I’ve been talking to head gardener and garden consultant, Steve Edney, whose family have grown dahlias for generations. And he only gardens organically, so his advice is chemical-free. See here for Steve’s advice on choosing and growing dahlias.
Firstly, he says that pest control is now about balance not eradication. As gardeners, we know that we can’t get rid of pests permanently. We can only minimise the damage they do.
This applies both to gardening without chemicals and gardening with. It doesn’t matter how strong the spray is; the slugs, snails, and earwigs will still come back.
So ‘it’s about balance,’ he says. You might get some nibbled leaves and petals, but the whole thing can still look beautiful even if not every flower is perfect.
Steve has just created a dahlia border for Canterbury Cathedral, using chemical-free gardening. Not only is this method good for wildlife gardeners, but it’s also good for people whose gardens get a lot of attention. You can see more views of the border and of Canterbury Cathedral in this video.
Steve and his partner Louise also grow plants in their own nursery, The No Name Nursery in Kent. They sell the plants at plant fairs around South East England. And plants for sale also have to look good!.
Dahlias are stunning flowers that can brighten up any garden. However they are also prone to pest problems. As a dahlia lover you want to keep your plants healthy and bud-filled. But what should you spray to control bugs on dahlias?
I’ve been growing dahlias for over 10 years on my small farm. In that time, I’ve dealt with all the common dahlia pests from thrips to Japanese beetles. Through trial and error, I’ve found organic sprays that knock back bugs without harming these delicate flowers.
In this article, I’ll share my top tips on what to spray for common dahlia bugs. I’ll cover when to spray, how often, and what active ingredients work best. Read on to learn how to protect your dahlias naturally!
The Most Common Dahlia Pests
Here are some usual suspects that chew holes in dahlia leaves and petals:
Aphids
These tiny, soft-bodied insects come in green, yellow, black or red. They cluster on stems and undersides of leaves, sucking plant sap Honeydew secretions then coat plants, promoting sooty mold growth
Thrips
Tiny winged insects that rasp plant tissue and drink juices. They leave silver-white scars on leaves buds and flowers. Thrips also spread viruses.
Cucumber Beetles
Shiny green or yellow and black striped beetles that skeletonize leaves. They transmit bacterial wilt disease as they feed.
Earwigs
Nocturnal insects with distinctive pinchers on their abdomen. They chew irregular holes in dahlia flowers and foliage.
Slugs & Snails
Slimy soft-bodied mollusks that chew ragged holes in leaves, disfigure flowers. They leave shiny slime trails as they move.
Japanese Beetles
Metallic green and copper beetles that skeletonize foliage in summer. They quickly devour dahlia blooms, leaving only the base behind.
Organic Sprays for Dahlia Bug Control
When dealing with dahlia pests, I always reach for natural and organic sprays first. These effective options don’t harm pollinators or other beneficial insects when used properly. Here are my top recommendations:
Insecticidal Soap
Potassium salts of fatty acids that dissolve soft bodied insects like aphids, thrips, whiteflies, and more. Spray it directly on bugs for quick knockdown. It also disrupts insect feeding. Mix according to label directions and apply weekly. Brands like Safer’s, Garden Safe and Concern all make effective insecticidal soaps.
Neem Oil
Pressed from the seeds of the neem tree, it contains azadirachtin that disrupts insect lifecycles. Neem oil smothers soft-bodied insects while deterring feeding by beetles. It’s most effective against young insects. Mix neem oil concentrate with water and a bit of insecticidal soap. Spray weekly focusing on the undersides of leaves. I use concentrated neem oil from brands like Monterey.
Pyrethrin
Pyrethrins are botanical insecticides derived from chrysanthemum flowers. They quickly knock down most insects they contact. However, pyrethrins break down quickly in sunlight. So reapply every 5-7 days for ongoing control. Look for pyrethrin concentrates to mix with water. I’ve had success with concentrates from Monterey and Bonide.
Spinosad
A natural bacterium that infects insect nervous systems when ingested. Spinosad is effective for thrip and beetle control. It’s slower acting than other natural pesticides, taking 3-5 days to kill insects. But it provides 5-7 days of residual control. Repeat applications weekly. I recommend Monterey’s Garden Spinosad concentrate.
Diatomaceous Earth (DE)
DE is fossilized algae with sharp edges that pierce soft bodied insects. It desiccates them, disrupting feeding. Apply a thin layer to leaves, stems and soil using a powder duster. Reapply after rain. Food grade DE works best. It’s safe enough to eat! I use Safer Brand Diatomaceous Earth.
Follow all label directions carefully when using any pesticide. Pay close attention to required protective gear, dilution rates and plant safety warnings. Never apply horticultural oils and insecticidal soaps to stressed or drought-stricken plants. Test spray a few leaves first to check for sensitivity before spraying the whole plant.
When to Spray Dahlias for Bugs
Timing is everything when it comes to pest management! Here’s when I recommend spraying dahlias:
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Early spring: Make a dormant spray of horticultural oil plus lime sulfur to smother overwintering pests on tubers before sprouting.
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When shoots emerge: Spray emerging growth with insecticidal soap to control early aphids and thrips.
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Every 7 days mid-spring until first frost: Keep plants coated with your pest spray of choice to prevent infestations from taking hold. Neem, pyrethrins and insecticidal soaps are good rotational options for prevention.
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At first signs of damage: Such as leaf stippling, skeletonized foliage or flower damage. Pick a targeted organic pesticide and spray promptly. Getting ahead of bugs is crucial!
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Before an event or harvest: Spray plants 1-2 days before cutting blooms, hosting a garden tour or party. This ensures beautiful, pest-free plants!
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After rain or overhead watering: Reapply DE, neem oil, pyrethrins and spinosad shortly after watering. These break down when wet and need refreshing.
How to Effectively Apply Pest Sprays
To get good bug control, proper application technique is vital:
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Read the label: Follow all instructions for mixing, diluting, plant safety and gear. Measure concentrate carefully using a graduated cylinder for accuracy.
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Use a pump sprayer: It allows targeted application on all plant surfaces with a fine, even mist. Misting wands work even better for thorough underside coverage.
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Spray in morning or evening: Avoid hot sun which can burn wet foliage. Morning dew can help adhere spray to plants. Aim for times with little wind to avoid drift.
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Cover blooms, both sides of leaves, stems: Thorough, uniform coverage is key. Repeatedly pressurize sprayer as you work to maintain a fine spray.
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Add a spreader-sticker: These agents help spray spread and stick evenly on waxy or hairy plants. I add a few drops of mild eco-friendly dish soap like Seventh Generation to each gallon of spray.
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Spray surrounding soil: For earwigs, beetles and other soil-dwellers. Avoid flowering plants that attract pollinators.
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Reapply after rain: Water washes off most botanical insecticides so they must be reapplied every 5-7 days anyway.
How to deal with earwigs without using chemicals
Steve says that when you see nibbled petals, it may not be snails that are to blame. It may be earwigs. They’re the number two pest on dahlias.
“An old chemical-free way to get rid of earwigs was to put a pot on its side with straw in it on top of a pole,” says Steve. The earwigs went up into the straw for shelter and you could tip them out somewhere else.
However, Steve has other ways of minimising earwig damage in dahlias.
Firstly, he says that some dahlias are more likely to attract earwigs than others. The big decorative dahlias with their layers of petals offer good hiding places for earwigs. So they are more likely to suffer.
But the simpler single and collerette dahlias don’t offer so much cover. So if you really don’t want earwigs, don’t grow the big decorative dahlias.
However, that seems a bit sad. Steve suggests that if you do want to grow them, smear some Vaseline around the main stems. The earwigs won’t be able to get past it.
Steve also says that earwigs are good for the garden except when they crawl on dahlias. They feed heavily on aphids, blackfly and greenfly.
Dead head dahlias early and often
Steve says that dahlias should be dead-headed when the outer petals start to fall off, instead of waiting until the whole flower dies and turns into seeds. While this advice isn’t wholly about pest control without chemicals, it does actually help.
In vegetable gardening, slugs and snails are the garden’s rubbish disposal experts. They ‘tidy away’ the older, decaying leaves. One way of minimising slugs in a veg patch is to keep trimming away older, outer leaves. Dead heading flowers when the outer edges start to go over is the flower gardening equivalent.
But it’s hard for me to do this when there’s still a big, colorful flower in the border! But when I look at the petal damage in my garden, I can tell that it’s mostly the older flowers that are dying. Earlier dead heading would minimise this.