Chrysanthemums in Aberdeen
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Common
 Chrysanthemum
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Common Pests:
-
Aphids
- Thrips
- Leafminer
- Earwigs
- Slugs 
- Whitefly
- Capsid Bug
- Caterpillars
- Red Spider Mite
- Vine Weevil
- Sciarid Fly
- Stool Miner

Common diseases: 
- White Rust
- Verticillium Wilt
- Powdery Mildew
- Crown Gall
- Chrysanthemum Rust
- Botrytis

Common disorders:
- Nitrogen 
- Phosporus
- Potassium 
- Magnesium
- Manganese
Boron
- Copper
- Iron
- High Salt levels

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Date last updated: 
22 June 2008

 

Thrips (last updated 22 June 2008 )

Thrips are small cylindrical insects known as thunder flies, 3-4mm long, the adults are winged. More than 150 species occur on plants in the UK. Colour varies from white through to black. They are difficult to spot on chrysanthemum foliage. By the time their feeding marks become apparent on the foliage there will be quite a colony present. They are much more difficult to control than aphids because many species like the Western Flower Thrips, Frankliniella occidentalis have become resistant to the pesticides available to amateur gardeners, and they can also pupate in the soil and re-infect plants when they become adults. The most widely known Thrips is Onion Thrips - Thrips tabaci.


thrips tabaci

Impact of Thrips

The method of operation is such that the mouthparts are driven into leaves and petals, the head then rocks backwards and forwards to scrape the tissue. The resulting semi-liquid mass can then be sucked out by putting the mouthparts together to act as a drinking straw. The result is a white patch on the leaf or petal. Brownish blobs of thrips excreta subsequently turn black and give the white patch a characteristic speckled appearance. There is often distortion to plant growth associated with thrips feeding on young growth but thrips do not feed on plant veins, an important point because this means that they are not controlled by insecticides acting systemically.


They are the vector for the Tomato Spotted Wilt Virus which can affect over 250 different plants in the UK. Therefore it is not just the danger of spreading virus from chrysanthemum to chrysanthemum but common plants like Impatiens, petunias, tomatoes and cucumbers can carry the disease. 

The symptoms of the virus disease are stunting, distortion and leaf mottling, some varieties being so susceptible that they die. Chrysanthemum cultivars also vary in their susceptibility to direct attack, some having brown, shrivelled flowers and extensively “silvered” foliage. 

The virus has different symptoms on different plants so it is hard to spot. Thrips like flowers of all kinds, chrysanthemums are no exception. A female Thrips lives for about a month and during this time lays about 100 eggs, quite often these are inserted into plant tissue with its ovipositor. They have a toxic affect on the plant and especially the petals, so it's not just the feeding damage but petals distort badly from the toxins during a severe attack. 

Odd Thrips arriving on plants just before the blooms mature can leave bleached marks on the tips of one or two petals. Thrips thrive in dry hot conditions; periods of rain will help to keep them under control. There is a biological control, a predatory mite Amblyeius cucumeris,  but it is only possible to use this when the plants are in the greenhouse. 

Control 
Bifenthrin will often control the common Thrips but Western Flower Thrips is a different matter. 

Commercial products containing - abamectin, teflubenzuron and thiacloprid have proven to give good control.



thrips damage on leaves

Other information 

 

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