Joanne in S.A. is having problems with budworms attacking her roses. Budworms are caterpillars of the Helicoverpa moth family (previously called Heliothis moths). These destructive pests also attack stressed plants of sweet corn, tomatoes, a range of other fruits and vegetable plants and ornamentals.
The moths lay their eggs at night on young foliage close to fruits or flower buds and the young caterpillars feed on the foliage first before moving into buds or developing fruits. After several weeks of feeding, the caterpillars burrow into the topsoil beneath the plant and pupate until rain that produces a burst of new plant growth will signal an opportune time for adult moths to emerge from pupa cases and lay eggs. If you netted plants after the first moth attack, they won’t be protected from further attacks because the pupating moths will be inside the netting.
The first thing to do is remove all damaged buds, fruits/vegetables and caterpillar-infested young foliage and give them to the chooks or dispose of them in a sealed plastic bag – not in the compost heap. Then spray young foliage near buds and fruit with a registered organic treatment that is effective against this moth larvae. Nature’s Way Caterpillar Killer and Naturalyte Insect Killer are a couple of examples. Check daily for individual eggs laid on young foliage and respray when necessary, or after rain. The caterpillars have to be controlled before they enter buds or fruit where the sprays are not effective.
Although rain stimulates egg laying, we have found that this moth only lays eggs on plants that have had a period of water stress. Plants can only absorb the elements they need for pest-resistance from damp soil, and water stress provides the conditions that make them susceptible to attack from this and other pests. Where water is in short supply, apply a 5 cm layer of mulch around your plants and use an upturned 2 litre plastic container with the base removed and the neck embedded into the top soil to apply water efficiently, directly to the root area of plants (see photo). After rain, give plants a drink of organic seaweed extract tea to assist in building disease-resistance.