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Rural Diary
1 February 2019 Gary Bosley

Don't let caterpillars steal your summer feed

When growing forage crops, there are usually weeds, pests and disease competing, consuming or destroying valuable feed.

The natural ecosystem keeps pests in check and stops them becoming an economic issue. However, sometimes with favourable conditions, they increase in numbers and start having an economic impact on the crop so need to be managed.

The plantain moth is a member of the carpet moth family and is made up of two species (Scopula rubraria and Epyaxa rosearia). While very little is known about these two species, they are commonly found in New Zealand and Australia and are of the type called “loopers”. The adult moths are quite small with a wingspan of 20 mm, both species look very similar and are light brown in colour with darker brown spots and a dark brown band towards the end of the wings.

With the increase in plantain as a stock feed, either as a stand-alone crop with or without clover, or as a constituent of pasture of another crop, caterpillars are rarely an issue in the establishment year, but numbers can grow to epidemic proportions in the second and subsequent summers. If you experience large numbers of moths through the summer (starting in December), then you can expect a large number of eggs laid which hatch quite quickly into caterpillars with a voracious appetite for plantain leaves. The lifecycle of these caterpillars is short, pupating and emerging as adults to lay more eggs and therefore more caterpillars several times through the summer months. In winter, they largely disappear, probably overwintering in the soil as a pupae.

To monitor for these pests through the summer months, walk through your plantain paddocks in the evening. If there are large numbers of small brown moths flying up in front of you, then look closer in the leaf litter and see if you can find small curled up caterpillars and evidence of their feeding on the plantain leaf. In years where there have been large numbers of moths, some farmers have observed 90 percent leaf area of plantain plants consumed by these caterpillars.

If you have identified moths in your crop, contact your local PGG Wrightson Technical Field Representative for a control plan.

Gary Bosley

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