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Lucerne leafroller

Agronomist, Ross Watson (Ross Watson Agriculture P/L), has reported lucerne leafroller (Merophyas divulsana) in several lucerne paddocks in the Hunter Valley, New South Wales. Ross says crops which are moisture stressed are particularly vulnerable to attack. Although they are a known pest of lucerne, the lucerne leafroller can cause damage to a wide range of host plants, including soybeans and clover.

Caterpillars are up to 15 mm long, yellowish-green to green with darker coloured heads. The larvae bind leaves together at the growing tips of plant stems. Several leaves are bent over and joined with silk to form a shelter. 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.

Feeding damage is most evident when the plants are nearing flowering. Crops that are cut or grazed in spring, summer and autumn are also at risk. Caterpillars feed on the terminal leaves and flowering stems. Heavily infested plants become stunted; both yield and quality of hay can be significantly reduced. Damage is often most important in moisture stressed and dryland crops.

To monitor lucerne leafrollers estimate the number of stems on which re-growth terminals are rolled. As a guide, spraying is thought to be worthwhile in grazing or hay stands when about 30% of the terminals are rolled in the first half of re-growth. However, it is generally not necessary to spray for lucerne leafroller unless seed production is threatened. Ross says in many cases, early cutting or grazing is being preferred as a way of reducing the economic damage caused by lucerne leafrollers. Maintaining optimum soil moisture levels can also help prevent economic damage, but is only possible in areas under irrigation.

Click here for images of the lucerne leafroller.

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