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Stone Fruits. Prunus is a genus of trees and shrubs, including the plums , cherries , peaches , apricots and almonds . It is traditionally placed within the rose family Rosaceae as a subfamily
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Stone Fruits • Prunus is a genus of trees and shrubs, including the plums, cherries, peaches, apricots and almonds. • It is traditionally placed within the rose family Rosaceae as a subfamily • The flowers are usually white to pink, with five petals and five sepals. The fruit of all Prunus species is a drupe with a relatively large "stone". Leaves are simple and usually lanceolate, unlobed and toothed along the margin.
Peach Diseases • Black knot • Brown rot • Perennial canker • Peach scab
Peach Diseases • DISEASE: Black knot • PATHOGEN: Apiosporina morbosa (Syn. Dibotryon morbosum) • HOSTS: members of the genus, Prunus,mainly affecting cultivated plum, prune and cherry and to a lesser extent wild plum and cherry.
Significance • Black knot is a disease that is most severe on cultivated crops in orchard and ornamental planting situations. • Black knot disease is mainly a problem in North America (Canada, the United States and Mexico) where it is indigenous. • Black knot has been reported on 24 species of Prunus but is most commonly found on wild and cultivated plums and cherries. The disease can be found throughout North America but is most commonly found in the northeast.
Black knot - Symptoms • Thick, black, irregular swellings on the twigs. The presence of these symptoms is often first noticed in the winter season when they are unobscured by leaves. However, the fungal disease-causing agent has been present for quite some time. • The pathogen's presence disrupts the normal growth of the twigs and a tumor-like growth forms at the infection site. • The first symptoms appear as small, light brown swellings of the current or previous season's growth. The the swellings turn olive-green in color with a velvety texture in 2nd season. The knots darken and appear to have a hard, brittle texture.
Disease Cycle cont. • Overwinters in the knots. The first ascospores are forcibly discharged at the time of bud break in early spring. Temperatures between 16°C and 27°C (60-80°F) are needed for discharge (continues until 2-3 wks. after bloom). • Ascospores are spread by air currents and rain splashing. Mainly the succulent green shoots and, occasionally, wounded tissues are most susceptible. • The knots develop very slowly, and by the end of the summer they appear only as small galls that might easily be overlooked. The following spring the knots enlarge very rapidly and are soft in texture with become greenish-brown color as conidia develop over their surfaces.
Cultural Management • Cultural management strategies are important in black knot management. Monitoring and pruning sources of inoculum. All shoots and branches bearing knots should be pruned out during the winter. This pruning should be completed before ascospore discharge begins in the spring. • Winter is also a good time to look for and remove sources of inoculum in nearby wild Prunus species in hedgerows and woodlots.
Management • Genetic resistanceVarieties may vary in their ability to tolerate or resist an infection. Resistance is as important as fruit characteristics, tree size, and flowering time. • Site selectionConsider the site location. Avoid planting new trees near areas with known problems such as abandoned orchards. • Biological controlInterest in biocontrol agents is increasing because of the loss of certain fungicides registrations and the fact that applicators would prefer to reduce their exposure to pesticides. • Chemical ManagementFungicides are normally only recommended for sites with valuable trees and/or severe infections levels. Fungicides work best as a protectant and are ineffective if cultural practices are not also employed.
Brown rot • PATHOGEN: Monilinia fructicola, M. laxa, and M. fructigena • HOSTS: Stone fruits (peach, nectarine, cherry, plum), almond, and occasionally some pome fruits (apple and pear)
Brown rot • The brown rot fungi cause a blight of blossoms and twigs and a soft decay of fruits of peaches, cherries, and plums. Thus, there are two distinct phases of this disease. • Blossom and twig blight • Fruit rot
Blossom and twig blight • This phase of the disease occurs in early spring when the trees are blooming, although twig blight also can occur during the fruit rot phase. • The anthers and pistil of the flower are infected initially. • Infected blossoms wilt, turn brown, and usually cling to the twig. Extension of the infection into the peduncle and twig results in a necrotic area in the woody tissue termed a “canker”. • Under moist or humid conditions, ash-gray-brown colored sporodochia bearing conidia form on the surface of diseased blossoms and twigs. A gummy substance usually exudes from the cankers, causing the blighted flowers to adhere to the twig.
Symptoms Blighted blossom, twig canker, gummy exudate, and tufts of conidia. Blossom and floral tube colonized by the fungus
Fruit rot • Fruit susceptibility to brown rot increases during the 2 to 3 week period prior to harvest. Increased susceptibility is associated with an increase in sugar content as the fruits ripen. • Tan-brown, circular spots are visible on the fruit. Under humid conditions, ash-gray-brown masses of conidia develop on these lesions. • If environmental conditions are wet and warm during fruit ripening, the entire crop can literally be destroyed “overnight”. • Diseased fruit that do not fall to the ground dehydrate and become shriveled “mummies” that cling to the branch. Sometimes the fungal infection extends from the fruit into the twig and branch.
Management of Brown Rot • Orchard location is important. Trees planted in orchards having poor air movement, and thus slow drying conditions, are more likely to have blossom blight and brown rot. • Sanitation practicesThe removal of diseased fruit mummies and blighted twigs from the trees and removal of fruit and mummies from the orchard floor can substantially reduce overwintering inoculum. • Post-harvest controlPractices used during harvest can significantly impact the amount of fruit decay following harvest. Picking and handling fruit carefully to avoid injuries, cooling fruit promptly after harvest by hydrocooling or forced air cooling, using clean containers to hold the fruit, and timely harvesting • FungicidesBlossom blight occurrence is very much dictated by the weather conditions. In areas where blossom infection occurs, 1 to 3 fungicide sprays beginning just as the blossoms open control blossom blight.
Perennial canker • Also called Valsa canker, Cytospora canker, Leucostoma canker, and peach canker, is one of the most common and debilitating diseases of peach trees. Successful long-term production of peaches is seldom possible if the disease is not controlled. • PATHOGEN: Leucostoma cincta • HOSTS: Stone fruits (peach, nectarine, cherry, plum).
Symptoms • Somewhat variable depending on which part of the tree is attacked. The most conspicuous and pronounced symptoms usually appear on major scaffold limbs and older branches. • Dark, sunken cankers expand along the limbs, producing large amounts of amber-colored or dark brown gum at their edges. As the cankers enlarge with age, infected tissues crack, dry out, and appear blackened; affected limbs become progressively more girdled, lose their vigor, and eventually die. • Gumming cankers can also be seen at other common sites of infection, including narrow-angled branch crotches, trunks injured by machinery, rodents, or insect pests, poorly healed pruning wounds, and leaf scars or winterkilled buds on young shoots.
Signs • In the early spring, conidia are exuded in a sticky mass from pycnidia embedded in the wood. Perithecia sometimes are also formed in dead tissue after a couple of years, but the ascospores are considered to be of minor importance in the disease cycle.
Management • 1. New plantings. Do not be establish next to old cankered blocks of peaches. Nursery stock should be canker free and not excessively large. Trees should be protected against peach tree borer before planting and promote wide-angle branching. • 2. Pruning and training. It is critical to train in a manner that maintains wide branch angles and an open center to the tree. Two of the most common sites of canker initiation are narrow-angled branch crotches and the weak twigs that develop within tree centers.
Management • 3. Winter hardiness. Horticultural practices should be designed to promote hardening off in the fall and prevent winter injury. • 4. Pest control. Brown rot, oriental fruit moth, peach tree borers, and rodents all cause cankers or injuries that can subsequently be invaded by the perennial canker fungi. • 5. Canker eradication. During the pruning operation, remove all cankers on small branches or limbs, making a thinning cut at least 4 inches (10 cm) beneath the edge of the cankered zone.
Peach scab • PATHOGEN: Cladosporium carpophilum • HOSTS: Stone fruits (peach, nectarine, cherry, plum). • This disease can affect twigs and leaf petioles, but the most serious damage results from fruit infection.
Symptoms • First appear on fruit when they are half formed to nearly full grown, about six to seven weeks after petal fall. • Small, round, olive-green spots about l/l6-l/8 inch in diameter develop on the fruit. • Spots are superficial and slowly enlarge. They may merge to form large, irregular blotches that turn velvety, dark olive-green or black. • Severely infected fruit may be stunted, become misshapen, or crack open. When fruits crack open, they are often invaded by other fungi that rot the fruit. • Leaves may also be infected by scab. Small (l/4 inch), round, and yellowish-green to yellowish-brown spots develop on the underside of the leaf.
Disease Cycle • The fungus overwinters in lesions on twigs. • Conidia are produced in the spring after petal-fall and are windblown or splashed about by rain. • The conditions which favor disease development are temperatures above 60°F for spore production, over 50°F (optimal 72°F to 86°F) for spore germination, and between 36°F and 95°F for disease development. Most infection occurs at the shuck-split stage of growth, although the fruit remains susceptible through harvest. • Spores from the fruit reinfect the twigs and leaves, completing the disease cycle.
Management • Fungicides - Most scab infection occurs between shuck-split and 6 weeks after shuck split. This period coincides with the peak spore production by the fungus. • Fungicide sprays during bloom and petal fall are not necessary for scab control. • Proper pruning increases air movement within the tree crown and decreases the likelihood of twig infection.
