All is not well in the greenhouse.
It’s been a long, dry summer, and though I water every day it’s been a struggle to get enough into the plants. Plus the lack of rain has meant humidity has been really low: even watering on the hot greenhouse path, so it evaporates into the air, gives only temporary respite.
That’s my excuse, anyway. Another excuse – though not a very good one – is that I glanced at the yellowing leaves of my cucumber plants without looking at them properly a week or two ago and thought to myself, ‘Ah – another bout of magnesium deficiency. Must remember to get some Epsom salts.’ And left it at that.
Had I looked closer, though, as I did this morning when I noticed the leaves were not only yellowing but going crispy and brown at the edges (not a symptom of magnesium deficiency I’ve ever come across), I would have noticed that on the underside of the leaves there was a spangling of tiny, tiny dots. By the time the alarm bells started ringing, there was also the telltale ‘spider’s web’ draped across the heel of the leaf, also with its load of tiny little dots: all unmistakeably red spider mite.
Despite the name, they aren’t red: not yet, anyway. Red spider mites are in fact a sort of yellowish green. They do turn orange, but that’s not till autumn and this is not the sort of autumn colour you want to be seeing. They do have eight legs, just like a regular spider, and spin webs – though not to catch prey but to protect themselves and act as a highway from one bit of your plant to the next.
I should have caught this when it was still at the tiny-dots-on-the-leaf stage, as now I’ve got webs I have what is embarrassingly known as a Heavy Infestation. The drying-up bit also means I’ve left it far too long to act, and my plants are in imminent danger of keeling over any moment: I see a couple of younger cucumbers are showing definite signs of droop.
There is quite a lot of new, green young growth coming through which doesn’t seem to be affected, so the moment I realised what was going on I took off the worst of the yellowing, curling older leaves: they weren’t going to do the plant any good any more anyway, looked unsightly, and by taking them away I have also removed the worst of the red spider mites too.
I also sprayed water all over the plants to make them damp: red spider mites love it hot and dry, so this is the one exception to the rule that you don’t water the foliage. Spraying upwards – i.e. on the undersides of the leaves – makes sure those little dots get the dousing they deserve.
But – and this is an important but – both of these measures are a temporary stop-gap. Red spider mites are very good at hiding in nooks and crannies and coming out later when you’re not looking, and my new growth is at risk too if I don’t do something: eventually, if I let it go completely unchecked, my cucumber plants will meet an untimely end. Which would be a pity, as they’ve been producing bucketloads of cucumbers – it’s ‘Tiffany’, an all-female variety producing long, large, smooth-skinned cukes – and are otherwise performing fantastically well.
I could use a biological control on this lot: Phytoseiulus persimilis, another mite but this time one which eats red spider mites instead of cucumber plants. I am very intrigued by biological controls: I’ve only ever used one, the nematode you water onto areas infested by slugs, and I couldn’t honestly say whether or not it was effective. I didn’t notice a dramatic difference: but on the other hand that year was quite dry so a good one for slugs (or rather, a bad one if you happen to be a slug) all over the garden, not just the bit that was watered with nematodes.
One of these days I shall do a proper trial in which I actually notice what difference it makes when you apply a biological control. They’re widely used in Kew and elsewhere: and I bet they don’t have red spider mite.
But right now I have an emergency on my hands and need a faster solution than a biological control which I’ll need to order online. So I’ve fallen back on my one-size-fits-all pest control: organic insecticidal soap, the one I used for my greenfly and blackfly earlier this year. In the greenhouse it should be even more effective as it doesn’t get rained off.
Next year, I shall be patrolling inside and out with a sharper eye for such things: caught early, these little bugs wouldn’t have caused nearly so much damage. This is one lesson I’ve learned the hard way.
[…] When bringing plants indoors, carefully check them for pests! Red spider mite can now be a problem: http://j.mp/9NR8d8 […]
Slugs are best controlled with Nematodes, I sell billions of them in the season, they must be used in damp condition to gain full effect, start with them mid March and apply every 8-10 weeks
Dont forget its now coming to Mole season, these little devils can cause havoc in the garden so be watchfull, there are numerous methods of control available