© Benaki Phytopathological Institute
Weed control benefit to cost ratio with pendimethalin
69
broccoli trials caused a reduction of market-
able yield of about 40-50% and pendimeth-
alin, particularly when used at the high rec-
ommended rate, could prevent most of the
yield loss. Hand weeding used by itself could
not prevent yield loss and when used in com-
bination with pendimethalin contributed to
only a small increase of yield. Pendimethalin
at the high rate was the most effective treat-
ment since it provided the best yield and re-
quired the least labour input for removing
escaping weeds in both experiments.
The best benefit/cost ratio values were
provided by the high rate of pendimethal-
in in both trials. A probably satisfactory, al-
though lower, benefit/cost ratio value was
also provided by the low rate of pendime-
thalin. Combining pendimethalin with hand
weeding results in lower ratio values but
they are in any case much better than when
hand weeding is used by itself.
The low hand weeding labour return val-
ues (1.4 and 2.6) indicate that hand weed-
ing itself cannot be a justifiable weed con-
trol method for broccoli. Hand weeding as
a supplementary measure of pendimethal-
in may sometimes be justified, however, as
indicated by the higher values especially in
the second trial.
Discussion
In almost all field trials, conducted in this
study with diverse annual crops, the best
weed control benefit/cost ratio at actu-
al farmers’ prices was obtained with a sin-
gle pre-emergence application of a residu-
al herbicide, namely of pendimethalin. Only
in one trial, due to a pendimethalin tolerant
weed species, best ratio was rather achieved
with a post-emergence herbicide (oxyfluor-
fen) but still the single pendimethalin treat-
ment kept the benefit/cost ratio at quite fa-
vourable levels (Table 2).
In all field trials, hand weeding provid-
ed the lowest weed control benefit/cost ra-
tio. The labour return value further indicat-
ed that hand weeding by itself cannot even
be used as a yield rescue method in all crops
examined except possibly the processing
tomatoes (Table 1). Hand weeding in pro-
cessing tomatoes may be justified by itself
in countries like Greece where field labour is
paid less than 10.5 €/ha and may be further
justified in countries where the field labour
is more expensive if combined with herbi-
cides like pendimethalin or s-metolachlor.
The onion trial, on the other hand, revealed
another important advantage offered by a
residual herbicide like pendimethalin (Table
2) that even in the presence of a herbicide
tolerant weed species, yield loss can be pre-
vented with a relatively shorter time of hand
weeding.
Alternative weed control methods to
the ones examined in this study, that are
used by farmers at least in processing to-
matoes, are: a) inter-row cultivations com-
bined with hand weeding or application of
a post-transplant herbicide and b) the use of
plastic mulch along the rows combined with
herbicide application and/or inter-row culti-
vations between the rows (Anzalone
et al.
,
2010). Expected benefit/cost ratios for the
processing tomatoes, under all alternative
weed control scenarios, are given as an ex-
ample in Table 5, assuming that all methods
are equally effective
in preventing a 50%
yield reduction. Due to the high cost of in-
ter-row cultivation and polyethelene (PE)
mulching, the expected benefit/cost ratio
from these methods is much lower than the
one expected from herbicide-based meth-
ods. Pendimethalin, usually being sufficient-
ly effective as a single treatment, is expect-
ed to provide a better benefit/cost ratio than
alternative herbicides in agreement with the
actual data from the respective field tria
l
.
Achieving the best weed control benefit/
cost ratio is to the farmer’s interests since it
helps to optimize weed control profitability,
but achieving maximal yield may also be im-
portant in an effort to overall optimize crop
profitability. In most trials, the single pen-
dimethalin treatment provided both best
weed control benefit/cost ratio andmaximal
yield (Tables 1 and 4). In some trials, howev-
er, the single pendimethalin treatment sig-
nificantly reduced yield loss but for maximal
