Control & Management

The key to controlling Wintergrass lies in its management using both chemical and cultural practices. Good cultural practices means keeping the lawn well maintained by regular mowing and fertilising, and not allowing bare patches to develop which will offer an ideal seed bed for Wintergrass germination.
Light infestations of seedlings may be easily hand weeded as Wintergrass has a very shallow root system.

Chemical Management

There are two main ways of approaching the management of winter grass with chemicals… pre-emergent control, which means spraying the lawn before the weeds emerge, or selective post-emergent control once the weeds have already germinated.

I prefer to use pre-emergent control for Wintergrass. A common saying is “One year of seeds brings seven years of weeds!” This might sound like an “old wives tale” but in fact, it’s true. Dealing with weeds before they have the chance to seed is the most efficient and effective way to have a healthy lawn. The use of a residual pre-emergent application can also eliminate the need for multiple post-emergent herbicide applications.

Common questions or concerns I hear about using a pre-emergent spray on Wintergrass include the following:

“It is February/March and I don’t have any Wintergrass. It seems a bit silly and a waste of money to spray nothing.”

Some lawns do not have a Wintergrass problem. This may be due to an extremely strong lawn that covers all areas well, with no weak spots. It could be due to good hygiene since the lawn was established, with minimal shade, cool, damp or worn areas. These people are lucky and should hold on to their money and spend it on anything else in the garden!!

However once a lawn situation shows a susceptibility to Poa (Wintergrass) it is a safe bet that it will re-appear yearly (as an annual grass does) and strengthen its hold in your lawn each year.

“Why shouldn’t we just wait until it is all up for the year and kill it then”?

Preventing seed production and plant reproduction are the compelling reasons for pre-emergent weed control strategies, as mentioned above. Wintergrass has an extended germination period that lasts from early Autumn right through Winter and into Spring. A pre-emergent product applied in Autumn kills seed roots and shoots before they emerge through the soil and set a seed head.

Removing Wintergrass (and some weed/grass species) after it has germinated and established still leaves the problem of its root mass underground. The Wintergrass plant (a monocot) has a thick fibrous root system, with the roots running deeper than its height on the surface. If mechanically removed, the roots hold onto soil, leaving pocks/divots in the lawn surface. If controlled with chemicals, the root mass rots underground but remains in the soil, leaving bare areas above which detract from the look of your lawn, and which provide an excellent place for more weeds to take hold.

“I have sprayed pre-emergent this year and had a good result with just a few plants breaking through. So does that mean I’ve won the war against weeds? I won’t have to spray anymore?”

It needs to be noted that a successful season’s control doesn’t mean you have won the war against that weed in that situation. Shaded, worn, sparse and damp areas are prone to annual attacks of weeds (in this case Wintergrass) year in, year out. Vigilance and organisation go a long way towards effective weed control. In areas proven to be a problem, I recommend yearly or twice-yearly control, as do the manufacturers of the various products.

In my experience the best results are achieved by spraying twice yearly for a period of not less than three years. In most cases you can then revert to a yearly application of the product to give satisfactory control. However there are exceptions to this, some clients have enormous Wintergrass problems and twice yearly applications are a must for prolonged control.

“What if I don’t spray at all? Will the Wintergrass die off in the Summer?”

Yes it will. In most cases a prolonged period of 33-35oC will burn the canopy off what is a cool season grass. Unfortunately there are also exceptions to this. Some Wintergrass will persist throughout an entire year, benefiting from reticulation systems being on throughout watering season. Then the problem becomes lawn-threatening as the new germination year plants mix with the older last year plants. The multiplication of plants can lead to dinner plate-sized weeds which choke out the lawn, especially through the cooler months.

“I didn’t use a pre-emergent spray and now its mid-Winter and things are a real mess, Wintergrass everywhere. Is there anything you can do?”

Yes, we can remove mature Wintergrass with a post-emergent product. Unlike the pre-emergent products which offer residual control, post-emergent control is best done during late-Spring when ALL plants are up for the germination year. If post-emergent control is done for the first time, then pre-emergent control is recommended the following Autumn as seeds have set and plants will re-emerge the following year, even though the active population has been cleared out for this year.

Post-emergent removal in the Spring is effective, but can leave the lawn surface with numerous bare patches, pitting and poor turf uniformity as discussed above. Lawn renovation and top-dressing is then often necessary to provide an even lawn surface again.

Mowing mistakes can result in discolored lawn tips, brown spots, and even severe damage to the lawn. Common mistakes are mowing too infrequently and cutting grass too short. Here are some tips on proper mowing technique:

Avoid Scalping

Letting grass grow tall and then removing more than 1/2 the leaf blade is called scalping and can damage the lawn. Mowing grass extremely low can also damage the lawn by cutting into the crown of the plants.

Sharpen Blades

Make sure your mower blades are sharp in order to cut cleanly. Dull blades can shred grass and cause discoloration at the tips because frayed grass blades lose moisture easily. Sharpen/replace the blades of rotary mowers several times each growing season. Reel type mowers usually only require sharpening once a year, but adjust them to ensure they cut cleanly. Some grass species have tough blades, which causes blades to wear quickly.

Be Gentle with Damaged Grass

Raise the mower height a notch or two when mowing a lawn that’s recovering from drought, insect damage or disease.

Don’t Cut Wet or Wilted Grass

Avoid cutting wet grass, which can cause brown spots because clippings clump together and smother your lawn. Cutting wilted grass, particularly during the hottest part of the day, can also cause severe damage to your lawn.

Know When to Mow

The best guide for mowing frequency is the growth of your grass. Plan to cut less than one-third of the grass blade in one mowing. Keep in mind that certain grasses require close mowing to stay healthy. Allowing these grasses to grow too high will promote thatch development.

So You Miss a Mowing?

During periods of rapid growth, lawns may require mowing as frequently as weekly. Sometimes we just don’t have time to mow as often as we’d like. If your grass has grown too high, reset your mower to a higher cutting level. A week later, reset the mower to cut at the normal height and mow your grass again.

Mowing Height

Select the proper mowing height for your lawn. Measure the grass plants after mowing a very small area, then adjust your mower as necessary. Always mow your lawn at the recommended cutting height.
A thriving warm-season grass will tolerate lower cutting heights with greater frequency during warmer months, as leaf production is prolific during October to April, but cutting heights should be raised in cooler months to aid photosynthesis.

Mowing After We Have Sprayed

To ensure the effectiveness of the application and to minimise exposure, the lawn should not be mowed for at least 24 hours following the application or until it has been watered, or it has rained and dried.

Don’t forget your garden watering roster

To find out your watering days, simply take the last digit of your house or lot number and apply it to the table below.

Experts agree these rosters will provide more than enough water to maintain a waterwise garden.

For more tips on how to be waterwise, visit waterwisewaysforwa.com.au or call the Waterwise Infoline on 131039.