Crunchy leaves, misty mornings, muddy paws: autumn walks are the best. But the season also drops a few hidden autumn dangers for dogs right onto the path. Here is what to watch for, from acorns and conkers to ticks and early darkness, and what to do if your dog swallows something.
In short
- Acorns, horse chestnuts (conkers) and wild mushrooms can make dogs sick. Do not let your dog chew or play with them.
- Rat poison and antifreeze are used more in autumn and are emergencies: call your vet straight away.
- Ticks do not stop in September. In the Netherlands they have been found on dogs all year round.
- It is dark early after the clocks go back on October 25, 2026. Make sure drivers and cyclists can see your dog.
Are acorns poisonous to dogs?
Yes, they can be. Acorns contain tannins, which can upset the stomach and, occasionally, damage the kidneys. A Dutch vet points out that green, unripe acorns and young oak leaves contain the most. Typical signs are vomiting, diarrhea, belly pain and a dog that is quieter than usual.
There is also a mechanical risk. Acorns are hard and round. Swallowed whole, they can get stuck in the gut. Under big oak trees in October, the ground can be covered with them, which is exactly where Rex loves to snack.
Horse chestnuts (conkers): pretty, but not a toy
The shiny brown chestnuts in spiky green shells that you find in parks are horse chestnuts. They contain aesculin, a substance found in the nuts, leaves and bark of the tree that is toxic to dogs. Signs usually show within one to six hours, but can take up to two days: vomiting, diarrhea, restlessness, belly pain and loss of appetite.
Conkers are also exactly the right size to lodge in the throat or intestines, and some dogs need surgery to get one out. So the classic autumn game of throwing a conker for your dog? Better swap it for a ball.
Wild mushrooms: treat every one as toxic
Autumn is mushroom season. Most mushrooms are harmless, but a few are dangerous, and even experts find it hard to tell them apart. Poison experts therefore advise treating any unidentified mushroom your dog eats as toxic until proven otherwise.
In the Netherlands, the death cap (groene knolamaniet) is the best-known deadly species. In 2015 a young poodle died in Naarden after licking or eating one beside a footpath. Mushrooms in your own garden? Remove them with gloves on.
Fallen fruit, compost and leftovers
Rotting apples and pears under the trees, a forgotten compost heap, a soggy pile of leaves: mold on decaying plant material can make dogs sick, with vomiting, twitching or tremors. Pet Poison Helpline warns that even small amounts from a compost pile can cause tremors or seizures within 30 minutes to a few hours.
Keep an eye on seasonal food too. Grapes, raisins and sultanas can cause kidney failure in dogs, and autumn treats with chocolate are best kept out of reach.
Rat poison and antifreeze: real emergencies
When it gets colder, people put out rat and mouse poison and prepare cars for winter. Both are on the fall hazard list of the Pet Poison Helpline.
- Rat and mouse poison can cause internal bleeding, breathing trouble or seizures. The baits are made to taste good, which also attracts dogs.
- Antifreeze often contains ethylene glycol, which tastes sweet. Depending on the size of the dog, a tablespoon or two can be fatal. The first signs can look like your dog is drunk, and they may seem to get better before kidney damage shows.
If you think your dog has touched either one, do not wait for symptoms. Call your vet immediately.
Ticks in autumn: no, the season is not over
According to the Dutch public health institute RIVM, ticks can be active as soon as it is warmer than 7 °C, and they are most active from March to October. A mild autumn day easily reaches that.
A Dutch-Belgian study found ticks on dogs throughout the year in nearly all Dutch provinces. It also found the tick Dermacentor reticulatus in new areas, some of them carrying Babesia canis, a parasite that can make dogs seriously ill. The researchers concluded that year-round tick control is justified. Ask your vet which protection suits your dog, and check the coat after every walk through tall grass or woods.
Ponds, ditches and blue-green algae
Blue-green algae (blauwalg) are mostly a summer problem, but a warm early autumn can keep them going. Official water checks in the Netherlands run during the swimming season, which ends on October 1 for most locations. After that, the status on zwemwater.nl may no longer be up to date.
Algae toxins can be serious for dogs, which drink the water and lick their wet coat afterwards. Rule of thumb: green scum, a paint-like layer or a bad smell means no swimming and no drinking. After a dip, rinse your dog with clean water.
Dark at five: be seen on evening walks
On Sunday, October 25, 2026, the clocks go back an hour. From then on, the evening walk often happens in the dark, in the rain, on wet roads with cyclists and cars. Reduced visibility makes it harder for drivers to see you and your dog.
- Wear something light or reflective yourself.
- Choose a harness or collar with reflective details, plus a small light if your route is very dark.
- Keep the leash short near roads and bike paths.
Our SCOBYDOG harness has reflective stitching, so headlights pick up your dog on the evening round. It goes on over the head in one click, which is handy when your fingers are cold and Luna is already at the door.
From our shop
SCOBYDOG No-Pull Harness
Slips over the head in 3 seconds. The front D-ring guides your dog back to your side, with pressure on the chest, not the throat.
Discover →Quick overview: autumn dangers for dogs
| Hazard | Why it matters | What you do |
|---|---|---|
| Acorns | Tannins, stomach upset, blockage | Leash on under oaks, "leave it" |
| Horse chestnuts | Aesculin, choking, blockage | No conker games, call vet if eaten |
| Wild mushrooms | Some are deadly, hard to identify | Treat all as toxic, photo for the vet |
| Compost, rotten fruit | Mold can cause tremors | Cover compost, clear fallen fruit |
| Rat poison, antifreeze | Bleeding, kidney failure | Emergency: call vet immediately |
| Ticks | Active above 7 °C, Babesia risk | Protection from your vet, coat check |
| Blue-green algae | Toxins in water and on the coat | No swimming if in doubt, rinse |
| Darkness | Drivers see you late | Reflective gear, short leash |
Tip from the SCOBYDOG team
Practise "leave it" at home with a boring treat on the floor, then with a toy, then outside. Reward big every time your dog looks at you instead. It takes a few weeks, but it saves a lot of acorn drama under the oak trees.
Has your dog eaten something suspicious? Call your vet straight away, even if your dog seems fine. Do not make your dog vomit yourself and never give salt water. Note what was eaten, how much and when, and take a photo or a piece of it (mushroom, packaging) to the vet.
Autumn walks are worth it: cooler air, fewer crowds, amazing smells. With a few habits, they stay safe too. And once November arrives, it is time to think about the next challenge: read our plan for a dog scared of fireworks.
FAQ
How many acorns are dangerous for a dog?
There is no safe number. It depends on the size of your dog, how many it eats and whether the acorns are green or ripe. Even one acorn can cause a blockage in a small dog. Call your vet if your dog has eaten acorns and seems unwell.
Are sweet chestnuts also toxic to dogs?
The chestnuts you usually find in parks and along streets are horse chestnuts, which are toxic. Sweet chestnuts are a different tree, but whole nuts and their spiky shells can still cause choking or a blockage. Do not let your dog eat either.
Do I still need tick protection for my dog in autumn?
Usually yes. Ticks can be active above 7 °C, and in the Netherlands they have been found on dogs all year round. Ask your vet which product suits your dog.
What should I do if my dog ate a wild mushroom?
Call your vet or an emergency clinic right away, even without symptoms. Take a photo or a piece of the mushroom with you. Do not try to make your dog vomit yourself.
Sources
- Which? (with Blue Cross and the Veterinary Poisons Information Service) – 6 autumn hazards dogs need humans to know about
- Pet Poison Helpline – Fall toxins poisonous to dogs and cats
- VCA Animal Hospitals – Protect your pet from these autumn safety hazards
- Rodi – Het spreekuur van dierenarts Marjolein: help, mijn hond heeft een kastanje op
- NH Nieuws – Poedel Fleurtje dood door supergiftige paddenstoel (2015)
- RIVM – Tekenbeten: wanneer zijn teken actief?
- Jongejan F. et al. (2015) – Novel foci of Dermacentor reticulatus ticks infected with Babesia canis and Babesia caballi in the Netherlands and in Belgium, Parasites & Vectors 8:232
- Zwemwater.nl – actuele waterkwaliteit en blauwalg
- Omroep Brabant – Zwemmen tussen de blauwalgen
- Rodi – Wintertijd 2026: wanneer klok verzetten?
Photos: Kat van der Linden / Unsplash, Claudio Grande / Unsplash, T (@tanyabarrow) / Unsplash
