Chemical Weed Control in Saffron Fields of Iran
S. Norouzzadeh, M. Abbaspoor, M. Delghandi
Agricultural and Natural Resources Research Center
Khorasan Razavi
Iran.
Keywords: ethalfluralin, ioxynil, metribuzin, tribenuron-methyl, trifluralin
Abstract
Field experiments were conducted to assess the efficacy of herbicides
applied pre- (pre-forking) and post-emergence (after harvest) in spring and
autumn during 2000-2002 in saffron fields of Mashhad and Gonabad located in
north-eastern and eastern parts of Iran, respectively. In spring trials, ioxynil
(750 g a.i. ha-1) and tribenoronmethyl (18.75 g a.i. ha-1) when sprayed at 6-8 leafy
stage of weeds after saffron harvest were more potent than metribuzin. In
autumn trials, weed control by ethalfloralin (1320 g a.i. ha-1) and trifloralin (960
g a.i. ha-1) when applied pre-emergence and before saffron flowering was
promising but caused also some damages on saffron, leading to yield loss.
Application of metribuzin (560 g a.i. ha-1) whether in spring or autumn,
controlled weeds without any saffron injury. Tribenuron-methyl and metribuzin
were the best treatments for weed control in saffron fields of Mashhad and
Gonabad, respectively.
INTRODUCTION
Saffron is derived from the stigmas of the saffron (Crocus sativus L). It is the
world’s most expensive spice and has been widely used in many countries (Bolhasani
et al., 2005). It is also increasingly used for drugs purposes (Behnia et al., 1999;
Bolhasani et al., 2005). Weed control in this perennial, small and low growing crop,
needs a lot of labor work. It has been reported that glyphosate and/or 2, 4-D / 2, 4-DP
are used to clean up the beds prior to the new season’s flowering and growth of
saffron in New Zealand (McGimpsey et al., 1997).
The choice of herbicide(s) depends on the kind of weeds present (McGimpsey
et al., 1997). Metribuzin inhibits photosynthesis of susceptible plant species by
inhibiting the electron transfer from primary to the secondary quinones (QA to QB) in
the electron transfer chain in photosynthesis. It is selectively used for control of
annual grasses and numerous broad-leaved weeds (Arregui et al., 2006). Tribenuronmethyl is a post emergence herbicide rapidly absorbed by foliage and roots and
translocated through the plant and inhibiting biosynthesis of the essential amino acids
valine and isoleucine (Dixonand and Clay 2004). Ioxynil is inhibitor of
photosynthesis at Photosystem II and it’s recently discovered mode of action is the
inhibition of cell wall synthesis primarily. Foliar application of ioxynil to broadleaved weeds causes growth inhibition and swelling of the stems (Thiel and Böger,
1986; Argese et al., 2005). Trifluralin is a selective pre-emergence herbicide used for
the control of annual grasses and certain broadleaf weeds on some crops like Cotton
and soybean. This herbicide interfering with synthesis of microtubular protein or
metabolism of endoplasmic reticulum membranes involved in microtubule assembly
(Wang et al., 1995). Ethalfluralin which is a member of so-called bleaching herbicides
can influence the plant growth by either inhibiting biosynthesis of chlorophyll or
carotenoids and by causing destruction of pigments already formed (Grichar et al.,
2004).
The objective of this study was the evaluation of the efficacy of herbicides
with different mode of actions, selected on the basis of dominant weed flora, on
weeds grown in saffron fields of Iran in different times of season.
MATERIALS AND METHODS
The layout was completely randomized block design with four replications.
The plot dimension was 3×6 m (18 m2). The weed density was calculated in 1 m2quadrate, 15 days after herbicide application. The treatments in Mashhad were
included: weed free and weed infested controls plus metribuzin (560 g a.i. ha-1),
tribenuron-methyl (18.75 g a.i. ha-1) and ioxynil (750 g a.i. ha-1) were sprayed in
spring after harvest and in early stage of weeds growth (6-8 true-leaf stage). The
treatments in Gonabad were: weed free and weed infested controls plus trifluralin
(960 g a.i. ha-1) and ethalfluralin (1320 g a.i. ha-1) both applied as soil-incorporated
(pre-forking) and foliar application of metribuzin (560 g a.i. ha-1) were applied before
saffron flowering in autumn. Treatments in Mashhad and Gonabad were the same in
the second year. In the third experiment in Gonabad (2002) the treatments were
consisted of: weed free and weed infested controls plus metribuzin (560 g a.i. ha-1)
applied before flowering in autumn or after harvest in spring, tribenuron-methyl
(18.75 g a.i. ha-1) and ioxynil (750 g a.i. ha-1) both were applied in spring after harvest
and in early stage of weeds growth (6-8 true-leaf stage).
RESULTS AND DISCUSSION
Weed flora of the experimental fields in Mashhad and Gonabad is shown in
table 1. The visual dominant weed species were Achillea millefolium and Malcolmia
africana in Mashhad and Gonabad, respectively. Cardaria draba was the second
dominant weed in both fields.
In spring application in Mashhad, ioxynil and tribenuron-methyl were more
effective than metribuzin against weeds (Fig. 1-1). Ioxynil, however, decreased the
saffron yield significantly (Fig. 1-2). Tribenuron-methyl was the best treatment for
weed control in Mashhad. In autumn trials in Gonabad, trifluralin, ethalfluralin and
metribuzin had the same effect on weed density (Fig. 1-3). Trifluralin and
ethalfluralin, however, made significant damage on saffron leading to yield loss
remarkably (Fig. 1-4). Weeds efficiently were controlled by metribuzin (Fig. 1-3) and
this herbicide caused the much less damage on saffron comparing to the trifluralin and
ethalfluralin (Fig. 1-4). In Gonabad in 2002 the application of herbicides, chosen from
the promising results of the previous experiments, again showed good effects of
metribuzin (when sprayed before flowering in autumn or after harvest in spring) and
tribenuron-methyl (Figs. 1-5 and 1-6). Tribenuron-methyl in Mashhad caused no
damage on saffron yield (Fig. 1-2) while in Gonabad it made significant damage
comparing to the hand weeding control (Fig. 1-6). It is mainly because younger and
stronger saffron plants were growing in Mashhad than in Gonabad. This is why the
saffron yield for hand weeding controls in Mashhad (Fig. 1-2) is almost two-fold of
that in Gonabad (Figs. 1-4 and 1-6). This difference could also partially be refered to
the better field situation and environmental conditions as well as weed flora growing
in each place.
In summary, tribenuron-methyl (18.75 g a.i. ha-1) and metribuzin (560 g a.i.
ha-1) were the best choices for weed control in saffron fields of Mashhad and
Gonabad, respectively. The results also showed application of soil-incorporated
herbicides i.e. trifluralin and ethalfluralin, not only needs to special equipments be
involved, but also leading to significant damage on saffron yield as well, especially
when it comes to the coming years yield and profits.
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Table 1: Alphabetically ordered weed flora in experimental fields.
Mashhad
Acroptilon repens
Chenopodium album
Coix lacryma jobi
Convolvulus arvensis
Cyperus rotundus
Daucus carrota
Erygeon bonaepartis
Hordeum glaucum
Hyoscyamus sp.
Lolium rigidum
Malva neglecta
Plantago lanceolata
Polygonum aviculare
Sochus oleraceus
Gonabad
Achillea millefolium
Alhagi pseudalhagi
Bromus danthoniae
Carthamus oxyacantha
Erysimum repandum
Filago sp.
Heliotropium dulosum
Hordeum glaucum
Hypecum pendulum
Malcolmia africana
Malva neglecta
Phalaris minore
Sophora alopecuroides
Fig. 1. Effect of metribuzin (560 g a.i. ha-1), tribenuron-methyl (18.75 g a.i. ha-1),
ioxynil (750 g a.i. ha-1), trifluralin (960 g a.i. ha-1) and ethalfluralin (1320 g a.i. ha1
) on weed density (1, 3, 5) and saffron yield (2, 4, 6), applied after harvest in
spring or before flowering in autumn in Mashhad and Gonabad. Trifluralin and
ethalfluralin were applied as soil-incorporated and the rest of the herbicides were
sprayed on foliage.