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Article

Response of Wheat to Pre-Emergence and Early Post-Emergence Herbicides

by
Thomas Gitsopoulos
*,
Ioannis Georgoulas
,
Despoina Botsoglou
and
Eirini Vazanelli
Institute of Plant Breeding and Genetic Resources, Hellenic Agricultural Organization-DIMITRA, 57001 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(8), 1875; https://doi.org/10.3390/agronomy14081875 (registering DOI)
Submission received: 27 May 2024 / Revised: 11 August 2024 / Accepted: 15 August 2024 / Published: 22 August 2024
(This article belongs to the Section Weed Science and Weed Management)
Browse Figures
Versions Notes

Abstract

:
A two-year field experiment was conducted in two consecutive seasons to evaluate the response of wheat to pre-emergence (PRE) and early post-emergence (EPOST) herbicides. The herbicides prosulfocarb (3200 g ai ha−1) and chlorotoluron plus diflufenican (1380 + 92 g ai ha−1) were applied PRE, whereas the herbicides flufenacet plus diflufenican (240 + 120 g ai ha−1) and flufenacet plus diflufenican plus metribuzin (119.7 + 119.7 + 44.8 g ai ha−1) were applied EPOST at the second leaf growth stage of wheat. Heavy rainfalls that followed the PRE treatments and cold temperatures that occurred during the EPOST applications resulted in crop injuries and reduced yields in prosulfocarb, chlorotoluron plus diflufenican and flufenacet plus diflufenican the first and the second year, respectively. Weather conditions such as heavy rainfalls and low temperatures that may occur during and after herbicide treatments should be considered to avoid crop injuries and increase crop safety.

1. Introduction

Control of grass weeds in winter cereals in Greece is mainly achieved by the post-emergence (POST) application of the acetolactate synthase (ALS) and/or the acetyl-CoA carboxylase (ACCase) inhibitors. However, herbicide resistance to both ALS/ACCase inhibitors in winter cereals is dramatically increasing worldwide, making POST applications of these two herbicide groups not effective [1,2]. Particularly in Greece, resistance of grass weeds to ALS and/or ACCase inhibitors has been documented in previous studies for Avena sterilis L., Lolium rigidum Gaudin, Apera spica-venti (L.) P. Beauv. and Lolium perenne (L.) ssp. perenne [3,4,5,6,7,8,9,10].
In recent years, Greek farmers who faced herbicide-resistance issues have shifted to active ingredients different from the ALS/ACCase inhibitors, such as the pre-emergence (PRE) herbicides prosulfocarb and chlorotoluron plus diflufenican and the early post-emergence (EPOST) flufenacet plus diflufenican and flufenacet plus diflufenican plus metribuzin. Although these active ingredients are not novel and entered Greek market many years ago, they have not been used or registered as herbicides for weed control in winter cereals.
Prosulfocarb is a thiocarbamate herbicide applied PRE or EPOST to winter cereals. Thiocarbamates are inhibitors of several plant processes such as the biosynthesis of fatty acids and lipids (not via the inhibition of the enzyme acetyl-CoA carboxylase), the biosynthesis of proteins, isoprenoids and flavonoids, the synthesis of gibberellin and the photosynthesis. Prosulfocarb is therefore considered a “multisite” herbicide and it is believed to inhibit the synthesis of very long-chain fatty acids (VLCFA), being effective for the control of a wide spectrum of broadleaf and grass weeds [11,12]. It has been used in Europe for broadleaf control in potatoes and legumes and it is also used in cereals for grass control. It is a short residual non-persistent, slightly mobile herbicide with low water solubility and limited translocation within plants. Prosulfocarb is absorbed primarily by the roots and shoots [11,13]. The primary action of prosulfocarb is at the mesocotyl, whereas the secondary action is via coleoptile and root uptake, leading to the inhibition of growth of shoots and roots and to the failure of leaf emergence from coleoptiles [11]. Grasses show more susceptibility to thiocarbamates when herbicides are absorbed near the coleoptilar node [14].
Chlorotoluron or chlortoluron belongs to phenylureas. These herbicides inhibit photosynthesis (PSII inhibitors) leading to plant death. Chlorotoluron is absorbed by roots and foliage, and it is effective in PRE or EPOST application against many broadleaf weeds and grasses of winter cereals [11]. It is combined with mecroprop herbicide to increase control of broadleaf weed species, whereas some wheat and barley cultivars may be injured [11]. It has moderate water solubility and it is moderately mobile and non-persistent in the soil. [13].
Diflufenican inhibits phytoene desaturase (PDS), an enzyme in the carotenoid biosynthesis pathway causing degradation of chlorophyll; it is a pyridinecarboxamide herbicide that causes chloroplast destruction, leaf chlorosis, leaf bleaching, necrosis of the tissues and consequently plant death [15,16]. It is applied PRE or EPOST in wheat and barley for the selective control of grasses and broadleaf weeds [11]. Diflufenican is absorbed by the shoots of germinating weed seedlings that become bleached and necrotic. It has low water solubility, it is slightly mobile and moderately persistent in the soil with minimal translocation within plants [11,13,17,18]. In the market, it has been usually commercialized in premixed formulations with other herbicides such as flufenacet to provide a wider spectrum of weed control [11].
Flufenacet is applied PRE or EPOST; it is absorbed by roots and shoots and translocates to the upper part of the plant. It is an oxyacetamide residual herbicide that controls grasses and certain broadleaf weeds by inhibiting the very long-chain fatty acids building in plants (VLCFA) [11,19,20]. Flufenacet has been used for the control of annual grasses in various crops either alone or in mixtures with other herbicides [11,21]. It is considered moderately soluble, moderately mobile and moderately persistent in soil. [11,13].
Metribuzin is a PSII inhibitor belonging to triazinone chemical family. It is a PRE and POST herbicide for the selective control of grasses and broadleaf weeds in cereals and in a wide range of other crops. Metribuzin due to its high solubility is a mobile herbicide with high leachability in soil [13,18]. Regarding its diodegradability, metribuzin is a non-persistent herbicide. This herbicide is predominantly absorbed by the roots and leaves and translocates acropetally in the xylem. It has been registered in a commercial herbicide mixture with flufenacet applied PRE or EPOST to wheat [22,23]. Details about soil adsorption and mobility, solubility in water and degradation of the herbicides used in the present study are presented (Table 1).
Crop selectivity is provided by the inactivation of the herbicide by the tolerant crop through various detoxification mechanisms [24]. Environmental conditions, such as rainfall and temperature can affect the level of herbicide selectivity. Soil-applied herbicides need soil moisture via rainfall or irrigation after their application to dissolve and activate. Depending on the soil type and the chemical properties of the herbicide such as water solubility and soil adsorption characteristics, rainfall can cause greater concentration of the herbicide in the soil solution or can move it downward into the root zone of the treated crop, resulting in higher herbicide availability to crops. Herbicides with moderate to high water solubility and those with medium to low soil adsorption are most likely to move downward into the soil after heavy rain, particularly in light sandy soils. Cold temperatures or any diurnal freezing following herbicide application may result in crop stress that can retard herbicide metabolism via the deviation from the optimal temperature range needed by the enzymes to detoxify the herbicides leading to crop injury; in addition, low temperatures can delay crop emergence, leading to greater time that a soil-applied herbicide comes into contact with the emerging shoots of the crop [17,25,26,27,28,29]. Higher risk of herbicide injury may be more apparent for prosulfocarb or chlorotoluron plus diflufenican that are applied PRE followed by flufenacet plus diflufenican and flufenacet plus diflufenican plus metribuzin that are applied EPOST.
In previous years, many Greek farmers have used these herbicides to manage L. rigidum Gaudin herbicide resistance. However, complaints about crop injury (e.g. reduction in crop emergence, leaf chlorosis, retardation in growth) have been recorded after the use of these soil-applied herbicides. To our knowledge, there has been a lack of experimental field data on wheat response to prosulfocarb, chlorotoluron plus diflufenican, flufenacet plus diflufenican and flufenacet plus diflufenican plus metribuzin. Therefore, this study was conducted to evaluate wheat response to the above-mentioned herbicides under field conditions and to provide knowledge to the farmers in terms of crop safety when using these herbicides as alternative options for weed control in wheat.

2. Materials and Methods

A field trial was conducted in 2020–2021 in a field that remained fallow the previous four years at the experimental area of the Institute of Plant Breeding and Genetic Resources of the Hellenic Agricultural Organization-DIMITRA at Thessaloniki, Greece. The same trial was repeated in the other half of the same field in 2021–2022. Bread wheat (“Oropos” cultivar) was sown with a seeding machine on 1 December 2020 (hereafter, trial A) and on 20 November 2021 (hereafter, trial B) in rows spaced 15 cm apart. For both field trials, the seedbed was prepared with a mouldboard plough followed by disc harrowing. No fertilization was added in both trials. In trial A, the herbicides prosulfocarb and chlorotoluron plus diflufenican were applied PRE on 3 December 2020, two days after sowing (2 DAS), whereas the herbicides flufenacet plus diflufenican (double EPOST mixture) and flufenacet plus diflufenican plus metibuzin (triple EPOST mixture) were applied at the 2nd leaf growth stage of the wheat, on 22 December 2020 (21 DAS). In trial B, the herbicides prosulfocarb and chlorotoluron plus diflufenican were applied PRE on 22 November 2021 (2 DAS), whereas the herbicides flufenacet plus diflufenican and flufenacet plus diflufenican plus metibuzin were applied EPOST herbicides at the 2nd leaf growth stage of the wheat, on 19 December 2021 (29 DAS). The herbicide rates and details of the herbicides applied are provided in Table 2.
Herbicides were applied with a hand-held AZO portable field plot boom sprayer fitted with six (6) Turbo Twinjet (Teejet®) TTJ60-11002 nozzles, TeeJet Technologies (Glendale Heights, IL, USA), calibrated to deliver 400 L ha−1 at 250 kPa pressure. Weed-free and untreated controls were included in both field trials. Weed-free controls were hand-weeded once almost 30 DAS for both trials. Plots measured 4 m × 3.5 m and all treatments were replicated four times in a randomized complete block design. The field soil was a loam soil (48% sand, 16% clay, 36% silt), with 7.88 pH, 0.340 ES (mS cm−1) and 1.33% organic matter content. Crop establishment, injury symptoms, plant height, number of spikes and crop yield were recorded to determine the response of wheat to herbicides. Crop establishment was determined by counting the number of wheat plants along 1 m of three randomly selected rows of each plot at 3 weeks after treatment (WAT). Plant height was calculated after measuring the height of twenty plants randomly selected from each plot on three different timings (January, February and March for each year); number of spikes was determined after measuring the spikes from four randomly selected quadrats (0.33 m × 0.33 m) within each plot; yield was obtained after harvesting the spikes from the above-mentioned four quadrats. Data of wheat response were subjected to ANOVA and analyzed separately for each trial due to the significant interaction between trials and treatments. Weed species density was recorded at harvest in the four randomly selected quadrats used for yield estimation for each plot in both trials. Weed control was visually determined at 120 DAS by using a 0 to 100% scale, where 0% was equal to no weed control and 100% to complete weed control compared to weeds’ abundance and growth in the untreated plots in both trials. Data of % weed control was subjected to ANOVA and pooled over trials since the interaction between trials and treatments was not significant. All means were separated using the Fisher’s protected LSD test at p = 0.05 level of significance. The GenStat Data Analysis Software package (version 10.0, VSN International, Hemel Hempstead, UK) was used for the statistical analyses.

3. Results

3.1. Trial A (2020–2021)

Daily mean temperature and total rainfall are presented from the time of wheat sowing until ten days after the EPOST herbicide treatments (Figure 1). Increased rainfall (>43 mm) was observed the first four days of sowing (4th to 7th of December 2020) and continued the following days; mean daily temperature ranged from 6.1 to 15.6 °C throughout the measured period (Figure 1).

3.1.1. Crop Density, Plant Height and Injury Symptoms for Trial A

Herbicide injuries were observed in the form of reduction in crop establishment and leaf chlorosis. More specifically, in plots treated with prosulfocarb the density of the wheat was reduced to 71 plants per row meter, which was comparable to all other treatments (Table 3). Leaf chlorosis was evident on plants treated with chlorotoluron plus diflufenican and flufecancet plus diflufenican and to a lesser extent on plants treated with flufecancet plus diflufenican plus metribuzin. At 44 DAS, plant height was similar in all treatments; at 73 DAS, plants treated EPOST with flufenacet plus diflufenican exhibited lower height compared with the untreated and the weed-free control, whereas plant height after chlorotoluron plus diflufenican treatment was comparable with the weed-free control. At 116 DAS, no significant difference in plant height was observed (Table 3).

3.1.2. Number of Spikes and Crop Yield for Trial A

Prosulfocarb significantly decreased the number of spikes (443 spikes m−2) compared with the weed-free (602 spikes m−2) and the untreated control (622 spikes m−2). Chlorotoluron plus diflufenican also caused reduction in spike number (526 spikes m−2); however, that was not comparable to the weed-free control. The two EPOST herbicides resulted in decreased spike production (558 to 567 spikes m−2); however, this was not different compared with the untreated and the weed-free control (Table 4). Although wheat plants treated with prosulfocarb produced a decreased number in spikes, they yielded (4.30 t ha−1) similar to the plants treated with chlorotoluron plus diflufenican (4.06 t ha−1).
Wheat plants treated with both the PRE herbicides produced lower yield compared with the untreated (5.43 t ha−1) and the weed-free control (5.79 t ha−1). The double and the triple EPOST mixtures resulted in 4.99 and 5.12 t ha−1 yield, respectively, similar to the yields of the weed-free and the untreated control (Table 4).

3.2. Trial B (2020–2021)

Daily mean temperature and total rainfall are presented from the time of wheat sowing until ten days after the EPOST herbicide application (Figure 2). That year, no heavy rainfalls followed the PRE treatments, as happened in trial A; in contrast, cold temperatures took place during EPOST application that continued the following days. The mean daily temperature from the time of EPOST application to the following seven days ranged between 2.8 and 5.8 °C (Figure 2), whereas the minimum daily temperature during that period dropped below zero degrees.

3.2.1. Crop Density, Plant Height and Injury Symptoms for Trial B

In trial B, there was no effect of PRE herbicides on crop establishment. Leaf chlorosis, however, was observed in plants treated with the EPOST herbicides. Although plants treated with flufenacet plus diflufenican were slightly shorter, plant height at 44, 82 and 122 DAS was not different among treatments (Table 5).

3.2.2. Number of Spikes and Crop Yield for Trial B

Wheat plants treated with prosulfocarb, chlorotoluron plus diflufenican and the triple EPOST mixture exhibited 498, 486, 464 spikes m−2, respectively, not different to 493 spikes m−2 recorded in the weed-free control. Decreased spike number after the treatment of flufenacet plus diflufenican and in the untreated control (424 and 394 spikes m−2, respectively) was observed compared with the weed-free control (Table 6).
Regarding the yield, wheat treated with prosulfocarb, chlorotoluron plus diflufenican and flufenacet plus diflufenican plus metribuzin produced yields of 5.04, 4.49 and 4.48 t ha−1, not different to the 5.01 t ha−1 produced in the weed-free plots, however, greater than the yield of the untreated control (4.14 t ha−1). Flufenacet plus diflufenican caused significantly lower yield (4.10 t ha−1) compared with the weed-free control and no different to that of the untreated control (Table 6).

3.3. Weed Control

The weed flora of the field mainly consisted of the following dicot weed species: Veronica spp., Lamium spp., Matricaria recutita L., Capsella bursa-pastoris (L.) Medicus, Papaver rhoeas L., and Fumaria officinalis L., at 2.4, 2.0, 1.0, 0.3, 0.3 and 0.5 plants m−2 in trial A and at 4.2, 3.0, 2.5, 0.5, 0.4 and 2.8 plants m−2 in trial B, respectively, in the untreated plots. From monocots, L. rigidum Gaudin was recorded at 0.5 and 0.7 plants m−2 in trial A and trial B, respectively. Veronica spp. and Lamium spp. followed by F. officinalis L. were the dominant weed species of the field. All herbicides highly controlled (>90%) almost all weed species (Table 7). Chlorotoluron + diflufenican and both EPOST mixtures showed greater control of F. officinalis L. compared with prosulfocarb; the latter did not control P. rhoeas L. (Table 7); however, this weed species was at low density and did not affect yield.

4. Discussion

The reduction in crop stand observed in trial A by prosulfocarb was attributed to the high rainfalls that occurred the following days after herbicide treatment. Post-planting rainfall after the application of prosulfocarb plus s-metolachlor at 2000 and 300 g ha−1, respectively, followed by soil incorporation with a single-disc seeding system, resulted in movement of the herbicide mixture into the furrow slot and to proximity to wheat seeds causing reduction in wheat establishment up to 57% [30]. However, such reductions in crop stand did not always translate to yield loss due to the ability of wheat to recover and increase the spike number per plant. In another study, prosufocarb (at 4000 g ai ha−1) reduced wheat emergence and density due to the heavy rain (100 mm) that occurred after herbicide application and before crop emergence, however, with no yield loss [31]. The same study revealed significant crop stand reduction, without yield penalty, after the application of chlorotoluron (2000 g ha−1) plus isoxaben (74.8 g ha−1) and prosulfocarb (2000 g ha−1) plus s-metolachlor (300 g ha−1) [31]. The mixture prosulfocarb (4000 g ha−1) plus trifluralin (720 g ha−1) caused a decreasein wheat density to 144 plants m−2 compared with the density of 207 plants m−2 of the untreated control; reduction was attributed to the higher herbicide concentration in the soil solution after a high rainfall and affected the shallow-seeded wheat seeds resulting in crop injury [32]. Prosulfocarb applied PRE (Boxer, at 5 L product ha−1) before irrigation caused permanent damage to wheat that was greater compared with the POST application and that was comparable to the damage rate of weed competition [33]. The primary pathway for prosulfocarb uptake is via roots, whereas the newly emerged seedlings can absorb the herbicide via their foliage. Wheat and barley can tolerate prosulfocarb because they have a smaller mesocotyl that provides prosulfocarb selectivity, in contrast to weeds that have a significant mesocotyl. Crops detoxify thiocarbamates by conjugation with glutathione both enzymatically via glutathione S-transferase (GST) and non-enzymatically [14]. Decreased wheat stands due to herbicide injury can recover without yield penalty by producing more tillers and spikes if reduced weed competition occurs and when adequate nutrition and moisture is provided [32,34]. In the present study, prosulfocarb-treated plants in trial A were injured and crop emergence was decreased. Although weed density and weed competition that year were low, prosulfocarb-treated plants did not increase their number of spikes, possibly due to the absence of fertilizer application. This possibly did not allow wheat to compensate herbicide injury and enhance tillering.
Regarding chlorotoluron, decreased seed germination of durum wheat was observed after a PRE application (Tolurex 500 SC, at 4.0 L product ha−1) along with a reduction in grain yield by 5.3% on average comparedwith the hand-weeded control [35]. Decreased durum wheat seed germination energy (around 79%) was recorded after the application of chlorotoluron alone or in mixture with diflufenican (Constel, at 4.5 L product ha−1). The same study revealed a significant reduction in the length of primary roots of durum wheat treated with chlorotoluron, diflufenican plus chlorotoluron and prosulfocarb (Krum, at 5 L product ha−1); furthermore, a significant decrease in length of coleoptile after chlorotoluron and diflufenican plus chlorotoluron was evident [35]. Chlorotoluron is quickly metabolized via the hydroxylation of the ring-methyl, and N-demethylation followed by sugar conjugation, whereas in the susceptible weed species the main metabolite is the toxic mono-N-demethylated compound [36,37]. Chlorotoluron metabolism is catalyzed by different cytochrome P-450 monooxygenases [38,39,40]. Exposure of wheat to increased levels of chlorotoluron resulted in oxidative stress that caused inhibition of growth of both roots and leaves; superoxide radical (O2-) accumulation was found in wheat roots and leaves causing lipid peroxidation, whereas chlorotoluron-induced hydrogen peroxidase (H2O2) was detected in wheat leaves which can damage the plasma membrane lipids and other biomolecules; chlorotoluron accumulation in plants was revealed to be positively correlated with the external chlorotoluron concentration [41]. Chlorotoluron is moderately soluble and moderately mobile in the soil [13]; the rainfalls that occurred in trial A possibly moved chlorotoluron beyond the depth of the wheat seeds and for this reason chlorotoluron plus diflufenican did not cause crop stand reductions compared with prosulfocarb that exhibits lower water solubility and leachability and possibly it was not moved downward as much as chlorotoluron [13]; however, that year chlorotoluron plus diflufenican caused leaf chlorosis and lower yield production. In contrast, both PRE herbicides did not cause any crop injury in trial B, where no heavy rainfalls occurred after their application. Therefore, the lower selectivity for both PRE herbicides observed in trial A could be attributed to the heavy rains that occurred that year after herbicide application.
Regarding diflufenican, this herbicide is rapidly metabolized by cereals; even so, it can cause small transient phytotoxicity symptoms on basal leaves, but with no adverse effect on crop development [13]. Diflufenican is rapidly metabolized via the nicotinamide and nicotinic acid to CO2, whereas any small transient patches on basal leaves may appear, although with no effect on crop development [11]. Crop selectivity is achieved by the differential diflufenican uptake between cereals and weeds along with the ability of the crops to metabolize the herbicide [17,42].
Flufenacet is detoxified by crops via glutathione (GSH) conjugation and by the formation of flufenacet oxalate [43,44], whereas metribuzin is metabolized either via deamination and dethiomethylation or by glucosine and homoglutathione conjugations [45,46]. Metribuzin is a herbicide with high solubility and low soil-binding that can be mobile in the soil water and available for leaching or plant uptake, particularly in sandy, alkaline soils with low organic matter [17]. Wheat injury was much higher in a sandy loam soil compared with a silty clay soil after a PRE application of metribuzin [47]. Another study reported the greater risk of wheat injury when rainfall appeared shortly after metribuzin application [48]. Other studies reported wheat injury due to prosulfocarb, flufenacet plus metribuzin or chlorotoluron related to rainfall or irrigation [23,31,32]. Increased wheat injury due to metribuzin uptake by roots was accompanied by higher rainfall and low temperature that took place after application [49]. In the present study, the low temperatures that occurred in trial B during and after the EPOST application of flufenacet plus diflufenican possibly affected herbicide metabolism and caused leaf chlorosis and reduced number in spike production with subsequent lower yield for. In contrast, in trial A where no cold temperatures occurred after the application of the two EPOST herbicides no effect on crop yield was detected, although some transient leaf chlorosis was observed. Injury symptoms in the form of crop stunting and leaf chlorosis have been reported after the application of both the double and the triple EPOST mixtures in bread wheat and barley under glasshouse conditions [50]. The same study revealed lower selectivity of flufenacet plus diflufenican compared with the triple EPOST mixture, possibly due to increased rate of flufenacet in the double EPOST mixture [50]. This is in line with the results of the present study that revealed lower selectivity for the double rather the triple EPOST mixture. Even intrial A where no yield loss after the EPOST applications occurred, wheat plants treated with the double EPOST mixture were slightly more affected compared with the plants treated with the triple EPOST mixture. The results of the present study revealed different response of wheat to the four herbicides tested. The high rainfalls and the low temperatures possibly decreased the selectivity of both PRE herbicides and of flufenacet plus diflufenican. Therefore, based on the results of the present and previous studies, farmers should be aware of the environmental conditions that will occur and follow herbicide applications. If such adverse environmental conditions are expected, farmers should postpone herbicide application to avoid herbicide injuries and ensure crop safety. However, this may cause less effective weed control, particularly if weeds manage to emerge and if treated at a later growth stage. Nevertheless, crop safety is considered a priority compared to weed control.
In trial A, weed density was low and no significant weed issues occurred. That was evident from the similar number of spikes and yield production between the untreated and the weed-free control - (Table 4). In that trial, wheat was seeded in December and the rainfalls that occurred by the end of November allowed the germination and emergence of many weed species. The weed control applied by the seedbed preparation along with the competitive ability of the crop resulted in low weed densities and no significant weed issues occurred in trial A. In trial B, weeds competed with the crop and reduced the yield in the untreated plots. Although the adverse environmental conditions reduced selectivity, they did not reduce the efficacy of the herbicides. In trial A, the rainfalls possibly resulted in the downward movement of the herbicides towards the wheat seeds that caused crop injury; even so, the increased soil moisture resulted in higher herbicide concentration in the soil solution that consequently caused high weed control as well. In trial B, low temperatures might have affected the herbicide metabolism of the EPOST herbicides in wheat, particularly that of the flufenacet plus diflufenican mixture; similarly, lower temperatures might have decreased weeds’ ability to metabolise the herbicides. Considering the high weed control achieved, the lower crop yield after flufenacet plus diflufenican in trial B was possibly attributed to the decreased herbicide selectivity rather than to weed competition. In both trials, weeds were highly controlled (>90%) by all herbicide treatments. A recent study reported that prosulfocarb applied PRE (Boxer, at 5 L product ha−1) before irrigation reduced the biomass of Melilotus officinalis (L.) Lam., Anagallis arvensis L., Malva parviflora L. and Rumex crispus L. by 100% and that of Lolium perenne L. by 97% [33]. In another study, P. rhoeas L., Sonchus oleraceus L., Avena sterilis L. and Bromus rigidus L. were not adequately controlled (<60%) by prosulfocarb (Boxer) applied at 5 L product ha−1 in no-till soft wheat; in contrast, L. rigidum Gaudin and Centaurea diluta Aiton were controlled by 80–95%, and Chrysanthemum coronarium L. by 60–80% [51]. In the present study, P. rhoeas L. was not controlled by prosulfocard, whereas, L. rigidum Gaudin was highly controlled. Chlorotoluron plus diflufenican applied post-emergence (Legato Pro425 SC, at 1000 plus 62.5 g ai ha−1, respectively) controlled Brassica napus L., C. bursa-pastoris (L.) Medicus, Galium aparine L., Stellaria media (L.) Vill, Viola arvensis Murray, Lamium purpureum L. and Veronica persica Poiret, by 95–100%, 91–100%, 81–93%, 97–100%, 87–99%, 83–100% and 90–100% [52]. These results are in line with the results of the present study that revealed increased control of Lamium spp., C. bursa-pastoris (L.) Medicus. and Veronica spp. by chlorotoluron plus diflufenican. High efficacy of flufenacet plus diflufenican plus metribuzin against Veronica spp., S. media (L.) Vill and Papaver spp. has been reported [53]; this is also in line with the results of the present study regarding Veronica spp. and P. rhoeas L. control. Similarly, for the control of L. rididum Gaudin, a recent study revealed that the four herbicides highly controlled (>90%) different resistant ALS/ACCase populations of L. rigidum Gaudin [50].

5. Conclusions

The results of the present study indicate that the two PRE and the two EPSOT herbicides can be alternative options for weed control in wheat. Nevertheless, growers should be aware of possible crop injuries due to environmental conditions. Heavy rainfalls following the PRE application of prosulfocarb and chlorotoluron plus diflufenican or cold temperatures after the application of flufenacet plus diflufenican and flufenacet plus diflufenican plus metribuzin may cause crop injuries leading to yield penalties. If such environmental conditions are expected to occur, farmers should postpone the herbicide treatments to ensure crop safety, although this mayresult in reduced weed control. Finally, although the interpretation of the results of the presented study were supported by previous studies, further research should be considered to test in depth the effect of rainfall and lower temperature on the selectivity of these four herbicides.

Author Contributions

Conceptualization, T.G.; methodology, T.G.; software, T.G.; validation, T.G.; formal analysis, T.G.; investigation, T.G.; resources, T.G.; data curation, I.G., D.B. and E.V.; writing—original draft preparation, T.G.; writing—review and editing, T.G., D.B. and E.V.; visualization, T.G.; supervision, T.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are unavailable due to privacy. The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agronomy 14 01875 g001
Figure 1. Daily mean temperature and total rainfall from the time of wheat sowing until ten days after the EPOST herbicide treatments for trial A (# date of wheat sowing; * date of PRE herbicide application; ** date of EPOST herbicide application).
Figure 1. Daily mean temperature and total rainfall from the time of wheat sowing until ten days after the EPOST herbicide treatments for trial A (# date of wheat sowing; * date of PRE herbicide application; ** date of EPOST herbicide application).
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Agronomy 14 01875 g002
Figure 2. Daily mean temperature and total rainfall from the time of wheat sowing until ten days after the EPOST herbicide treatments for trial B (# date of wheat sowing; * date of PRE herbicide application; ** date of EPOST herbicide application).
Figure 2. Daily mean temperature and total rainfall from the time of wheat sowing until ten days after the EPOST herbicide treatments for trial B (# date of wheat sowing; * date of PRE herbicide application; ** date of EPOST herbicide application).
Agronomy 14 01875 g002
Table 1. Soil adsorption and mobility, solubility in water and soil degradation of the herbicides.
Table 1. Soil adsorption and mobility, solubility in water and soil degradation of the herbicides.
HerbicideSoil Adsorption and Mobility
(mL g−1) *		Solubility in Water
(mg L−1) **		Soil Degradation (Days) (Aerobic) ***
Prosulfocarb169313.29.8
Chlorotoluron147.227612.5
Diflufenican22150.0564.6
Flufenacet273.35139
Metribuzin48.310,70019
* Organic-carbon normalized Freundlich distribution coefficient (Kfoc); ** at 20 °C; *** degradation time for the chemical concentration to decline to 50% of the amount at application (DT50 field).
Table 2. Herbicide active ingredients (ai), grouped by HRAC (Herbicide Resistance Action Committee), mode of action (MoA), product information (trade name, type of formulation, % ai and manufacturer) and herbicide rates applied in this study.
Table 2. Herbicide active ingredients (ai), grouped by HRAC (Herbicide Resistance Action Committee), mode of action (MoA), product information (trade name, type of formulation, % ai and manufacturer) and herbicide rates applied in this study.
Herbicide AiHRAC
Group		Mode of Action (MoA)Product InformationHerbicide Rate
(g ai ha−1) #
1.prosulfocarb15Inhibition of very long-chain
fatty acid synthesis		Boxer 80 EC
(80% ai)
Syngenta Crop Protection AG(Basel, Switzerland)		3200
2.chlorotoluron
+
diflufenican		5
+
12		Inhibition of photosynthesis at PS-II Serine 264 Binders
+
Inhibition of Phytoene Desaturase		Carmina Max SC
(60% + 4% ai)
Nufarm GmbH & Co KG (Linz, Austria)		1380
+
92
3.flufenacet
+
diflufenican		15
+
12		Inhibition of very long-chain fatty acid synthesis
+
Inhibition of Phytoene Desaturase		Fosburi 600 SC
(40% + 20% ai)
Bayer AG
(Leverkusen, Germany)		240
+
120
4.flufenacet
+
diflufenican
+
metribuzin		15
+
12
+
5		Inhibition of very long-chain fatty acid synthesis
+
Inhibition of Phytoene Desaturase
+
Inhibition of photosynthesis at PS-II Serine 264 Binders		Herold Trio SC
(17.1% + 17.1% + 6.4% ai)
Bayer AG
(Leverkusen, Germany)		119.7
+
119.7
+
44.8
# grams active ingredient per hectare.
Table 3. Wheat density and plant height at 44, 73 and 116 DAS as affected by herbicide treatments.
Table 3. Wheat density and plant height at 44, 73 and 116 DAS as affected by herbicide treatments.
TreatmentWheat Density13.1.21
(44 DAS ^)		11.2.21
(73 DAS)		26.3.21
(116 DAS)
Plants m−1cm
Prosulfocarb71.0 b * (5.55) #15.4 (0.34)21.9 ab (0.79)49.0 (2.10)
Chlorotoluron + Diflufenican84.7 a (5.49)15.9 (0.40)20.6 b (1.56)46.8 (1.21)
Flufenacet + Diflufenican92.5 a (6.59)15.6 (0.62)17.2 c (0.44)47.5 (1.22)
Flufenacet + Diflufenican + Metribuzin86.4 a (4.70)16.5 (0.30)22.7 ab (1.22)50.8 (1.66)
Untreated control88.7 a (4.67)15.9 (0.50)23.4 ab (0.52)50.2 (0.88)
Weed-free95.2 a (4.09)16.1 (0.61)24.3 a (1.15)52.1 (1.20)
LSD ## (5%)12.92ns **3.09ns
^ DAS = Days After Sowing; * means followed by the same letter within each column are not statistically different at 5% level of significance; # standard error of mean (in parenthesis); ## least significant difference; ** ns = not significant.
Table 4. Spike number and yield as affected by treatments for trial A.
Table 4. Spike number and yield as affected by treatments for trial A.
Treatment2020–2021
Spikes m−2t ha−1 **
Prosulfocarb443 b *(22.3) #4.30 bc(0.28)
Chlorotoluron + Diflufenican526 ab(49.3)4.06 c0.39)
Flufenacet + Diflufenican567 a(31.3)4.99 abc(0.37)
Flufenacet + Diflufenican + Metribuzin558 a(23.9)5.12 ab(0.33)
Untreated control602 a(17.9)5.43 a(0.27)
Weed-free622 a(33.5)5.79 a(0.21)
LSD ## (5%)96.60.945
* Means followed by the same letter within each column are not statistically different at 5% level of significance; # standard error of mean (in parenthesis); ## least significant difference; ** = tonnes per hectare.
Table 5. Plant height at 44, 82 and 122 DAS as affected by herbicide treatments.
Table 5. Plant height at 44, 82 and 122 DAS as affected by herbicide treatments.
Treatment5.1.22
(44 DAS *)		12.2.22
(82 DAS)		24.3.21
(122 DAS)
cm
Prosulfocarb9.65 (0.39) #12.33 (1.21)39.7 (1.94)
Chlorotoluron + Diflufenican9.48 (0.63)12.26 (1.45)40.5 (3.07)
Flufenacet + Diflufenican9.50 (0.33)11.86 (0.68)38.6 (2.21)
Flufenacet + Diflufenican + Metribuzin10.23 (0.13)12.53 (0.67)42.2 (1.34)
Untreated control9.96 (0.49)12.25 (0.87)37.6 (1.63)
Weed-free10.09 (0.36)13.19 (0.41)41.2 (1.29)
LSD ## (5%)ns **nsns
* DAS = Days After Sowing; # standard error of mean (in parenthesis); ## least significant difference; ** ns = not significant.
Table 6. Spike number and yield as affected by treatments for trial B.
Table 6. Spike number and yield as affected by treatments for trial B.
Treatment2021–2022
Spikes m−2t ha−1 **
Prosulfocarb498 a *(23.0) #5.04 a(0.13)
Chlorotoluron + Diflufenican486 ab(20.2)4.49 ab(0.20)
Flufenacet + Diflufenican424 bc(26.4)4.10 b(0.02)
Flufenacet + Diflufenican + Metribuzin464 ab(18.3)4.48 ab(0.17)
Untreated control394 c(20.5)4.14 b0.27)
Weed-free493 a(31.0)5.01 a(0.18)
LSD ## (5%)66.40.566
* Means followed by the same letter within each column are not statistically different at 5% level of significance; # standard error of mean (in parenthesis); ## least significant difference; ** = tonnes per hectare.
Table 7. Weed control (%) of the main weed species as affected by the herbicides tested (data was pooled over trials).
Table 7. Weed control (%) of the main weed species as affected by the herbicides tested (data was pooled over trials).
Herbicides/Weed SpeciesVeronica spp.Lamium spp.F.
officinalis		C.
bursa-pastoris		M.
recutita		P.
rhoeas		L.
rigidum
% control *
Prosulfocarb96 (1.25) #94 (1.13)92 (0.92) b **91 (1.30) b92 (2.14)41 (4.79) b94 (1.55)
Chlorotoluron + Diflufenican98 (0.92)97 (0.92)96 (1.13) a93 (1.49) b94 (1.70)94 (1.87) a93 (1.34)
Flufenacet + Diflufenican96 (1.57)98 (0.95)97 (0.92) a98 (1.64) a94 (1.25)99 (0.92) a97 (0.92)
Flufenacet + Diflufenican + Metribuzin98 (0.92)98 (0.92)96 (1.13) a95 (0.95) ab97 (0.92)97 (1.01) a96 (1.48)
LSD ^ (5%)ns ***ns3.014.11ns5.26ns
* Based on 0–100% scale, where 0% = no weed control, 100% = complete weed control compared to weeds’ abundance and growth in the untreated plots; ** means followed by the same letter within each column are not statistically different at 5% level of significance; *** ns = not significant; # standard error of means (in parenthesis); ^ least significant difference.
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Gitsopoulos, T.; Georgoulas, I.; Botsoglou, D.; Vazanelli, E. Response of Wheat to Pre-Emergence and Early Post-Emergence Herbicides. Agronomy 2024, 14, 1875. https://doi.org/10.3390/agronomy14081875

AMA Style

Gitsopoulos T, Georgoulas I, Botsoglou D, Vazanelli E. Response of Wheat to Pre-Emergence and Early Post-Emergence Herbicides. Agronomy. 2024; 14(8):1875. https://doi.org/10.3390/agronomy14081875

Chicago/Turabian Style

Gitsopoulos, Thomas, Ioannis Georgoulas, Despoina Botsoglou, and Eirini Vazanelli. 2024. "Response of Wheat to Pre-Emergence and Early Post-Emergence Herbicides" Agronomy 14, no. 8: 1875. https://doi.org/10.3390/agronomy14081875

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