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Lucerne leafroller

Agronomist, Mick Duncan (Northern Agriculture), has reported lucerne leafroller caterpillars causing damage in several lucerne crops around Tamworth, in the North West Slopes and Plains district of New South Wales. The caterpillars have caused typical feeding damage, characterised by rolling and webbing of leaves at the growing tips of plant stems.

Mick says the affected paddocks appear to be those that have been left unstocked for some time, or in the case of hay paddocks, have not been cut for 3-4 months. In one paddock, about 30% of the plants showed signs of terminal leaf damage as a result of lucerne leafroller feeding. Although a known pest of lucerne, the lucerne leafroller can cause damage to a wide range of host plants, including soybeans and clover.

Lucerne leafroller caterpillars are up to 15 mm in length, yellowish-green to green with darker coloured heads. Caterpillars often drop from plants on silken threads when disturbed. Adult moths are 8 mm long and are yellow-light brown in colour, often with dark irregular markings on the forewings. The adults can be found in lucerne at most times of the year. Eggs are laid on the upper surfaces of the leaves.

The lucerne leafroller (Merophyas divulsana) is a pest of lucerne at any crop stage, but is usually more problematic in warmer months, particularly autumn and late spring. Reports at this time of year are rare. Feeding damage is most evident when the plants are nearing flowering. Infested lucerne plants become stunted; both yield and quality of hay can be significantly reduced. Damage is often most noticeable in moisture stressed and dryland crops.

It is generally not necessary to spray for lucerne leafroller unless seed production is threatened. As a guide, spraying is thought to be worthwhile in grazing or hay stands when approximately 30% of the terminals are rolled in the first half of re-growth. Early cutting or grazing is a way of reducing the economic damage caused by this pest. Maintaining optimum soil moisture levels can also help prevent economic damage, but is only possible in areas under irrigation. Mick says spraying is probably not warranted at present, particularly in paddocks where grazing is possible.

Click here for images of the lucerne leafroller.

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