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Stem borer

Agronomist, Tim Trevethan (Landmark), has reported the presence of white heads within an irrigated wheat crop south of Coleambally, in the Riverina district of New South Wales. Tim noticed the presence of a small hole in the last node of affected plants. When these stems were split open, Tim located small caterpillars that have been identified as Ephysteris silignitis. This caterpillar feeds on the inside of wheat stems, and appears to restrict the transport of water and nutrients within plants.

Ephysteris silignitis is a rare pest, and may go undiagnosed in wheat paddocks due to its cryptic feeding habits and damage symptoms - which superficially resembles crown rot. Previous experiences with this species in northern New South Wales and southern Queensland suggest damage is usually confined to a single tiller per plant at a relatively low incidence throughout wheat fields. It is thought that infected tillers will flower normally, but soon after flowering, the stem dies upwards from the last node as a result of caterpillar feeding. This results in the appearance of white heads. Infected tillers are typically green and apparently healthy from the last node (including the flag leaf) down. Generally only one caterpillar is found per stem.

There is very little known about Ephysteris silignitis. It is believed to be a native species, one of three in this genus found in Australia, each associated with stem boring. Ephysteris silignitis is a small caterpillar, approximately 10-12mm in length. They are a creamy-light yellow in colour, with a darkened head capsule. The caterpillars are believed to make a small entry hole about the size of a pinhead at, or just below, the first node up from the base of the plant. The larvae then feed within the stem moving upwards towards the head. It appears that once the stem begins to dry out, the larva bore a hole in the stem and exit.

Although difficult to estimate, Tim says the area of damaged plants is probably about 1-2% of the entire paddock. The crop is at the early dough stage. There are no known control options once caterpillars are entrenched inside wheat stems. The life cycle remains unknown, and therefore it is unclear whether there is an effective time to control moths before laying eggs. There is also uncertainty of the seasonal conditions (and years) in which the incidence of this pest is likely to be high.

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