However, all is not well. They are infested with Whitefly. When I brush my hand over them, clouds of little white flies emerge. These are the Cabbage Whitefly Aleyrodes Proletella, not to be confused with the similar-looking Glasshouse Whitefly Trialeurodes vaporariorum, which infests indoor plants, especially tomatoes and peppers.
The tiny scale-like nymphs of this annoying pest cluster on the undersides of brassica leaves. The photo below shows a mix of adult flies and nymphs. The latter come in a range of colours from white through yellow to brown.
The nymphs suck the sap of the plants and excrete a sticky substance known as honeydew which promotes the growth of black sooty mould.
Although large brassica plants are normally strong enough to survive the sap-sucking, the sooty mould often affects them more severely, because it retards their growth and encourages the ingress of other diseases.
If you follow the link earlier in this post you will see that even the much-esteemed Royal Horticultural Society considers that this pest is well-nigh impossible to eradicate. The best you can hope for is to "keep it under control". Easier said than done! The scaly bodies of the nymphs seem designed to protect them from pesticides. And of course the waxy leaves of the brassica plants mean that pesticide sprays don't adhere very well anyway. So what to do?
I am trying a rather basic remedy: I filled a spray bottle with water to which I added 3 crushed cloves of fresh garlic and a few drops of washing-up liquid. I have liberally doused the Brussels Sprout plants with this spray. My theory is that the washing-up liquid will help the garlic-infused water to stick to the leaves for long enough to kill at least some of the Whitefly nymphs. Of course this relies on the premise that garlic will kill Whiteflies, which may be entirely false! Garlic seems to kill many pests (it has also been in the news recently being used as a remedy for Ash Die-back disease), so maybe it will help here. I have also done my best to gently rub off as many of the nymphs as possible, which is no mean task even when you only have six plants. Between them they have a lot of leaves.
The RHS thinks that Cabbage Whitefly do little real damage, because they affect the parts of the plant that are not normally eaten. "Fortunately, cabbage whitefly only infests outer leaves and usually causes little real damage to parts of the plant that are consumed. Therefore infestations can usually be tolerated", they say. Well, I'm not so sure, because I was definitely planning to eat the Brussels Tops, the cabbage-like crowns of the plants. We'll see how it goes.
To avoid being too pessimistic, I'm finishing this post with a couple of arty photos for you (taken on a rainy day):
I stopped growing cavolo nero because of all the whitefly it attracts. I shall watch with interest to see if your spray works.
ReplyDeleteOh how frustrating. I suppose that protecting the plants from the cabbage moths may have made a cozy place for whitflies. I've certainly had that experience when trying to protect plants from birds, the aphid populations tend to boom under cover where they are protected from the predatory insects that keep their populatioons in check.
ReplyDeleteWe have them too and they are nuisances, The sooty mould that they cause also stops the leaves accessing sunlight and is yukky too. I read somewhere that all the oilseed rape planted nowadays -which also is a brassica - has created more foodplants for them and consequently the things have increased. There certainly seem to be far more now than there used to be. Another reason to hate the fields of oil seed rape.
ReplyDeleteI had a really bad aphid infestation. Bad enough that they got inside the cabbages a bit this year. At least they can be killed by soap. Luckily whiteflies don't survive our climate. Sometimes they get brought in and proliferate over the summer if people don't inspect their bought plants well enough, but usually I don't have trouble with them. I guess it is one benefit of all that snow and ice we get.
ReplyDeleteI have been recommended to use a fine mesh cover. I found this for sale but its very expensive! https://www.harrodhorticultural.com/ultra-fine-insect-mesh-netting-pid7805.html
ReplyDeleteSo did it work?
ReplyDeleteOnly partially.
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