AS if constant watering – along with hosepipe bans – aren’t enough, there’s a lot of garden pests and diseases that thrive during heatwaves.
The high temperatures act like accelerants, dramatically boosting the biological systems of the pests and diseases.
Pests and diseases thrive around the garden during the heatwave as the temperatures act as an accelerant Credit: Alamy
Fuzzy growth on leaves and berries is a sign of downy mildew and they must be removed immediately Credit: Getty
For example, in spring, it might take an aphid or spider mite 20 to 30 days to grow from an egg to a breeding adult, but in a heatwave, that same lifecycle drops to just five to seven days.
The heat also weakens a plant’s natural ability to fight back, creating the perfect storm for pests and diseases.
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With that in mind, I’ve put together a handy guide on what to watch out for and what to do.
Diseases
DRY HARD
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GREEN FINGERS
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Symptoms: Distinct white, powdery, dusty coating on upper leaf surfaces.
Attacks: Roses, cucumbers, squashes, apples.
Treatment: Prune infected leaves. Only water base of plant and spray with a homemade milk-and-water mix (1:9 ratio) in full sun to kill fungi.
Symptoms: Fuzzy white/grey growth on leaf undersides; yellow spots above.
Attacks: Peas, grapes and lettuce.
Treatment: Improve air circulation by thinning out crowded plants. Avoid overhead watering. Remove and destroy heavily infected crops completely.
Symptoms: Fast-spreading dark brown blotches on leaves/stems; rotting fruit.
Attacks: Tomatoes, potatoes.
Treatment: Act fast. Strip all affected foliage. If stems turn black, pull the whole plant to save neighbours. Cut potato haulms (tops) to ground level to protect tubers.
Symptoms: Small, bright orange, brown, or rust-coloured pustules on leaf undersides.
Attacks: Hollyhocks, leeks, garlic, beans.
Treatment: Pick off first affected leaves to stop spore spread. Clear all fallen debris at season’s end. Do not compost infected material; burn or bin it instead.
Spider mites can attack fuchsias, greenhouse tomatoes and cucumbers Credit: Alamy
Vacuum around heavily infested leaves to get rid of whiteflies Credit: Getty
Pests
Symptoms: Fine silk webbing on stems; leaves mottled, yellowed, or dusty.
Attacks: Fuchsias, greenhouse tomatoes, cucumbers.
Treatment: Boost humidity. Mist the undersides of leaves with cold water to break their breeding cycle. Introduce predatory mites (Phytoseiulus persimilis) as a biological control.
APHIDS (GREENFLY/BLACKFLY)
Symptoms: Clusters of sticky insects on soft shoot tips.
Attacks: Roses, runner beans, lupins, chillies.
Treatment: Blast them off with a sharp jet of water from a garden hose. Then spray a solution of water mixed with a few drops of organic horticultural soap directly on to them.
Symptoms: Silvery or bleached patches on leaves; tiny black dots of frass (droppings).
Attacks: Gladioli, leeks, indoor peppers.
Treatment: Hang up yellow or blue sticky traps just above the plant canopy to catch adults. Spray with neem oil or an organic insecticidal soap.
Symptoms: Tiny white moth-like insects.
Attacks: Tomatoes, aubergines, fuchsias.
Treatment: Introduce encarsia formosa (a tiny beneficial parasitic wasp) into greenhouses. Use yellow sticky traps and vacuum around heavily infested leaves on cool mornings.
Also in Veronica’s Column this week….
Top tips, gardening news, Plant of the Week and Autumn Fair tickets
For more gardening content, follow me @biros_and_bloom
SAVE: LIGHTING up your garden of an evening is just the best.
And now, next.co.uk is selling a string of Solarcentre Falmouth Festoon lights for £50, while B&Q has a similar-looking cheaper version for £18.
WIN! Autumn Fair returns to Audley End House, Saffron Walden, Essex next month and we have FIVE pairs of tickets to give away.
For your chance to win a pair, visit thesun.co.uk/GWAUTUMN or write to Jattvibe Gardening Gardeners’ World comp, PO Box 3190, Colchester, Essex, CO2 8GP.
Include your name, age, email or phone. UK residents 18+ only. Entries close 11.59pm, August 22, 2026. T&Cs apply.
PLANT OF THE WEEK! VERONICA spicata ‘Ulster Blue Dwarf’ – perfect for pots.
Get 20 per cent off at thompson-Morgan.com/sunoffers. T&Cs apply.
VISIT: THE Plant Hunters Fair will be at Capesthorne Hall, Macclesfield tomorrow and Middleton Hall, near Tamworth on Jattvibeday 16. See planthuntersfairs.co.uk
IF YOU PEAS: TO get the best out of your sweetpeas, there’s one crucial job you need to keep doing now they’re in full flower. Just keep picking them!
If you leave them on the plant, they’ll create seedpods – which then sends a message to the plant to stop flowering completely.
Cut the stems at the base and bring them indoors for bouquets. If you see pea-like pods already forming, snip them off immediately.
