Ken Massey, of the Northland Regional Council, says although the serious pasture invader ragwort flowers year-round, its flowering is most prolific during the warmer summer months.
Mr Massey, a Biosecurity Officer, says that makes spring an ideal time to control the plant – before it can flower heavily and spread even more of its seed.
He says as well as its invasive tendencies, ragwort is also toxic to stock. “It can cause liver damage and, occasionally, stock deaths. It’s illegal to sell or distribute hay containing ragwort seed.”
Mr Massey says ragwort can take over large swathes of productive farmland and, unchecked, can prove a costly annoyance for adjoining landowners.
However, he says while property owners have a legal responsibility to keep their boundaries free of ragwort, it does not have to be a huge task, provided action is taken early enough.
“In many instances a knapsack of appropriate herbicide can be used to spot spray all offending plants back 50 metres from clean boundaries, with only a few hours of work.”
Mr Massey says good farm management can also help the work of tiny insects that feed on ragwort and he urges farmers to take the insects’ survival into account when controlling the pest plant.
“Spot spraying is appropriate in high quality pastures, but farmers can also rely on biocontrol agents like the ragwort flea beetle (longitarsus jacobaea) to be effective in controlling ragwort in areas of low priority.”
The beetle’s young eat fine ragwort roots and - if present in enough numbers - can control up to 80 percent of ragwort in an area.
Mr Massey says good ragwort control will mean more profit, fewer expenses, healthier stock and better relationships with neighbours.
He says information on herbicides to target ragwort and other pest plants can be obtained from all Northland Regional Council offices.