How to Control Winter Grass (Poa annua)

Winter weeds are a problem, like any seasonal weeds. But the dreaded Winter Grass (Poa annua) is one of the worst.

At this time of year, we also start to see Winter weed pressures. It’s hard enough for the lawn fanatic to cope with the decline in growth rate and possible dormancy during this time. Now add exposure to pesky weeds like Winter Grass and we can start to see real problems.

What is Winter Grass?

Winter Grass is known as an annual cool season grass. This is not to be confused with a cool season turf variety as this is one grass type we definitely do not want to establish.

Botanically referred to as Poa annua, Winter Grass is often given little respect when it comes to lawn care. Those that have become aware of it and have identified it in their lawns learn from the experience pretty quickly and implement measures to combat further outbreaks. This is something we highly recommend for all lawn fanatics before the fact.

Unfortunately for us all, Winter Grass appears widely throughout Australia so it’s quite likely you will encounter this problematic weed at one stage or another.

Winter Grass germination

Winter Grass is very versatile and thus has the potential to germinate in all areas of a lawn, from full sun exposure right through to highly shaded areas.

Upon germination, Winter Grass appears light green in colour and, for those that have used Iron throughout the growth season, it’s plant will be clearly visible.

As it nears maturation, Winter Grass becomes a thick, tufted (clumping) plant, and this is definitely something we want to avoid.

Soil temperatures and moisture content in your profile allow it to thrive. If the conditions are right, a Winter Grass plant can mature very quickly. The biggest problem we face here is the plants’ ability to produce seed heads. Winter Grass is a prolifically seeded plant, and this poses ongoing problems year after year if not controlled correctly with the right products and time of year of the application.

If we are not proactive when it comes to treating this plant, Winter Grass can be difficult to control particularly in cooler seasons. Historical papers document that the Winter Grass plant not only requires minimal light to start germination, but it also requires a cooler temperature range. As our temperatures decline and days become shorter, we move closer to that perfect range for Winter Grass pressures. That optimal temperature range for Winter Grass is between 10-11 to 16-17 degrees, making late Autumn and Winter ideal.

The famous quote that is used throughout the Turf Industry, “One year of seeds delivers seven years of weeds” could not be truer when it comes to Winter Grass. Allowing this plant to mature and seed will undoubtedly cause the decline of your lawn as the unsightly Winter Grass takes over.

How to control Winter Grass

There are three methods of controlling Winter Grass, the first of which being manual removal. Although it has a very intense root system, it is also a shallow rooted plant which makes for easy removal by hand.

Selective post emergent is your next option; there are Herbicides available to suit your grass variety to help with control of Winter Grass. Personally, we see this as masking a problem that will come back to haunt you later on. The other train of thought leads us to consider how much chemical you will apply during these seasons to control your outbreak, remembering that the constant use of Herbicides does our environment and ecology no favours.

The third and most effective way to control a Winter Grass outbreak is pre-emergent control. Pre-emergent Herbicides are specifically designed to target such weeds and prevent the germination of seeds if applied correctly. Pre-emergents have a residual factor that can range from 10 weeks to 6 months depending which product you apply, making it the most popular way to combat an outbreak.

Winter Grass Wrap Up

Winter Grass is a weed/plant that, as a lawn fanatic, we want to avoid at all costs. It does not matter what Turf variety you are growing, whether you cylinder mow or use a standard push mower. If the stars align, this plant will inevitably germinate if you are not protected.

Post-emergent control is not always the magic fix either, as it can take several seasons of applications to deplete the seed stock that was deposited by previous outbreaks.

Eliminating the chance of allowing this plant to germinate is in your best interest. Yes, the plant can die off during longer periods of hot temperatures (north of 33 degrees) and will only leave small patchy areas for us to deal with.

So, before we start to encounter the full brunt of the Winter Grass pressures, investigate pre-emergent for peace of mind this season and protect your investment.

Pre-emergent can be applied as early as late March. A lot will depend on your location, what temperatures you are currently experiencing and what is forecast. Do your research and find the one that best suits you and knock Winter Grass from your lawn.