Correlation of Chemical Analysis of Residual Levels of Aminocyclopyrachlor in Soil to Biological Responses of Alfalfa, Cotton, Soybean, and Sunflower

Abstract

Researchers, product registration personnel, and growers desire the ability to chemically detect residual amounts of herbicides in soil at concentrations below those necessary to cause phytotoxicity to sensitive nontarget or rotational crop plants. Alfalfa, cotton, soybean, and sunflower, crops sensitive to low concentrations of aminocyclopyrachlor in soil, were planted at field test sites approximately 1 yr after aminocyclopyrachlor methyl was applied. Soil samples were collected when rotational crops were planted and were analyzed for aminocyclopyrachlor by a method based on high performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS), with a limit of detection (LOD) of 0.1 part per billion (ppb) (soil oven-dry weight basis). Loglogistic dose–response analysis correlated visual phytotoxic plant responses to residual concentrations of aminocyclopyrachlor in the soil. Concentrations of aminocyclopyrachlor estimated to cause 25% phytotoxicity to alfalfa, cotton, soybean, and sunflower were 5.4, 3.2, 2.0, and 6.2 ppb, respectively, 20 to 60 times greater than the LOD of the analytical method available for soil analysis. Results from these studies suggest this HPLC/MS/MS method of analysis can be used to indicate potential risk and severity of plant response for alfalfa, cotton, soybean, and sunflower, and for other plant species once dose–response curves for these additional species are established. This chemical assay may be particularly important if researchers desire to study the concentration, movement, and dissipation of aminocyclopyrachlor in soil or as part of a forensic investigation to better understand the cause of an unanticipated or undesirable plant response.

Sensibility of plant species to herbicides aminocyclopyrachlor and indaziflam

“…The sensitivity of soybean, sunflower (Westra et al, 2008;Strachan et al, 2011), cotton, beet (Strachan et al, 2011) and alfalfa (Westra et al, 2008) to aminocyclopyrachlor has already been described in the literature by other authors. Strachan et al (2013) has also reported that soybean is highly sensitive to auxinic herbicides (aminocyclopyrachlor, aminocyclopyrachlor methyl, aminopyralid and dicamba) and used this species as a bioindicator of volatilization of these herbicides.…”

“…Thus, the I 50 value of these crops was higher than the highest dose tested (> 50 g ha -1 ) ( Table 1). Strachan et al (2010Strachan et al ( , 2011) also tested the sensitivity of various species to aminocyclopyrachlor and found that none of the Liliopsida species were sensitive to this herbicide, so that even the soil application of 64 g ha -1…”

“…Typical of auxinic herbicides, aminocyclopyrachlor is translocated systemically (Bukun et al, 2010), but it is effective in much lower doses than other auxinic herbicides such as 2,4 D (Turner et al, 2009). Studies conducted in a greenhouse by Strachan et al (2011) showed that the species of the class Liliopsida have increased tolerance to aminocyclopyrachlor applied to the soil than species of the class Magnoliopsida. Studies conducted by Oliveira Jr.…”

Experimental methods to evaluate herbicides behavior in soil

“…On the other hand, analytical analysis, such as chromatography, with detection systems that range from simple UV (ultra violet) absorbance detection to sophisticated mass spectrometric analysis, can accurately quantify residual concentrations of the herbicide, even in low concentration. However, they are expensive requiring specialized equipment and laboratory infrastructure (Strachan et al, 2011). Moreover, when studying the behavior of certain compounds in the soil both non-radiolabeled and radiolabeled herbicides can be used.…”

Soil Factors Effects on the Mineralization, Extractable Residue, and Bound Residue Formation of Aminocyclopyrachlor in Three Tropical Soils

“…For residual herbicides such as aminocyclopyrachlor, although its persistence in soil is indicative of good weed control, even at low application rates it may damage sensitive plants such as soybean, cotton, sunflower, and alfalfa [9]. Conklin and Lym [10] reported that aminocyclopyrachlor's 50% dissipation time (DT50) ranged from 3 to >112 days in four US soils.…”