“Rockview” is a 640 ha mixed farming enterprise 15 kilometres north east of Lockhart. It consists mainly of red loam and self-mulching clays on country varying from near flat to fairly undulating terrain. The northern boundary backs onto the Galore Hill Nature Reserve.

My wife, Fiona, and I run approximately 300 Bond ewes plus 350 weaner replacements as well as cropping between 280 and 320 ha annually. On the property we grow canola, lupins, barley, oats and wheat in varying proportions each year. There is no set rotation, flexibility being the order of the day. This year 285 ha is under crop.

I had very little interest in, or knowledge of, herbicide resistance two years ago. It was in 1988 when I first discovered I had a chronic resistance problem. After a routine inspection to see how well Hoegrass had worked I was shocked to discover that in one paddock the ryegrass was flourishing and the wild oats were dying.

The paddock had been sprayed with 950 ml/ha of Hoegrass on June 24. The Hoechst representative was contacted and advised me to use 1.5 L/ha.

The paddock was once again sprayed on August 1. When there was no sign of the ryegrass dying, the Hoechst representative was contacted again and resistance was suspected.

To confirm these suspicions a field trial was conducted. As shown in Table 1 the results were quite dramatic as Hoegrass at 8 LIha had no effect on the ryegrass. Due to the advanced stage of the ryegrass at the time of the trial no chemical gave an economic result but there were indications that Grasp^(R) and SertinQ^(R) did give some control, which was encouraging.

Table 1. The effect of herbicide application on resistant ryegrass control in wheat, 27 days after treatment (September 9, 1988)

w.a. = Howet at 0.25%

On reflection I remembered that the year before, when the paddock was sown to lupins, Fusilade had only given a marginal result on ryegrass, but because I had also used 1.8 L/ha of trifluralin the ryegrass never dominated.

From the paddock history given in Table 2 it can be seen that crop activity has been intensive - 10 crops in the last 13 years. Fortunately I had undersown the 1988 wheat crop with clover so I have been able to rest it for the last two years.

Table 2. History of paddock containing resistant ryegrass

My long-term program for the paddock is to establish a lucerne pasture and keep ryegrass to a minimum.

My program for this year is as follows:

1. Graze pasture very heavily this spring and spray fallow with Roundup in September before seed set. To ensure the ryegrass does not set seed the paddock will be kept grazed after spraying.

2. Combine - work it shallow at 5 to 7 cm on the first rain in 1991, so as not to bury the ryegrass seed.

3. Incorporate 3 L/ha simazine + 2 L/ha trifluralin and sow to Gungurru lupins.

4. In 1992 trifluralin will be used again and the paddock will be sown out to lucerne and clover using a light rate of canola as a cover crop. Canola should not follow lupins if the lupins have had sclerotinia so I might have to reappraise the situation.

Other options I see to keep ryegrass under control are:

1. hay cutting in the pasture phase;

2. sowing wheat or barley only if sclerotinia restricts lupin or canola sowing. Grasp appears to be a herbicide I can still use on this paddock.

The lesson I have learnt from my experience is to monitor sprayed paddocks very closely. If areas of ryegrass survive where wild oats have died, then start to worry. Ride or walk across the paddock 2 to 3 weeks after spraying to check for effective kill. If resistance is suspected use a hand-held garden spray with a rate 8 to 10 times the normal rate and spray the suspect area. About 3 square metres would be enough.

If paddocks have a long history of one particular herbicide (for example Hoegrass), be careful - resistance problem probably already exists.

Conclusions

My herbicide resistance problem might have been hastened by the light rates of Hoegrass I used.

When winter pasture cleaning grasses, it might be advisable to use simazine and Gramoxone in June rather than using simazine and Fusilade as the Fusilade might be hastening the resistance to ryegrass when you rely on Hoegrass in your next wheat crop.

Do not spray crops for a cosmetic effect.

Rotate chemicals which have different mode of action. In my case I have switched to Grasp and will only use Hoegrass occasionally.

Because many farmers have bulk handling systems, the swing away from seed grading worries me. By sowing seed with even low weed levels, resistance could be spread.

It also horrifies me what might happen if we have another 1982 drought and grain is freely traded from farm to farm on a mass scale.

Having resistant ryegrass is not the end of the world, but I do not see any easy cure. However, vigilance and careful rotations with alternate crops and chemicals will delay the development of herbicide resistance on the farm.