Herbicides Assesment for Weed Control and Cost Analysis in a Tomato (Solanum lycopersicon L.) Crop in the State of Yucatan Mexico ()
1. Introduction
Current regulations at the international and national level are driving to a gradual reduction and prohibition of the herbicide Glyphosate aiming to promote healthier agri-food systems in order to avoid soil and water contamination. Under this context, Mexico has launched agroecological transition policies; the reduction and eventual elimination of Glyphosate by 2024 being the main objective [1] .
In December 2020, Mexico established a presidential decree for the institution of the Federal Public Administration to carry out actions to gradually replace the use, acquisition, distribution, promotion and import of Glyphosate and all other pesticides containing its active ingredient. The replacement must be toward the use of sustainable and culturally appropriate alternatives to maintain crop production and be safe to human health, amicable to the biocultural diversity of the country and the environment [2] .
However, this is not an easy task since Glyphosate has gained popularity due to its cheaper acquisition by producers. Unfortunately, the economic analysis of the herbicide is limited, since the negative effects on human health and nature are not taken into account [3] .
In the particular case of tomato production (Solanum lycopersicum L.) in the state of Yucatan, weed control is carried out by applying several herbicides, including Glyphosate, as the principal one, applied in pre-transplanting. Weed competes with the crop for space, light, nutrients, and water; and also serves as an alternate host for begomoviruses and important biological vectors [4] .
In the state of Yucatán Mexico, the farmers control weeds based on a combination of hand weeding in crop lines, application of Glyphosate in pre-transplant and paraquat in post-transplant. This is ineffective for being a high cost and highly-labor demanding practice that needs to be repeated two or three weeks, depending on the environmental conditions.
Due to the foregoing, the National Institute of Forestry, Agricultural and Livestock Research (INIFAP) of Mexico, launched in 2022 a strategy, based on the project: “Alternatives to the use of glyphosate for weed control in Mexico.” to control weeds from germination to emergence of different crops, such as tomatoe, but keeping in mind the cost/benefit ratio ($).
In accordance with the strategy, this work aimed to assess the effect of different commercial herbicides to control weeds and their phytotoxic effects in tomato, considering the cost-benefit ($) of each treatment.
2. Materials
2.1. Location
The research was carried out in the Agricultural Unit “José López Portillo Pozo 3”, in the municipality of Muna, Yucatán, Mexico; located at the coordinates 20˚25'10'' north latitude and 89˚29'41'' west longitude in a soil classified as K’ankab lu’um in Mayan terms and Luvisol in the World Soil Reference Base (WRB) [5] .
2.2. Identification of Weed Species
The weed species were identified under field conditions a week before the establishment of the treatments, using 12 squares of 1.0 m2 (1.0 × 1.0 m) to record the coverage and frequency of appearance of each species.
The frequency of appearance, abundance and dominance of each species were recorded and the Importance Value Index (IVI) of each weed was calculated adapting the methodology described by Gámez López et al. (2011) [6] . The Importance Value Index (IVI) was developed by Curtis & McIntosh (1951) [7] . It is a synthetic structural index, developed mainly to rank the dominance of each species in mixed stands and was calculated as follows: IVI = Relative dominance + Relative density + Relative frequency [8] [9] . According to Campo and Duval (2014) [10] , these three parameters are calculated as follows:
1)
2)
3)
3. Methods
3.1. Management and Herbicides Application
The study was carried out from August to December 2022 (autumn-winter cycle) starting with the land preparation by passing a heavy harrowing twice. In the second week of August, the contact herbicide Paraquat (200 g of active ingredient L−1) was applied at a dose of 10 mL of commercial material per liter of water, to eliminate the first vegetation.
Five treatments were evaluated in five repetitions: in the first four treatments, pre-emergent herbicides (Pendimethalin, Clorthal Dimethi, Trifluralin and Ethalfluralin), mixed each one with the contact herbicide Bentazon, were applied three days before the transplanting (2/Sep). Subsequently, two more applications of Bentazon alone were made at 10 (September 15) and 29 days after transplantation (Oct 4).
Treatment five was the Producer’s Control, based on Glyphosate before transplanting, plus hand weeding in the crop line and application of contact Paraquat in the streets after transplanting. In this control treatment, Glyphosate was applied, in post-emergence of weeds, three days before transplanting the tomatoe (Sep 2). Hand weeding was carried out in the crop lines (40 cm wide band) and Paraquat applied on the streets, 29 days after transplanting (4/Oct).
The doses used (Table 1) were determined using the herbicides manufacturers and those suggested by INIFAP [11] . Legal authorization for Mexico and USA for other vegetable crops, was also considered. Crop management was carried
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Table 1. Herbicide treatments for weeds control in a tomato crop (Autumn-Winter period 2021-2022).
*Weight percentage of main components; (HRAC) = Herbicides Resistance Action Committee 2020; TC = Toxicological Category.
out according to recommendations of Avilés et al. (2010) [11] for Yucatan Mexico conditions
3.2. Experimental Design and Statistical Analysis
Five treatments with five replications were established, under drip irrigation conditions, and the information was analyzed in a randomized complete block design. The experimental units were of 375 m2 (50 m long by 7.5 m wide).
As a phytometer the tomatoe hybrid DRD 8551 was used, transplanted at 21 days old as seedlings, after being germinated under controlled conditions. Each experimental plot had 625 seedlings (16,750 plants ha−1). Data were subjected to an Analysis of Variance (ANOVA), Mean Comparison Test by Tukey’s method (p ≤ 0.05) using the Statgraphics Centurión program, version 16.1.2.0.
3.3. Total Coverage of Weeds (%)
The percentage of coverage was measured visually, adapting the methodology described by Rodríguez et al. (2008) [12] and Gámez López et al. (2011) [6] for weed populations. 15 quadrants of 50 × 50 cm (0.25 m2) were used per treatment (three quadrants per repetition) at 15, 30 and 45 days after herbicide application (da). Subsequently, the data were transformed to arc sine root of x for statistical analysis (ANOVA) [13] .
3.4. Evaluation of Phytotoxicity Height of Plants
For phytotoxicity, the percentage of mortality and the symptomatology of herbicide damage were evaluated using the method proposed by the European Weed Research Society (EWRS) cited by Pérez et al. (2014) [14] (Table 2).
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Table 2. Reference values suggested by the European Weed Research Society (EWRS) for weeds control and crop phytotoxicity.
Source: Urzúa (2001), cited by Pérez et al., 2014.
3.5. Cost Analysis ($)
A preliminary analysis of profitability per treatment was carried out considering the costs of the products and the application days per hectare as compared to the estimated cost of the producer (combination of manual and chemical control). The cost reduction ($) of each treatment was calculated when comparing the production cost of the producer, as 100%, against the production cost of each treatment.
4. Results
4.1. Identification of Weeds
Eight dominant weed species were detected: Nutsedge (Cyperus ligularis), Xtes (Amaranthus dubius), Pants’ iil (Boerhavia erecta), White yew (Urochloa panicoides), Guinea grass (Megathyrsus maximus), Tsi’ tsi’ n (Artemisa vulgaris), Crow’s foot (Digitaria sanguinalis), Purslane (Portulaca oleracea). 65.9% of the weeds were narrow-leaf species (Cyperus ligularis, Urochloa panicoides, Megathyrsus maximus and Digita-ria sanguinalis) and 34.1% broad-leaf species (Amaranthus dubius, Boerhavia erecta, Artemisa vulgaris and Portulaca oleracea).
According to the Importance Value Index (IVI), the outstanding species were: Cyperus ligularis (Cyperaceae), Amaranthus dubius (Amaranthaceae) and Boerhavia erecta (Nyctaginaceae) with values of 82.1%, 37.6% and 30.3%, respectively (Figure 1).
4.2. Total Coverage of Weeds (%)
The Analysis of Variance (ANOVA) detected highly significant differences between treatments at 15, 30 and 45 days after application (daa). At 15 daa, Tukey’s test (p ≤ 0.05) showed that the best treatments were T4 (Ethalfluralin + Bentazon) and T3 (Trifluralin + Bentazon) with 4.50% and 5.70% coverage respectively, compared to the Control of the producer with 31.40% (Table 3).
At 30 and 45 daa, all treatments were better than the Control; with a weed cover range from 2.05% to 3.13% vs. 32.0% of the Control at 30 daa. At 45 daa the cover ranged from 2.10% to 3.50% against 12.60% of the Control (Table 3).
Due to the dominance of Cyperus ligularis (nutsedge), the analysis of weed cover was divided into both “broadleaf and grass weeds” and “nutsedge” in order to know the effects of the treatments to control that specific kind of weeds.
In relation to the presence of broadleaf weeds and grasses, the evaluations (Table 3) at 15, 30 and 45 daa showed that all treatments were most effective than the Control with values of 0.06%, 0.06%, 0.14% and 0.12% for T1, T2, T3 and T4 respectively vs. 3.6% of the Control at 15 daa.
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Figure 1. Relative Importance Values (RIVs) of weeds in percentage.
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Table 3. Weed coverage (%) as related to weeds herbicides in a tomato crop at 15, 30 and 45 daa.
Note: Different letters mean statistical significant differences (p < 0.05, Tukey).
At 30 daa the values for the same above-mentioned treatments were: 0.45%, 0.45%, 1.23% and 0.64% against 62.0% for the Control; and again, at 45 daa very low weed cover were found with 0.00%, 0.20%, 0.24% and 1.40% vs. 11.6% of the Control (Table 3).
In the particular case of Cyperus liguralis, at 15 daa, the best treatments, were: T4 (Ethalfluralin + Bentazon) and T3 (Trifluralin + Bentazon) with 4.50% and 5.70% coverage, being statistically similar to each other and different from the Control with 31.40%. At 30 and 45 daa, all treatments were better to eliminate weeds than the Control and the cover values ranged very low. At 30 daa the cover values ranged from 2.05% to 3.13% vs. 32% of the Control and at 45 daa the ranges were from 2.1% to 3.5% vs. 12.64% of the Control (Table 3).
4.3. Cost Analysis ($)
Regarding the cost analysis, two different analyzes were carried out; one considering the costs for the exclusive control of Cyperus ligularis (nutsedge) and the second one without the use of the herbicide Bentazon used to control C. ligularis. This was done because the costs increased considerably when controlling only the nutsedge.
Table 4 describes the unit costs of herbicides and treatments as of September 2022, according to the doses per hectare used. All treatments cost were compared to the estimated costs of the combined control used by the producer in the first 30 days after transplanting. It is observed that only T1 (Pendimethalin + Bentazon) reduced the cost marginally by 2.69%, while the other treatments were more expensive than the Control. Applying T4 (Ethalfluralin + Bentazon) the cost increased 6.34% while applying T2 (Clorthal Dimethil + Bentazon) the cost increased quite a bit with 72.36%.
However, when excluding the herbicide Bentazon it was observed that using Pendimethalin, Ethalfluralin and Trifluralin the costs can be reduced by 79.12%, 64.91% and 61.86% with respect to the Control (T5); the mixture of Clorthal Dimethil + Bentazon only reduced the cost by 4.07% (Table 5).
5. Discussion
Tomatoes are very sensitive to weed competition especially in the early stages after transplanting [15] . Singh and Twpathi (1988) [16] showed that competition can reduce yield by 42% to 70% when it occurs during the first 15 to 45 days after transplanting.
It has been proven that when the predominant weed is nutsedge (Cyperus spp), as in the present study, underground interference with this species reduces
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Table 4. Profitability of different herbicides applied for weed control in a tomato crop (Autumn-Winter period 2021-2022).
1Treatments 1 - 4: One pre-emergent herbicide application and two of Bentazon. 2Treatment 5: One application of Glyphosate, one hand weeding and one application of Paraquat. **Total Cost: Cost of herbicides and three wages per application during first 30 days after transplanting. ***Calculation expression: (T5 − TN˚)/T5 * 100.
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Table 5. Profitability of different herbicides applied for weed control in a tomato crop eliminating the Bentazon herbicide (Autumn-Winter period 2021-2022).
1Treatments 1 - 4: One pre-emergent herbicide application. 2Treatment 5: One application of Glyphosate, one hand weeding and one application of Paraquat. **Total Cost: Cost of herbicides and three wages per application during first 30 days after transplanting.
the accumulation of dry matter in tomato shoots from 18% to 19%, while space competition aboveground the reduction is from 9% to 19%.
When both types of competition occurs, at the same time, a decrease of 28% to 34% in the dry matter is presented and the nitrogen content, as nitrate (NO3), in the sap can be reduced more than 18% [17] .
According to Johnson (1975) [18] , the management of nutsedge can be highly effective through the application of Bentazon, with an effectiveness of 98% to 100% without damaging the crop.
The Bentazon can control C. liguralis without damaging the soybeans, unlike Glyphosate and Perfluidone, which severely affect this crop [19] . In both cases, a slow acropetal translocation of Bentazon induced to an effective elimination of the original reproductive tubers. The present study also supports these findings, since no phytotoxic effects were detected after transplanting when using Bentazon in combination with pre-emergent herbicides.
6. Conclusions
Tomato is a very sensitive crop to weed competition, especially after transplanting. In the state of Yucatan Mexico, weed control is carried out with the application of several herbicides such as Glyphosate in pre-transplantation. Currently, Glyphosate is prohibited. Therefore, new effective and low-cost herbicides need to be recommended.
In this research the main findings were that:
1) All treatments exhibited high efficacy in controlling broadleaf weeds, grasses, and nutsedge up to 45 days after application: Pendimethalin + Bentazon, Clorthal Dimethil + Bentazon, Trifluralin + Bentazon, and Ethalfluralin + Bentazon. Furthermore, none of the treatments induced phytotoxicity in the tomato plants.
2) Only T1 (Pendimethalin + Bentazon) reduced the cost marginally by 2.69%. The other treatments were more expensive than the Control (T5) of the producer.
3) When excluding the herbicide Bentazon, in the combining treatments, applying Pendimethalin, Ethalfluralin and Trifluralin can reduce costs by 79.12%, 64.91% and 61.86% respectively.
Acknowledgements
We thank the National Institute of Forestry, Agricultural and Livestock Research (INIFAP) of Mexico for financing this work as part of the project called: Alternatives to the use of Glyphosate for weed control in Mexico. (Alternativas al uso del Glifosato para el control de Maleza en México.)