The run of warm, humid and wet weather we’ve had lately really favours pests and diseases in our gardens. This month I’d like to run through the main pest and disease challenges for gardens in our area and the best approaches to controlling them.
There’s no one perfect solution for pest and disease control in the garden, but my philosophy is to minimise the use of chemical sprays (insecticides, fungicides)-you’ll get better natural control and plant resistance to pests and diseases if you avoid using a “blanket” spray response whenever you start to see them.
The main pests in my garden are aphids on roses and some fruit trees; borers in ornamental and some native trees; cabbage moth/cabbage white butterfly caterpillars on brassica vegies; christmas beetles on eucalypt and silver birch trees; cherry slug on ornamental and fruiting cherry, plum and pear trees; mealy bugs on indoor plants; snails and slugs on vegies and annual flowering plants.
Ladybird beetles, small birds and some wasps provide natural control for some of these insects as long as you don’t repel or kill these through over-use of chemical sprays. Keep plants fertilised and well watered-healthy plants will thrive and minimise insect damage. White oil is a low toxicity spray effective against aphids and mealy bugs. Traps can be used to reduce the populations of some insects and snails or slugs. As a last resort, I sometimes use the low toxicity, natural insecticide pyrethrum spray.
The main plant diseases in my garden are the fungus induced black spot in roses; downy and powdery mildew in roses, some fruit trees and vegies; and leaf curl in peach, nectarine and apricot trees.
Where possible, look for shrub and tree varieties that are more resistant to these diseases. Avoid overhead watering onto the leaves of plants, especially in the evening and ensure good air circulation between plants by not overcrowding. Remove and burn fungus affected leaves from plants. As a last resort, spray the plants with a fungicide such as lime sulphur or triforine after winter pruning and if plants become affected by fungus.
By Ian Rogan