There’s nothing worse than carefully hardening off your beautiful seedlings only to plant them out and have some critter munch them to a bare stalk overnight. Or, cosset some tender plants in the greenhouse only to find a mite or a thrip has sucked them dry. No matter what we do as gardeners, it always seems like something is out to thwart our hard work.
They say that information is power. If you know what might be out to get your plants, and can recognise the early signs of potential destruction, you’re in a good place to make sure the damage doesn’t get any worse.
The RHS keeps tabs on the worst diseases and pests that are likely to assail UK gardeners in any given year. This Top 10 is compiled from the most enquiries it receives from gardeners across the year, to help you stay on your guard and tackle issues before they become a problem.
Hayley Jones, RHS Principal Entomologist, lists the worst culprits: "According to the RHS State of Gardening report (2025) the most frequent plant health issues encountered by the UK's gardeners include honey fungus, rose black spot, powdery mildew, slugs and snails, vine weevil and box tree moth.”
Typically, the RHS list is split by gardeners’ enquiries about ‘Pathology’– things relating to fungus or disease – and ‘Entomology’, the critters that are likely to attack your plants. In the Top 10 there are some repeat offenders – powdery mildew, slugs and snails, black spot, spider mites and box tree moth seem to be perennial problems. But there are always some new challenges that gardeners need to be aware of, lest their fruit and flowers end up curled up from disease or munched by avoidable pests.
The top ten most challenging diseases confronting gardeners this year are:
Disease #1: Honey Fungus
This fungus spreads underground and can kill the roots of woody or perennial plants. If you peel the bark back at ground level, the telltale signs are white growth on the wood. It spreads with black or brown cords, or rhizomes through the soil and occasionally may actually sprout honey-coloured fungi in autumn. Signs your plants are suffering from honey fungus are the top part of the plant dying back, small leaves and even a big flush of fruit or flowers – just before the plant dies altogether.
Solution: dig up all infected material and burn or send to landfill. There is no chemical control, but you can put in a physical barrier to prevent its spread.
Disease #2: Rose Black Spot
The worst disease your roses can get, Diplocarpon rosae shows up on leaves in spring in purple or black splotches. Infected leaves may drop and severely affected plants will lose them altogether, flowering much less.
Solution: choose the right variety and practice good hygiene around the plants (ventilation, clean tools and pots). Remove affected material and burn, pruning off diseased stems. Fungicides can be used to control black spot but the RHS does not recommend their use because of the wider, adverse environmental impact.
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Disease #3: Apple & Pear Scab
Spread by the airborne fungus Venturia inaequalis, evidence you have apple scab turns up on leaves anywhere from spring to autumn. Scab looks like green blotches on leaves, blistering on stems or black, scabby marks on fruit. You can still eat fruit that is only lightly affected but if it has begun to crack, the apples will rot. Venturia pyrina is a similar fungus affecting pears.
Solution: prune off affected stems and get rid of any diseased fruit and leaves. The RHS lists a number of apple and pear cultivars that are resistant.
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Disease #4: Phytophthora root rot
Most of the damage from Phytophthora root rot takes place below ground and signs your plant is suffering only appear on the plant once the disease has really taken hold. It happens mostly in waterlogged or heavy soil and sometimes it’s hard to tell if it’s that, or the root rot that is causing problems. Plants will often wilt, turn yellow or brown and may eventually die.
Solution: destroy affected plants and refresh/improve the surrounding soil, adding drainage.
Disease #5: Powdery mildew of Prunus
An otherwise sturdy plant, Prunus laurocerasus (Cherry Laurel) can be affected by powdery mildew. This fungal disease can distort leaves and parts may turn brown. Instead of the whole leaf dropping, just the diseased part will crumble away, leaving holes.
Solution: removing and destroying diseased material can slow its spread, as will chopping off infected stems. Choosing the right location for the plant will help, including planting in full sun and making sure it has plenty of airflow. Avoid irregular watering which stresses the plant but make sure to water the leaves.
Disease #6: Bacterial leaf spot (Shothole) and canker of Prunus
The telltale signs of this bacterial infection are oozing, gummy holes in dead bark in spring and summer, and small, brown spots on leaves that eventually fall out, leaving them looking like they’ve been ‘shot’ with pellets, hence ‘Shothole’. Shoots may also die back quickly. The disease thrives in wet conditions.
Solution: prune in summer when the plant is strongest, cutting out all diseased wood and using a wound paint. Don’t put the cuttings on the compost heap, burning or sending to landfill is best.
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Disease #7: Blossom wilt of fruit trees
A family of fungi are responsible for the withering and dropping of the blossom and fruit on a range of trees including apples, pears, cherries, and peaches. The blossom will shrivel in spring and pustules may appear, especially when it’s wet.
Solution: chop off the diseased material and remove rotten fruit. The RHS has a list of resistant cultivars.
Disease #8: Pear rust
Although it’s called pear rust, this disease actually needs both pears and junipers to thrive. The clearest sign you have rust are orange spots on the top of the leaves in summer and early autumn, and canker can also appear on pear branches. Juniper stems will have swellings and an orangey, jelly-type growth. The infection doesn’t usually kill the tree but, left untreated, it can reduce vigour over time.
Solution: take off the affected leaves and stems but don’t over-prune as this could weaken the tree more than the disease.
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Disease #9: Apple and pear canker
While this fungus affects both fruit, apples are the most at risk. Neonectria ditissima attacks bark and can cause the death of the branch. It may also attack the main trunk. Once there, canker is perennial and you may see raised edges as the tree attempts to regrow bark over the dead wood.
Solution: canker loves wet conditions and acid soil. To control an infection, cut off infected wood back to the green and use wound paint to prevent disease entering the fresh area.
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Disease #10: Peach leaf curl
Peach leaf curl does exactly what it says on the tin – if the plant is infected by the fungus Taphrina deformans, the leaf will twist, crumple and thicken, possibly turning red in the process. Leaves will drop and the tree will weaken. Fruit can also be affected.
Solution: protect from rainfall on the leaves but don’t prevent insects for pollination or water from reaching the roots. Affected leaves can also show white spores, removing twisted leaves before this shows can reduce infection the next year.
Pest #1: Slugs and snails
It’s a perennial source of surprise for gardeners to discover that only a few slugs actually damage live plants. Most feed on dead matter, even other dead slugs and snails. They’re a vital part of your garden’s ecosystem, helping you compost as well as being food for other wildlife.
But, the ones who do like live plants can play merry hell with young hostas and vegetable seedlings and other soft-leaved plants. Some like to eat the fresh leaves, others live underground, munching on roots and tubers, including prize potatoes.
Solution: acceptance. Allowing that some damage will happen reduces frustration more than anything. “We encourage gardeners to tolerate a certain amount of plant damage and to avoid using pesticides, in order to build up a healthy garden ecosystem where the problem organisms and their natural enemies can reach balance,” Hayley suggests.
However, it is possible to manage the extent of the destruction. Transplant plantlets when they’re older and more robust, and cover with cloches. Encourage predators such as hedgehogs and birds, and perform an evening hunt to pick and relocate slugs to areas like the compost heap. Barriers like sand or eggshells have no scientific proof that they work, beer traps or nematodes do kill slugs without using pesticides but these do kill beneficial slugs as well as the plant munching ones.
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Pest #2: Vine weevil
It’s not the insect you can see that causes the most damage, but its grubs that live underground feasting on plant roots. The adult beetles do damage foliage but not usually enough to harm the whole plant. Containers provide ideal conditions for the vine weevil to thrive as in open ground roots are more spread out, clay soils restrict their movement and there are more natural predators. That said, they can and do cause a lot of damage to certain plants in the open, including strawberries, Primula and Heuchera. Plants suffering from vine weevil damage can wilt and die.
Solution: pick off adult weevils in the evening, look under pots during the day or in leaf litter where they shelter. A healthy wildlife ecosystem including birds, hedgehogs and other beetles will predate both the vine weevils and their grubs. Sticky traps can help in the greenhouse.
Pest #3: Box tree caterpillar
Box has had a tough run of it lately with fungal box blight decimating carefully curated topiaries right, left and centre. But it’s the box tree caterpillar (the larvae of the moth) that is currently worrying gardeners contacting the RHS.
It’s only been in the UK since 2007 but it’s now well established in the south-east of England and likely to continue causing problems for the foreseeable future.
The biggest sign you have an infestation is webbing over your hedge or plant and patches of dieback plus stems stripped of leaves. Eggs are difficult to find making it quite hard to remove them by hand.
Solution: It is possible to pick off the caterpillars by hand, they’re quite long and have a greenish/yellow body with black and white stripes. Birds and wasps will prey on them but it’s not certain they do enough to stop an infestation. Nematodes can be used but the mixed nematode for fruit and vegetables does infect other animals.
“For plant-feeding invertebrates, encouraging their natural enemies and hand removal can help keep numbers down,” Hayley explains.
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Pest #4: Greenhouse thrips
Thrips, or thunderbugs, are tiny insects that swarm during dry weather, often preceding thunderstorms, and while they cause cosmetic damage to plants, they don’t often cause severe damage or kill the plant. Because they suck on the sap, an attack from thrips can cause mottling of leaves, distort growth or cause leaves to turn brown or silvery. They’re not just limited to the greenhouse and since 2010 their impact has been seen on evergreen shrubs in southern England.
Solution: overall, the advice is to tolerate thrips as they don’t kill plants. But, you can limit their impact by separating affected plants from others, put plants that will tolerate it outside and quarantine new plants to make sure you’re not introducing thrips to your environment. “New plants should be checked thoroughly to avoid introducing any new plant health problems into the garden. For diseases, the right watering regime and hygiene (including tidying up affected plant material and cleaning tools) is usually essential to minimise spread,” Hayley adds.
Pest #5: Woolly aphid
Despite their cute name, woolly aphids take up residence on apples, cotoneasters and pyracanthas, sucking sap and creating conditions for fungal diseases to enter. The good news is they and the damage they cause are easy to spot – soft, lumpy growth on bark, often near old pruning cuts. Colonised branches are covered in a fluffy, waxy material that comes from the brown insect (they themselves do not sport a woolly coat).
Solution: let nature take its course and encourage predators like ladybirds. Alternatively squish colonies between finger and thumb.
Pest #6: Glasshouse red spider mite
The bane of the vegetable gardener in particular, the glasshouse spider mite is a tiny, sap-sucking arachnid that thrives in the dry conditions of the greenhouse. Feeding on a wide range of plants, it can damage cucumbers, tomatoes, aubergines and peppers to the extent the plant will eventually die.
Solution: damp conditions limit mite damage but doesn’t control them completely. Reduce overcrowding during the growing season, have a good tidy in late summer and clean greenhouses thoroughly using disinfectant, reducing the chance of females overwintering. Predatory mites, such as Phytoseiulus persimilis, can be bought via mail order as a biological control.
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Pest #7: Aphid on Buddleja
A rather specific complaint from gardeners to the RHS, nevertheless the buddleja has become a popular garden plant, as well as self-seeding readily in wider areas and along trainlines.
Buddleja are attacked by a specific insect – the Melon-cotton aphid, tentatively identified by the RHS as Aphis gossypii. The aphids feed on the underside of the buddleja leaf causing mottling and curling. The RHS is currently conducting research into the geographical spread of the disease and is inviting the public to report sightings via a survey that can be found here.
Solution: pinch and squeeze or encourage natural predators including ladybirds and earwigs.
Pest #8: Greenhouse mealybugs
Up close, mealybugs look a little like woodlice (‘slaters’) but they’re actually related to scale insects. Sap sucking bugs, they like the warmth which is why they’re most often found in the greenhouse. They’re usually spotted by the fluffy white wax they leave behind or black mould. They also excrete honeydew in large numbers making the plants sticky.
Solution: Remove affected or dropped leaves and dispose of plants that are significantly infested. The Cryptolaemus montrouzieri ladybird predates the mealybug and can be ordered online.
Pest #9: Ants
Ants don’t usually cause harm to plants themselves but they can end up fighting off ladybirds to protect an aphid population because the latter is a source of their much-loved honeydew. They’re also helpful predators themselves, feeding on other invertebrates such as caterpillars – and other ants. The most damage they typically do is to disturb soil through the creation of underground nests. Red ants (Myrmica) can give gardeners a sting if a nest is disturbed but it’s not a significant injury for most.
Solution: unless they’re particularly bothersome, it’s best to leave ant colonies alone. Ant heaps can be swept flat before mowing, and uneven ground caused by nests levelled and turf relaid.
Pest #10: Soft scale group
Scale insects hardly look like insects at all, and more like smudges on a leaf. They are, in fact, a flat, pale yellowy/brown insect that sucks sap and produces honeydew. The first sign you have scale insects is that your plants will have large sticky areas and may even have sooty mould on top. The insects themselves will be found on the underside of leaves and stems.
Solution: healthy plants can easily survive some scale insect presence but if they are starting to cause significant damage, ladybirds or nematodes can help control them. The specific nematode, Steinernema feltiae, can also infect other animals so only use if the infestation is troublesome.
Fighting pests and diseases in the garden can sometimes seem like an uphill struggle, and naturally gardeners want to do all they can to avoid losing prized fruit, veg and flowers. The RHS advises that a mix of vigilance, zen and letting nature do its thing is the way forward.
“Problems can be minimised by choosing the right plant for the right place,” suggests the RHS’s Hayley. “Strong, healthy plants are naturally more resilient and less likely to suffer serious damage.” Bugs and diseases may be annoying but with the right management, they’re more of a pest than a problem.
