WILLOW WEED

Persicaria maculosa 

Download the PDF

DESCRIPTION

Willow weed is an annual plant that grows in spring and summer, and dies off in late autumn.

It can be either a sprawling plant or an erect plant, depending on the location; in open areas with little competition it will tend to sprawl and spread laterally, while in more competitive surroundings such as a crop, it will initially sprawl but can then develop in a more erect form to a height of about 40cm.

As the name suggests, the leaves are shaped similarly to those of a willow tree, being sword-shaped, up to 15cm long by just 4cm wide, and dark green in colour.  There is generally a dark brown/black irregular spot in the centre of the leaf’s upper side, and at the base of the leaf is a sheath with a distinct fringe of hairs.

The stems are tinged with red, although not as intensively red as the similar plant, the water pepper.

The flowers of the willow weed appear in mid-summer, and are small and pink in colour, occurring in tightly-packed cylindrical bunches to 4cm in length, occurring at the ends of the stems.  The flowers of similar water pepper can usually be distinguished by their distinctly greener colouring, and the fact that water pepper flowers grow in much looser and more open bunches than do the tightly packed cylinders of willow weed.

HABITAT

Willow weed prefers cultivated land, especially where conditions are dampish, and is found throughout New Zealand.  

Willow weed is a particularly invasive weed, and affects both crops and pastures.  At times it can be a very serious weed in crops as its rapidly sprawling habit can overwhelm and suffocate a young crop especially in the spring.

POISON

In pastures it is rarely eaten by stock, and is suspected of causing stock poisoning illness and death both in NZ and overseas. 

MANUAL REMOVAL

An important point to consider when dealing with willow weed is that although it produces a large number of tiny triangular seeds from which it reproduces, willow weed also readily reproduces from stem fragments, including very small ones. Successful manual removal of the plant therefore requires the careful collection and removal from the site of every part of it.

Willow weed is killed by frosts, but fresh seedlings appear each spring.  The seeds will remain viable in the soil for a very long time, and complete eradication may take several seasons to achieve.

HERBICIDES TO CONTROL WILLOW WEED

In most situations, because of the rapid and invasive nature of willow weed, it will have to be dealt with via herbicides.

Boom Spray Herbicides to Kill Willow Weed

In both pasture and crops, boom spraying is the way to go.  Willowweed is best controlled when it is in its younger stages of growth, especially up to the 4-leaf seedling stage.  Control beyond that stage becomes less certain.  As with virtually all weeds, the best results will also be achieved if it is sprayed while it is actively growing in good conditions.

The most used boom spray options for Willow-Weed are:

Pasture

• MCPA750 at 2-3L/Ha in 200-300L of water.
• Rainbow & Brown 2,4-D 720 Amine at the higher rate of 3.4L/ha will control seedlings well, with no damage to pasture grasses.  Clover damage is minimised where clover is largely dormant, or has been hard grazed shortly before spraying.  
• In pasture Dicamba 500 SL - 100ml plus 260ml MCPA750 in 100L water per hectare or
• Dicamba 500 SL - 120-140ml plus 595ml 2.4.-D 720 Amine per 100L water per hectare.

Both of these spray options are likely to cause some temporary suppression of clovers in pasture.

Crops

• Dicamba 500 SL - rate varies depending upon the crop and may perform better in some situations when mixed with MCPA750 or 2.4.-D 720 Amine.  Read the Dicamba 500 SL  Product leaflet for exact rates. 
• MCPA750 at 2-3L/Ha in 200-300L of water.
• Rainbow & Brown 2,4-D 720 Amine at the higher rate of 3.4L/ha will control seedlings well

Spot Treatment Herbicides to Kill Willow Weed

• Glyphosate  is effective as a spot spray but its use is rarely practical due to the damage to the surrounding crop or pasture plants.  Generally boom spraying will be necessary in crop and pasture situations anyway, due to willow weed’s invasive nature, but any of the glyphosate herbicides at label rates will work when spraying out a pasture.
• Rainbow & Brown 2,4-D 720 Amine will control seedlings at 55ml/10L water.