© Benaki Phytopathological Institute
Weed control benefit to cost ratio with pendimethalin
67
with pendimethalin+oxyfluorfen (45.3). The
cost of labour, on the other hand, dramat-
ically reduced the ratio value to 1.4 when
pendimethalin+oxyfluorfen was supple-
mented with hand weeding pointing out that
the maximum yield treatment is not neces-
sarily the most profitable one for the farmer
.
The hand weeding labour return value
was very low (0.4) in onions and was only
slightly improved (1.3-1.4) when hand weed-
ing was combined with pendimethalin, in-
dicating that hand weeding can hardly be
a justifiable method for weed control in on-
ions
.
In agreement to this were also the ben-
efit/cost ratio values which were very favour-
able with the use of herbicides but became
dramatically lower when the herbicides
were supplemented with hand weeding.
A second field trial with spring-seed-
ed onions in Greece the next year (results
not presented
)
confirmed the above state-
ments. In that trial, pendimethalin (applied
pre-emergence or early post-emergence at
the whip stage of onions) provided the best
benefit/cost ratios (17.0 and 15.1 respective-
ly), post-emergence oxyfluorfen and the
combination pendimethalin + oxyfluorfen
provided a lower ratio (6.5 and 7.1 respec-
tively) and hand weeding the lowest (1.0).
Maximum yield was obtained with pendi-
methalin early post-emergence. The hand
weeding labour return value was better
(5.2) in this experiment due to faster growth
of onion seedlings in spring and again im-
proved by pendimethalin or pendimethalin
+ oxyfluorfen (7.0-12.3). It is worthy to note
the absence of a pendimethalin tolerant
weed species in this trial and the lower ben-
efit/cost ratio values due to a lower farmer’s
price for onions at this season.
Cotton trials
Results from a cotton field trial are pre-
sented in Table 3.
As shown from the yield data, weeds di-
minished cotton yield and pre-emergence
pendimethalin (applied at the lowest and
the highest recommended rates) was ca-
pable of preventing yield loss significant-
ly. The maximal cotton yield was obtained
with either hand weeding applied alone (3
times, total of 503 hrs/ha) or hand weeding
applied for a shorter time as a supplemen-
tal treatment to pendimethalin. Similar yield
was obtained with combined application of
the low pendimethalin rate with fluometur-
on, another pre-emergence herbicide com-
monly used by farmers as no selective post-
emergence herbicide is available for cotton.
Best weed control benefit/cost ratio was
provided by the low pendimethalin rate
treatment (11.5), followed by the combined
pendimethalin+fluometuron (9.1) and the
high pendimethalin rate (8.4) treatments. The
cost of labour, on the other hand, reduced the
ratio value to below 4 when hand weeding
was used alone or as a supplementary treat-
ment to herbicides, pointing out that in cot-
ton also the maximum yield treatments are
not the most profitable ones for the farmer.
The labour return value in cotton was
low (4.5 €/hr) and hand weeding by itself
is again not justified. The herbicide treat-
ments, particularly the ones with the low
pendimethalin rate and the combination
of pendimethalin+fluometuron, improved
the labour return value (9.6 and 10.5 €/hr,
respectively) and therefore hand weeding
may be justified as a supplementary mea-
sure to these treatments, in cases where the
maximal yield is desired.
Similar trends had been observed in an-
other trial conducted in Greece the previous
year (results not presented). The best bene-
fit/cost ratio was provided by pendimethal-
in at the high or the low rate (4.6 and 3.9 re-
spectively) and the worst by hand weeding
or pendimethalin+fluometuron (0.9 and 0.5
respectively).
Lower best ratio values in this trial are
due to lower yields that year. The hand
weeding labour return value was again low
(4.7) and improved most by the low pen-
dimethalin rate (9.0) and the combination
pendimethalin+fluometuron (9.2).
Broccoli trials
Results from two trials with broccoli are
shown in Table 4.
The yield data indicate that weeds in the
