Monitoring Effectiveness

Monitoring Injection Efficiency

During 2013 and 2014, the Tarrangower Cactus Control Group carried out a monitoring and evaluation program. The aim was to assess the effectiveness of the glyphosate injecting technique used by the volunteers at our regular monthly field days. Glyphosate diluted at 1:3 in water and 2-4ml injected into lobes was used on each field day.

A Field Day Record Sheet was completed recording details of weather, terrain, cactus growth patterns and dispersion. A section of the site that was representative of the whole was also chosen and pegged out, which became the monitoring plot. The total number of wheel cactus plants within the monitoring plot was recorded, plus a count of the total number of treated cactus within the plot.

Initially the kill rate at each site was determined each month for 3 months, recording the number of plants unaffected by injection with glyphosate, the number damaged, dead and re-growing. However it was later decided that a 3 month period was not long enough to properly determine the kill rate, so the follow-up counts were changed to 1, 3 and 6 months after injection. The plots were also photographed at each time point.

Conclusions from this program were:

  • When either 3 or 6 months was used as the end point, the plant kill rate varied between 10% and 100%

  • This large variation was probably partly due to the fact that 3 different volunteers recorded the data and used varying numbers of plants in their defined plots, and therefore the sample size was not consistent.

  • Kill rate extremes were also likely affected by the large variation in the size of the plants in the defined plots, as some plots contained only small plants while others contained mostly large plants.

  • The conditions recorded were also very subjective and measures not well defined, such as the water content of the plants.

  • There was no obvious effect of uptake of the herbicide from weather conditions as the recorded conditions were very similar on most field days, e.g. no precipitation, low-medium humidity, little wind and cloud cover, similar temperatures and times.

  • At either the 3 or 6 months end point, only small and medium sized plants were completely dead. Most of the large plants were not dead and still partially growing, which was most likely because not all outer lobes of these plants had been injected. This was probably due to the physical difficultly for the injector to reach all of the lobes at the time of first attack.

  • However when all the outer lobes of a plant were injected, 33% Glyphosate proved to be a very effective herbicide.

A Student Feedback Questionnaire has also been developed for use with students groups. It explores their knowledge of cactus and control methods prior to the field day, what they learned from the field experience, what aspects they liked the most and the least about the experience and whether they would come again and if they would recommend such field days to other students.