An Aphid infestation

On the weekend I discovered my Bay tree was infested with Aphids. This is the first time in a couple of years I’ve seen a plant in our garden really inundated, and there was not a ladybird in sight!

Looks like the natural Aphid predators we have been nurturing have all gone quiet for Autumn, and there was nothing stopping these wretched pests from taking hold.

White aphids under a bay leaf

Black aphids — far more numerous

I found hundreds of Aphids on the under side of every leaf. What tipped me off? The tops of the leaves are covered in sooty black mould:

The Aphids exude a sticky sweet substance as they feed on the leaf. This stuff is a perfect food for sooty black mould.

Well, when I saw this I was most unhappy. Just up the slope we used to have a pair of topiary trees that became infested with sooty mould and no matter what I did, I couldn’t get rid of it. We ended up removing them (they were also very, very ugly)!

I don’t want to lose my lovely Bay tree, so I went to work with my secateurs to prune the worst of the sooty black mould away. The tree won’t mind a trim, I haven’t been pruning it since we planted it and it was getting a little tall.

The back of the tree was much worse where there is more shade. I took a fair bit from low down and behind to let the air flow more freely here.

Once I was happy with the new shape I took some soapy water and a rag and scrubbed away at the sooty mould:

I can’t say this was hugely successful! Maybe I should have used soapier water? Or a toothbrush, maybe. Quite a lot of the aphids wiped off from the underside of the leaves, leaving me with (still a lot!) of the more sticky ones. But I didn’t make much headway on the mould up top.

As you can imagine, washing a tree by hand takes a long time! I did the best I could, but the morning started to get away from me. At some point I realised I would have to just get on with the white oil and return to my nagging children! 🙂

I make up my own white oil using a recipe from Gardening Australia. Jerry Coleby Williams suggests you make up a batch of oil and store it for up to three months in a jar:

• 2 cups of vegetable oil (sunflower or cheap bulk olive oil)
• 1/2 cup dishwashing detergent

When you want to use it, shake this up well and add 1 tablespoon to each litre of water. I find I hardly ever need white oil any more, so I’ve stopped storing it in bulk. Instead I just scale the recipe to suit my pressure spray bottle.

I use a pressure sprayer to save my hands from pumping a trigger

Spray the whole plant

Make sure you get the under side of the leaves

I coated the leaves and stem well with the spray, especially the underside where the aphids are actually hiding. I also coated the leaves without aphids to make sure the pests don’t take control there too.

Here are a couple of spray tips:

• Avoid spraying in really hot weather, or the leaves will clog with oil and suffer
• Avoid spraying in hot sun, because the oil can get very hot and burn your leaves
• Floppy and hairy leaves (like lettuce and lamb’s tongue) are not suitable to spray because they will burn
• Gently bend the stems over so that you can get more easily at the undersides of the leaves. That way you spot where you’ve missed and the spray dribbles all over
• Check the leaves after rain to see if they still feel a bit oily. If not, you might need to spray again to recoat the aphids

In a week I will check the aphids and see how many have died off, and if there are new aphids there. I will probably need to spray a total of three times, two weeks apart.

I think I will also look up the Bay tree and see what fertiliser and soil condition it likes, just to make sure it can get back to full health quickly!