Weeds

Amaranthus .

There are a number of different species of Amaranthus in NZ. They tolerate drier, warmer conditions than many other weeds, making them problem weeds in Maize and other summer crops.

They typically germinate in late spring, flowering in summer. Most found in NZ are annuals, and die in the first winter frosts.

Californian thistle .

Californian thistle is probably the most invasive broadleaf weed in New Zealand pasture with reports estimating $700 million in lost pastoral farm revenue each year. This perennial thistle limits farm productivity by reducing both pasture production and pasture utilisation. Trials show that 30% ground cover with Californian thistle (13 stems/m2) can cut ewe liveweight gains by 29% over a 12-month period. Californian thistle also triggers scabby mouth disease.

Hedge Mustard .

Hedge Mustard A tap-rooted annual, hedge mustard can be a problem in newly-sown or open pastures. Seedlings form rosettes which in turn quickly produce upright flowering stems 1m or more high.

Stock avoid this plant, leading to poor pasture utilisation. Control is best achieved at seedling to rosette stage.

Fathen .

Fathen is an extremely fast-growing weed with excellent survival mechanisms. In good conditions it can grow up to 1m high before flowering, but in dry situations it will flower and produce seed before it is 4cm high. It also has a very thick waxy layer which coats the leaves in dry weather. This is designed to hold moisture in the plant, but it is equally effective at preventing absorption of herbicides. Fathen can grow densely in spring-sown pastures. Spraying pre-flowering gives the most effective control.

Buttercup .

Most common in dairy pastures, particularly on less free draining soil types. Creeping and giant buttercup can be particularly invasive and are not easy to control. May require two applications in the spring to ensure adequate control. Find out more

Ragwort .

Ragwort is a very difficult weed to control and spreads easily. It grows all year round and is established from both seeds and old existing roots. Ragwort is a poisonous plant to stock and becomes more palatable when sprayed, so stock must be kept away until it has died down.

Yarrow .

Yarrow is a very widespread weed, common througout NZ in drier areas.

It is a fragrant perennial white or sometimes pink flowers, often forming large patches in pasture.

The leaves are dark green and feathery.

It spreads either via seeds or rhizomes to produce new plants.

Water Pepper .

Water pepper is common in low-lying regions of NZ, growing on river banks and in marshy areas. It is also sometimes an aquatic plant in small clear streams.

Stinking Mayweed .

Growing from 25 to 55 cm tall, stinking mayweed is a member of the daisy family. The flower has a yellow centre and white petals

Stinking mayweed is an annual winter herb, with a bitter taste, and unpleasantly strong odour when crushed. The stems are erect and densely branched.

Mallow .

Creeping mallow is a common weed in the North Island. It forms a low mat of circular or heart shaped green leaves.

The flowers are red or orange in colour. It often grows in lawns and pasture. The creeping stems can be up to 1m long, rooting where they touch the ground.

Black Nightshade .

Black nightshade is common in lowland cultivated habitats in NZ. It is typically less than 75cm tall, and often found in crops and gardens. It belongs to the same Solanum family as tomatoes, eggplands, capsciums and potatoes.

Dandelion .

Dandelion is often a problem in many pastures. Effective control is only possible during the seedling stage because the plant is both deep rooted and perennial. Taproot re-growth is poorly controlled. In new pastures, spray early before the taproot becomes established.