24 May 2022

Customer Question – Treating Scale Insect

Q. “I have discovered what I think is scale on my hydrangea plants. I’ve read on the RHS website that ladybirds can eat scale but I don’t see anything about that on your website. I’ve recently bought adult ladybirds and ladybird larvae from your company to control an aphid problem. But I don’t see any of the ladybirds in my garden anymore so wanted to enquire if I should order a new batch to deal with this scale problem. I would be grateful for any help or assistance! “ Jennifer

A. Thanks for the message and yes this is classic scale (great picture), but ladybirds are not what we would suggest as the scale insects tend to stay attached to the same spot and therefore would be hard for the ladybirds to attack. We do however have a nematode treatment for scale which you spray on and is very effective at controlling Scale Insect.

Scale insects are motionless and are stuck firmly to the stem and the underside of leaves (often around the veins) from which they suck the sap. They are dome shaped, about 0.6cm fully grown, light brown when young but gradually darken as they mature. They feed on the sap of the plant, leading to a yellowing of the leaves and in extreme cases total defoliation. Scale insects produce large quantities of honey dew which drips onto the lower leaves. Initially clear and sticky, it is then colonized by sooty mould, which is unsightly and reduces the ability of the plant to produce food, leading to further weakness and loss of vigor. This mould and honeydew are the first signs of an attack. A female scale insect produces a mass of eggs i.e. between 500 and 2000! and then dies. The eggs are laid under the scale which protects them as they develop. The eggs hatch to produce a crawler stage which settles on a suitable part of the plant, starts to feed and becomes immobile. The length of the life cycle depends on temperature but at 20°C it normally takes 10 weeks from egg to adult.

Control Scale Insect UNDERGLASS & OUTDOORS by spraying with Scale Nematodes AS SOON as you see scale and the temp is 14°C/58°F.  The Scale Nematodes are applied 3 times at 3 week intervals, so we send you 3 SEPARATE deliveries at 3 weekly intervals. The 1st delivery of nematodes are delivered by 1st class post and will fit through the letterbox and should be popped in the fridge until needed – they will have an expiry date of approx 2 weeks and should be used before this date. Mix the nematodes with water and spray the infected plants, concentrating on the undersides of the leaves and stems and then keep the foliage moist for 12 hours. This can be achieved by damping down the leaves with a gentle soft water spray, being careful not to wash the nematodes off, or by covering the plant with polythene (put the plant in a bin bag if small enough) for 12 hours following treatment. 2 more lots of Scale Nematodes will then be delivered at 3 weekly intervals and the whole process is repeated 2 more times. Our price includes 3 introductions of Scale Nematodes sent by 1st class post at 21 day intervals. N.B. Please note that once the scale insects are killed, they will remain on the plant, which will often lead people to believe that the control is not working. The first indication that the control is working is that honeydew will stop being produced so if the mould is washed off – SB Invigorator is very good at doing this – it will not come back. The scale itself can be removed by hand.

Available to buy now