Epyaxa rosearia and Scopula rubraria are found throughout New Zealand and Australia and have been dubbed the plantain moth after their appearance in the last few years munching through plantain leaves while in the caterpillar stage.
As farmers increasingly sowed plantain-dominant pastures to combat drought conditions, the plantain moth was making more of an impact, devastating paddocks last summer in the North Island and as far south as Canterbury, Ferguson said. Milder winters might also be allowing numbers of the moth to increase to levels not seen before.
“We really knew very little if anything about these moths until last summer when farmers started reporting the damage,” he said.
A six-month Beef + Lamb New Zealand farmer-initiated technology transfer project begin assessing the problem last summer and Ferguson hoped to apply for further research money to continue the work this coming season.
The plantain moth belongs to a group of moths commonly called carpet moths and is less than 20mm wide with light brown wings with darker spots and a darker brown band towards the end of its wings. They are noticeable flying up from a crop when disturbed.
The caterpillars are loopers, raising part of their body off the ground or plant when moving, are either brown or green, and less than 20mm long. They feed on plantain leaves causing small holes and in severe cases only the leaf veins are left.
Plantain which is under stress due to drought conditions seems to be more susceptible.
It’s believed the moth has a short life span, from egg to caterpillar to moth in as little as seven weeks, and can produce several generations per year. They’re most commonly seen in late summer but disappear by late autumn. It is believed moths can lay up to 100 eggs.
“Farmers could look at their crop and everything is fine and come back 10 days later and it’s gone,” Ferguson said.
“We’ve seen up to 11,000 caterpillars in 1m2.”
Farmers should be on the lookout for the moth in early summer and be ready to spray with a broad spectrum insecticide suitable for caterpillars.
“There is nothing registered on the market for the moths at the moment but one application of an insecticide should stop numbers building up. It seems second- and third-year paddocks are most at risk, as the population starts to build up the first year but it’s not until the second and third year that they are at a level where the damage is seen.”
NZ plantain yields vary between 10 and19 tonnes drymatter a year, similar to ryegrass pastures, and can be productive for up to five years when weeds become a problem. The leaves have a higher mineral content (P, K, S, Ca, Mg, Na, Zn, Cu, B, and Co) than ryegrass but can become less digestible with age and recommendations are to feed frequently when the species reaches 25cm in height.
For more information visit pestweb.co.nz.
