Pigweed (Portulaca oleracea)
Pigweed is also known as Common Purslane. It is a prostrate, succulent annual that often forms a dense mat. These dense vegetative mats use available soil moisture and nutrients, and screen out light to the soil surface, and prevent the emergence of other seedlings. It has reddish stems that originate from a central point, and radiate out like spokes of a wheel.
This is not the same as Horse purslane (Trianthema portulacastrum).
Pigweed is an alternative host of pests and diseases such as Root Knot, Pin, and Reniform nematodes.
It is a highly invasive weed and one reason for this is its large production of seed. One plant can produce up to 250,000 seeds over a season. The seed survives in the ground for several years, but germinates rapidly after soil disturbance and when it is exposed to light. This together with its rapid growth means it has a competitive advantage over turf especially if it is under stress. Also, it is drought tolerant, although it does best in moist, fertile soils.
After you finish reading this, you will be able to:
- Identify Pigweed or Purslane.
- Know the habitat of Pigweed.
- Know the best cultural and chemical options to control Purslane.
Pigweed has negative allelopathic effects on seed germination, and seedlings.
Because of produces a large numbers of seeds, Common Purslane quickly colonizes warm and moist sites. Its ability to regrow from severed stems, allows the weed to regrow from stem or root fragments.
A unique competitive advantage of this weed is its ability to switch from C4 metabolism to crassulacean acid metabolism (CAM) in the presence of short days or when under drought stress. This means Pigweed closes its stomata during the day in dry conditions to reduce water loss, and opens them at night to take in carbon dioxide it needs for photosynthesis.
How to Identify Pigweed.
Pigweed has a much-branched, often reddishcreeping, fleshy hairless stem, that is 20-50 cm long
Category: Broadleaf (Dicot)
Flower: Pigweed flowers are yellow, have 4-6 petals (often 5), and are 3-10 mm long. These are often single or in small clusters, in the forks of leaves.
Height: Prostrate.
Leaf length: The hairless wedge-shaped leaves, alternate along stems, and are 5-25 mm long,
Leaf width: The leaves are 3-15 mm wide
Reproduction:
Pigweed spreads mainly by seeds but vegetative reproduction possible from re-rooting stem fragments.
The seeds germinate in late Spring and through the Summer, and spread long distances by wind, water, and by passing through the guts of birds. These seeds can remain viable for up to 40 years.
Pigweed seedlings emerge once temperatures exceed 24°C, and following rainfall. 4 to 6 weeks after emergence plants flower, and can have several flushes of flowers depending on the conditions.
Mature seed can be produced within as little as 6 weeks of germination. Pigweed plants are susceptible to lower temperatures, and begin to die once temperatures begin to fall in early Autumn. After an irrigation or rainfall, Purslane germinates very near to or at the soil surface in large numbers.
The burial depth of seed is also a significant factor in germination rate. Seedling emergence has been found to be greatest at the soil surface, and declines exponentially with increasing soil depth
The fleshy stems of common purslane can remain moist and viable for several days after cultivat
Comments: Horse Purslane is thick, and flat at the nodes. Its taproot is white or brown in colour with fibrous hairs that reach to a depth of 30-50cm. Stems are maroon-purple, hairy, and erect.
Habitat: Pigweed is found from sea level to about 2500 m, and is a common weed of crops, pastures, gardens, disturbed sites, waste areas, footpaths and roadsides. Favours high fertility soils with moderate moisture, but capable of growing in nearly all soil types. However, growth and establishment is particularly favoured in soils with higher nutrient levels, including higher phosphorus and nitrogen.
For more information on weeds check out our weed ID Chart.
How to control Pigweed.
You can control Purslane by cultural and chemical means, but successful management of this weed is best if you adopt an integrated approach.
Cultural control:
In healthy, well-established turfgrass, Pigweed is usually not a problem. It is more of a problem in weak, poorly maintained turfgrass. Therefore, feed your turf properly and cut it at the right height to maintain healthy, competitive turfgrass.
The first step to manage Pigweed is to prevent it in the first place, as once Common Purslane becomes established it is difficult to control. Avoid bringing common purslane into uninfested areas and clean equipment like mowers etc. before allowing them to enter clean areas.
Personally we have seen big issues with this weed after cultivation, as this tends to bring deeper weed seeds to the surface where they then germinate after irrigation.
If Pigweed is flowering remove the plants offsite to ensure that viable seed is not released.
Chemical control:
In Australia, a number of chemicals are registered, for instance: 2,4-D, Dicamba, Pendimethalin, Propyzamide, and Glyphosate but not all of these for turf use.
Pre-emergent Control.
If you use preemergent herbicides make sure they are present at the soil surface when seedlings emerge and have been activated with an irrigation . If you treat too late in the season to mature plants, control is often erratic and seed set may have already occurred.
In the USA the pre-emergents herbicides Dithiopyr, Pendimethalin, and Propyzamide will control Pigweed. Although in Australia, Metolachlor is only labelled for suppression of pigweed and another option here is BASF Freehand herbicide.
Postemergent control
Dicamba, and 2,4-D are effective postemergent herbicides in turfgrass and are available to the home gardener. Another option is Quali-Pro Crest. If you this, use it with a Crop Oil Concentrate like ProForce Voltage MSO.
In South Africa, Casper Turf is registered to control Purslane at 600 – 800g /Ha.
If you use glyphosate and water quality is an issue then we recommend the use of ProForce Manta Ray.
