Chrysanthemum and Dahlia
There are a large number of insect pests associated with dahlias and chrysanthemums, the largest of these insect groups is the APHID group, comprising thousands of different species of sap sucking and predatory insects. It would be impossible to go into all the different species here so for simplicity we will concentrate on the main common types that a grower of dahlias will come across. In the Aphids the 3 main types are Greenfly, Blackfly and Whitefly.
Greenfly, Aphids & Whitefly
The most common group of aphids generally green in colour usually found at the top of the plant close to buds on the softer parts of the plant. Size approximately 1 mm in length six legged flightless insect. Causes damage from sucking the plant’s sap and producing sugary excrement that coats the leaves and stem providing ideal conditions for sooty mould to gain a hold. Also a source of transmission of plant viruses.
Any treatment for control of greenfly should be backed up with a fungicide treatment to prevent secondary infection of sooty mould.
The two spotted spider mite is prevalent in hot dry conditions in the UK, Prevention is easier than control. Although there are some very effective miticides available to control this pest. To prevent a build up of this pest it is important to keep growing plants humid, a spay of water under the leaves should prevent the pest somewhat.
These are the tiny brown specs of dust that fun all over the light coloured flowers, usualy seen on the lighter flowers because the barker colours mask them. By tiny in size we are talking about an eighth the size of a pin head! color is light brown. An easy way to check for presence of thrip is to take a piece of white paper to the open bloom on a warm day and place the paper under the flower and tap the bloom to dislodge the thrips. if you see brown dust scuttling all over the paper the you’ve got thrips.
Wasps and Bees
Have you ever seen the damage wasps can cause to the stem of a dahlia plant? they strip off the outer cuticle of the stem to get at the sugar laden sap the plant produces. They are a difficult pest to deal with and care should be taken when tackling them, they Sting!. It is difficult to recommend one chemical or otherwise that will get rid of them as they are very resistant to many of the chemicals listed. The best solution i can come up with is to trap them in sugar solution mixed with insecticide and placed in a bottle fixed to a cane in amongst the dahlias.
A small burrowing grub that eats dahlia tubers from the inside out, prevalent if potatoes have been grown on the dahlia beds in previous years. Also to be found in recently incorporated turf when preparing new ground from grassland.
Controls. Sterilisation of growing beds. Steam sterilisation or application of Dazomet.
Pretty self explanatory these pests will devour laves and leave plants looking like the proverbial net curtains.