Broccoli and Aphids

This query arrived without the pictures first so I imagined sooty mould, as it turns out I wasn’t far wrong. This Broccoli crop is supporting a healthy community of Aphids. Have a look at the image below, you can see a thick grey mass tucked snugly up beneath the Broccoli floret. Hundreds of them These little beasts are having a lovely time sucking the goodness out of the plant, so much so that the floret opposite is maturing unevenly. The sap sucking is also what causes the leaves to curl.
Aphids are insects that suck sap. They love soft, quick growing plants like fruit trees and roses in spring. Yum, juicy. There are lots of Aphid species, each one targeting a different plant type and their colour often reflects the plant they enjoy feasting on most. Some are yellow, some a beautiful green and these ones have adopted a grey to camouflage them amongst Broccoli.
Aphids infest plants quickly. Blink and the stems of your favourite plant are suddenly thickly coated in little fat bodies. They are also relatively easily disposed of with systemic chemicals such as Confidor. Aphids are a pest that we scout for regularly and spray only when we find them.
Liz and many other gardeners want a solution to the aphid problem that doesn’t involve chemicals. The most common suggestion is to hose them off, but you might find this option even more anti social under current circumstances.
Their bodies are so soft they can be manually squashed, but with an infestation like this one squashing will be both messy and time consuming.
Soft chemical options are Clensel and white oil. Clensel, a soap solution and white oil just clog up the insect’s ability to breath. Have a look at the Clensel link; there are all sorts of ‘alternative’ pesticides.
The ‘ideal’ solution is Bugs for Bugs. (I use inverted commas because we are all aware of the problems associated with the importation of Cane Toads as a biological control agent). The only problem is, I am note sure that predatory bugs are available in retail packages. If you know anything about packaged lacewings or ladybirds please let me know.

Judi wrote

“Good morning Peter, Please can you advise me of a small problem I think I have I have built myself a worm liquid farm from a large council bin, (bought I might add) has been working fantastic until recently, it now is full of a tiny insects. My liquid went from one litre a week of worm liquid down to about 1/4 btl. I take it the insects have something to do with this. Can I spray, it was suggested I use vinegar, but will this affect the worms. Would appreciate your advice."

I have had plenty of feedback on worms both from gardeners and some retail nurseries. I have also discovered mountains of information on the web, but I am not sure any of it specifically answers Judi’s question.

The little flies are almost certainly Sciarid Flies also known as Fungus Gnats or to most nurserymen: S**t Flies (a bit coy I know but this is a family newsletter). Sciarid flies feed on decaying organic matter, so they love worm farms & compost. Their larvae burrow into plant stems & roots and they are quite resistant to chemical controls. Chemicals have to be rather strong so they are best avoided. The most effective controls are rather clever. Most important in a nursery environment is hygene, ie. Clean up your mess. Puddled water and piles of dirt and loose potting media are bad news. I’ sure you can imagine how potting mix collects under benches and in corners around a nursery. The other solution is regular application of Nematodes. Nematode is just a fancy name for worms, but this microscopic little blighter arrives in a Chinese take away container and has to be stored in the fridge. The nematodes are applied as a soil drench. Once in the soil they attack the larvae of the Sciarid Flies. Phew, that was the short version.

That’s why the worm farm and compost bin have a lid, to keep the flies out. Of course it never works and the flies set up shop in the bin. Can they hurt your worms? I doubt it.

What will hurt worms? Acid, that’s why I get into trouble for putting citrus and onion scraps in the compost at home. So it’s also pretty clear that we shouldn’t put vinegar into the worm farm.

The other common worm ‘problem’ appears to be over feeding…wait there’s a light turning on here. Too much food, the food rots, provides food for Sciarid Flies and possibly makes the whole environment acidic, acid environment upsets the worms! Wow, got there.

Judi, cut back on the worm food! Mark our truck driver used to deliver 1 tonne of carrots per week to a commercial worm farm in the UK, so he swears by carrot. Richard Thomas (check this web site, it’s a beauty) suggests your worms will eat their own body weight every day or two. How can you tell their body weight? I don’t know, but I’m pretty confident that if the Sciarid Flies start hanging around you are over feeding. Richard has since told me that worms do eat less over winter so you have to modify how much you feed them.