Damon Mcknight
Photinias are large shrubs that are native to Asia and are now a common sight in gardens in Australia and the eastern portion of the United States. They are popular with homeowners because they are low-maintenance, grow tall, and provide privacy. However, they are susceptible to a number of pests and diseases, including the photinia fungus (also known as photinia leaf spot), fire blight, and aphids. Wet photinia leaves can also attract fungus growth. This article will explore the possible causes of damage to photinia leaves and provide advice on how to prevent and treat these issues.
| Characteristics | Values |
|---|---|
| Genus | About 30 species of small trees and large shrubs |
| Origin | Asia |
| Height | 4–15 m tall |
| Branches | Irregular crown of angular branches; often thorny |
| Leaves | Alternate, entire or finely toothed; 3–15 cm in length and 1.5–5 cm wide; glossy and shiny; red, green |
| Flowers | White to pale pink; 5–10 mm diameter; mild, hawthorn-like scent |
| Fruits | Small, roundish, apple-shaped, red berries; 4–12 mm across |
| Hardiness | Depends on species; frost-resistant |
| Propagation | Easily propagated by cuttings |
| Pruning | Requires regular pruning |
| Common pests | Aphids |
| Common diseases | Photinia leaf spot; fire blight |
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What You'll Learn
Photinia leaf spot
The disease thrives in cool, moist environments, particularly in the fall and spring. Overuse and close planting of red-tipped photinia have led to constant, yearly attacks by the photinia fungus. The red tips of new growth, which made these shrubs so popular, are particularly vulnerable to the fungus. Once the disease takes hold, it is challenging to control, and it can eventually weaken the plant to the point of death.
To prevent photinia leaf spot, it is important to rake up and dispose of all fallen and infected leaves, as well as removing affected branches. The area under and around the shrubs should be covered with new mulch to contain any remaining leaf parts and spores. It is recommended to avoid repeated trimming of endangered shrubs to encourage new, red growth. Instead, trimming should be confined to the dormant winter months, and all clippings should be disposed of properly.
Chemical treatments are available, and fungicides containing Chlorothalonil, propiconazole, or myclobutanil can be effective. However, these fungicides may need to be applied regularly, every one to two weeks, to be effective. In severe cases of infection, it may be best to replace the affected plants with alternative species.
To reduce the risk of photinia leaf spot, it is advisable to plant a mixed hedge with varied species rather than a single-species hedge. Staggering new plantings can increase light and airflow around the shrubs, creating less favourable conditions for the fungus to thrive. Additionally, ensuring good air circulation and avoiding excessive moisture can help prevent the spread of the disease.
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Fire blight
To treat fire blight on Photinia Red Robin, prune away affected leaves and stems, cutting back to healthy wood to prevent the spread of infection. Once you have removed the infected parts, apply a copper fungicide to protect the remaining healthy tissue and prevent the recurrence of the disease.
To prevent fire blight, rake up all fallen leaves, and if the shrub is already infected, remove all affected leaves and branches. Cover the area under and around the shrubs with new mulch to cover any leaf parts and photinia fungus spores that remain.
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Aphids
Green aphids are a common pest of Photinias, attacking the younger shoots of the plant. To ensure healthy growth, it is important to protect these young shoots from aphid infestations. One method of control is to apply a mixture of Potassium soap and Neem oil as soon as aphids are noticed, or a good quality pesticide spray, always following the instructions on the product.
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Wet leaves
Fungal leaf spot diseases, such as Entomosporium leaf spot, can cause leaves to appear wet and are often favoured by humid conditions. This disease results in reddish-purple spots on leaves, which eventually fall off. To manage this, ensure your photinia is planted in well-drained soil and avoid wetting the foliage when watering. Remove and dispose of infected leaves, and consider applying a fungicide to protect healthy leaves.
Downy mildew is another fungal pathogen that can cause leaf wetness. It typically affects young leaves first, resulting in yellow to brown lesions on the upper leaf surface, while the underside of the leaf may appear grey or brown with spores. Spacing plants adequately and ensuring good air circulation can help prevent this issue, as well as avoiding overhead watering. Remove infected leaves and apply appropriate fungicides to manage the spread.
Bacterial leaf spot can also cause similar symptoms, with small, wet-looking lesions on leaves that may fall off the plant. This disease often occurs following periods of rain or overhead watering. To manage bacterial leaf spot, ensure your photinia has good air circulation and avoid wetting the foliage when watering. Remove infected leaves and apply a suitable bactericide to protect healthy leaves.
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Pruning
Photinias are large shrubs that can grow up to 10 to 15 feet tall and 5 to 8 feet wide. They are admired for their red-tipped new growth and are commonly used for hedging and landscaping. Photinias are also quite resilient and not very prone to diseases. However, they are susceptible to Entomosporium leaf spot, a fungal infection that causes small, circular, red spots on both the upper and lower surfaces of new leaves. If left untreated, the spots enlarge and become dark, purplish circles surrounded by gray, dying tissue, eventually leading to leaf drop and possibly plant death.
To prevent and manage this fungal disease, proper pruning techniques are essential. Here are some detailed instructions on how to prune your Photinia:
Timing:
- The best time to prune Photinias is after they flower in spring. Pruning after spring blooming encourages new growth and helps maintain the shape and size of the shrub.
- You can also prune Photinias in the fall after their growth spurt to further balance their shape and size.
- Additionally, pruning at the end of winter will give you more red leaves, but you may sacrifice the flowers as you will be cutting off the flower buds.
- Avoid pruning during the active growth periods of the fungus, which are typically the fall and spring when the weather is cool and moist. Instead, prune during the dormant winter months to reduce the risk of fungal infections.
Techniques:
- Thin out older branches first to trigger the growth of new shoots and to allow more light to reach the center of the shrub.
- To promote rejuvenation, you can cut back the entire shrub at once to about 6 inches (15 cm) above the ground. However, this method may leave an unsightly gap in your landscape.
- For a less drastic approach, spread the rejuvenation process over three to four years. Each year, cut one-half to one-third of the stems to about 6 inches (15 cm) above the ground, starting with the oldest and largest stems and then moving on to the weak and misshapen ones.
- You can shape your Photinia as you wish—into cones, spheres, columns, or other topiary forms. The more you prune, the faster it will grow, so feel free to get creative!
Remember to dispose of all clippings properly, especially if they show signs of fungal infection, to prevent the spread of the disease to other parts of your Photinia or other susceptible plants in your garden.
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Frequently asked questions
There are a few possible reasons why your photinia leaves are being eaten. Firstly, check for common pests such as aphids, which are tiny insects that can often appear due to over-fertilization. Another possible reason could be the bacterial pathogen fire blight, which causes leaves to appear wilted, curled, and burnt. Finally, it could be due to the photinia leaf spot fungus, which commonly affects new growth and causes dark, purplish circles on the leaves.
To prevent pests like aphids, you can simply wipe them off with soapy water. For fire blight, infected plants must be reported and destroyed as it is a quarantine pathogen. To minimize the risk of photinia leaf spot, maintain good airflow around the plant, avoid wetting the leaves, and practice proper pruning and leaf removal to keep the plant healthy.
Common signs of pests or diseases affecting your photinia leaves include the presence of dark spots, wilting, curling, or burnt-looking leaves. You may also notice the presence of tiny insects or aphids on the leaves or new growth. If you notice any of these signs, take appropriate action to identify and address the issue promptly.
