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

9 th EWRS Workshop on Physical and Cultural Weed Control 69
Samsun, Turkey, 28 – 30 March 2011
evaluated based on the size of their standard errors (see upper limit of the curve, Table 3). The
difference was only pronounced at 12 HAS treatments compared to 0 HAS applications. For
example, corn flamed with the highest propane dose of 87 kg ha –1 at 0 HAS had 60% injury
compared to significantly higher injury of 74% at 12 HAS with the same propane dose (Table 3).
The same tendency was demonstrated by velvetleaf showing 80% injury when flamed with 87 kg
ha –1 at 0 HAS and 93% injury when flamed at 12 HAS with the same propane dose. Similar trends
occurred for green foxtail and soybean. On the basis of visual ratings, broadleaf species (e.g.,
soybean and velvetleaf) exhibited more injury compared to grasses (e.g., corn and green foxtail)
when flamed with the highest propane dose (87 kg ha –1 ). For example, significantly higher injuries
were for soybean (89%) and velvetleaf (93%) compared to corn (74%) and green foxtail (82%) at
12 HAS. These results suggest that broadleaf species were more susceptible to flaming than grasses.
It is interesting to note that plants flamed with the lowest propane dose (29 kg ha –1 ) during the
afternoon hours exhibited similar level of injuries as the plants flamed with the middle dose (43 kg
ha –1 ), and in some cases with the highest propane dose (87 kg ha –1 ) flamed during the morning
(Figure 1b). For example, velvetleaf plants showed a maximum injury of 75% when flamed with 29
kg ha –1 propane during the afternoon while 68% injury was evident with 43 kg ha –1 propane during
the morning (Table 4). Similar trends occurred with other plant species. The calculated HAS90
values for most of the curves occurred around 9 to 12 HAS suggesting that flaming was more
effective during afternoon. These results also suggest that flaming would likely be less effective if
conducted at night.
Fresh Weight. There was no propane dose by time of day interaction for fresh weight. Therefore,
the data were averaged across propane doses (Figure 2). Averaged across doses, fresh weight was
greater in the plants flamed immediately after sunrise compared to the plants flamed during the
afternoon (e.g., 8 and 12 HAS). Fresh weights of the plants flamed during the morning were 11.9,
5.7, 2.6, and 2.7 g plant –1 for corn, green foxtail, soybean, and velvetleaf, respectively (upper limit
of the curve, Table 5). However, with the exception of corn, fresh weight of each plant species was
reduced significantly when flamed during the afternoon. Fresh weights were 10.9, 3.8, 1.5, and 1.6
g plant –1 for corn, green foxtail, soybean, and velvetleaf, respectively (lower limit of the curve,
Table 5). These results suggest that the efficacy of flaming can be improved by flaming during the
afternoon. For example, there was a 50% improvement in green foxtail control when flamed at 12
HAS compared to 0 HAS. Similar trends occurred with other plant species resulting in 73% and
69% improvement in soybean and velvetleaf, respectively, when flamed at 12 HAS compared to 0
HAS.
In our study, all plant species had the lowest leaf RWC around 8 HAS (Table 2). However, all
species exhibited more injury when flamed during the afternoon hours (8 and 12 HAS) regardless of
the propane dose (Table 3). It is important to notice that the inflection point for plant injury (Table
4) and the lowest leaf RWC in all the treated species occurred around 8 HAS (Table 2).This
suggests that leaf RWC is likely one of the factors affecting plant response to propane flaming. Our
results are similar to those of Taylor-Hill et al. (2007) and Taylor (2008), who also measured the
effectiveness of flaming at 8 A.M., 12 P.M., 4 P.M., and 8 P.M. and reported improved weed
control with the noon and 4 P.M. treatments compared to the other treatment times. They mentioned
that the differences in weed control among flaming times could not be explained by differences in
temperature, relative humidity, or the presence/absence of dew.
Results from this study also indicate that plant susceptibility to flaming varied among species
and broadleaf species were more susceptible to flaming than grasses. Our findings are consistent
with the results previously reported in the literature (Ascard 1994; Knezevic et al. 2009a, 2009b;
Ulloa et al. 2010a, 2010b, 2010c, 2010d). It is interesting to note that plants from broadleaf and
grass families differed in the way they responded to the heat (Wszelaki et al. 2007; Ulloa et al.
2010a). It has been shown that leaves of annual broadleaf species turned brown and died within a
few days after flaming, resulting in no regrowth whereas leaves of grass species turned white