Pests & Diseases


What Pests & Diseases do Dahlias get?

Common pests that can affect Dahlias are Thrips, Aphids, Two Spotted Mite, White Fly, Cut Worms, Mealy Bug, Snails, Powdery Mildew. and Virus.


When Controlling Pests it is very advisable to understand what your chemical will control.


It is best to use Specific Chemical for a Specific Pest.

If you use a “Kill-All Spray” you are likely to wipe out most of the predators (Goodies).


Without Predators the number of Thrip/Aphids will explode because there are no “Goodies” to assist controlling them.


Insecticide for Insects                                 Thrips & Aphids

Miticide for Mites                                          Red Spider (Two Spotted Mite) Broad Mite

Fungicide for Fungus                                 Powdery Mildew,

Nematicide for Nematodes                         Eelworms (Nematodes)

Weedicide for Weeds                                  Weeds


If you want to know what to use contact your Garden Centre or chemical supplier & ask for the product for the specific pest.


It is advisable to rotate your brand of chemical to reduce any buildup of resistance.

Powdery Mildew

The first signs of Powdery Mildew is the appearance of that Greyish White Powdery looking stuff.

This can explode in a matter of days covering all the leaves.

 Powdery Mildew.jpg

The signs of an infection are usually first seen on the lower leaves of the plant.

Powdery Mildew is best controlled with preventative sprays of fungicides applied at least three times during the growing period. (Early Feb, March & April)

Heavy infections of Powdery Mildew will affect any seed collection and the reduced vigour of the plant will affect the development of the tubers.


Virus appears in a variety of forms and severely distorts leaves & stunts plants.

There is no cure.

Any infected plants will only continue to infect surrounding plants.


 Virus Digging.jpg

If the affected plant is not removed the virus will be transferred to neighbouring plants magnifying the problem for the following season.

I say “Virus in Dahlias is the same as Aids in Humans”, there is no cure.


How do I know it is Virus?

If your plant is stunted, leaves are twisted & curled and all the main veins on the leaves are yellow.

These symptoms are very easily confused with a mineral deficiency.

Green Veins with yellow areas between

= Nutrient Deficiency.

Virus Yellow.jpg

Green Veins

Yellow Veins or Twisted/Distorted Leaves = Virus

There is no cure

The plants & soil below were


Virus 1.jpg     Virus.jpg 

Virus 2.jpg            Virus 4.jpg

 Virus 5.jpg


 Digging out is the ONLY Cure

Virus Digging.jpg


Enquiries and comments to

John Menzel-

08- 85837369              0408 837369