AgPest Alert – 7 May 2019

Damage from grass grub and porina now showing

Region: Bay of Plenty, Waikato, Gisborne, Hawkes Bay, Taranaki, Manawatu, Whanganui, Wellington, Nelson, Tasman, Marlborough, Canterbury, West Coast, Otago, Southland.

In grass grub or porina prone areas, check pastures for damage which is now showing. Grass grub damage is indicated initially by loss of clover and subsequently by patches of pasture turning yellow and later becoming soft underfoot.
Porina damage initially appears as small (approx 5 cm dia.) areas of bare ground.
Both pests should be controlled as early as possible to maximise returns and protect long term pasture production and quality. Although heavy rolling or high stocking rates may provide some level of grass grub control, conventional insecticide (diazinon) may be the only recourse. It is now generally too late to obtain good control of porina using diflubenzuron, although caterpillars from late February/March flights in the North Island and the South Island West Coast are still susceptible. In most cases, porina control now needs to be by conventional insecticide.

Time for broadleaved weed herbicide

Region: All NZ

Check new pastures and apply herbicide as necessary to control broadleaved weeds (6-8 weeks after establishment).

Damage from black beetle larvae showing

Region: Northland, Auckland, Bay of Plenty, Waikato

In the northern North Island, damage from black beetle larvae may be showing. Unfortunately, little can be done to prevent this. Adults are deterred by AR37, Endo5 & NEA2 endophyte-infected grasses, which will reduce egg laying and larval numbers. See DairyNZ Pasture Renewal Guide.

Tasmanian grass grub damage may be showing

Region: Gisborne, Hawkes Bay

In areas where Tasmanian grass grub can be a problem, damage may be seen. Check pastures, particularly around stock camps and assess numbers to determine if insecticidal control is warranted.

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