25th May - Guildford Grass - A Case Study

Without any doubt my worst weed is guildford grass, Romulea rosea. One of the reasons it is so much trouble was because I thought it wouldn't be. I made the mistake of thinking that some exotic species would not be a problem. I thought I could get on with removing the blackberry, broom, gorse and all the classic woody weeds and leave the insignificant weeds for later. However given the right conditions, any species of plant can take over.

In my desire to create a suitable environment for the smaller plants, I certainly created a paradise for guildford grass. To get on top of this weed, I had to understand it.

Guildford grass is an Iris. It has a bulb about the size of a marble. It spreads by seeds. The sprouting of the bulb seems to be triggered by the April break. By June its leaves are visible.

It then sends up a single leaf as high as it can. This is so it is above the surrounding vegetation. The first thing it has to do is to convert the stored nutrients in the bulb to usable form. For this it needs the chemicals produced by photosynthesis. That is why it has to send the first leaf as high as possible. This is its first weakness. At this stage attack number one can be launched against it.

At first I tried glyphosate. However I soon learned that when it first emerges, it is unaffected by glyphosate. The early attack has to be manual. Since I had so much of it I had to start when it was first visible. This is at the beginning of June. It is very visible at this time since it is one of the few plants actually growing at this time. I simply dig them out. I seem to get about 80% of the plants at this stage.

By the end of July this single leaf can be very tall and very strong. It can be up to 50cm high. This is the ideal stage to paint the leaf with Glyphosate. I make up a one to two mixture of glyphosate to water, as recommended for a “Roundup Wand”. However I then use a suitable size paint brush. I grasp the guildford grass leaf as low as possible above the surrounding vegetation with my left hand. I am right handed. I then paint the leaf, with the glyphosate solution as my left hand slides up the leaf. I attempt to leave the leaf standing upright so as not to contaminate the surrounding vegetation. Note that where the guildford grass is dense I can grab many guildford grass leaves in my left hand. Using this method I can kill about 80% of the remaining mature plants.

The next attack against it I launch in September – October. This is when it flowers. It produces a very visible flower which it thrusts up above the surrounding vegetation. I then use a tool similar to a large screwdriver to loosen the soil near the plant and I grasp it as close to the ground as I can and pull it out. This way I get rid of about 80% of the remaining adult guildford grass.

However by this time the guildford grass knows that it is under attack. Juvenile plants that would not have flowered until the next year decide they should flower. It is therefore necessary to make a number of sweeps pulling out the plants as they flower. Fortunately it a reasonably pleasant job since it is the time when flowering, and other wonderful plants, at Wirrapunga is reaching its optimum.

I can therefore combine this job with a general monitoring of how things are going. Every time I have made a sweep of pulling out flowering guilford grass plants, I have discovered a new plant species at Wirrapunga. This year a tall leek orchid flowered for the first time.

By November – December, depending a bit on the season, Guilford grass is setting seed. At this time the stem is reasonably thick, about a centimetre in diameter. Each plant has up to half a dozen seeding stalks, each with a seed pod on the end. The bulb is at its smallest, actually smaller than the diameter of the stem. All the nutrients are up in the plant itself. This makes the plant at its easiest time to simply pull it out.

This is when I make my final round. If the season has been kind and the soil is soft, the plant is easy to pull out. If the soil is hard and dry then often the stem will part from the bulb. However the bulb does not seem to survive this trauma so the result is the same.

If all goes well I have removed all the plants that would have flowered that season but, unfortunately I am not finished yet. Firstly not all bulbs sprout each year, secondly I have missed many of the juvenile plants and finally I have the pheremone problem. The soil is rich in ungerminated seeds built up over years of seeding. It is the classic "one years seeding, seven years weeding" problem. After three years of not allowing any guildford grass plants to seed and removing millions of plants, I have many more juvenile plants appearing each year. I will let you know how long before I can claim victory.

Happy weeding!!