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Scale Insects

My acer tree under attack from scale insects

In a rare spell of dry weather the other day I ventured out to drop off some veg peelings into the compost bin. Pausing to have a quick nosey about the garden and see how everything was coping with the deluge of rain we’ve been experiencing I spotted with a sinking feeling an assault on my acer. Peering under the leaves I could see little limpet-like bumps on the branches and trunk of the tree. A couple of years ago I had had the same problem with my Viburnum bodnantense so I knew it was a type of scale insect.

Scale insects suck the sweet, sugary sap from plants, weakening the plant and possibly transmitting viruses. They start life as eggs and then hatch into their nymph stage where they look a little like aphids. These nymphs crawl over the plant looking for somewhere to settle and develop into a scale where there will sit happily sucking on the carbohydrates flowing around the plant just below the surface of the branch. Eggs are then laid under the protective surface of the scale.

Now is the perfect time to go out and check over your plants for any pests like this. Plants are putting on a lot of growth at the moment, especially with all this rain. This new growth is particularly sweet and juicy and has yet to toughen up so it is a prime target for pests. When looking for pests like this start with the new leaves and buds. Aphids, in particular, love this fresh, new growth.

As for dealing with them. The scale itself protects the insect and any sprays are most effective when used on the egg or nymph stage. You could use a systemic pesticide, sprayed on the leaves it is absorbed by the plant and carried throughout the plant, as the pests eat the plant they absorb the chemical and die. There are natural pesticides, such as fatty acid sprays but these need to be used regularly because they don’t persist on the plant for a long period of time and are not suitable for the scale stage of the insect.

I garden organically though and the best way to deal with pests like this is with your fingers. It is, I have to admit pretty disgusting. You can use an old toothbrush, just dipped in some water and then run up and down the affected branches and this is what I started doing. My acer is a bit more delicate than the Viburnum though and after a while I gave up with the toothbrush and resorted to the good old ‘finger squishing’ technique. Messy yes, but effective. As I was scouring the plant for any more signs of scales I also spotted some of the nymphs congregated on the leaves so these were squished, too. I’ll keep an eye on the tree over the next month or so.

Scale insects are quite common on greenhouse and conservatory plants and because these protected spaces have good growing conditions they can survive all year having several generations of offspring.

I also spotted this …

Tasty Marsh Marigold

Tasty Marsh Marigold

needless to say this slug didn’t last much longer!

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