Scented Geraniums and how to control Pests or Insects

(August 01, 2013)




Scented Geraniums and the topic of Pests

The pelargonium genus, including the Scented Leaf’s, as a group of varying types are relatively easy to grow and pests are not a major problem compared with some other plants.  However, plants and insects do go hand in hand and there are the ‘goodies’ and the ‘baddies’ and it is beneficial to understand which are which.  Apart from insects the other problem that may occur is a fungal disease and I shall write another article in our Hot Topics to cover this area.


 whitefly adult

whitefly eggs

The scientific study of insects is called Entomology.  Without getting too technical, as this is way out of my comfort zone, entomology is a branch of Zoology and this ultimately comes under Biology.  That’s a lot of ‘ologies for a gardener but if you love plants it is useful to understand something about insects; we tend to refer to the insects that cause the damage as being pests.  Apart from the pests there are also beneficial insects that should be encouraged, e.g lady birds and bees.

To learn more try doing a Google search - beneficial insects in the garden

For now, though, back to the pests.


greenfly adult 2

greenfly eggs with ants
with ants


Some insects may cause a problem with Scented Geraniums, however, they are not always easy to identify.  To the left of this article I have provided photos and it is recommended that you invest in a magnifying glass as some pests are barely visible to the naked eye:

‘THE BAD GUYS’ - high on the list to look out for are:

  • Whitefly
  • Greenfly
  • Aphids
  • Red spider mite
  • Slugs

To a lesser degree also look out for:

  • Thrips
  • Capsid bug
  • Caterpillars
  • Vine weevil


is a collective name
for many different
types of insects


As a Specialist Grower of the Scented Leaf group we are not immune from insects, nor can anyone who grows plants profess to be.  As I mentioned earlier, plants and insects go together and as with all life on this planet everything is part of the overall eco-system.  Survival of all living things = a dependency on something else that is living.  It also involves the survival of the fittest and that is why it is important that your Scenteds remain healthy and are cared for in the correct way.  When any plant is neglected it is an invitation for uninvited guests to take up residence.  Any type of decaying plant material will attract pests, i.e. the ‘Bad Guys’, as the rotting debris is what provides them with their food supply.

Red Spider Mite

red spider mite adult

red spider mite eggs
eggs on leaf



Biological Control of Pests = will not work with Scenteds

This is a non-chemical method of controlling certain pests by predators.  It relies on the introduction of specific natural enemies of insect pests.

Wherever possible we do prefer our Nursery to be as ‘organic’ and non-chemical as possible, however, after substantial research and many telephone calls it has been confirmed that there isn’t a particular or suitable biological pest control for Scented Geraniums.  Introducing a natural predator in to our polytunnel or greenhouse is, therefore, pointless as it will not be effective.  We have asked the ‘Experts’ why this should be so and the answer is that even they do not know why a ‘bad’guy’ insect will take up residence in a Scented Geranium, yet, the 'good guy' predators will rarely go near this group of plants.  This information was supplied to us by a leading Entomolgist who works on biological control research in connection with plants.




Chemical Control of Pests

If pests do become a real problem the only solution to assist the plants to survive will be a chemical insecticide and there are different ways of administering this, see below.  Having said this with careful monitoring of individual plants on a regular basis and the correct care it is possible to stay on top of the pests without the use of insecticides.  Personally, if a particular plant had succumbed to a really bad attack of, say, greenfly and looked desperate I would throw the plant away as you couldn’t be sure that all of the eggs had been removed even if you had carefully removed the adult greenfly. 


Capsid Bug

capsid bug




There are 3 different methods of application:

  1. spraying
  2.  systemic
  3.  fumigation

WARNING, ALL CHEMICALS ARE DANGEROUS AND SHOULD BE HANDLED WITH GREAT CARE - when using any type of chemical always put on heavy duty protective gloves and do not use every day household gloves, as they are not strong enough.  Wear a facial mask.  Always read the Manufacturer’s instructions carefully before using any chemical and do not deviate from there advice.



Common type of
UK Caterpillar

cabbage leaf caterpillar



(a)  Liquid insecticide is diluted in cold water, as per label instructions, and application can be by means of a small one litre plastic bottle which incorporates a trigger spray.  
This type of trigger spray bottle is on sale in supermarkets, garden centres and hardware shops and are cheap to purchase. 
ALWAYS write on the bottle using a permanent marker stating what insecticide you have had in it and do not use it for any other purpose. Buy additional bottles for other types of applications, as they really are cheap.
A 1ltr to 2ltr sized bottle is used for spot spraying on an odd house plant to control a small outbreak of green or white fly.  Also used for Epson Salts application for foliar feeding
(b) For use in a conservatory or greenhouse where large numbers of plants are involved a more powerful pressure spray is required.
(c) It is recommended that a facial mask is used when spraying any chemical, especially in a confined space.
(d) Spray around the plant in a methodical way and ensure that the underside of leaves are treated.  Tip the plant to avoid the chemical dripping in to compost and damaging the root ball.
(e) Spraying in a greenhouse or polytunnel.  Turn off air circulating fans.  Always walk backwards away from the spray.
(f) IMPORTANT – after the completion of spraying leave the plant to stand for 24 hours; preferably away from other plants and out of direct sunlight.  Do not water and do not feed for at least 24 hours. 

Vine Weevil

vine weevil

vine weevil larvae
creamy white

vine weevil damage to a leaf
leaf damage



A systemic application, in horticulture terminology, refers to the ingestion of the diluted insecticide through the plant tissue.  The plant takes up the mix in to its system which subsequently results in it becoming toxic to a browsing insect.  There are 2 ways in which the insecticide is ingested:

  1. through the root system, by adding the dilution to the watering system
  2. by spraying the underside of the leaves, the dilution will be ingested by the stomata cells.  These cells need to be open for ingestion to take place

    For the best results:

a)    chemicals should be diluted in to warm water  and the temperature should be within 20 to 25 deg. C.

b)    when spraying the underside of the leaves the air temperature should be in the region of 15 deg. C and above or the stomata cells will remain closed.  Lower than this temperature will render treatment non-effective.

Slugs & Snails

slugs various
Slugs - there are
many types

snails various
Snails - various




Fumigation may be used in greenhouses, polytunnels, sheds etc., wherever unwanted insects or pests are present.  However, it is not recommended for the inexperienced gardener, as it is considered to be dangerous.  This method should only be utilised by a competent or professional person who really understands the risks that they would be taking, i.e. to themselves, the plants and their surroundings.

WARNING - There are pros and cons for using fumigation and a lot of care, safety precautions and common sense is needed.  Always wear strong protective gloves, especially when lighting the container as there is a tendency for the chemicals to instantly ‘flare’, which is dangerous and poses the risk of fire.  Always follow the Manufacturer’s Instructions.

  • Basically, a fumigator is a chemical smoke bomb in a container. 
  • There is a method of setting light to the chemicals either by a blue touch paper or ignitable cord sticking out of the container. 
  • Once ignited the chemicals ‘flare’ out of the container in to the surrounding atmosphere in a smoking form.
  • The smoke drifts through the enclosed area and eventually settles on everything within the area.  NB:  Some fumigators will leave a messy residue but the modern types do not leave any residue.  It is perfectly safe to use the modern fumigators without removing the plants and there isn’t any adverse after effects to the plants.
  • The enclosed area should be quickly closed once the fumigators are lit.  There should not be any openings at all or the smoke will escape.
  • The enclosed area should remain shut for 24 hours for the fumigators to work and nobody, people or pets, should be allowed to enter.
  • After 24 hours open the doors and windows and ventilate well for a few hours before resuming normal operations.

PLEASE NOTE:  When a fumigator is used either in a greenhouse or polytunnel all living insects will be killed; this includes the ‘good guys’! 

With correct care
Scented Geraniums
are relatively
Pest free!!


Identifying the ‘Bad Guys’ is not always easy
Overall Scented Geraniums are a problem free plant to grow and are relatively easy to care for.  However, as we have mentioned previously, plants and insects do go hand in hand and there are a few pests that are very partial to the Scented Leaf group.  It is essential to monitor all plants on a regular basis and when an impending attack is spotted evasive action should be urgently taken to prevent the possibility of considerable damage.  There are many reasons why a certain plant may be attacked or preferred over its neighbour and this is a topic for another article.

To learn more about the individual insects we recommend that you either do a Google search or try Wikipedia for a change.

There are numerous different types of chemicals available to treat infected plants, both for in the home and around the garden.  It is often very confusing to understand what does what do, or mean?  Here’s a basic explanation:

  • Insecticide – a chemical control of insects, either by spraying, systemic or fumigation
  • Pesticide – is any substance or mixture for preventing,, destroying or repelling pests.  This may be either biological, chemical, a disinfectant or a device
  • Fungicide – a chemical control of fungal infections, used to treat the affected area of the plant
  • Herbicide – a chemical control of weeds or unwanted plants, use with extreme care as many will kill ALL plants in the area being treated


If you have any questions regarding the subject of Scented Geraniums and how to control Pests please Contact Us direct.













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