Soft Scale Insects.
I was recently looking at some small spare mother plants that had been put outside for a few weeks, apart from a little thrips damage, I spotted an old enemy, soft scale insect.
There are more than 25 different species of scale insects in the UK, but two types of soft scale [Coccus hesperidum and Saissetia coffeae] are the ones that concerns us as the pest that usually infest cannabis.
The adults of Coccus hesperidum are 3-5mm long, green to brown in colour, oval shaped and appear slightly flattened. Saissetia coffeae is slightly smaller, only 3-4mm long, dome-shaped and dark brown with an H shaped ridge. Young scale known as ‘crawlers’ are pink/buff and only visible to the naked eye when massed together. Once they leave the protection of the adult scale shell, they are not easily seen until they settle and develop their own scale covering.
C. hesperidum adults produce around 2-3 live crawlers each day over a period of 2-3 months (around 300 in total). These disperse almost immediately over the plant. They choose a site, usually near the plant's veins or stems, settle down and develop their scale covering.
S. coffeae adults lay about 2000 eggs under the scale before dying. The crawlers hatch and disperse searching for a suitable feeding site on the plant. They are parthenogenetic, so no males are produced, so each new crawler in turn will produce another 2000, in a mother/cutting/veg room new generations will be continuous throughout the year. At a temperature of 18-20°C the complete life cycle can be as little as two months..
These little devils can be brought indoors by bringing in plants from the outside or on clothes at the crawler stage. Once indoors they will multiply very rapidly as I have outlined above, “it only takes one.”
Scales can be seen on stems and both the top/underside of leaves. Heavy infestations may result in poor growth or even killing a plant, they also transmit plant viruses. Soft scale produce copious amounts of a sticky liquid called honeydew, it is excreted by the scales and deposited on the foliage.
If you find even one, do not ignore it or else you will find this in no time:-
Chemical Control and Eradication.
Hard control, spraying with imidacloprid [Bio Provado Ultimate Bug Killer] will usually eradicate light infestations with one treatment, but if it has got to a point where there are several generations 2 or more sprays may be needed for complete eradication.
A softer treatment for organic growers, is to spray with soft soap, this spray must contact the scale directly to be effective, so spraying all leaf/stem surfaces to run off is needed, several applications will be needed for total eradication.
Finally Biological control.
The best product at present contains two types of parasitic wasp Metaphycus helvolus and Encyrtus infelix and is worth trying if the infestation is not too heavy.
The above bio control is expensive, it can be found at ladybird plantcare both preditors together should work well in the environment to be found in the mother box, but its not something I have tried personally. oldtimer1.
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