Bumper summer for native moth
April 16, 2014
Farmers in the North Island are reporting to AgResearch plantain crop damage from a normally benign New Zealand native.
The Epyaxa rosearia is a widespread native New Zealand moth, occasionally reaching pest levels, that feeds on a range of plants including plantain. Its recent appearance in large numbers in plantain crops has given rise to the name plantain moth.
Reports started to come in around early December from farmers concerned about the number of plantain moth caterpillars they were seeing in their fields and the resulting damage occurring in plantain crops, says AgResearch scientist Mr Colin Ferguson.
“Some farmers have reported up to 90% of their crop being decimated by the insect.”
Until recently the plantain moth has caused little concern to farmers.
“It is a native of which we know virtually nothing, but its activities this summer has put it firmly on our radar,” says Mr Ferguson.
“In the past plantain used to be planted within a mixture of ryegrass, chicory and clover. Due to its drought resistant properties we are seeing more and more farmers using plantain as a monoculture: single source pasture. These plantain crops should last a number of years but it looks as though populations of the moth build up in the first year and, assuming conditions are right, it is those second year crops that are getting hit by moth populations which increase exponentially.”
Mr Ferguson says the effects of the move to plantain as a single source forage crop was compounded by the very mild conditions last winter.
“The mild conditions allowed a greater number of moth eggs to hatch and more of the caterpillars and moths survived right through the winter. Warm, dry summers, like the one we are having now, are perfect insect breeding conditions and as result the plantain moth population has just exploded in some areas.”
Normally the growth of plantain is so great that feeding by these caterpillars has very little impact on plant production. Occasionally however, severe damage is reported as a consequence of very high caterpillar numbers and may be concentrated in some paddocks while others close by are unaffected.
Why, and how, this situation arises is currently unknown but is under investigation. Crop health, plant stress and growing conditions may have a significant role to play in the severity of damage observed.
Although current information suggests the moth is widespread throughout New Zealand, Mr Ferguson has had no reports of damage to plantain south of the Manawatu.
“This may be because weather conditions do not allow the moth to breed as many times as it does in northern areas.
There are no registered insecticides for control of plantain moth caterpillars but broad spectrum insecticides with good activity against other caterpillars may also provide control of plantain moth. AgResearch scientists strongly recommend consultation with agrichemical professionals before using these insecticides for off-label use.
“We believe that treatment in early summer, if moths are present then, would knock back the season’s first generation leading to less pressure for autumn pastures,” says Mr Ferguson.
“Further investigation into this and grazing management practices is underway. As a general guide a healthy crop will tolerate more insect damage than an unhealthy one.”
About the Plantain Moth
Moths are small, less than 20mm wide, light brown with darker spots and a distinct darker brown band towards the end on the wings. It belongs to a group of moths commonly called carpet moths. When present the moths will often fly up from the crop in front of people, stock or vehicles, sometimes in very large numbers, particularly in autumn.
Caterpillars are brown and small, less than 20mm long. They are known as loopers as they raise part of their body off the ground or plant when moving.
Very little is known about the biology of this insect.
It appears to have a short generation time and several generations per year are likely leading to the massive numbers sometimes seen but this needs further study. It is most abundant in late summer and largely disappears from crops in late autumn. It probably feeds on a wide range of plants and appears to find plantain and Caucasian clover to its liking having been observed causing noticeable damage to both. The caterpillars feed on the plant leaves causing small holes which can join up and in severe cases leave only leaf veins.
Generally little plant damage is attributed to this insect but it has been recorded as causing damage to Caucasian clover and is very commonly found in plantain stands.
Too little is currently known about this insect for management options that may affect build-up of caterpillars to be suggested. When its biology is better known some options may present themselves.
More information about the Plantain Moth found at www.agpest.co.nz, the directory of New Zealand’s most damaging pests and weeds. Farmers can also sign up to receive management and control advice specific to their region through the AgPest Pest Alerts.