6.2 Diseases of Stone Fruits

1. 6.2 Diseases of Stone Fruits

2. 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

3. CHERRY • BACTERIAL CANKER • BLACK KNOT • BROWN ROT • LEAF SPOT • POWDERY MILDEW • PRUNUS NECROTIC RINGSPOT VIRUS • SILVER LEAF

4. PLUM • BACTERIAL SPOT Xanthomonas pruni • BLACK KNOT • BROWN LINE or CONSTRICTION DISEASE • BROWN ROT • PLUM POX VIRUS (PPV) • PRUNE DWARF VIRUS

5. 6.2.1 Brown Rot of stone fruits • Introduction: • Brown rot is one of the most important diseases of stone fruits in the mid-Atlantic region. • Field losses of nectarines can be extensive if conditions favorable for disease development occur during the blossoming or preharvest and harvest periods. Losses of peach vary with susceptibility of the cultivar.

6. Symptoms • 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.

7. 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.

8. 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.

9. Symptoms • On nectarines, brown rot sometimes occurs as quiescent infections which can be detected as small, circular, necrotic lesions on immature fruits. • Immature or mature fruit with brown rot infections will sporulate profusely, shrivel, and become tough grayish-black mummies. • Decaying fruit in cold storage or transit may appear black with little or no sporulation.

10. Peach brown rot (2005.06,Meixian,Shaanxi )

11. Plum brown rot (2005.06,Meixian,Shaanxi )

13. Cup-like apothecia which produce ascospores formed on fruit mummies Twig blight

14. Disease Cycle • 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.

21. Monitoring • 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.

22. 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.

23. 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.

24. 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.

25. Management • 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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.

31. Chemical 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. 

32. 小结 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

33. 6.2.2 Peach leaf curl

34. Significance • 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.

35. Symptoms • 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

36. 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 .

38. Pathogen Taphrina deformans(Berk)Tul

40. Disease Cycle • 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).

41. 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.

42. Management • Non-chemical control • Collect and dispose of infected leaves before the bloom of spores appears. This is useful because it limits the number of spores overwintering on the plant.

43. 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.

44. 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.

45. 小结 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

46. 6.2.3 Peach scab

47. Symptoms • 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.

48. Symptoms

50. Pathogen • Fusicladium carpophilum，also called :Cladosporium carpophilum， • Sexual: (Venturia carpophilum). • Peach scab is caused by a fungus which can be extremely 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.