In January 2013 the RSPCA Landcare Group presented preliminary findings in Gecko on their Holly experiment. Now 3 years after treatment (nearer 2.5 – 4 years), the results are slightly different.
A major conclusion is that you cannot be sure of the effectiveness of your treatments on Holly for at least two to four years later. So the follow up work is more time-effective if left for at least 2 years after the initial treatment.
Most bush regenerators consider Holly to be one of those weeds where the results of treatment are often inconsistent. Some of the reasons for this is believed to be: the time of year, the technique used and/or plant size. The RSPCA Landcare group started to test these theories in late 2010 by setting up 5 plots to be treated over a 15 month period –treating the holly in the four seasons. In total 275 plants were treated covering a range of plant sizes.
In July 2014 some plants were totally covered by fallen trees after the huge windstorm of July 2011. Other plants and their markers could not be found probably because both plant and marker had rotted away. So 161 plants were found and assessed. The trial found that a 100% kill rate could be achieved at any time of year as long as the chosen technique was done correctly.
The overall effectiveness of the trial was 92.5% – only 12 plants had any sign of life out of 161. The herbicide used throughout was undiluted Glyphosate. The 3 techniques used were – cut and paint, scrape and paint, and drill/fill. Approximately 50 plants were treated with each technique, covering all seasons. The results are too small to be conclusive however the indicators are that:
For plants under 10 mm diameter at the base – both cut & paint or scrape & paint works
Between 10 mm and 40 mm – the scrape & paint technique works best
For plants over 40 mm – drilling works the best
DISCUSSION OF RESULTS
Cut and paint (C&P)
Of the 53 plants treated by C&P, there was a 13% failure rate (7 Plants). One failure was due to poor technique (the cut was too high – 80 mm above ground level) resulting in 4 shoots sprouting below the cut.
Most of the failures were plants between 10 and 40 mm diameter at the base.
The highest failure rate occurred using the cut & paint technique, even using the larger sample size of plants monitored previously (Sept 2012). However it is worth noting that there was a 10 out of 10 success rate for C&P plants 40-54 mm.
Scrape and paint (S&P)
Out of the 55 plants treated by S&P, 4 were not effectively killed (7% failure or 5% compared with larger monitoring sample).
3 of the unsuccessful treatments were on multi-stemmed plants where not all stems had been scraped; the other was where the plant was larger than 40mm diameter.
Drill & inject
Of the 53 plants treated by drilling and injecting neat herbicide, only 1 was not effective (1.9% failures). This was a multiple stemmed plant with many suckers, which appeared to have not all been scrapped.
The technique used was to drill holes at about 40 mm spacing in a ring around the base. Only 5 plants treated by drilling had a base diameter less than 40 mm, so it is difficult to come to any conclusions as to the effectiveness of drilling smaller plants. However it is possible to use a smaller size drill bit.
CONCLUSION
The sample size is too small for the results to be conclusive on the best technique to use for each size plant in each season.
This pilot study does indicate that:
- Holly can be treated effectively in all seasons.
- Both the cut and paint and the scrape and paint techniques are effective for plants less than 10mm diameter.
- The Cut and Paint technique only works if cuts are no higher than ground level
- Scrape and Paint is the most effective technique for plants between 10 and 40mm diameter at ground level.
- Plants larger than 40mm are best drilled and injected.
- Plants with multiple stems or suckers can be treated effectively by a combination of drill& inject and scrape and paint techniques, as long as all stems/suckers are treated.
| Summary of Sample Size and Results | ||||||||
| TECHNIQUE | Size of Holly Stem in mm | |||||||
| 0-9 mm | 10-24 mm | 25-39 mm | 40-54 mm | 55-69 mm | > 70 mm | July 2014 total | total @Sept 2012 | |
| CUT & PAINT sample | 7 | 18 | 13 | 10 | 3 | 2 | 53 | 91 |
| number alive | 0 | 4 | 2 | 0 | 1 | 0 | 7 | |
| % failure | 0 | 22% | 15% | 0 | 33% | 0 | 13% | 8% |
| SCRAPE & PAINT sample | 14 | 25 | 8 | 6 | 1 | 1 | 55 | 75 |
| number alive | 0 | 2 | 0 | 1 | 1 | 0 | 4 | |
| % failure | 0 | 8% | 0 | 17% | 100% | 0 | 7% | 5% |
| DRILL sample | 0 | 0 | 5 | 17 | 10 | 21 | 53 | 63 |
| number alive | 0 | 0 | 0 | 0 | 0 | 1 | 1 | |
| % failure | 0 | 0 | 0 | 0 | 0 | 4.80% | 1.90% | 1.60% |
| TOTAL SAMPLE | 21 | 43 | 26 | 33 | 14 | 24 | 161 | 230 |
| number alive | 0 | 6 | 2 | 1 | 2 | 1 | 12 | |
| % failure | 0 | 13.90% | 7.70% | 3% | 14.30% | 4.20% | 7.50% | 5.20% |
By Lyndal Sullivan