Identifying the Best Herbicides for Weed Control in Chicory (Cichorium intybus)

Abstract

Chicory (Cichorium intybus) is a commercially cultivated root crop in many countries of the world. Weeds have a depressing effect on the growth and development of root chicory. There are currently no herbicides registered for use on chicory in the Russian Federation. The objective of this work was to identify potential herbicides for controlling a broad range of weed species under the soil and climatic conditions of the Russian Federation. For the field experiment, herbicides were selected according to: (1) previous studies in USA, EU and South Africa; (2) the spectrum of weeds controlled; and (3) the probability of crop damage. All the herbicides used were registered in Russia for the control of certain weeds in other crops. Crop biomass, damage, and weed control were assessed to identify suitable herbicides. The results suggested that the best weed control herbicides would be a Zeta, SC (100 g/L imazethapyr) and Paradox, SC (120 g/L imazamox). These herbicides controlled, on average, 80% or more of the dicotyledonous weeds such as lamb’s quarters (Chenopodium album), field pennycress (Thlaspi arvense), and sow thistles (Sonchus spp.). Since these herbicides do not reduce chicory biomass, they can be considered for registration or use on chicory.

1. Introduction

Chicory (Cichorium intybus) is a valuable vegetable, technical and medicinal crop in many countries of the world [1]. Varieties of salad and root chicory are used for cattle feed as forage [2], as well as in the food and pharmacological industries. For example, it is used in coffee production [3], in the baking and confectionery industry, in the production of extruded grain products [4], in medicine as the most important source of prebiotics, in pharmacology (intibine is used as a heart rate optimizer), in some hepatoprotectors [5], and in alcohol production [6]. The chicory root contains up to 72.0–77.0% water, 1.0–1.2% protein, 0.1–0.3% fat, 1.0–6.0% sugars, 12.0–30% inulin, 1.3–1.8% fiber, 1.1–1.9% ash, 0.3–0.4% phosphorus, 1.3–1.4% potassium, and 0.3–0.4% calcium [7]. Chicory leaves are rich in calcium, iron, the antioxidants lutein and zeaxatin, as well as vitamins A and beta-carotene [8]. The content of inulin in chicory root is 15–20% [9]. Inulin-containing plants are of great importance for human health and longevity, and are important and profitable crops in many developed and developing countries of the world [10]. According to the Food and Agriculture Organization Corporate Statistical Database (FAOSTAT), global production of root chicory in the year 2000 was over 1,000,000 tons [11].

However, there has been a decrease in the yield of chicory in recent decades, which may be due to a lack of high-quality seeds [12]. In 2020–2022, the situation worsened against the background of the COVID-19 pandemic. Many agricultural producers were forced to suspend the production of chicory root due to the high proportion of manual labor in the cultivation and harvesting of chicory, and the need to comply with social distancing measures [13]. Currently, Belgium is a world leader in the production and export of chicory root. An amount of 300–500 thousand tons of chicory are collected annually in this country on an area of more than 6 thousand hectares. This is followed by France, the Netherlands, Poland and South Africa, producing a total of more than 100 thousand tons of root crops per year.

According to business analytics, in the coming decades, North America will become the fastest growing market for the production and consumption of chicory in the world [8].

Historically, in the territory of modern Russia, chicory was cultivated in the Yaroslavl region. Currently, Russian agricultural producers do not grow chicory on an industrial scale due to a lack of special forage harvesting equipment, the high proportion of manual labor required during cultivation and harvesting, and a lack of chemical plant protection products approved for use in chicory [14,15,16].

Weeds have a depressing effect on the growth and development of root chicory. Compared with many cereal and dicotyledonous plants, the phenological phase of chicory regrowth takes place much later, which creates favorable conditions for the growth and development of weeds [17]. The common weeds are Artemisia biennis, Capsella bursa-pastoris, Coronopus didymus, Galinsoga ciliata, Galinsoga parviflora, Matricaria chamomilla, Senecio vulgaris, Solanum nigrum, and Sonchus species [18]. As the experience of advanced chicory-producing countries shows, high yields of root crops are obtained when soil cultivation is combined with the use of herbicides [19].

Management practices cited in literature for weed control in chicory are typically limited to mechanical or grazing strategies [20]. However, few herbicides are registered for use in the EU countries, the USA and South Africa. For example, the herbicide benfluralin is widely used on chicory crops against cereal weeds [21,22]. Therefore, the use of benfluralin during pre-emergence or pre-sowing treatment at application rates from 1.3 to 1.71 kg/ha reduced weediness (up to 90% in some experiments), but did not affect chicory plants. The use of the herbicide imazethapyr when spraying chicory, in the phase of 2–5 leaves of culture development, leads to the suppression of many dicotyledonous and monocotyledonous weeds of the Cyperaceae family. Imazethapyr is approved for use in Canada, the United States and Australia [23]. However, according to the results of Robinson D.E. et al., [24] imazethapyr can cause slight leaf necrosis in the crop. Desmedifam and phenmedifam as part of Betanal 22, EC proved to be effective against lamb’s quarters (Chenopodium album), chickweed (Stellaria media), field mustard (Sinapis arvensis), corn spurry (Spergula arvensis), cockspur (Echinochloa crus-galli), and field mint (Mentha arvensis). At the same time, an increase in the yield of chicory was noted in the variants treated with this herbicide [19,25]. There are currently no herbicides officially recommended for protecting chicory from weeds in the Russian Federation.

Thus, the purpose of this work was to evaluate the use of herbicides for weed control in chicory (Cichorium intybus) under the soil and climatic conditions of the Russian Federation.

2. Materials and Methods

2.1. Chicory and Soil

For the field experiment we chose the root chicory (Cichorium intybus) of the Petrovsky variety (Figure 1), which was selected by scientists from the Rostov Vegetable Chicory Experimental Station, Rostov, Yaroslavl region, Russia [26]. This variety has a well-leafed rosette, a large leaf surface area (6583.4 cm²), and is a short-rooted variety, which accelerates the harvesting process due to the use of special forage harvesting equipment. This, in turn, significantly reduces the cost of production.

The field experiment was carried out in the Rostov District of the Yaroslavl region (57°02′ N, and 39°15′ E).

The soils of the site are umbric Albeluvisols [27], of medium loamy mechanical composition, and are characterized by a low level of groundwater. The arable horizon has a high degree of saturation with bases, and is characterized by low hydrolytic acidity. The content of organic matter in the plow horizon is an average of—1.8%, with total nitrogen—0.2%. The content of exchangeable potassium throughout the profile is 17–20 mg/100 g of soil. The soil of the experimental plot is well supplied with mobile phosphorus—20–25 mg/100 g of soil. The main properties of the soil are presented in Supplementary Table S1.

2.2. Pesticides

For the experimental treatment, we chose five pesticide formulations that were produced by «Avgust» Inc. (Russia), Syngenta AG, Bayer AG: Zellek-super, EC (104 g/L haloxyfop-P-methyl); Paradox, SC (120 g/L imazamox); Zeta, SC (100 g/L imazethapyr); Fuzilad Forte, EC (150 g/L fluazifop-P-butyl); Betanal 22, EC (160 g/L desmedifam + 160 g/L phenmedipham).

Zellek-super, EC (104 g/L haloxyfop-P-methyl) is a post-emergence herbicide for all types of grass weeds in dicotyledonous crops. Paradox, SC (120 g/L imazamox) is a post-emergence herbicide against annual cereal and dicotyledonous weeds on soybeans and peas, as well as varieties and hybrids of rapeseed and sunflower resistant to imidazolidinone. Zeta, SC (100 g/L imazethapyr) is a systemic pre-emergence (soil) herbicide for the control of annual and perennial dicotyledonous and cereal weeds in soybeans and peas. Fuzilad Forte, EC (150 g/L fluazifop-P-butyl) is a post-emergence herbicide for suppressing annual and perennial grass weeds in sugar, fodder beets and other crops. Betanal 22, EC (160 g/L desmedifam + 160 g/L phenmedipham) is a selective herbicide for post-emergence control of annual dicotyledonous weeds (including amaranth species) in sugar, table and fodder beet crops. All actives were >98.0% pure and met international standards. The main properties of these pesticides are provided in Supplementary Table S2. The active ingredients of pesticides are actively used in the USA, EU, Australia and South Africa for cereals and dicotyledonous weed control in chicory.

2.3. Experimental Design

The field trial was carried out in three replicates in May 2022. The size of the experimental site was 360 m², the area of one plot was 12 m², the shape was rectangular, and the location was randomized. The length of the growing season in 2022 was 145 days.

Data on meteorological conditions for the growing season in 2022 are presented in Supplementary Figures S1 and S2.

The growing season of 2022 was characterized by low air temperatures in May and September and high temperatures in the summer months, with a sharp lack of precipitation throughout the entire period (for example, in June and September, only 11 mm fell in each month, with long-term averages of 71 mm and 63 mm, respectively). This negatively affected the growth and development of the root chicory, both in the first and second years of vegetation.

High air temperatures and insufficient precipitation prevented the formation of large root crops. As a result, their productivity turned out to be low, the leaf rosette was more compact than usual, and the shape of the root crop in all varieties was more elongated. Root crops were harvested only at the beginning of October.

The plants of the second year of vegetation were lower than usual. The number of flowers was fewer and they faded quickly. The lack of moisture led to the fact that the set seeds were puny, with a small amount of endosperm and a weak, small-sized embryo, which negatively affected the yield of seeds and their sowing qualities.

Herbicide treatment was carried out on 20 June 2022 in the phase of 2–3 true leaves of crop development, at a plant height of 2–5 cm. The pesticides were applied according to the minimum and maximum application rates (

Table 1. Treatments applied to chicory.

Treatment	Trade Name	Rate, L/ha	Timing of Applications	Water Rate on 30 m2, L/ha
untreated control	-	-	-	-
Haloxyfop-P-methyl	Zellek-super, EC	1,0/1,92	2–4 true leaf stage	1500
Imazamox	Paradox, SC	0,23/0,33	2 true leaf stage
Imazethapyr	Zeta, SC	0,5/1,0	2–5 true leaf stage or about 30 days after sowing
Fluazifop-P-butyl	Fuzilad Forte, EC	0,85/2,5	2–3 true leaf stage
Desmedifam + Phenmedipham	Betanal 22, EC	1,0/3,0	Sequential spraying of crops in the 2–4 true leaf stage

).

All treatments were applied with a backpack sprayer “Finland” for 5 L poured 0.4 L solution. The entire volume was completely sprayed onto one plot (12 m²), spread evenly over the entire area of the plot. After processing three plots with the minimum concentration, the plots with the maximum concentration were treated. Before changing the herbicide, the sprayer was flushed with clean water. The experimental design for one pesticide active ingredient is shown in Figure 2.

Chicory injury and weed densities were estimated 2 weeks after the herbicide applications by visually comparing each herbicide treatment with the untreated control. Chicory biomass in a square-meter area in the center of each plot was determined 2 weeks after herbicide treatments by clipping chicory at the soil surface and weighing after drying at room temperature.

The experiment was carried out in three replicates. After herbicide treatment and before harvesting, the chicory samples were stored at −20 °C until the subsequent pesticide residues analysis.

2.4. Assessment of Pesticide’s Residual Quantities

Residual quantities were measured using an Agilent 1200 series HPLC with a quadrupole time-of-flight mass spectrometric detector (6520 Accurate-Mass Q-TOF LC/MS, ionization source electrospray (Agilent Technologies, Santa Clara, CA, USA). The limits of the quantification were as follows: for imazamox—8 µg/kg, for haloxyfop-P-methyl and fluazifop-P-butyl-16 µg/kg, for phenmedipham and desmedifam—32 µg/kg. The presence of imazethapyr was assessed qualitatively by searching for characteristic parent and daughter ions.

Absolute calibration with analytical standards was used for quantitation. The correlation coefficient was 0.999. The simultaneous extraction of pesticides was carried out from 5 g of chicory roots with 20 mL of acetone for 15 min in an ultrasonic bath, followed by filtration of the supernatant through a red tape, after which the extraction was repeated again and the extracts were combined [28]. Then, the volume of the solution was measured and 5–10 mL was applied to a C18ec cartridge (Isolute) (400 mg), previously prepared by passing 5 mL of acetone. The eluent after the application of the sample was collected in a 50 mL distillation flask, the cartridge was additionally washed with 5 mL of acetone, and the eluates were combined. To determine haloxyfop-P-methyl, imazamox, imazethapyr, and fluazifop-P-butyl, the extracts were evaporated to dryness on a rotary evaporator. To determine phenmedipham and desmedifam, the extract was dissolved in 20 mL of an aqueous solution of hydrochloric acid (pH = 2), transferred to a separatory funnel (2×10 mL with 60 s ultrasonic treatment), and extracted twice with 20 mL of methylene chloride. The extracts were combined and evaporated to dryness on a rotary evaporator. The evaporated extracts were transferred with 1 mL of acetonitrile into chromatographic vials by treatment in an ultrasonic bath for 30 sec. The volume of the injected sample was 10 µL, and chromatographic column was Phenomenex Synergy Polar-RP 80A C18 100 × 3.0 mm, 1.8 μm. Eluents were water (A) and acetonitrile (B) with the addition of formic acid (0.1%) in a gradient mode (0 min—20% «B»; 12 min—80% «B»), flow rate was 0.4 mL/min.

Source and mass spectrometer settings:

-

electrospray source (ESI) in positive-ion mode;

-

Source temperature: 325 °C;

-

drying gas flow (nitrogen): 3 L/min (desmedifam and phenmedifam—10 L/min);

-

nebulizer pressure: 20 psig;

-

capillary voltage: 3500 V;

-

fragmentor voltage: 75 V;

The characteristic parent and daughter ions used to qualify and quantify the herbicides, and the collision energy for all pesticides are given in

Table 2. The m/z of ions and energy of the collision cell.

Pesticide	[M+H]+, m/z	ion 1, m/z (Quantification)	ion 2, m/z (Confirmation)	The Collision Energy, eV
Haloxyfop-P-methyl	376,0	316,0	288,0	20
Imazamox	306,1	261,1	246,0	20
Imazethapyr	290,3	159	177	20
Fluazifop-P-butyl	384,1	316,0	328,0	20
Desmedifam + Phenmedipham	318,1	182,1	108,1	5
	318,1	182,1	136,1	5

.

The retention time: haloxyfop-P-methyl—8,2 min, fluazifop-P-butyl—9,2 min, imazamox 6,0 min, phenmedipham—3,8 min, desmedifam—7,1 min. The limit criterion for linearity was the range above r ≥ 0.995.

2.5. Statistical Processing of the Results

Statistical data analysis was conducted in Excel and STATISTICA 10 programs. The results shown in the charts and text are given as mean values, and standard deviation (SD) is indicated unless noted otherwise. Verification of statistical hypotheses was performed at significance 0.05 unless noted otherwise. Means and the least significant differences at the 5% level were calculated by one-way analysis of variance (ANOVA).

3. Results

3.1. Chicory and Weeds Visual Injury after Herbicide Treatments

The damage to weeds and chicory was evaluated 2 weeks after herbicide treatment. On each plot, the heights of three prevailing weeds—lamb’s quarters (Chenopodium album), field pennycress (Thlaspi arvense), and sow thistles (Sonchus spp.)were taken into account (Figure 3). There were no cereal weeds on the field.

Paradox, SC and Zeta, SC controlled all weeds present in the plot area. There was greater separation among herbicides in their control of lamb’s quarters, field pennycress and sow thistles. Betanal 22, EC treatment proved to be less effective. Zellek-super, EC and Fuzilad Forte, EC also did not have a noticeable effect on the studied weeds; plant height did not differ significantly from control.

The effect of herbicides on chicory plants was also investigated. Betanal 22, EC caused yellowing and burns on chicory leaves. For quantitative accounting, five groups of plants were randomly taken from each plot (the plants were closely planted, so it was not possible to separate them in dry heavy soil). For each plant, the length of the ground part was measured (from the junction of the rhizome with the stem to the end of the longest leaf) and the number of leaves (cotyledons were not taken into account). The maximum number of leaves was noted on plots treated with Paradox, SC and Zeta, SC (Figure 4).

At the same time, the height of the leaves under Paradox, SC and Zeta, SC treatment was less than in the other variants (Figure 5).

Betanal 22, EC at the maximum application rate (3,0 L/ha) reduced chicory biomass to a significant extent (Figure 6).

Chicory biomass was increased compared with the nontreated control by Zeta, SC at the minimum application rate (0.5 L/ha).

On herbicide-treated plots, weed growth was strongly inhibited, which contributed to the formation of more leaves by chicory plants and the spread of the rosette in width. On the control plots, as well as those treated with Zellek-super, EC and Fuzilad Forte, EC, the plants had, on average, fewer leaves, but they were longer. This was most likely attributable to the strong spread of tall weeds in these plots. In the plots treated with Betanal 22, EC, the average number of leaves was less than in other variants, and at the same time their height was also small. This could be explained by the negative effect of Betanal 22, EC on chicory plants. Zeta, SC and Paradox, SC, even at minimal application rates, caused yellowing, growth inhibition, and inhibition of seed formation to the field pennycress (Thlaspi arvense) (Figure 7).

As a result of the study, Zeta, SC and Paradox, SC used even in minimal application rates, were selected as the most promising herbicides because of safety to the crop, levels of weed control, and acceptable crop yields. Herbicides Betanal 22, EC was less effective against weeds and inhibited chicory plants. Zellek-super, EC and Fuzilad Forte, EC are graminicide herbicides; they did not have a noticeable effect on the development of dicotyledonous weeds, and did not inhibit chicory.

3.2. Analysis of Pesticides Residual Amounts

The validation method results are given in Supplementary Table S3. Pesticide residues were analyzed on days 0 after the herbicide treatments, and 120 days after planting when chicory roots were harvested in mid-October (

Table 3. Pesticide residues in chicory roots.

Trade Name	Substance to be Determined	Min/Max Rate, L/ha	Analyzed Objects	Content of the Substance, mg/kg
Zellek-super, EC	Haloxyfop-P-methyl	1,0/1,92	chicory roots	Not detected
Paradox, SC	Imazamox	0,23/0,33		Not detected
Zeta, SC	Imazethapyr	0,5/1,0		Not detected
Fuzilad Forte, EC	Fluazifop-P-butyl	0,85/2,5		Not detected
Betanal 22, EC	Desmedifam + Phenmedipham	1,0/3,0		Not detected Not detected

).

The results of chromatographic determination of the herbicide residual amounts showed that the pesticides in the studied application rates do not accumulate in roots.

4. Discussion

The results from the field experiment suggested that the best weed control herbicides would be a Zeta, SC (100 g/L imazethapyr) and Paradox, SC (120 g/L imazamox). These pesticides controlled, on average, 80% or more of the weed population. Further research is needed to improve weed control and enhance chicory root yield.

The results obtained are consistent with previous studies. Collins J. et al. [29] showed in a field experiment in Australia the suppression of dicotyledonous weeds and a monocotyledonous weed of coco-grass (Cyperus rotundus) when treated with imazetapir at application rates of 200 mL/ha and 400 mL/ha, applied in the phase of 2 leaves of chicory development and no more than 3-leaf development of dicotyledonous weeds.

In another US field trial, imazamox, foramsulfuron, thifensulfuron, triflusulfuron, and flumetsulam were found not to reduce chicory density. At the same time, imazamox controlled more than 70% of lamb’s quarters (Chenopodium album) and more than 95% of other weed species [30]. According to Pittman et al., [31], in a field experiment in Oklahoma, pendimethalin at a rate of 4500 g/ha, imazethapyr at a rate of 210 g/ha, and flumetsulam at a rate of 56 g/ha were safe to use on chicory crops regardless of the season.

In New Zealand, in a field experiment evaluating the biological effectiveness of herbicides on crops of pasture grass mixtures of chicory (Cichorium intybus), narrowleaf plantain (Plantago lanceolata), red clover (Trifolium pratense), and white clover (Trifolium repens), haloxifop-P-methyl successfully suppressed growth and development of hemlock, sorrel and nightshade without injury to cultivated plants.

In Australia, in a growing experiment on crops of alfalfa and chicory (Cichorium intybusL.), studies were carried out to evaluate the effectiveness of 20 herbicides and tank mixtures based on these. The results of this study indicate that there are several herbicides/mixtures that have the potential to control a wide range of broadleaf weeds (with the exception of plumeless thistles) in chicory seedlings. Among independent herbicides (not mixtures), the minimum levels of damage to chicory plants were caused by flumetsulam, imazamox, simazine and imazethapyr [32].

In Canada, in a field trial, chicory crops were sprayed with herbicides at the 4–5 true leaf stage of crop development. After 15, 22 and 35 days after treatment, the height and degree of damage to the plants was evaluated. Tifensulfuron-methyl at a rate of 6 g/ha, triflusulfuron-methyl at a rate of 35 g/ha, and setoxydim (500 g/ha) had no effect on chicory. Cloransulam-methyl at a rate of 17.5 g/ha and imazethapyr at a rate of 75 g/ha 15 days after treatment caused a slight necrosis of the leaves of the culture; however, after 7 days, according to the results of the second measurement (22 days after spraying), the chicory was completely restored. None of the listed herbicides had a significant effect on the height of the chicory [24].

An analysis of works published back in the USSR showed that pre-emergence Isopropyl-n-chlorophenyl carbamate and post-emergence Betanal (phenmedifam) herbicides were actively used to control weeds on chicory crops. According to Danilchenko G.E. [19], as a result of a three-year field experiment on chicory, the use of isopropyl-n-chlorophenyl carbamate herbicide increased the yield of root crops by 2.1–2.4 t/ha compared with the control (an increase of 2.4 t/ha (10.1%), which was obtained by applying 3.5 kg/ha of isopropyl-n-chlorophenyl carbamate). When using 3.0 kg/ha of Kerb-50 (500 g/kg of propizamid), the yield of root crops increased by 9.8 t/ha (by 39.0%). The largest increase was 7.9 t/ha (34% more than in the control) when using Betanal. The application rate of Betanal 0.95–1.1 kg/ha reduced the infestation of crops by 86.5–65.2% and reduced the air-dry mass of weeds by 69.9–56.9%. All of the studied herbicides controlled lamb’s quarters, common chickweed, field mustard, and corn spurry. Vilchik V.A [25] recommended treatment with Betanal in phases up to 4–5 true leaves of weeds, and strictly after the appearance of 2–3 true leaves of chicory, in dry cloudy weather at a temperature of 19–22 °C.

5. Conclusions

Previous studies and our data have shown that the herbicides Zeta, SC (100 g/L imazethapyr) and Paradox, SC (120 g/L imazamox), taking into account the studied application schemes (min/max application rates, development phase of the protected crop, weed growth phase), turned out to be effective and safe. According to the results of chromatographic analysis, these herbicides did not accumulate in chicory roots and did not cause crop damage. Formulations based on imazethapyr and imazamox could be used by agricultural producers on chicory root crops to control dicotyledonous weeds such as lamb’s quarters (Chenopodium album), field pennycress (Thlaspi arvense), and sow thistles (Sonchus spp.).