I planted a nice red-flowering dipladenia climber a few months ago and just noticed it’s not looking so good. Some leaves are yellowing and it has masses of these yellowish insects with black legs on the stems. They look like aphids, but I’ve never seen them this colour before. Can you help?
R. Brown, Auckland Answer
These are oleander aphids, which feed mostly on plants in the Apocynaceae and Asclepiadaceae families, including oleanders, swan plants, hoyas, dipladenias and mandevillas, all of which have milky, somewhat sticky sap that the oleander aphid is capable of digesting. Oleander aphids are all female, the adults giving birth to live young without the need for fertilisation. When there’s no shortage of food and plenty of room for the population to expand all the young are wingless, but when population density is high or food becomes scarce, winged young will be produced to fly off and start new colonies elsewhere. The adult aphid produces several young each day and within a short period of time these mature and also start reproducing, so large populations can build up very quickly.
If you look closely on the lower part of the stem in the photo you can see large ‘mother’ aphids surrounded by their smaller offspring. Their sap-sucking is debilitating your plant, so you need to take some action. You could simply run your fingers along the stems, which will crush many of the soft-skinned aphids, or blast them off with a jet of water. Alternatively, spray these easy-to-kill pests with one of the many available insecticides, such as pyrethrum, insecticide oil, neem or a natural acid spray, such as Yates Nature’s Way Organic Citrus, Vegie & Ornamental Spray.