Bacterial Canker (bacterium - Pseudomonas syringae): Elongated cankers develop at the base of buds and randomly on the trunk and scaffold limbs and are most prominent during late summer and fall. Damaged areas are slightly sunken and somewhat darker in color than the surrounding bark. At both the upper and lower margins of the canker, narrow brown streaks extend into the normal tissue. As the trees break dormancy in the spring, gum is formed by the surrounding tissue and may exert enough pressure to break through the bark and flow. The area beneath the canker has a soured odor.
Cankers start developing in the fall at the base of a bud or at a wound and increase in size during the winter becoming visible in early spring. If infection takes place early in the fall, the area is walled off by callous tissue and cankers are not produced.
The bacterium is a rather weak pathogen and causes serious damage only when a tree is in a dormant condition or weakened due to unfavorable growing conditions. The bacterium is spread by wind, rain, and nearby infected buds, leaf scars, and other wounded areas. It is felt that much of the movement of this disease is through diseased nursery stock. Selection of clean nursery stock helps reduce inoculum from being introduced into an area.
Avoid using high nitrogen fertilizer rates in the late spring or early summer. Trees should enter dormancy normally rather than encouraging late fall growth which is more easily infected at abscission time. Prune when the trees are fully dormant (January and February). Trees pruned early in the year prior to dormancy can be infected with the bacterium carried on pruning shears. Trees showing signs of bacterial canker should be left and pruned after healthy trees have been completed. Early pruning encourages late fall growth of trees which are more susceptible to the bacterium. Infection most often occurs in the fall. Trees should be sprayed with a copper-containing fungicide at leaf drop.
Peach Leaf Curl (fungus - Taphrina deformans): The peach leaf curl fungus is found in all areas. It affects leaves, flowers, tender shoots and fruits. Infected leaves are characterized by puckering, thickening and curling. Diseased leaves become pale yellow to light green and shed after a short time. On young twigs, the disease appears as small, seldom-noticed swellings. Fruit and blossoms shed when infected and are seldom observed by growers. Disease development is related to air temperature at the time buds are opening. If surface moisture is present and the air temperature is near 68 degrees F, infection can take place. Temperatures above 86 degrees F and below 40 degrees F inhibit the fungus. If surface moisture is not present then infection does not take place. After the disease is visible, control is impossible. Copper fungicide sprays applied at the beginning of dormancy have proven very satisfactory. Chlorothalonil can also be used at leaf shed and just prior to bud break.
Bacterial Spot of Peach and Plum (bacterium - Xanthomonas pruni): Symptoms are observed first as small, circular, or irregularly shaped lesions, pale green in color. During early development, lesions almost always are visible at the tip of the leaf. surface. In advanced stages, angular lesions are formed and surrounded by a halo of lighter colored tissue. The inner portion of the lesion turns black and falls out after a time, giving the leaf a "ragged" or "shot hole" appearance. Leaves heavily infected with bacterial spot turn yellow and eventually fall. The disease first appears as a small, olive brown, circular spot on the fruit surface. Spots become slightly darker and depressed as the bacteria develops. Lesions are scattered over the fruit surface. The most conspicuous phase in advanced stages of fruit infection is "pitting." "Pitting" results when bacteria kill cells in the lesion. As surrounding healthy tissue grows, a "pit" is formed. This "pit" serves as an entry for other diseases such as brown rot. A "gum flow" often results from the lesion and further disfigures the fruit. The area below the "pit" is corky and unpalatable.
Fruit infected with the bacterial spot organism is unsuitable for sale except as culls. Twigs are damaged by two distinct types of lesions. "Spring cankers," develop in young succulent twigs of the previous summer's growth. They appear as water-soaked, slightly darkened blisters about the same time as first leaves appear. As the season progresses, the epidermis over the lesion ruptures and releases bacteria. The lesion then dries and becomes inactive. "Summer cankers" are restricted in size with indefinite margins. Bacteria overwinter in late infected twigs. The "fall cankers" are invisible as are these "summer cankers." "Spring cankers" are related to the amount of foliage infection which occurred the previous year.
Bacteria develop in leaves and serve as inoculum for later fruit, leaf and stem infections. leaves, and stems. Repeated infection occurs throughout the growing season as long as the environment is favorable for disease development. In the fall, bacteria enters twigs and undergo limited development. If trees are still actively growing, the bacteria will be walled off. Chemical control during the season is difficult. Dormant sprays have been somewhat effective, if the spray is timed to protect stems during the fall infection period. Copper containing fungicides should be applied just as the leaves begin to shed.
Peach Scab (fungus - Cladosporium carpophilum): Peach scab is a fungus which reduces attractiveness of fruit and can cause leaf spotting. The fungus is found wherever peaches are grown. It is most apparent on late season varieties. Peach scab is often called "freckles" or "black spot." On peach the disease is distinguished by irregularly defined, olive-colored spots. (Figure 1) Lesions normally occur around the stem. Host cells are killed, and since they are unable to expand, small cracks are formed. Lesions formed on young twigs serve as a means of overwintering by the fungus. Primary infection in the spring comes from spores produced in twig cankers formed the previous year. They are spread by wind and rain. Fruit infection normally occurs at petal fall, shuck split and first cover. Once infection occurs, 40 to 70 days may elapse before the disease is visible. Control is by repeated applications of an approved fungicide during the critical period around shuck split.
Coryneum Blight of Stone-Fruit (fungus - Coryneum beijerinckii): Blight lesions on fruit and leaves are small, circular, purple spots which in advanced stages spots on the leaves fall out giving the leaf a ragged appearance. Defoliation seldom occurs unless infection is severe. Twig cankers produce inoculum the next spring. Severely infected twigs die. On fruit infection is a superficial purple spot. Rarely is it severe enough on the fruit to be an economic problem. For most effective disease control, apply dormant sprays immediately after leaves are shed or just prior to budbreak in spring.
Brown Rot (fungus - Monilinia fructicola): This fungus attacks fruit in blossom stage at maturity, and during storage. Surface moisture and moderately warm temperatures favor fungus development. Blossom blight is the stage where blossoms become brown and water-soaked. The fungus grows down the pedicel into the stem resulting in dark brown, sunken areas. These areas often completely girdle the stem and cause twig dieback. In some instances, young fruit may become infected but not show symptoms of the infection until the fruit matures. During periods of high humidity, diseased blossoms and infected peduncles from the previous crop become covered with "tufts" of gray spores. These spores serve as inoculum for later infections as the fruit matures. The fungus enters through natural openings or wounds and rapidly develops a brown, water-soaked lesion on the fruit. Healthy fruit touching diseased fruit quickly decays. The brown rot fungus overwinters in mummies, stem cankers and on infected fruit peduncles. Dried fruit beetles can as vectors for the fungus. Control is by applying fungicide during pink bud, bloom, petal fall, and at preharvest. Increased fungicide applications at preharvest and during harvest may be required during periods of rain. Orchard sanitation is also an important part of brown rot control.
Rhizopus Rot (fungus - Rhizopus stolonifer): This fungus is most active during warm, humid weather. Fruit infection results in a "black whiskered" appearance caused by fungal strands which produce an abundance of black spores. Rhizopus rot only attacks peaches and plums at maturity. Disease prevention is based on orchard sanitation, use of fungicides, and refrigeration. Remove decayed fruit from the orchard or disk it under the soil surface. Picking containers should be such that fruit receives a minimum amount of handling. Picking boxes are inexpensive and can reduce fruit losses. They should be treated regularly with Captan to prevent fungal spread. Dip or use a high pressure fungicide spray to wet containers. Treat containers daily during periods of high brown rot incidence. Allow them to dry before using. Packing equipment should cause minimum damage. Pad any area where fruit will drop onto a belt or roller. Clean grading and packing equipment periodically to eliminate possibility of contamination. Use a solution of one part household bleach and nine parts water to wash conveyor belts, rollers, and packing tables. Make sure all equipment is dry before using. After grading, place fruit in packing containers which have not been used previously to store fruit. Container walls should be strong enough to be stacked in storage. Material used in fabricating containers should retain its strength after continued exposure to high humidity in cold storage. Use a well-planned spray schedule to prevent normal loss. Fruit that is to be stored must be refrigerated.
Rust (fungus - Tranzschelia discolor): Rust occurs on both peach and plum trees. Reddish-brown pustules occur on the lower leaf surface marked by a yellow spot on the upper surface. It causes leaves premature defoliation which reduces tree vigor. When rust appears, apply wettable sulfur on a 14-day schedule. This will not totally control the fungus but will reduce disease incidence of disease.
Phony Peach (virus): This virus disease of peaches does not cause rapid death of the tree but results in reduced growth and fruit size. Twigs on diseased trees have shortened internodes and increased lateral branching. The general appearance is a dwarfed, compact growth pattern with dark green foliage. After a few years, the wood becomes brittle and terminal dieback is common. Infected trees leaf out first in the spring and hold their foliage later in the fall. Fruit also ripens earlier on diseased trees. Disease is spread by root grafting and leafhoppers. Remove all trees showing symptoms of phony peach and destroy wild plums growing near the orchard.
Peach Yellows (mycoplasma): The disease has been observed in Texas and is caused by a mycoplasma. Fruits on diseased trees ripen from a few days to three weeks prematurely, have a bitter taste, and are reduced in size. Varieties which normally have red skin are abnormally bright. Leaves are chlorotic, fold upward, and tend to droop. Infected trees leaf out prematurely. The disease is spread by grafting and feeding by the plum leafhopper Macropsis trimoculata (Fitch). After infection, it may be 40 days to three years before disease symptoms are visible. Use only bud wood from healthy trees and destroy any trees which show typical disease symptoms.
Peach Mosaic (virus): This is a virus disease which affects peach and plum trees. General symptoms are delayed foliation with small, narrow, crinkled, mottled, yellow leaves. Internodes are shortened, and lateral buds break give a rosette appearance. Fruit is deformed resulting in bumpy, misshapen fruit. Spread is by grafting and insects. Plant trees from reputable nurserymen. Remove all virus-infected trees as soon as they are discovered.
Pythium Root Rot (fungi - Pythium spp.): Affected trees have reduced feeder root development which results in a slow decline of trees. P. irregulare is favored in cool soils (55 degrees F.), and P. vexans is active in warm soils. Pythium spp. feeds on the small feeder roots and makes the trees more susceptible to stress conditions such as heavy fruit set and drought. Roots develop necrotic lesions when infected with either of the two species of fungi. Avoid replanting in old peach soils. Chemical control has not proven effective against this complex of organisms.
Phytophthora Root Rot (fungus - Phytophthora cinnamomi): Roots infected by this fungus show extensive root necrosis. This necrosis will be present on the large roots and trunk while Pythium Root Rot is restricted to smaller feeder roots. Although Phytophthoral Root Rot has not been verified in Texas, its presence is suspected based on its wide distribution. Phytophthora Root Rot is most severe on replant soils or in areas where the orchard is planted poorly drained soils.
Cytospora Canker (fungus - Cytospora leucostoma): The fungus which causes Cytospora Canker is a weak pathogen and is rarely a problem in well cared for orchards. The first symptom is the formation of a small pimple-like canker on a limb. During the growing season small streams of gum are formed at each pimple. In most cases a callus layer forms around the damaged area and the canker is walled off. In a few cases the canker growth will resume in the fall after the callus growth is slowed. Cytospora Canker may become established in a limb following a mechanical damage which injures the bark or it may invade pruning cuts. Maximum spore release is in June, but infection can occur at any time due to the continual presence of spores in the trees. Affected trees should be pruned to remove the canker sites and fertilized with above normal levels of fertilizer.
Waterlogging (physiological): Peach trees growing in soils which do not drain well are characterized by rapid yellowing and wilting of the foliage. Although waterlogging can occur at most any time during the growing season, results are the most serious during the warmer months of the year. In controlled tests, five days elapse from the time the trees are waterlogged until wilting occurs at 80 degrees F, and 12 days elapse from the time the trees are waterlogged until wilting occurs at 62 degrees F. Plum rootstocks are much more tolerant of the waterlogging problem. It requires 10 days at 80 degrees F and 45 days at 62 degrees F before plums show the effects of waterlogging. Waterlogging is associated with poor interval drainage within a field. A yellow to gray clay subsoil can indicate poor drainage. Prior to planting, core samples should be taken to determine the subsoil condition within a field. It is best to take the core samples when the soil is wet. If free moisture is present in the sample hole 24 hours after digging, this would indicate a problem with drainage. If any gullies or ditches exist within a field, they can yield valuable information as to the condition of the subsoil. Although waterlogging is most often associated with land which has little or no slope, it can also be a problem on a field which has a major slope if the subsoil restricts water movement.
Poria Root Rot (fungus - Poria spp.): Poria Root Rot is caused by a soil- borne fungus which forms a thick, white to slightly off-white mycelium growth at the base of the tree trunk. This growth can may extend out from the base for 6 to 12 inches and from one-half to one inch thick. Trees infected with Poria root rot show a slow decline. A more rapid tree death occurs when the tree is infected by a second pathogen such as Pseudomonas syringae (Bacterial Canker). No control is recommended at this time.
Crown Gall: (See section on Crown Gall.)
Mushroom Root Rot: (See section on Mushroom Root Rot.)
Cotton Root Rot: (See section on Cotton Root Rot.)
Root Knot: (Nematode - Meloidogyne spp.)
Rootstock Root Knot (Meloidogyne sp.)
Okinawa Resistant
Nemaguard Resistant
S-37 Resistant
Lovell Susceptible
Elberta Susceptible
Nemared Resistant (Has not been
extensively evaluated
in Texas)
Different races do exist between species, and they have been shown under greenhouse conditions to attack "resistant rootstock."