Honeydew is an important food source for ants, so knowing how to control honeydew-producing plant pests can benefit ant control programs.
Honeydew is the sticky, clear secretion produced by leaf-feeding insects as they feed on plant sap. The key insects that produce honeydew are aphids, soft scale insects, mealybugs, whiteflies, leafhoppers and psyllids. Apart from the direct damage that a large number of leaf-feeding insects can cause to the health of the plant, the high sugar content of honeydew gives rise to secondary problems such as the appearance of sooting moulds and ants, which feed on the honeydew.
During summer, pest managers may be asked to deal with the plant pests spotted by homeowners, so it’s important to know how to identify and deal with these pests. But given their symbiotic relationship with ants, pest managers should always inspect for their presence when dealing with ant problems.
Many species of ants, such as Iridomyrmex species, have a symbiotic relationship with some of these sap-feeding insects – the ants get food, and the sap-feeding insects get protection. As a result, without intervention, the numbers of both sap-feeding insects and ants will increase rapidly, affecting the health of the plant and increasing the number of pests in the garden.
Sometimes it is necessary to eliminate the sap-feeding pests to reduce the ant problem and sometimes it is better to deal with the ant problem first to reduce the number of sap-feeding insects. Here we will look at three of the key sap-feeding insects: aphids, mealybugs and scale insects.
Aphids
Aphids are relatively easy to control. Certainly, spraying the plants with a suitably registered product is relatively straightforward, but it does have negative side effects. As such sprays have a broad-spectrum of activity, they will also eliminate beneficial insects (that would otherwise control aphids) and there is also the danger of impacting honeybees.
Alternatively, spraying plants with a strong jet of water will knock the aphids off – once knocked off, they rarely climb back on. Soap sprays can also be used (suitable for organic gardeners), which are also effective on white fly. However, it is important to be careful not to burn the plants. Avoid spraying in hot sun and spray the soap residue off with water after a couple of hours to minimise burning.
Mealybugs
Mealybugs (main picture, above), with their waxy cuticle tending to repel many insecticide sprays, are often more difficult to control. Sometimes they can be a lot more difficult to locate as they will often hide in folds in the stem and leaves, which also makes it harder to apply any insecticide. Physical removal of infected foliage is probably the most effective method.
However, for larger infestations this isn’t really practical. The use of a 10-25% isopropyl alcohol solution can also be effective (but check for leaf burn – phytoxicity, first). Controlling the ants directly can also be an effective option, as it will allow any natural predators of mealybugs to do their work, reducing their numbers over time.
Scale insects
Like mealybugs, scale insects have a waxy covering that repels many sprays. There are hard scale insects and soft scale insects; only the soft scale insects produce honeydew. Much like mealybugs, controlling the ant problem will allow their natural predators to move in.
If a helping hand is needed, a horticultural oil (white oil) is a good option. Horticultural oils are refined petroleum products that penetrate and kill the insects, without harming the plant.
By inspecting for sap-sucking pests when dealing with ant problems, pest managers can develop a more effective ant management strategy, demonstrate their expertise and provide the homeowner with some added value horticultural pest control.
