What pest is attacking my Campsis radicans?
Barry England, by email
Stefan says: This is an infestation of scale insects. There are many species of these curious and troublesome creatures. The scalelike objects you can see on the stems are protective shells and beneath each one is the female insect which lays hundreds of eggs. After several weeks the baby scale insects, or nymphs, hatch and crawl away to infest other parts of the plant. They're often referred to as crawlers and have limited powers of movement from one plant to another, although outdoors they're often blown by the wind. Usually, the introduction of the pests to a garden or greenhouse comes on new plants, which
should always be checked carefully.
Many species of scale insect are parthenogenetic, which means male insects are rare and/or unnecessary because the females can continue to produce eggs without needing to mate, which obviously increases hugely their potential to increase the population.
The damage to plants is caused because scale insects suck sap by inserting a tiny feeding tube, called a stylet, into the tissues and when hundreds or thousands of them are doing it at the same time, the plants will eventually and inevitably decline in vigour.
There's then the added complication that, as with other sap-sucking creatures, the plants become covered with a sticky secretion called honeydew, which is produced by the insects, and in turn, this encourages the growth of black mould fungi called sooty moulds.
Scale insects can be treated by using an approved insecticide spray but timing is critical. If you use a magnifying glass, the crawlers can be seen quite easily and infested plants should be treated when these crawlers are active. Then, because some of them will escape the treatment, a second application of insecticide should be made about two weeks after the first. When individual shoots or branches are almost covered with scales however, it's sensible to cut them out and destroy them.