Horseweed in Canberra, ACT
 

Fleabane (Conyza spp.)

Fleabane also known as Horseweed, germinates in the spring and can become a major weeds in the summer. It is a summer annual but it can sometimes occur during the winter months. It is a tall growing dicot with a tough, hairy stem, and as it matures its stem becomes hard and woody.

Dark green leaves are alternately arranged and have toothed margins with fine hairs coating the surface. These hairs coupled with its woody stem make it very difficult to control.

When immature or when existing in closely mown turf, Horseweed initially appears as a flat, rosette like weed, however as it matures the stem lengthens with leaves forming around the entirety of the stem.

Large clumps of flowers form around the top of the tall stem in the Spring and Autumn,  and these form fluffy clusters as seeds begin to form.

After you read this, you will be able to:

  • Identify Fleabane or Horseweed.
  • Know the habitat of Fleabane.
  • Know the best options to control Fleabane or Horseweed.

 

 

How to Identify Fleabane.

 

Category: An annual or short-lived perennial.

Flower: Flowers are white to yellowish Flower head, cylindrical to bell shaped, 5-6 mm long,

Height: 1-2 m tall
Leaf length: 2-10 cm long

Leaf width: The leaves are 1.5 cm wide, and covered in soft hairs.

Reproduction: Fleabane seeds are spread by wind, and mature Flaxleaf Fleabane produces an average of 110,000 seeds, that can be viable for up to 18 months. Fleabane seeds only emerge from on or near the soil surface. When sown on the surface, 5% of the seed remains viable after 12 months. After burial at 50 millimetres (mm) and 100mm for 12 months, 10% and 15% of buried seeds maintain viability.

Optimum temperature for germination is 20C with a base temperature of 4.2C and a maximum temperature for germination of 35C. 50% emergence occurs 4-5 days after moisture is supplied, at 20C

Comments: The leaves are grey-green, oblong to wedge shaped to oval and twisted near the base. They are densely hairy and the edges are smooth, toothed and often wavy. Those near the base often wither early.

Habitat: Fleabane is primarily a weed of roadsides, especially if bare soil exists where it can germinate. More on lawn and turf grass weeds is in our weed ID chart.

 
 
 

 

 

How to control Fleabane.

Both cultural and chemical control will control Fleabane in your lawn and turf.
 
 
 
 
 

Cultural control:

An integrated approach will give the best chance to control Horseweed.

  • Monitor areas early during the germination period.
  • Spray weeds when they are a small rosette and before stem elongation starts.
  • Consider using an adjuvant to improve herbicide uptake.
  • Moisture stressed plants are much more difficult to control with herbicides.
  • Rotate herbicide mode of action groups.
  • Control plants in surrounding areas so they don’t flower and act as a source of seed to infest turf sites. Managing the soil seed bank is critical for long term Fleabane management.

 

Fleabane is not a great competitor, so a healthy and dense turf cover will outcompete this weed. The key is to improve the competitiveness of your turfgrass.

This means feeding you turf properly, cutting at the right height for the turf species present and limiting soil compaction. Trying to mow this weed out is not effective and will encourange this weed.

If the soil is not compact then hand pulling after stem elongation works, but on heavier, compact soils you will need a fork to prevent the plant breaking and regrowing from the base.

 

 

 
 
 
 
 

Chemical control of Fleabane:

The first point is that Fleabane have been confirmed as glyphosate resistant. However, you can best control Fleabane when it is are emerging, mainly in early spring, and still small. Small Fleabane plants are relatively easy to kill and a late post-emergent application of some phenoxy herbicides during spring can control them.

Due to their hairy nature add an organosilicone surfactant (ProForce Scrubwet) at 200 mL/100 L for optimum results.

The other trick is too make sure that your water rates are not too high. If they are, then the adjuvant will become too dilute to have any benefit.

It can be difficult and expensive to kill mature Fleabane, especially in mid to late Summer. That’s why its important too target small, actively growing weeds. Factors such as weed age can have a negative impact the results that you get.

 

Pre-Emergent Herbicide.

The only Pre-emergent herbicide currently registered for turf is BASF Freehand.

 

Post-Emergent Herbicide.

It is vital to use herbicides when the weed is a small rosette only 5 cm in diameter or smaller, as control efficacy declines as plants mature. An adjuvant enhances active ingredient movement into the plant, improves rainfastness and herbicide performance. Gilba Solutions recommends the use of ProForce Manta Ray if water quality is an issue.