Pesticide for killing thrips

[ChrisR]

I had a bad infestation 5 years ago and after spray drenching my plants with Spinosad twice, a week apart ,it wasn't until last year that I started to see them return in any numbers. I'll do it again next Spring when I've got another bottle. I've just been spot spraying them with the little I have left when I see them in my Conophytum flowers and they immediately start to writhe around with contact and are dead soon after.

[Ali Baba]

Thanks I will look out for those Orius! I gave up using chemicals for control of thrips last year. They always come back eventually, the eggs are partially protected by being inserted in the hosts epidermis, and the pupal stage is in the compost which makes effective control by contact insecticides difficult. A nasty pest!!

[KathyM]

Thanks for all the advice; I hadn't thought thrips were a big problem for succulent plants but I guess they are from the number of replies! I haven't actually seen thrips on my plants yet so perhaps I would be best putting some yellow sticky traps on the windowsill and only using something if I spot them.

[Terry S.]

Blue sticky traps are actually more attractive to Western Flower Thrips than the more common yellow ones.

These thrips are now endemic in our greenhouses and most growers will have them. Stick something into the centre of a flower and see if any tiny creatures start moving around. They are more obvious in spring and autumn, less so during the heat of summer. Some people have had damage to cacti from them but usually the only affect is on Lithops where they create a band of dead tissue at right angles to the fissure.

Abermectin and Spinosin are the effective controls but not available to the amateur in the UK. We were told at the Haworthia Convention last year that one needs to go to a Californian cannabis-growing-aids shop to buy your spinosin. The speaker was otherwise having all the pollen, that was needed for his hybridisation program(me), eaten by the thrips.

[ChrisR]

I've had a similar problem with my cono flowers this year........not only eating the pollen but I've actually seen petals fall off otherwise fresh flowers as they have been chewed by thrips! Buds have often developed into misshapen flowers or not developed at all, a bit of a disaster for seed production this season.

[Ali Baba]

In my experience they are very partial in their attacks on plants. Some can be really badly affected, whilst others are barely touched. Opuntioid cacti seem particularly affected, particularly the flowers where the outer petals can be damaged enough to fuse the flower parts together stopping the flower opening properly.

Yellow-spined cacti and soft bodied cacti seem particularly susceptible, activity over winter is particularly damaging, usually producing a scar at the stem apex which only becomes visible when the plant grows in the spring (as in Lithops damage as mention above by Terry).

Some plants are so susceptible as to be unable to grow properly without some spraying, eg Peniocereus and notably Astrophytum caput-medusae, and some Avonias. Seedlings of all types seem particularly at risk.
They also produce some odd effects on particular cacti, banding thicker spines with pale marks, and reducing the spine length in more delicate spines presumably by feeding on the young spinelets as they develop at the stem apex. This is very obvious on Mammillaria leutheyi where the contrast betwen 'thripped' areoles and normal areoles is very stark. I note a few people have asked about similar damage on their Mammillarias on this forum, so it may occur on other species too.
Very severe scarring of the epidermis can occur in some susceptible plants, mimicking damage caused by mites.
As Chris has said, they can really damage flowers on Conos and Lithops, perhaps because the flowering in the late summer and autumn coincides with maximum thrips reproduction as the temperatures are falling.

Thrips can be very difficult to spot, the adults are very mobile and fast moving, and will hide very quickly from a human gaze. The larval stages which do the most damage are very small and yellow and slower moving. You need at least a x7 lens to spot all stages. Damage is usually accompanied by small black spots (the thrips droppings) which is diagnostic.

As has been mentioned a couple of times, blue sticky traps work well, but they are only useful in determining if you have thrips, they dont control the pest effectively. Predatory mites are also used commercially, but you need frequent applications and they only work within certain parameters of humidity and temperature. Mexican Pinguiculas catch hundreds of them, but again only the adults. Mexican Pinguiculas will grow happily amongst your cacti and succulents.
Here's a few pictures:

Mamillaria leutheyi showing spine malformation zone then regrowth of normal spines after spraying with acetamiprid.

Ariocarpus agavoides seedling growing out of winter damage. Regrowth since introduction of predatory mites.

Stem apex of Melocactus violaceus seedling showing very subtle spine banding and mild spine distortion from mild thrips attack.

[Paul D]

They are capable of doing serious damage to cacti. I have had some problems with this. A summary of how serious the problem is in the UK is here:
http://randd.defra.gov.uk/Document.aspx ... 5_ABS.docx

[Ali Baba]

Thanks for posting that Paul, interesting (but rather depressing) reading

[conolady]

Spinosad is on both eBay.co.uk and Amazon.co.uk. It's expensive, of course, imported from the States, but not too bad...

[KathyM]

I have got a couple of Pinguicula plants on the windowsills and can't see anything other than fungus gnats and a few aphids stuck to the leaves, so that's kind of reassuring I suppose. I will try to find some blue sticky traps, they don't seem to be seen much.

I have been baffled by the damage on a Lepismium plant for a while now and I am wondering if that is thrips - pale sunken patches on the stems with tiny dark dots. I haven't seen anything on it though.