Wireweed (Polygonum aviculare).
Wireweed (Polygonum aviculare) is also known as Prostrate Knotweed, Pigweed and Knotgrass, and is a common weed of amenity turf. It is a problem on heavily worn and compact soils such as council sports grounds. You can even see this weed thriving in cracks in pathways.
On golf courses and sports grounds, Wireweed thrives in irrigated areas, is very resistant to heavy use, and you can often see it in goal mouths.
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.
Wireweed is a good indicator weed for soil compaction.
Why is Wireweed such a Problem?
- Wireweed tends to germinate and emerge during turf establishment.
- Knotweed competes for moisture and nutrients. This is a big problem when you are trying to establish turf.
- It is allelopathic to Couchgrass.
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 can 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 flowers develop in small clusters and are pink to white with 5 petals. The stems are prostrate, have multiple branches and have a wiry appearance.
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.
Impact of Wireweed.
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.
How to Control Wireweed.
Cultural control.
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.
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.
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- 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.
