Unwanted moth spreads its wings

FAR seed research manager Richard Chynoweth says the red clover casebearer moth (Coleophora deauratella) was discovered in Auckland in October 2016, setting off alarm bells and prompting nationwide monitoring.

 Special pheromone traps were imported and distributed to red clover growers up and down the country during this summer’s clover growing and flowering period.

“Traps were placed on farms from the lower North Island to the south of the South Island,’ Chynoweth says.

“The results are not good news for red clover growers, with moths being found on farms, roadsides and other areas everywhere from Wairarapa to Southland. 

“As it was first identified in Auckland, we can assume they will be found across the North Island as well. Given the numbers and spread of this pest, it seems likely to have been here for quite a while. I guess it’s been around for at least a decade and could have been affecting red clover seed yields for several years.”

Red clover casebearer is a small moth (about 8mm long) and is very similar to two other species of clover casebearer moth (Coleophora spp.) already well established in white clover in NZ, however in this case it’s principal host is red clover. Adult moths lay eggs on developing red clover flower heads and once hatched the larvae tunnel into the florets to feed, destroying the growing seed. 

As the larvae grow, they stick onto a chewed-off floret, using use it like a cape for protection and camouflage. Feeding damage to seeds can severely impact crop yields.

Chynoweth says because little is known about red clover casebearer in NZ, researchers have a lot of work on their hands.

“We will continue to monitor its spread, but more importantly we need to understand its life cycle and exactly how that links with the red clover growth cycle. Once we have a clearer idea of that, we can start to consider control options, so that arable farmers can continue to grow this specialist crop.

“Late last year did initial laboratory insecticide trials and the results indicate that some insecticides currently registered for use in clover crops are effective against red clover casebearer moth. However, field trials will be required, as adult moths moving within the foliage of a growing crop may not receive a direct application due to location in the foliage. Further work will investigate whether any of the parasitoid species which already help to control other Coleophora spp. in white clover crops could be of use.”

In the meantime, farmers who wish to check their crops for the presence of red clover casebearer should inspect flowers looking for millimetre sized holes chewed into the base of individual florets and/or distinctive black droppings, also at the base of the florets. 

They may also be able to see the case bearing larvae, which look like small red-brown cigars on the flowers. If evidence of casebearer is found, discuss management with a crop agrichemical advisor.

This work is done by FAR with support from the Seed Industry Research Centre.