AgResearch entomologist Richard Townsend says that means insecticides such as Dimlin may have good kills of caterpillars produced from one stage of the flight season but later caterpillars in the season could survive.
The project is studying pasture pests on the West Coast and has only one year of data collected so Townsend says the next two years will be needed to validate the information they have found to date. About 10 porina moth trapping sites have been distributed between Westport and Whataroa to identify how many of the possible seven species of porina exist in the area and work out their flight season.
Porina has long been a problem on the West Coast – in more recent years manuka beetle populations have exploded on some flipped land as well as humped and hollowed developments which creates a perfect environment for the beetles. However, Townsend says natural diseases are finally helping control the manuka beetle population as pastures mature.
“As pasture gets older and disease starts coming in – and if you don’t cultivate again – you tend to see populations getting a bit lower. So manuka beetle tends to become a sporadic problem.”
Landcorp researcher Jessica Dunbar is working with the project and says the choice of pasture species, pasture management and effluent application is also helping farmers battle the effect of manuka beetle.
Species such as plantain and tall fescue have proved more tolerant to the voracious pasture pest while farmers tend to graze pasture to a higher residual to take the pressure off already stressed plants.
Dunbar says the biological controls in the form of fungus and bacteria that help control the pests are reappearing in the soil around six to seven years after flipping.
As farmers battle porina and manuka beetle Townsend says grass grub has now been identified in sites around Westport.
“Up until three or four years ago we hadn’t found grass grub in pastures on the West Coast and the only place we’ve found it has been in small populations around Westport. So we are monitoring it and hope to be able to tell people if it is spreading.”
