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Keeping Cats Safe: Weed killer

26th June 2020

  •   Keeping Cats Safe
Keeping Cats Safe: Weed killer

For this month’s Keeping Cats Safe we are looking at products and chemicals that are commonly used in the house and garden that can be harmful to cats. In this article we’re looking at weed killers.

There are a wide variety of different products available for controlling or killing weeds, but those for domestic use contain only a few different herbicidal compounds. If you believe your cat has been exposed to a weed killer, it’s important to note the name or ingredients so your vet can decide on the best treatment, and if you believe your cat has ingested herbicide, it’s important to seek veterinary advice.

Cats can be exposed to weed killers by walking on recently treated grass or brushing past wet plants and then grooming themselves. They can also lick up spills, chew treated plants, or be exposed to ‘spray drift’.

Below we will be looking at some common herbicides.


Glyphosate is in many products and is effective against different types of weeds. It’s applied after the weed has started to grow. It’s primarily available in liquid formulations and is considered to be of low toxicity. Many products contain polyoxyethylene amine which helps the product to penetrate the plant surface, and this is believed to be responsible for some of the toxic effects.

Clinical signs
  • Vomiting
  • Anorexia
  • Lethargy
  • Diarrhoea
  • Tremors
  • Drowsiness
  • Dilated pupils
  • Severe respiratory signs are a feature of exposure and can be fatal
  • Eye and skin irritation are also possible
Chlorophenoxy derivatives

These are frequently found in combinations in products and used in lawn feed and weed products. They are available in granular form or as a liquid.

Clinical signs
  • Salivation
  • Vomiting
  • Abdominal discomfort
  • Lethargy
  • Ulcers in mouth
  • In severe cases there may be bloody stools, anorexia, progressive weakness and myotonia.
Ferrous sulphate 

This product is used as a moss killer. It may be available directly as the chemical, but is more commonly found in ‘lawn feed, weed and moss killer’ products which contain a fertiliser, herbicide and the moss killer (ferrous sulphate). These are often available as granular products and are usually used between March and October to revive the lawn.

Clinical signs

This product can cause toxicity because the body can’t eliminate excess iron. Overdose causes gastrointestinal irritation and more severe problems if a large quantity is ingested. Walking on a treated lawn can cause local irritation and licking treated grass or grooming the product can cause gastrointestinal irritation, vomiting, hypersalivation, diarrhoea and polydipsia.

Fatty acids

Octanoic acid (caprylic acid), decanoic acid (capric acid) and nonanoic acid (pelargonic acid) are some naturally occurring fatty acids that are found in some weed killers, especially those labelled as organic.

Clinical signs

Few cases of exposure have been reported, probably because cats are repelled by the smell. In the small number of cases that have been reported, cats have developed irritation or ulceration in the mouth, anorexia, salivation and a high temperature. Prolonged contact can cause severe skin irritation.

Always use these products according to the manufacturer’s instructions. Preventing free roaming cats from coming into contact with these products can be difficulty, and if you’re concerned it may be best to manually remove weeds and avoid the use of herbicides.

If you suspect that your cat has ingested a weed killer or herbicide, seek veterinary advice.

Keep up to date with the rest of the Keeping Cats Safe campaign here.

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