine cultivars.

• Because of weather factors and good grower management practices in most years, however, the disease often causes little or no significant damage or loss.

• For this reason, the destructive potential of leaf curl is frequently underestimated to the point where important control measures may be forgotten or delayed.

Significance

• Infected leaves are severely deformed and often display a variety of colors ranging from light green and yellow to shades of red and purple.

• The fungus causes the meristematic cells at leaf margins to proliferate quickly and randomly, which results in the leaves becoming variously wrinkled, puckered, and curled

Symptoms

• As these infected leaves mature, naked asci containing ascospores of the pathogen are produced on the surface giving them a dusty appearance, after which the leaves turn brown, shrivel, and drop from the tree.

• Many infected fruits drop early and go unnoticed; those that remain may become crooked at the stem end like a small yellow squash, while others develop reddish to purple, wart-like deformities on the fruit surface .

Symptoms

Taphrina deformans(Berk)Tul

Pathogen

The pathogen occurs commonly almost wherever peaches are grown, and overwinters as blastospores in protected crevices in the bark and around the buds.

Primary infections are the most damaging and occur during the early spring from bud swell, when the bud scales loosen, until the first young leaves are fully emerged from the bud.

Infections on young peach leaves occur at temperatures of 50 to 70 F (10-21 C). Little infection occurs below 45 F (7 C).

Disease Cycle

The incidence of infection is greatest when rains wash the overwintered spores into the bud and cool temperatures lengthen the time that the emerging leaves are exposed to the pathogen, before they are fully expanded and can resist penetration by the fungus.

When temperatures following bud swell are warm and early leaf development is rapid, infections rarely become established, even when spring rains occur.

Disease Cycle

• Non-chemical control Collect and dispose of infected leaves before the bl

oom of spores appears. This is useful because it limits the number of spores overwintering on the plant.

Management

Erect a polythene or glass structure to cover the top and front of the tree between January and mid-May.

Trees so sheltered from rain and dew show only very mild symptoms in comparison with unprotected trees.

Ensure the sides are left open so that pollinating insects can enter. You should also carry out hand pollination.

If a tree suffers leaf loss, boost its vigour with an application of fertiliser and make sure it is kept well watered and mulched.

Management

• Chemical control Applications of fungicide must be timed carefully.

A copper fungicide (Vitax Bordeaux Mixture, Murphy Traditional Copper Fungicide) or mancozeb (Dithane) should be applied as the buds begin to swell and then repeated 14 days later.

Bud swelling normally occurs in late January or early February but may be delayed in colder districts.

Spraying must be completed before flower buds open. Another application at leaf fall may also be beneficial.

Management

• 发生概况：分布？ 危害？经济损失• 轻病害识别：为害？发病时期？症状特点？• 病原：形态特点• 病害发生发展规律：越冬、传播、入侵• 发病及其影响因素：寄主抗病性、早春的气候条件• 综合防治：加强果园管理；药剂防治

小结

6.2.3 Peach scab

• The most notable symptoms of peach scab occur on the fruit, where small, greenish, circular spots gradually enlarge and deepen in color to black as spore production begins.

• Fruit lesions are most common on the shoulders of the fruit, but can occur anywhere on the surface. Where numerous, they often coalesce and may lead to cracking of the skin as the fruit enlarges, allowing rot organisms to enter.

• The overwintering twig lesions are clearly visible during the early season as small, grayish, more or less circular, slightly sunken lesions on the previous season's shoot growth.

Symptoms

Symptoms

• Fusicladium carpophilum ， also called :Cladosporium carpophilum ，

• Sexual: (Venturia carpophilum).• Peach scab is caused by a fungus which can be extr

emely damaging to trees throughout the mid-Atlantic region because of the typically warm, wet weather during the day through the mid-season period. The disease appears to affect all cultivars of peach and is known to occur on nectarines and apricots as well.

Pathogen

• The fungus overwinters in twig lesions.   • In the spring, spores are produced on the lesion surfa

ce (primary inoculum) and are washed or splashed primarily by wind-blown rain to fruit, leaves, or new growing twigs.  

• On peaches, fruit are first susceptible starting 5-7 days after shuck split.  

Disease Cycle

• Periods of rainfall with temperatures of 65-75 F are optimal conditions for infection. 

• Although fruit remains susceptible until harvest, the 4-week period following start of shuck split is the most critical period for infection to occur.  

• The time from infection until lesions are visible may be 4-6 weeks.  Thus, infections occuring within 4 weeks of harvest do not result in visible lesions.

Disease Cycle

All varieties are susceptible to scab, with some being more severely effected than others. 

Generally, scab is most severe the first year the trees bear fruit (usually 3rd growing season). 

This results from the large numbers of twig lesions that develop during the first two growing seasons.

Low-lying planting sites should be avoided and trees should be properly pruned to allow good air circulation, thus promoting rapid drying of fruit, twigs and leaves.

Management

Fungicides such as captan and wettable sulfur provide adequate control of this disease if applications are properly timed. 

On peaches, sprays should begin about 1 week after petal-fall. 

Sprays on nectarines and apricots should begin at about petal-fall.  

Subsequent sprays should be applied at 10-14 day intervals until approximately 1 month before harvest. 

During the month before harvest, sprays applied for brown rot control will help reduce late season scab infections on the fruit, twigs and leaves.

Management

• 发生概况：危害？• 轻病害识别：为害？发病时期？症状特点？• 病原：种类• 病害发生发展规律：越冬、传播、入侵• 发病及其影响因素：寄主抗病性、早春的气候条件• 综合防治：加强果园管理；药剂防治

小结

6.2.4 Crown gall

Crown gall is worldwide in occurrence, attacking 140 plant genera in 60 different families.

Plants most commonly damaged in Texas by crown gall are pecan, peach, blackberry, grape, apple, pear, willow, pyracantha, euonymus, rose, fig, and crabapple.

Significance

Damage to infected plants results from interruption of water and nutrient movement up the stem.

Galls also interfere with normal growth and development, therefore, infected plants may be stunted and unthrifty.

With many plants, the amount of damage depends on where the gall or galls are located and how many are present.

Death can result if galls girdle the primary trunk or stem. Infected plants are more sensitive to winter injury and drought stress.

Significance

Crown gall first appears as small round overgrowths on stems and roots.

As they enlarge, the galls become woody with a rough and irregular surface.

Aerial galls can develop but most are found at or just below the soil line. Galls range from pea-size to larger than 1 foot in diameter.

Symptoms

• Agrobacterium tumefaciens

Pathogen

Crown gall bacteria infect plants through wounds, such as those arising from cultivation, transplanting, wind damage, insect injury, etc.

Wounds that have healed beyond a certain point are no longer susceptible to invasion.

After establishing itself in the wound, the bacterium transforms normal plant cells to tumor cells.

Disease Cycle

Once this has taken place, the tumor cells are able to reproduce without the bacterium being present.

Although crown gall of plants is very much like cancers in humans and other animals, there is no relationship between crown gall and animal cancers.

Crown gall has been studied extensively by scientists in their search to understand cancerous growths.

Disease Cycle

Control is primarily dependent on prevention. Pruning off galls is not effective since the bacterium is systemic and gall tissue can reproduce itself.

Chemical control with antibiotic drenches has shown promise; however, they are not practical at this time.

Inspect plants for crown gall before purchasing. Plant only crown gall-free trees and shrubs.

Remove and destroy heavily infected and weakened plants. Dig up as many roots as possible.

Management

Replace with a more resistant type plant if possible.

Avoid wounding plants while mowing, cultivating, etc.

Keep plants in an active growing state with proper fertility and watering.

Heavily infected nursery fields should be planted to a grass crop for three years before planting susceptible nursery stock.

Management

Control root feeding insects. Dip grafting and pruning tools regularly in a disin

fecting solution, such as 70 percent alcohol, 10 percent sodium hypochlorite (common bleach) or potassium permanganate solution (1 ounce in 2 gallons of water).

Management

• 发生概况：分布？ 危害？• 轻病害识别：发病时期？症状特点？• 病原：细菌病害；生理特性（ Ti- 质粒）• 病害发生发展规律：越冬越夏、入侵部位、传播、• 发病及其影响因素：温湿度；土壤理化性质；嫁接

方式• 综合防治：选用无病苗木；苗木消毒；处理土壤；

生物防治；及时防治地下害虫

小结