AgPest Alert: 1 October 2021

In summer-active grass infested pastures consider forage crops to selectively spray out summer-grasses before renewal.

Region: Northland, Auckland, BOP, Waikato, Taranaki

If your run-out pasture was infested with summer-active grass weeds last summer, consider growing a forage crop for one or two summers prior to sowing the perennial pasture. This provides the opportunity to selectively spray the summer-active grasses and prevent weed seeds from replenishing the seed bank and infesting newly sown pastures. Forage crops will also disrupt clover root weevil populations allowing better subsequent establishment of young clover.

Field horse tail is an invasive plant that is near impossible to destroy.

Region: Manawatu

Field horsetail (Equisetum arvense) is a very difficult to control perennial weed that regrows each spring/summer from an extensive underground root system. Preventing establishment is the best form of control. Make sure your contractors machines are clean and ask where the machines have been.
This root system comprises actively growing rhizomes that can penetrate to more than 1 m in depth, from which green fern-like fronds grow each year. Attached to the deeper rhizomes are small tubers which remain dormant while the rhizome stays alive. Upon the death/decay of the rhizome, or when it becomes detached due to cultivation or other means, the tubers are able to produce new plants.

Clover root weevils in pasture may reduce amount of N fixed by clover.

Region: All of NZ

In established pastures with high levels of clover root weevil the clover may be adding little in the way of nitrogen to the pasture and compensatory nitrogen applications may be required.

Ordering grass seed? 

Region: All of NZ

When ordering grass seed select suitable endophytes and check that the endophyte you select has been assessed in the grass variety you order. In ryegrass, AR1 and AR37, and diploids with NEA2, will protect against Argentine stem weevil, AR37, Endo5 and NEA2 against black beetle and AR37 against porina. See DairyNZ Pasture Renewal Guide for a guide to endophyte selection.

Endophyte levels in the seed should be at least 70% and have been assessed in the last 3 months.

Direct drilling?

Region: All of NZ

If direct drilling new pastures or crops check for slugs as these can devastate establishing seedlings. An application of slug pellets may be required, or control may be achieved by heavy stocking rates.

Use treated seed in black beetle prone areas to reduce adult numbers.

Region: Northland, Auckland, Bay of Plenty, Waikato

Northern North Island watch for clover flea damage to clover.

Region: Northland, Auckland, Bay of Plenty, Waikato

In Northland, South Auckland, Waikato and the Bay of Plenty watch for clover flea damage to clover – this appears initially as small holes in leaves, more severe damage results in only leaf veins and the lower leaf surface remaining making the crop appear silver. Treat early if required to maximise effectiveness.

Pasture renewal required after grass grub/porina damage?

Region: Taranaki, Manawatu Wanganui, Wellington, Nelson Tasman, Marlborough, Canterbury, West Coast, Otago, Southland

For pastures badly affected by either grass grub or porina over winter and needing renewal, consider direct drilling. This will preserve naturally occurring diseases of these pests that are building up in the soil and which will provide long term population regulation. Leave sowing as late as possible as both pests, especially in the south, may still be feeding and could devastate establishing seedlings. Be aware that slugs and clover root weevil may also be present in damaging numbers.

Look for porina flights.

Region: Taranaki, Manawatu Wanganui, Wellington, Nelson Tasman, Marlborough, Canterbury, West Coast, Otago, Southland

At the end of the month look for porina flights – indicated by large numbers being attracted to lights at night, as these can indicate when to adopt control measures at a later date if required.

Look for brassica springtails before sowing brassica crops.

Region: All of NZ

Place a white card or cloth on the soil surface and gently disturb the soil around it. This will cause the springtails to jump and land on it making them easier to see.

Be vigilant for new weeds which you have not seen before.

Region: All of NZ

In newly planted crops, scout for new weeds and weeds that have survived spraying with herbicides. Get these identified by sending photos to AgPest as they may be either a serious new incursion or have become resistant to herbicides. In either case it is important to get this sorted before they become established over large areas. Report weeds at

Are you noticing any weeds surviving after spraying?

Region: All of NZ

Weeds becoming resistant to herbicides is an increasing problem, we already have nodding thistle resistant to 2,4-D and MCPA and giant buttercup resistant to MCPA and flumetsulam. If you suspect you have resistant weeds and want them tested contact AgPest.

Watch out for Yellow Bristle Grass on the roadside, it is rapidly moving south.

Region: Canterbury, Marlborough, Nelson, Manawatu

Yellow bristle grass (YBG) is continuing to expand its range and is rapidly moving south into Manawatu and Canterbury. Watch for an upright grass with many compact, yellow-tinged seed heads appearing on the roadside. Take measures to stop it moving onto your farm. For more details see


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