It’s surprising how few gardeners bother to get their noses down in the shrubbery but to become a garden nasties super-sleuth, you’ll need to get up close and personal. Taking just five minutes a week to spot early signs of leaf-munching critters or plant lurgies can help prevent any serious damage since the sooner a pest or disease is identified, the easier it is to deal with.
Don’t worry, not every leaf spot, scab, discolouration or beastie is something to worry about, like us plants can feel under the weather often showing symptoms simply caused by planting conditions or environmental stress. Even the smartest gardens are vulnerable to garden pests and hedging diseases, luckily most of them aren’t life-threatening and can be easily remedied or avoided with quick-action and savvy plant husbandry.
Fab leaves = Fab plants
Right folks, listen up!
We’re heading back to the school biology lab to learn the only thing you’ll ever need to know about tackling garden pests and diseases. Do you remember being taught that plants use sunlight, water and carbon dioxide to create energy and oxygen?
That’s the nub right there.
This process happens in the leaves so if leaves are healthy and bereft of nasties, it stands to reason your garden plants are going to be firing on all cylinders, whereas damaged leaves chomped by common garden pests or affected by disease aren’t going to be performing at their personal best. It’s time to step in and lend a helping hand.
What to look out for
It’s relatively easy to become your own garden doctor and assess your plant ailments by using our quick guide which will help you head off the baddies before they cause serious problems. Commonly, look out for leaves notched at the edges, black or brown patches, misshapen, stunted, curling or yellowing leaves or stems crowded with an army of small bugs that all indicate you might have unwelcome intruders.
We share our gardens with thousands of insects, some beneficial, some harmful. The loveliest gardens are home to all types of bugs, some do a sterling job helping decompose plant matter, enrich the soil or aid pollination that allows plants to blossom or the bad guys that cause plant damage. Our useful guide helps you identify and deal with the main culprits using free or affordable eco-friendly methods since spraying with insecticide not only kills the baddies but the goodies too.
Sap-sucking aphids, less than 3mm long are the first on our hit list, easily spotted grazing on hedges, roses, shrubs and perennials and infesting young, soft-growing plant tips from spring to summer.
With over 500 species in the UK alone, they include green, grey or blackfly and come in many cunning disguises; yellow, light green and even pink, some covered in a woolly layer, like the beech woolly aphid and they multiply quickly.
How to spot them: If leaves or stems are covered with sticky honeydew, a waste secretion left by aphids or scale insects, it’s a sure sign of infestation.
Best remedy: Luckily, aphids are slow movers. The moment you spot them, get rid of them by wiping the affected leaves with a damp cloth, use insecticidal soap or horticultural oil, hose with cold water or spray with an eco-insecticide.
2. Scale insect
Another prime bunch of sap-suckers are scale insects, limpet-like bugs with protective shells that make them difficult to budge. There are more than 25 species and they are active all year round.
How to spot them: Like aphids, they leave behind a sticky honeydew substance, a sure sign the little blighters are present, look out for white egg masses on both stems and the undersides of leaves, weak or poor young plant growth.
Best remedy: Remove scale insects using a brush and warm soapy water, cotton wool soaked in methylated spirit or spray with an eco-insecticide.
3. Winter moth caterpillars
Winter moth caterpillar is the common name given to any species of adult moth that generally lay eggs from November to late April so it’s easy to think you should be on the lookout for moths. However, it’s the caterpillar stage in a moth’s life cycle that causes the most damage to leaf buds, leaves, blossoms and fruit from March to summer as the larvae transform into caterpillars, happily munching their way through your greenery.
How to spot them: Notched leaf edges or holes in the centre of leaves, petals that look chewed and stunted leaf buds.
- Remedy: Eliminate the eggs, eliminate the problem. Between November and April take precautionary measures using grease bands or barrier glue around the base of trees or shrubs to prevent the female moths from clambering up to lay eggs in the first place.
- Natural remedies are always best so planting wildlife-friendly hedging to encourage nesting birds is an effective way of dealing with these creeping green menaces.
- A Blue Tit chick can eat about 100 caterpillars a day and when you think a typical nest can have around 16 hatchlings, adult tits need to forage for about 1,000 caterpillars daily. That’s an impressive number of garden pests snaffled without you ever lifting a finger.
4. Spider Mite
If you’re a greenhouse or conservatory gardener you might have already battled with Red Spider Mites but since they’re tiny, it’s easy to miss the little blighters. Enjoying warmth, and by default your precious houseplants, (although they feed on outdoor plants too,) it’s not until leaves start yellowing, curling or dropping prematurely you realise you have a problem.
How to spot them: Look out for speckled leaves with dusty undersides or fine webbing dotted yellow, spun between leaves.
- Remedy: Spider mites like hot and dry conditions so create a more humid environment by misting indoor plants with warm water, placing bowls of water near plants and increasing ventilation.
- As long as the temperature is above 20°C you can introduce Phytoseilus persimilis into the greenhouse and conservatory, beneficial mites that feed on the pesky critters.
- Outdoors, regular hedge clipping coupled with a good weekly blast of the hosepipe should keep them at bay, just make sure you dispose of the clippings immediately.
5. Vine Weevil
Shy, night-crawling adult Vine Weevil beetles eat leaves causing unsightly notching which is rarely fatal but it’s their voracious offspring that you need to watch out for. Plump fingernail-sized creamy grubs hatch in pots and containers, merrily fattening up by feeding on plant roots. Good for them, not so good for your plants.
Known to infest a wide range of ornamental and fruit trees, hedging and perennials, these pointy-snouted 10mm, dull black beetles are active from spring to summer.
How to spot them: You can be forgiven for not noticing something is up until leaves drop, or plants wilt and keel over. Known to infest a wide range of ornamental and fruit trees, hedging and perennials, these pointy-snouted 10mm, dull black beetles are laying eggs from spring to summer.
- Remedy: Harnessing nature to do the dirty work for you is always the first port of call. Plant hedgehog or bird-friendly shrubs and hedges, make a small pond to encourage frogs and toads who all enjoy a tasty vine weevil grub.
- Otherwise, lay out newspaper under hedges or pots and give plants a good shake to dislodge vine weevils if you suspect their presence and squish them. (Sorry, sounds harsh but there you are.)
- Where practicable, upturn pot-grown plants and inspect the roots for grubs in autumn and winter, pick them off and squidge.
- Nematodes watered over pots from March to May and again, from August to November release deadly bacteria that kill the grubs and should be enough to break the lifecycle. (Soil temperature needs to be above 5°C to be effective.)
Fungal disease accounts for approximately 85% of the most common plant troubles including leaf discolouration, rust, scab, mildew, root rot and wilt. Some are more easily treated than others and a few left untreated can cause plant death.
1. Honey fungus
Sounds cosy, doesn’t it? Don’t be fooled! Honey fungus is one of the most invidious fungal diseases in the UK, a destructive parasitic fungus that spreads underground attacking the roots of healthy trees, shrubs, hedging, woody and perennial plants. Unfortunately, you might be unaware of it for years since the symptoms are only visible above ground once the disease has taken hold.
It’s a tough disease to combat however, if you have a known honey fungus contamination in your area, we have several disease-resistant plants. Box, Hornbeam, Griselinia, Lavender, Lonicera nitida, Yew, Holly, Hebe, Hazel and Blackthorn all are great choices.
How to spot it: Unusual, wilting, leaves that are pale and undersized.
Fruit and flowers fail to form or are stunted.
Small, cracks in bark, white mushroom-smelling fungal growth at the base of plants or under the bark.
Golden brown mushrooms can also appear briefly on infected wood and stumps, usually in late summer or autumn.
If you suspect you have Honey fungus, strip back the bark to investigate.
Dig around the base of the tree or scrub and look for black bootlaces that look very much like roots but are hollow.
- Remedy: Prevention is better than cure so where possible plant disease- resistant varieties where possible.
- You’ll have to dig out the affected shrubs, surrounding plants and contaminated soil to minimise potential spread to other parts of the garden. Nothing is 100% effective but this might help curb the spread. Destroy all material and take infected soil to landfill.
- Honey fungus lives and spreads in dead, rotting wood or old tree stumps so dispose of or burn any woody garden debris.
2. Powdery mildew
Powdery mildew is a fungal disease which mainly occurs on the leaves of roses, fruit, vegetables and perennials. Often associated with poor watering, powdery mildew appears in summer and autumn.
How to spot it: Light grey or dusty white patches or spots are easily visible on leaves.
- Remedy: Remove all affected stems and leaves, taking care to collect all fallen leaves around the garden where spores can overwinter and destroy or dispose of the debris.
- Avoid overfeeding plants since lush, young foliage is particularly vulnerable.
- Provide regular watering and good drainage and plant in full sun where possible, (shade lovers are obviously exempt but no less susceptible.)
Phytophthora or root rot is a fungal disease that attacks plant roots and is a common cause of root and base stem decay affecting a wide range of trees and shrubs. It is generally found in heavy clay or waterlogged soils.
How to spot it: Light grey or dusty white patches or spots are easily visible on leaves.
Roots appear blackened and finer roots rot away.
Above the ground, symptoms arise once the root decay is well advanced. Deciduous plants will yellow and branches are likely to die back, whereas conifer plants will turn a dark matt green or brown.
- Remedy: As this disease is largely caused by waterlogged soil, it’s important to improve the drainage with grit or land drains.
- Ensure potted plants drain freely.
- If you are experiencing a Phytophthora infestation, remove and destroy all infected plants and replace topsoil in affected areas as soon as possible.
- To avoid root rot plant species which are less susceptible to Phytophthora, such as Berberis, Hornbeam, Leylandii, Hazel, Hawthorn, Photinia and Western Red Cedar.
1. Bacterial Canker
Bacterial Canker (Pseudomonas syringae) is a disease caused by two closely related bacteria that affect the stems and leaves of many stone fruit trees including plums, peaches, apricots and cherries (cherries are members of the Prunus family) although thankfully Prunus laurocerasus (Cherry laurel) and Prunus lusitanica (Portuguese laurel) are more resistant to this disease.
Bacteria enter old pruning or tree wounds normally during autumn, winter and early spring. If damage is confined to a single injury from whacking the trunk with a trimmer or lawnmower, just leave it to heal. However, if multiple areas are affected, it’s likely to be canker, especially if leaves above the affected areas have curled, yellowed or died. Left untreated, the tree will eventually die.
How to spot it: Often called ‘shothole’ after the small brown holes that appear in midsummer, expect to see premature yellowing and misshapen leaves, and sunken dead areas of bark that ooze a gummy amber liquid (Gummosis) that dries rock hard by the end of summer.
- Remedy: Prune in July or August when trees are actively growing to reduce the chance of infection.
- Scrape off any ooze, cut out cankers plus and dispose of cuttings and bark immediately to prevent spread.
- Seal pruning cuts as you go with wound paint.
- Disinfect pruning tools between cuts with a mild bleach solution to limit spreading the infection further.
Plants are at risk as the weather warms up in spring and it is spread to healthy plant tissue by rain splashes, wind and insects.Typically, it enters branch tips, scorching new growth and travels down the tree, killing blossoms, limbs and shoots, and if left untended can potentially kill the tree.
How to spot it: Branches, stems and leaves look scorched and dry and sometimes rusty coloured lesions weeping brown-orange liquid appear on hot days.
- Remedy: Choose resistant varieties where possible and the moment you spot it, prune approximately 28 cm below diseased wood and destroy prunings.
- Dip pruning shears into bleach, Jersey fluid or methylated spirits as recommended by the RHS whilst you prune to avoid further spread.
3. Box Blight & Caterpillar
Box blight (Cylindrocladium buxicola) is a fungal disease affecting any plant in the Box (Buxus family) and can be triggered by hot, humid weather. Unsurprisingly gardeners in the South are more likely to encounter it than in Northern areas. Another close relative, Volutella Blight is much easier to deal with but never mind the Latin, if you suspect your topiary, hedging or parterres are affected, act quickly as the unsightly brown patches can take two growing seasons or more ages to repair.
That said, not once in over eight years has a customer reported blight following the supply of our plants and we’re pleased that our careful cultivation methods act as a deterrent.
Whilst we hate mentioning Box caterpillars it’s only fair to flag up the issue since many gardens have been affected in recent years by these very hungry caterpillars that can strip box plants bare in a week.
Fortunately, such is the popularity of these timeless, evergreen shrubs, the trend shows no sign of slowing. Buxus sempervirens remains one of our top 10 best sellers, customers buying tens of thousands of plants each year.
Frankly, unless you look very hard it’s tricky to work out if your plants are affected by blight or caterpillars, so here are some handy pointers to help you make the correct diagnosis. If in doubt you can check the EBTS (European Boxwood and Topiary Society) for their map of geographical caterpillar locations and see if the area where you live is affected.
How to spot Box blight: Leaves turn crispy brown and fall, leaving ugly bare patches, Black streaks and dieback on young stems.
Volutella doesn’t have black streaks but you may notice pink spores on the underside of leaves.
- Remedy: In dry weather, lay out plastic sheeting or newspapers and prune out the brown patches as well as the area around them and dispose of prunings immediately.
How to spot Box caterpillars: From mid-March to October look for green-yellow caterpillars with black heads and body markings and fine, silky webbing on leaves. Make sure you look at the base of plants as well as deep into the foliage because they’re very good at hide and seek.
- Remedy: Pick them off daily (yes, daily!) by hand, squish or drown them in a bucket of water, then prune out the dry brown papery patches.
- Whilst there are chemical sprays available that harm beneficial wildlife, they are not thought to be as effective as using natural bacteria, such as Bacillus thuringiensis.
- Few remedies are 100% effective so vigilance, pruning and good garden hygiene are your best defences.
For more tips on looking after your garden then visit our blog!