It sometimes feels like as soon as we begin to enjoy our garden, so do the pests and diseases! Warm and damp weather can promote lush growth on our plants, which seems to send a signal to pests and diseases to come in and take up residence.
But identifying the common ones and knowing how to manage them will ensure our plants and ecosystems stay healthy and in balance. Because for many of our pests there is a natural predator ready to devour them for us, eliminating the need to resort to sprays. So while keeping our plants in tip-top condition can be challenging, observation is our first line of defence.
It’s important to understand your garden needs to have pests in order to have predators, so try and resist the urge to manage them immediately and wait and see if nature will solve the problem for you.
Aphids are soft-bodied sapsuckers that can weaken plants by feeding on new, sappy and lush growth. And with around 175 species in Australia, there’ll be an aphid that’ll love nearly every vegetable and ornamental plant in your garden.
The most common aphids are black, grey, green and woolly aphids. Black aphids are common on alliums – they’re very small and cluster around the base and underside of leaves. They can be teated with a simple white oil spray. Grey aphids, commonly found on brassicas, are actually targeted by a predator wasp that lays its eggs inside it, parasitising it. As its larvae grows, the shell of the aphid resembles a small rice bubble.
Woolly aphids are mostly found on older apple trees and have a fluffly, waxy coating. In small numbers, woolly aphids won’t harm a mature tree, but can be treated by ‘painting’ them with methylated spirits.
2. HARLEQUIN BUG
Hard-bodied sapsuckers, Harlequin bugs use a needle-like mouthpart called a proboscis to pierce the tissue of the host plant. Despite being quite pretty in appearance, they cause a lot of damage to plants and fruit trees if they’re in large numbers. Initially attracted to common weeds like marshmallow, dock and wireweed, keeping on top of host weeds and cleaning up fallen branches or bark where they hide will reduce the severity if an infestation occurs. Manage them by flicking them into a bucket of warm, soapy water or simply squash them between your fingers.
Scale are hard- or softbodied sapsuckers that can be found on the leaves, stalks and growing shoots of plants. Scale can’t move around easily, so excrete a honeydew-like substance that is eaten by ants. The ants will actually ‘farm’ the scale, moving them around the plant and protecting them. The sticky substance causes sooty mould to grow on the plant and is a telltale sign that you may have a scale infestation. Scale can either be scratched off if in small numbers or sprayed with a white oil, but be aware using white oil in temperatures of over 30 °C can burn the leaves of your plant.
4. PEAR AND CHERRY SLUG
Pear and Cherry Slug is a common pest on many fruit trees, not just pear and cherry trees. Looking very much like a small slug or leech, they’re actually the larvae of sawfly which lays its eggs on the foliage of trees like quinces and plums.
More likely to occur in the warmer months, they’re usually shiny black or dark brown in colour, around one centimetre in length and you’ll notice their arrival by brown skeletonised patches on the leaves after munching through the surface. Pear and Cherry Slug can be treated by spreading wood ash or lime over the tree’s foliage or, for smaller infestations, simply squashed between your fingers. If you have chickens and allow them to scratch around underneath your fruit trees, they can help break the cycle by eating the over-wintering pupae in the soil.
Rust is a general term that refers to up to 5000 known species of plant-attacking fungi. Common rust is the most familiar fungal disease that attacks everything from roses and snapdragons, tomatoes and raspberry canes and even lawns. Most common in warm and humid conditions, it will appear as slightly raised white or orange spots on leaves and stems. Severe infestations will deform and yellow leaves and can weaken the plant.
Prevention is always better than cure with rust, so ensure raspberry plants and broadbeans have good airflow. Don’t water overhead too often or too late in the day as this will leave the foliage wet. Remove and dispose of rust-affected leaves, and adding a thick layer of mulch will prevent any disease spores from splashing back onto the plant.