X-Disease
Beginner
This pest affects:
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Scientific Name
Peach X phytoplasma
Identification
Newly infected trees may have only one diseased branch during the current season, but with a year or two the entire tree will become infected, and vigour and yield will decrease dramatically.
Peach
Leaves
- In midsummer, irregular yellow spotting which becomes reddish purple water-soaked spots not limited by leaf veins
- Upward rolling of the leaf at the margins
- Necrotic areas soon develop and drop out leaving a shot-hole effect and tattered leaves
- Progressive defoliation of stems from the base upward, with only a rosetted tuft of leaves remaining at the shoot tips
Fruit
- Premature fruit drop
- Remaining fruit are smaller, lacks flavour often with a bitter taste
Tree
- Diseased branches are more susceptible to winter kill
- Symptoms are generally more severe during hot summers
- Within the first two years of infection both healthy and infected symptomatic branches on the same tree
- Usually by the third year after infection, most branches will show symptoms
- Young trees die within 1 to 2 years after the first symptoms appear
- Older trees gradually decline in vigour and often die from winter kill or other opportunistic diseases
Cherry
Sour cherries seem to be a little more seriously affected in that dieback and decline are often associated with the disease. Symptoms also vary depending on rootstock
Mahaleb rootstock
- Trees are usually killed midsummer or early the following year
- Pits and grooves are present in the wood at the graft union
- In advanced stages may cause browning of the bark
- Leaves turn pale with a reddish tinge and curls upward
Mazzard rootstock
- Trees decline slowly over many years
- Leaves may be smaller than normal, pale green or more upright
- Terminals may appear more dense because of growth from normally dormant buds
- Scattered fruit are small and pink at harvest and have a bitter flavor and a leathery texture
- Affected fruits may be mixed on the same branch with unaffected fruit
Chokecherry (reservoir host)
- Leaves turn yellow by mid June with gradual reddening far in advance of normal fall colouration
- Stunted with shortened internodes and die back of branches increases each year, usually dying within 1 to 3 years after exhibiting symptoms
Often Confused With
Bacterial spot - angular, brown to black or purple spots along midvein, tips and margins; black spots on fruit; entire tree affected
Nitrogen deficiency - damage usually most evident along the midrib and entire leaves may turn red; entire tree affected
Perennial canker on peach- sunken cankers on scaffolds and trunks with rings of callus and blackened gum; leaves on cankered shoots seldom fall, even though they dry out and die
Bacterial canker on cherry – cankers on trees with leggy appearance caused by extensive killing of leaf and flower buds and spurs on wood 3 years of age or older
Phytophthora root rot - above-ground symptoms fairly uniform throughout the canopy of the tree; crown and/or roots visible, rotted areas that are generally brick-red to brown in and are often characterized by a sharp line of demarcation between healthy and diseased tissue while roots on trees affected by X-disease appear normal
Period of Activity
Transmission of the organism to peach may occur any time when leafhopper vectors are active, between June and freeze-up in the fall. Symptoms do not appear until late spring or early summer of the following year.
Scouting Notes
Be aware of the presence of wild chokecherry in proximity to peach orchards. No routine monitoring is required.
Threshold
No threshold established. Infected cherry trees near peach orchards should be removed immediately to prevent spread.
Advanced
This pest affects:
|
|
|
Scientific Name
Peach X phytoplasma
Identification
Newly infected trees may have only one diseased branch during the current season, but with a year or two the entire tree will become infected, and vigour and yield will decrease dramatically.
Peach
Leaves
- In midsummer, irregular yellow spotting which becomes reddish purple water-soaked spots not limited by leaf veins
- Upward rolling of the leaf at the margins
- Necrotic areas soon develop and drop out leaving a shot-hole effect and tattered leaves
- Progressive defoliation of stems from the base upward, with only a rosetted tuft of leaves remaining at the shoot tips
Fruit
- Premature fruit drop
- Remaining fruit are smaller, lacks flavour often with a bitter taste
Tree
- Diseased branches are more susceptible to winter kill
- Symptoms are generally more severe during hot summers
- Within the first two years of infection both healthy and infected symptomatic branches on the same tree
- Usually by the third year after infection, most branches will show symptoms
- Young trees die within 1 to 2 years after the first symptoms appear
- Older trees gradually decline in vigour and often die from winter kill or other opportunistic diseases
Cherry
Sour cherries seem to be a little more seriously affected in that dieback and decline are often associated with the disease. Symptoms also vary depending on rootstock
Mahaleb rootstock
- Trees are usually killed midsummer or early the following year
- Pits and grooves are present in the wood at the graft union
- In advanced stages may cause browning of the bark
- Leaves turn pale with a reddish tinge and curls upward
Mazzard rootstock
- Trees decline slowly over many years
- Leaves may be smaller than normal, pale green or more upright
- Terminals may appear more dense because of growth from normally dormant buds
- Scattered fruit are small and pink at harvest and have a bitter flavor and a leathery texture
- Affected fruits may be mixed on the same branch with unaffected fruit
Chokecherry (reservoir host)
- Leaves turn yellow by mid June with gradual reddening far in advance of normal fall colouration
- Stunted with shortened internodes and die back of branches increases each year, usually dying within 1 to 3 years after exhibiting symptoms
Often Confused With
Bacterial spot - angular, brown to black or purple spots along midvein, tips and margins; black spots on fruit; entire tree affected
Nitrogen deficiency - damage usually most evident along the midrib and entire leaves may turn red; entire tree affected
Perennial canker on peach- sunken cankers on scaffolds and trunks with rings of callus and blackened gum; leaves on cankered shoots seldom fall, even though they dry out and die
Bacterial canker on cherry – cankers on trees with leggy appearance caused by extensive killing of leaf and flower buds and spurs on wood 3 years of age or older
Phytophthora root rot - above-ground symptoms fairly uniform throughout the canopy of the tree; crown and/or roots visible, rotted areas that are generally brick-red to brown in and are often characterized by a sharp line of demarcation between healthy and diseased tissue while roots on trees affected by X-disease appear normal
Biology
X-disease is caused by a phytoplasma that lives in the phloem of host species. It is an economically important disease of stone fruits including sweet and sour cherry, peach, nectarine and Japanese plum, although peach is the primary concern. Wild chokecherry (Prunus virginiana) is the main reservoir of the pathogen.
The disease is readily transmitted by budding or grafting but the primary mode of dispersal is through insect vectors. Several species of leafhopper transmit X-disease between different susceptible plant species. Leafhoppers acquire the X-disease pathogen while sucking juices from the leaves of infected plants. After the pathogen has multiplied in the insect for 2 or 3 weeks it can be injected through saliva into healthy leaves during leafhopper feeding. Once a tree is infected, the pathogen multiplies and spreads within the tree’s phloem. In most cases the pathogen will spread downward into the trunk and rootstock and upward into the rest of the tree although distribution of the phytoplasma within a tree is irregular.
Leafhoppers overwinter as eggs in the leaf litter primarily at the edges of orchards. In spring, the eggs hatch and nymphs develop on weedy and woody plants in wood lots and fence rows. These leafhoppers are thought to feed on nearby X-diseased chokecherry where they acquire the X-phytoplasma. In June, leafhoppers adults move into the orchards. Symptoms develop on the trees the year following infection. Leafhoppers can continue to transmit X-disease to peach trees during September and early October, but many of the late-season transmissions fail to cause disease because the pathogen does not become established in the plant following late-season transmissions. Relatively mild winters may allow more of the late-season transmissions to persist through winter and may therefore contribute to increasing severity of X-disease.
X-disease may also be transmitted to peach from infected sweet and sour cherry. Other reservoirs of X-disease include certain weeds such as clover species, dandelion, and several rosaceous species including strawberry and blackberry. Maximum spread in stone fruits occurs from mid August through October when high concentrations of the pathogen are present in the leaves and leafhopper populations are increasing in orchards. The most significant spread of X disease is from cherry to cherry, from cherry to peach, or chokecherry to either cherry or peach. Spread of X-disease from peach to peach by leafhoppers appears to be of minor significance.
Period of Activity
Transmission of the organism to peach may occur any time when leafhopper vectors are active, between June and freeze-up in the fall. Symptoms do not appear until late spring or early summer of the following year.
Scouting Notes
Be aware of the presence of wild chokecherry in proximity to peach orchards. No routine monitoring is required.
Threshold
No threshold established. Infected cherry trees near peach orchards should be removed immediately to prevent spread.
Management Notes
Remove wild chokecherry from within 250 m of susceptible orchards. Cutting, burning, bulldozing or deep plowing are only partly effective because the bushes may re-sprout.
Apply brush killers to wild chokecherry both summer and autumn. Treated areas must be re-examined annually during the growing season to ensure complete eradication.
Removed and destroy all infected trees as soon as they are found in nurseries.
New trees may be safely replanted the following spring. It is not necessary to remove X-diseased peach trees to prevent spread of the disease, because peach trees do not act as a source of inoculum for the leafhopper vectors. In young orchards, infected trees can be removed and replanted after the source of inoculum (hedgerow chokecherries or seedling sweet cherries) has been identified and removed. X-disease does not remain active in the soil.
Information included above excerpted from:
- http://www.scaffolds.entomology.cornell.edu/1999/6.21_diseases.html
- Integrated Pest Management for Stone Fruits L.L. Strand ed.
- http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3206_08.pdf
- http://ucanr.org/sites/cccoopext/files/80935.pdf
- http://www.ct.gov/caes/cwp/view.asp?a=2815&q=376862
