Wireweed (Polygonum aviculare).
Wireweed (Polygonum aviculare) is also known as Prostrate Knotweed, and Knotgrass, and is a common weed of amenity turf. This weed favours worn and compact soils such as council sports grounds and Wireweed control can be very difficult. You can even see Knotweed thriving in cracks in pathways.
On golf courses and sports grounds, Wireweed thrives in irrigated areas, is very resistant to wear, and you often see it in compact goal mouths.
After you read this you will be able to:
- Identify Wireweed.
- Know its habitat and lifecycle.
- Know the best way to manage this weed.
Why is Wireweed a Problem Weed?
- Wireweed forms dense vegetative mats, and has a strong, deep taproot. This means it spreads quickly, and outcompete other plants for water, nutrients, and light.
- Once Wireweed establishes it is difficult to control, especially on compact soils.
- Wireweed produces large numbers of seed, and these remain viable for several years.
- Wireweed tends to germinate and emerge during turf establishment.
- It is allelopathic to Couchgrass.
- It is often mistaken for Spotted Spurge or Common Purslane, which further complicates chemical control.
- Knotweed causes dermatitis in sheep and humans. Horses and stock that consume large quantities of seed may develop enteritis.
- Wireweed may also contain toxic nitrate levels, and horses have died from nitrate poisoning after eating it in hot dry weather.
Table Showing Differences between Wireweed, Spurge and Purslane.
Weed | Spreading | Leaves | Leaf shape | Leaf Hairs | Milky Sap | Flower Colour | Reproduction |
Knotweed | Yes | Alternate | Lanceolate or elliptic to oblong | None | No | White to green | Seed |
Prostrate Spurge | Yes | Opposite. Often has a dark spot in the centre of the leaf. | Small and oval | None | Yes | White | Seed |
Purslane | Yes | Alternate or opposite | Club shaped and fleshy | None | No | Yellow | Seed and stem fragments |
Wireweed favours a soil pH greater than five. Soil compaction and heavy N use also favour it, but Wireweed also tolerates drought and low fertility soils.
Knotweed is a good indicator weed of soil compaction.
Wireweed Identification.
Wireweed is an aggressive low-growing warm-season annual or biennial dicot. It has small oval leaves with a purple sheath around the base of each leaf. The branch leaves are about half the size of the stem leaves, and the stems root at the nodes.
Wireweed flowers mainly in the Autumn and the Spring, and large numbers of flowers appear along the base of the leaves.
The pink to white flowers have 5 petals and develop in small clusters. The stems are prostrate, have multiple branches and have a wiry appearance.
Photosynthetic Pathway: Wireweed is a C3 weed.
Reproduction of Wireweed.
When you disturb a large seed bank and then irrigate, these seeds germinate and Knotweed then becomes a problem. This is often the case when you resurface sports grounds or fairways.
- The leaves have no hairs, and Wireweed has a strong, deep, fibrous tap root.
- It tends to germinate in the Spring, and first appears when soil temperatures are only around 4°C.
- The stems do not end in a flower head. Instead the small flowers occur in the leaf axils.
How to Control Wireweed.
What is the Treatment Threshold for Wireweed?
Cultural Control of Wireweed.
- Wireweed thrives in compact soils, and so if you relieve soil compaction it creates less favourable soil conditions for this weed.
- Prostrate Knotweed has a thin taproot so you can remove this by hand.You are best to do this on young plants in moist soil.
Chemical Control of Wireweed.
Pre-emergent Control of Wireweed.
Post Emergent Control of Wireweed.
Products containing Dicamba usually provide better results, but you can’t use these safely on Buffalo Grass.
- 2,4-D. This tends to burn the top of Wireweed but it then grows back.
- Warhead Trio. Safe on Buffalo grass.
- Contra M herbicide. Don’t use Contra M on Buffalo grass.
- Weed Blast MA. Safe on Buffalo grass.
- Casper Turf. Don’t use Casper Turf on Buffalo grass.
- Dicamba. Don’t use Dicamba on Buffalo grass.
- Stature. Stature Turf Herbicide is safe on all established cool and warm season grasses. Not for home garden use. A non-ionic surfactant is recommended.
Table of Post Emergent Herbicides for Wireweed.
Product | Active | Chemical Group | Rate/Ha | Comments | |
2,4-D | 2,4-D | 4 | 1.8-3.2L | Wet foliage thoroughly. DO NOT mow lawn for 1 week before and at least 1 weed after application. DO NOT use on Buffalo grass (WA only). | |
Casper | Prosulfuron + Dicamba | 2 + 4 | 800g-1Kg | Apply from Autumn to Spring. Use high rates in cool months or if high weed pressure. Control takes 4 to 6 weeks. Use an NIS at a rate of 0.25 to 0.5% v/v. | |
Contra M. | Dicamba + MCPA | 4 | 6.5L | Apply in 250-400L water. DO NOT use on Buffalo grass. After use do not mow for 2 days before or after application or fertilize within two weeks. | |
Dicamba | Dicamba | 4 | 1.2L + 3.2L of 2,4-D Amine 625g/L | Use a minimum of 1000L/Ha water. Do not spray on Buffalo or Bent Grass. | |
Stature | MCPA + Bromoxynil + Diflufenican | 4 + 6 + 12 | 2L | Apply to actively growing weeds. Complete control may take 4 to 6 weeks. A repeat application maybe needed in 4 � 6 weeks. Use a surfactant for difficult to wet weeds. Apply in 200 to 500 L of water. Transient discolouration may occur up to 21 days following application. | |
Weed Blast MA | Bromoxynil + MCPA | 6 + 4 | 3-6L | Apply in a minimum of 500L/Ha water. DO NOT mow for 2 days after treatment. | |
Warhead | MCPA + Clopyralid + Diflufenican | 4 + 12 | 5L | You may see discolouration on kikuyu, carpet grass and Queensland blue. Avoid overlapping. Use an NIS. | |
Post emergent Herbicide research on Wireweed.
- Among a group of eighteen herbicide treatments, only six control Knotweed over 80%.
- These include products containing 2,4-D, Dicamba, Metsulfuron, or Chlorsulfuron.
- Treatments relying on Bromoxynil, Triclopyr, Clopyralid, Quinclorac, Metribuzin, Rimsulfuron, Foramsulfuron, and Trifloxysulfuron sodium, do not provide adequate control of Pigweed in couch grass.
- Diflufenican, the active in Warhead Trio provides long-lasting pre-emergent control.
Non Selective Control of Wireweed.
- Glufosinate-ammonium provides control for 4 to 6 weeks, but it regrows and recovers due to the limited movement of glufosinate.
- Glyphosate. You can use Glyphosate but if you use Glyphosate, and water quality is an issue then use ProForce Manta Ray.
The following are non-selective but also have a long term residual and stop re-growth of Wireweed.
- Renegade. Renegade stops germination for up to 12 months, and reduces the need for multiple herbicide applications.
- Numchuk Quad. This gives effective post and pre emergent Knotweed control for up to 12 months.
- Cortex Duo. Cortex Duo gives a rapid knockdown of Wireweed, and residual control for up to 3 months. It is also safe to use around trees.
