What is Guildford Grass
Guildford Grass is also known as Onion Grass. It is a thin wiry weed that is very difficult to control due to it having a corm that can survive underground in hot, dry temperatures. It is not a broad leafed weed do cannot be controlled with your normal broad leaf weed killers. You can also recognize Guildford grass as it is very difficult to mow, especially with a cylinder type mower, and it will often be left standing up after you have passed over it. It appears in Autumn and carries on through winter before dying back in spring, usually from competition from the healthy spring growth of other varieties of grasses and the heat. Even though the top growth will die in summer it will leave the corm in the ground ready for next season.
Causes of Onion Grass.
The main causes of an infestation are bare ground in Autumn and a lack of competition from other grass varieties. This means if your grass is in poor condition you are more likely to have a problem.
Turf Management Practices
Guildford Grass does not respond to fertiliser applications, so fertilising your lawn in Autumn and Winter will encourage your turf to be more vigorous so it can smother out the Guildford grass. Also Guildford Grass is sensitive to having its foliage removed, so low mowing with a slasher type mower will weaken the plant and dramatically reduce the infestation. You will need sharp blades; however, the stem is less woody low to the ground so you will have a better chance of actually cutting the plant.
To eradicate this weed you need to use products with Met Sulfuron – Methyl. Branded products with this active include Ken Met, Associate and Brush Off. Guildford Grass should be sprayed when old corm is exhausted and new corm is emerging, so about 6 to 8 weeks after onion grass has emerged (autumn). Spraying later in the season when flowering will kill the flowers and seeds but not the corm.
Met Sulfuron – Methyl is also very effective at killing broad leaf weeds such as clover, doublegee and onehunga, as well as Cape Tulip and Sour Sob.