December 02, 2021

10 Most Common Pests and Diseases Found in Hedging Plants

Here at Glenmore, we promise the best disease and pest-free plants, but sometimes, we are faced with existing plant problems which we have no idea how to handle.

So, here's the top 10 most common pests and diseases found in UK hedging, along with how to spot them and ways to treat them (both naturally and chemically)!

1. Aphids

These are the most common type of pest to be found on hedging/shrubs. They are sap-sucking bugs, that will infest young growing tips of plants during spring and summer.

How to spot them: Look out for general weakening of the young plant growth, or distortion. A sticky residue will be left behind by the aphids, too, which can result in black moulds (which is not actually harmful to the plant, themselves).

Natural control: Natural predators, i.e. hoverfly larvae and ladybirds, or try wiping off with a damp cloth (though this will only work for small infestations).

Chemical control: There are many pesticides on the market for aphids, but the most effective will contain either Cypermethrin or Deltamethrin. Make sure you read the label for instructions, too.

What do Aphids look like?

2. Scale Insects

These are sap-sucking insects that protect themselves with a shell-like scale.

How to spot them: You may notice small bumps on the underside of the leaves or the stems. Some types of scale insects will leave a white covering to protect their eggs (only in the summer), which is usually the first time you will notice them. You do not have to worry much about light infestations as they cause very few problems.

Natural control: Brush off the pests with warm, soapy water. Please note, it is only possible to use this method on woody stems.

Chemical control: Any pesticides including Cypermethrin or Deltamethrin will be the most effective. Ensure you spray onto the plant in May or June, and make sure you read the instructions before use.

What do Scale Insects look like?

3. Vine Weevil

These are beetles that attach many plants and tend to feed on the plant's roots- completely ruining the plant's chance at survival.

How to spot them: Adult weevils will appear as dull, black, long bugs that are about 10mm long (as pictured). They are generally found during the summer, and tend to eat away at leaf margins. On the other hand, Vine Weevil grubs are about 5-10mm long and will appear as a creamy colour. They live in the soil and eat away at the young roots in autumn/winter. This will often result in death of the plant.

Natural control: Make sure you place an upturned umbrella at the base of the plant and give it a good shake to capture the weevils. Alternatively, try using a nematode Steinernema kraussei, which can be found in garden centres- simply water onto the soil during August/September.

Chemical control: There are no chemical pesticides available for those planted into the ground- though you can buy acetamiprid for potted plants.

What do Vine Weevils look like?

4. Winter Moth Caterpillars

These appear when adult moths lay eggs in November through to April. The caterpillars then emerge in spring and eat away at young, developing leaves.

How to spot them: You will usually notice attacks from Winter Moths during spring, as the young leaves are eaten. In terms of damage, this is generally spotted during Summer, when the holes have enlarged from the leaf's growth- by this time, the caterpillars are no longer on the plant.

Natural control: Simply encourage some birds into the garden- they will feed on the small, winter moth caterpillars.

Chemical control: The most effective pesticide for these caterpillars will include Cypermethrin or Deltamethrin. Make sure you read the label for instructions.

What do Winter Moth Caterpillars look like?

5. Spider Mites

These are usually found in greenhouses. They will generally show as fine, pale mottling on the leaf's upper surface. You will find they're generally easier to see with a magnifying glass.

How to spot them: When a plant is infested with Spider Mites, a pale, fine mottling will show on the top of the leaf. The underside will have little yellow-green mites/eggshells. In terms of severe infestations, however, a silk webbing may appear on the plants, and the foliage will likely lose its colour.

Natural control: Spider Mites are not generally a major pest outdoors, so can be easily handled. If they infest your young growth, simply cut back the hedge then burn the trimmings.

Chemical control: Pesticides including acetamiprid will give some good control- make sure you always read the label for instructions, first.

What do Spider Mites look like?

6. Powdery Mildew

This is a fungal disease which appears on the foliage and covers the whole surface of the leaf. This disease has a high-water content, meaning it can survive in dry conditions.

How to spot it: Powdery Mildew will appear as a white powder that covers the whole surface of leaves and green stems during summer/autumn. It can often result in distortion of young tissue and leaves.

Natural control: Make sure you are watering the plant during dry weather- especially any newly planted hedges/shrubs. This will reduce stress. Rake up the leaves during Autumn, and burn- do not compost.

Chemical control: Any treatments containing tebuconazole will be the most cost effective. As always, make sure you read the label for instructions.

What does Powdery Mildew look like?

7. Honey Fungus

This fungus spreads underground and attacks and kills the plant's roots. Plants that are particularly vulnerable to this disease include Photinia, Beech, Holly, Privet, Yew, and Prunus.

How to spot it: The plant's foliage will look poorly developed and pale- may even see some early autumn colouring. Twigs will probably die back completely. In some cases, brown, mushroom-like fungus will appear at the base of the plant. Below ground, the roots will die and rot, and a specific, white fungal covering will show under the plant's low bark.

Natural control: There are not any specific methods known to treat Honey Fungus, but you can remove dead/dying material from the soil, and burn, then replace with topsoil.

Chemical control: There are no chemical treatments for Honey Fungus.

What does Honey Fungus look like?

8. Phytophthora

Phytophthora will attach and then kill the roots of young plants, resulting in death. This is mainly found in hedging, trees, and shrubs.

How to spot it: Foliage of deciduous species will turn yellow. Twigs and branches will likely die. Conifers' foliage will turn dark green/brown. This is becuase of a lack of water uptake- as the roots are being destroyed. This disease is often mistaken for honey fungus or drought.

Natural control: Make sure you improve the soil's drainage immediately- try using grit or land drains. Remove any infected plants and destroy, too. Then replace with topsoil. Plant with less vulnerable species.

Chemical control: There are no chemical treatments for Phytophthora.

What does Phytophthora look like?

9. Bacterial Canker

This is also known as the Shothole disease. It appears as small, brown spots on the foliage, and will generally affect the Prunus species.

How to spot it: Little, brown patches will show up on the leaves in the middle of summer. The middle of these will then fall through, leaving a hole- hence the nickname "Shothole." Dead areas will also appear on the branches, often along with some amber coloured residue. Severe cases will result in whole branches dying.

Natural control: Restrict pruning your Prunus species to July/August when they are most resistant. Paint the pruning wounds with a sealant- must contain copper.

Chemical control: There are no effective chemical treatments for Bacterial Canker, as of yet.

What does Bacterial Canker look like?

10. Fireblight

This is a minor disease, as it is often too cold for the disease to spread effectively. It enters a plant through the blossoms, causing them to then fade away and die.

How to spot it: Fireblight will appear as dead/wilted foliage. You will have to remove blossoms if you are suspicious of infection. Shoots may also shrivel up if the infection spreads further. A slimy, white residue may appear on the tips of infected shoots in damp weather.

Natural control: Simply prune and burn any signs of infection as soon as possible. Clean your secateurs with formaldehyde or Jeyes Fluid, to avoid contaminating any other plants.

Chemical control: No effective chemical treatment for Fireblight, yet.

What does Fireblight look like?

Aphids

Aphids