Joint Toxicity Determination of Clopyralid, Picloram and Benazolin Mixtures on Broad-leaved Weed Lapsana apogonoides Maxim. in Rape Fields

Xiong LI Jingbo LI Huifang DENG Yunyun ZHOU Kaifa GUO Xiongmei ZHU Chenzhong JIN Guiying LIU

Abstract ［Objectives］ This study was conducted to investigate the compounding of three herbicides: clopyralid, picloram and benazolin, so as to improve the effectiveness of herbicides. ［Methods］ With Lapsana apogonoides Maxim. as the target and clopyralid, picloram and benazolin as the test agents, seven gradient concentrations were set up to determine the joint toxicity of the three agents. ［Results］ When the compounding ratio of picloram, clopyralid and benazolin was 2∶1∶6, the maximum co-toxicity coefficient was 290.0. ［Conclusions］ The compounding of picloram, clopyralid and benazolin has a significant synergistic effect on L. apogonoides, which reduces production costs and environmental pressure, providing technical support for the effective control of broad-leaved weeds such as L. apogonoides.

Key words Clopyralid; Picloram; Benazolin; Rape; Weeds; Joint toxicity

Received: May 28, 2021  Accepted: July 29, 2021

Supported by Double First-class Applied Characteristic Disciplines in Hunan Province (Plant protection); Excellent Agriculture and Forestry Talent Cultivation Project of Hunan Institute of Humanities, Science and Technology; New Agricultural Science Research and Reform Practice Project in Hunan Province (XJT［2020］94).

Xiong LI (1988-), female, P. R. China, master, devoted to research about plant protection technologies.

*Corresponding author. E-mail: 532479626@qq.com; 45952729@qq.com.

Clopyralid is a kind of growth hormone synthetic herbicide with a chemical structure similar to most natural plant growth hormones. It has strong conductivity. After spraying the herbicide on weeds, the roots and leaves of plants absorb it first, and it is quickly transmitted to entire plants, causing hormones in plants to be disordered, stimulating the synthesis of ribonucleic acid in plants, controlling or stopping the continuous division and growth of their cells, depleting nutrients, and ultimately destroying vascular bundles and causing the death of weeds. Currently in crop registration of the Ministry of Agriculture, clopyralid is mainly applied to rape. The agent has fast transport speed in plants and excellent control effect, so clopyralid can be widely used to control broad-leaved weeds in rape fields［1］.

Picloram is a systemic post-emergent herbicide. After being sprayed with the herbicide, the leaves and roots absorb the herbicide, which are guided up and down to move through entire plants. The mechanism of action is to make plants produce nucleic acid, form excessive ribonucleic acid, and cause abnormal growth of stems and leaves and depletion of nutrients, and hinder the normal transport function of vascular bundles. It is suitable for rape, wheat and other crops, and can prevent and control a variety of harmful broad-leaved weeds, such as Lapsana apogonoides Maxim., Sonchus arvensis L., and Cirsium arvense var. integrifolium. It is safe for rape and wheat throughout the growth stages［2］.

Benazolin is a systemic organic heterocyclic herbicide. After the leaves absorb the agent, it is transported to whole plants, and then the synthesis of nucleic acid and protein is blocked in different parts, which eventually causes weeds to wither and die［3］. It is suitable for controlling broad-leaved weeds in rape and wheat fields.

The compounding of herbicides［4］, on the one hand, can improve the effectiveness of  herbicides, that is, the synergistic effect of herbicide combinations, and on the other hand, can save costs. The control agent selected in this study was broad-leaved weed control agent isopropyl oxalate for rape field.

Materials and Methods

Experimental materials

Seeds: L. apogonoides is the main broad-leaved weed in the rape fields in Loudi area, and the test weed seeds were collected from the rape fields in Loudi area.

Drugs: 21% picloram, produced by Hebei Wanquan lihua Chemical Co., Ltd.; 30% clopyralid, produced by Chongqing Shuangfeng Chemical Co., Ltd.; 50% benazolin suspension, Hefei Xingyu Chemical Co., Ltd.; 10% isopropyl oxalate EC, produced by Qiaochang Modern Agriculture Co., Ltd.

Instruments: Analytical balance; nursery basin; fully automatic self-propelled spray tower (self-made).

Experimental methods

Cultivation of L. apogonoides seedlings

The cultivation of seedlings adopted the greenhouse cultivation method. The L. apogonoides seeds were sown in nursery pots with a diameter of 10 cm at a sowing depth of about 1 cm, and nutrient substrate soil was used. The indoor temperature was (15±2) ℃ during the day and (10±2) ℃ at night, and the light period was about 10 h a day.

Single-dose toxicity determination

The whole plant level measurement method was adopted. The seedlings were planted at the stage of 1 leaf and 1 heart after the emergence of L. apogonoides, and 20 plants were left in each pot. When L. apogonoides grew to the 3-leaf stage, a herbicide was sprayed with a self-propelled spray tower (self-made), and the herbicide activity was determined according to the concentration of the herbicide within a certain range and the lethality of the aboveground parts of L. apogonoides seedlings. Specifically, in the 3-4 leaf stage of the above seedlings, each seedling pot was set with 20 L. apogonoides seedlings growing uniformly, and the stems and leaves were sprayed with a spray tower at a pressure of 0.4 MPa. In this experiment, the concentration gradients of the 4 kinds of drugs were different. Among them, the dose gradient of picloram is 0.00, 0.0175, 0.035, 0.070, 0.140, 0.210 and 0.280 g/L; the dose gradient of clopyralid was 0.000 0, 0.016 8, 0.027 5, 0.045 0, 0.090 0, 0.180 0 and 0.360 0 g/L; the dose gradient of benazolin was 0.000, 0.050, 0.100, 0.200, 0.400, 0.800 and 1.600 g/L, and the dose gradient of isopropyl oxalate was 0.000, 0.005, 0.010, 0.020, 0.040, 0.080 and 0.160 g/L. Each treatment had 3 replicates. After 3 weeks of application, the lethality of L. apogonoides was counted. The data processing calculation software was Sigmaplot, and curve fitting was performed using following equation: y=C+ (D-C)/［1+ (x/EC50)］b, obtaining the median lethal concentration EC50.

Joint toxicity determination

The method for determining the median lethal concentrations of compound preparations was the same as in "Single-dose toxicity determination".

In the joint toxicity determination of clopyralid, picloram and benazolin, we set 80

The calculation formula is as follows:

Co-toxicity coefficient (CTC)=［Determined toxicity index of mixture (A+B+M)/Anticipated toxicity index of mixture (A+B+M)］×100%(1)

Determined toxicity index of mixture (ATI)=［EC50 of standard agent isopropyl oxalate/EC50 of mixture (A+B+M)］×100%(2)

Anticipated toxicity index (TTI) was calculated according to Anticipated toxicity index (TTI) of mixture (A+B+M) = Toxicity index of agent A × Mass percentage of agent A in the mixture + Toxicity index of agent B × Mass percentage of agent B in the mixture + Toxicity index of agent × Mass percentage of agent M in the mixture.

Toxicity index of single drug (TI)=(EC50 of standard agent/EC50 of tested agent)×100%(3)

Results and Analysis

Single-dose toxicity determination

The results are shown in Table 1. Benazolin had the lowest toxicity to L. apogonoides, with an EC50 of 1.183 g/L. Picloram and clopyralid were highly toxic to L. apogonoides, with EC50 of 0.152 and 0.114 g/L, respectively. The most toxic was the control agent isopropyl oxalate, with an EC50 of 0.040 g/L.

Joint toxicity determination

The results are shown in Table 2. When the active ingredient ratio of picloram, clopyralid and benazolin was 3∶1∶4, the toxicity was the highest. When the effective ingredient ratios of picloram, clopyralid and benazolin were 3∶1∶4, 2∶1∶6, 2∶2∶8, 1∶2∶10 and 1∶3∶12, the co-toxicity coefficients were 242.5, 290.0, 283.2, 233.3, and 192.5, respectively, all of which showed synergistic effects. When the active ingredient ratio of picloram, clopyralid and benazolin was 2∶1∶6, the maximum co-toxicity coefficient was 290.0, and the corresponding EC50 under this compounding ratio was 0.115 g/L.

of soluble sugars, facilitate the fermentation of lactic acid bacteria, and improve the taste of the feed. The orthogonal experiment results showed that when adding 4% of brown flour into potato plants and adjusting moisture to 65%, A2B2 silage had a pH of 4.2 and an ammonia nitrogen content of 8.93 mg/g. The sensory evaluation of the silage could reach level 2, with the highest score. The optimal amount of lactic acid bacteria added was 20 g/kg, and the optimal amount of cellulose was 10 g/kg.

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