Physical and Cultural Weed Control Working Group of - European ...

9 th EWRS Workshop on Physical and Cultural Weed Control 81
Samsun, Turkey, 28 – 30 March 2011
Can image analysis be a tool to measure changes in vegetation cover
after flame treatments?
A.M. Rask 1 , P. Kristoffersen 1 & C. Andreasen 2
1) Forest and Landscape, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 23,
DK-1923 Frederiksberg C, Denmark and 2) Department of Agriculture and Ecology, Crop Science,
Højbakkegårds Allé13, DK- 2630 Taastrup, Denmark.
In many countries the risk of pollution of the environment has led to restrictions on the use of
pesticides in urban areas, and herbicides are often replaced by flame weeding. Flame weeding
controls a wide range of annual weed species, but plant species with protected meristems, such as
grass weeds, pose a special problem because of their ability to regrow after the treatment.
Therefore, repeated treatments are necessary, which increase the costs. In this study, the changes in
vegetation cover of the test species Lolium perenne (L.) (perennial ryegrass) was measured by
image analysis during an entire growing season. Measurements of the effect of non-chemical weed
control by flaming can be done in several ways. The most used method is to take biomass samples
from the experimental plots and dry and weigh the plants. Dry weight of plants gives a useful
estimate of the effect of the treatment. If the aim of the investigation is to measure the effect of
repeated treatments, the removal of the biomass makes is impossible to measure how regrowth
would occur under normal conditions. Additionally it is very labour demanding. Other methods can
be used, such as measuring light reflection, visual assessment, or, as in our case, use of image
analysis.
In the present study, a large number of treatment plots were treated with a gas burner with
different doses (0-180 kg gas ha -1 ) and time intervals (2-10 yearly treatments). To measure the
treatment effect on regrowth, images were taken every second week (14 days after the last
treatment) from May to October 2008. The experiment was repeated in 2010. To avoid camera
shaking and to get images of the same size, a camera mounting was used. All images were taken
with a Canon EOS 400D (iso speed and shutter speed manually adjusted). Camera position was
vertical. To obtain diffuse light on sunny days the camera mounting was covered with nylon
material. Inside the “tent” a frame (0.63*0.45 m = 0.27 m 2 ) was placed with a white balancing
reference in order to calibrate the colors to different illumination. Three times a year, biomass
samples were taken and the results from these data were compared with the results from the image
analysis. The data showed that it was possible to achieve full control of L. perenne with flaming,
but it highly depended on the number of treatments as well as the dose that was applied. Image
analysis can be an easy measurement method of vegetation cover but did not give precisely the
same results as biomass measurements, because of overlapping vegetation. However, image
analysis was a useful method to get a fairly precise estimate of the effect of the treatments.