Peach Leaf Curl

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Orchard severely infected with peach leaf curl

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Beginner

This pest affects:

Scientific Name
Taphrina deformans

Identification
Leaves

Reddened or paler in colour than normal
Blistered, distorted, puckered and thickened
Often, the oldest 2-3 leaves are affected (first leaves to emerge in the spring) while the newest leaf tissue has no signs of symptoms
Only a few leaves of a tree may be affected, or the infections may be so numerous as to involve almost the entire foliage
As the season progresses, the red colouration becomes less pronounced and a greyish or powdery coating (the spores) appears over the upper surface of the leaves
The leaves gradually turn brown, wither and fall from the tree in the latter part of June or early July
Following the loss of leaves a new set of leaves will be produced from dormant buds

Branches and terminals

Young terminal shoots may sometimes be affected and are reduced in length, appear swollen, pale green or yellow in colour, exude gum and produce only curled leaves
When terminals are injured, lateral branching may occur leading to “witches broom ”
Death of trees due to repeated loss of foliage. This generally takes a period of approximately 3 to 5 years
Affected trees are more susceptible to winterkill

Fruit

Infected fruit show raised, irregular rough patches or bumps/nodules that are often red in colour long before healthy fruit show any colour change
The raised bumps/nodules often appear along the suture line of the affected fruit
Many infected fruits drop early
Fruit 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
Blossoms may fail to set fruit or the young fruit may drop
Fruit set may be reduced or prevented in the following year

Often Confused With
Green peach aphid – curled terminal leaves contain colonies of live aphids or cast skins if they are old colonies; no red blistering

Powdery mildew on leaves – twisted, curled leaves covered with white powdery sporulation

Period of Activity
Leaves are susceptible only while juvenile (in the bud).

Fruit infection occurs from petal fall until air temperature remains greater than 16 C.

Scouting Notes
It has generally been observed that peach leaf curl is favoured by cold, wet weather when the leaf buds are breaking dormancy and beginning to open. Temperatures of 10-15°C are favourable for infection.
Monitoring during bloom is done for the purpose of assessing the effectiveness of the control program and planning for next season. Monitor young leaves on sample trees for early foliar symptoms and record the incidence of leaf curl on sample trees

Threshold
By the time symptoms are visible, it is too late to control the disease.

Advanced

This pest affects:

Scientific Name
Taphrina deformans

Identification
Leaves

Reddened or paler in colour than normal
Blistered, distorted, puckered and thickened
Often, the oldest 2-3 leaves are affected (first leaves to emerge in the spring) while the newest leaf tissue has no signs of symptoms
Only a few leaves of a tree may be affected, or the infections may be so numerous as to involve almost the entire foliage
As the season progresses, the red colouration becomes less pronounced and a greyish or powdery coating (the spores) appears over the upper surface of the leaves
The leaves gradually turn brown, wither and fall from the tree in the latter part of June or early July
Following the loss of leaves a new set of leaves will be produced from dormant buds

Branches and terminals

Young terminal shoots may sometimes be affected and are reduced in length, appear swollen, pale green or yellow in colour, exude gum and produce only curled leaves
When terminals are injured, lateral branching may occur leading to “witches broom ”
Death of trees due to repeated loss of foliage. This generally takes a period of approximately 3 to 5 years
Affected trees are more susceptible to winterkill

Fruit

Infected fruit show raised, irregular rough patches or bumps/nodules that are often red in colour long before healthy fruit show any colour change
The raised bumps/nodules often appear along the suture line of the affected fruit
Many infected fruits drop early
Fruit 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
Blossoms may fail to set fruit or the young fruit may drop
Fruit set may be reduced or prevented in the following year

Often Confused With
Green peach aphid – curled terminal leaves contain colonies of live aphids or cast skins if they are old colonies; no red blistering

Powdery mildew on leaves – twisted, curled leaves covered with white powdery sporulation

Biology
Peach leaf curl occurs primarily on peach and nectarine and sometimes on apricot.

The fungus overwinters as conidia in microscopic cracks and crevices in the bark. When the buds start to swell, conidia are washed between the loose bud scales where they come in contact with developing leaves and start to infect them. The spores can germinate and penetrate the young leaves before they emerge and cause symptoms. Only juvenile plant tissues are susceptible to infection, so if no spore germination occurs at bud break, then little damage results for that year. Infections on peach leaves occur at temperatures of 10-21 C. Little infection occurs below 7 C. The incidence of infection is greatest with cool temperatures that lengthen the time that the leaves are exposed to the pathogens, before they are fully expanded and can resist penetration by the fungus. When temperatures are warm and early leaf development is rapid, infections rarely become established.

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

As the leaf infections age, they turn gray and appear powdery. Taphrina produces another type of spore (ascospore) on the upper surface of the diseased leaves. During wet weather, ascospores produce additional conidia. However, these conidia do not infect leaf tissue causing new infections They are washed or splashed to other parts of the tree where they overwinter until the next spring. Infected leaves generally drop in early summer.

Both spore types can remain inactive for several years on the peach tree until conditions are suitable for infection to occur.

Period of Activity
Leaves are susceptible only while juvenile (in the bud).

Fruit infection occurs from petal fall until air temperature remains greater than 16 C.

Threshold
By the time symptoms are visible, it is too late to control the disease.

Management Notes
All cultivars are susceptible to leaf curl to some degree, although Redhaven and cultivars derived from Redhaven are more resistant to leaf curl than Redskin and cultivars derived from Redskin.

After infected leaves drop, trees will generally produce new leaves. The extra stored energy required for this new growth stresses the tree. In severe cases, canker infections develop more easily and trees may fail to develop adequate winter hardiness. Minimize the stress by supplying some extra fertilizer, particularly nitrogen, irrigating and thinning the crop.

Management with fungicides – Fungicides are used to control peach leaf curl in commercial orchards. A fall spray should be applied no earlier than 90% leaf drop. A spring spray must be applied when the buds are swelling but before they have opened. It is not possible to control the fungus once it has entered the leaf. Poor disease control is usually a result of spraying too late; that is, after budswell. In a planting containing peach and nectarine cultivars, sprays must be timed for that cultivar which shows the earliest movement of buds. None of the fungicides registered for brown rot or powdery mildew during the growing season will help to control leaf curl.

See OMAFRA Publication 360, Fruit Crop Protection Guide:

Chapter 5 - Peaches:: Recommendations for peach leaf curl at Dormant and Fall spray

Some information included above excerpted from;

Tender Fruit

Peach Leaf Curl

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