Amaranth
Amaranth is a very invasive Summer annual weed, that germinates in the Spring and then flowers from the late Summer onwards.
Jerry Spencer 
Amaranth is a very invasive Summer annual weed, that germinates in the Spring and then flowers from the late Summer onwards. There are two main varieties in Australia and these are A.viridis (Green Pigweed) and A. retroflexus (Redroot Pigweed).
Why is Amaranth a Problem Weed?
Amaranth is a problem weed because it is very competitive. This is because:
- It emerges early and grows rapidly.
- It germinates in low light conditions.
- Amaranth has a C4 photosynthetic pathway. This enables it to thrive under heat and drought conditions better than many other species.
- Redroot Pigweed has Allelopathic properties.
- It has a rapidly growing root system.
- It is a large seed producer.
- The seed remains viable for a long time.
- In warmer climates it grows all year-round.
- There are a lack of herbicides options for its management in turf grass systems.
Redroot Pigweed.
- This is a hairy, annual herb that grows up to 1 m tall. The very hairy stems are red towards the base, and it has a red taproot.
- It contains toxic nitrates and oxalates in its roots and leaves. Cattle are at risk of nitrate poisoning if they eat large amounts of immature Red Pigweed stems. It also causes kidney damage.
- You often find this weed in wet areas.
- Amaranthus retroflexus produces at least twice the root length of most other weeds in the first month of growth. This fast-growing root system allows it to quickly access soil moisture in competition with other species.
- Redroot pigweed is most common in new turf areas where turf grass is not very dense or competitive.
Green Pigweed.
- Amaranthus viridis is a short-lived herbaceous plant that grows to 1 m tall. Its leaves are light green, have no hairs and often have notched tips.
- Green pigweed is often mistaken for Redroot Pigweed but it does not have a red taproot.
