Vapor Movement of Synthetic Auxin Herbicides: Aminocyclopyrachlor, Aminocyclopyrachlor-Methyl Ester, Dicamba, and Aminopyralid

Abstract

Aminocyclopyrachlor, a newly discovered synthetic auxin herbicide, and its methyl ester, appear to control a number of perennial broadleaf weeds. The potential volatility of this new herbicide and its methyl ester were determined under laboratory conditions and were also compared to dicamba and aminopyralid with the use of enclosed chamber and open-air plant bioassays. Bioassays consisting of visual estimates of epinastic responses and kidney bean and soybean leaf-width measurements were developed to measure vapor release from glass and plastic. Vapor release of aminocyclopyrachlor from glass surfaces was undetectable under laboratory conditions, and no phytotoxic responses were observed when plants were exposed to vapors emanating from various surfaces. Results were similar to those of aminopyralid, indicating the risk of plant injury from vapor movement of aminocyclopyrachlor and aminopyralid was very low. When combined with 1% methylated seed oil, vapor release of aminocyclopyrachlor-methyl ester reached 86% 192 h after application to glass surfaces. Phytotoxic responses of plants exposed to vapors emanating from various surfaces treated with aminocyclopyrachlor-methyl ester were similar to responses to dicamba under enclosed incubation conditions, but were less in outdoor, open-air environments. Studies are needed to understand better the risk of injury to nontarget plants due to vapor movement of aminocyclopyrachlor-methyl ester under field applications.

Sensibility of plant species to herbicides aminocyclopyrachlor and indaziflam

“…According to Strachan et al (2010) these intoxication symptoms in Magnoliopsida species are similar to those observed when applying the herbicide aminopyralid, which also has the same mechamism of action. For beets, seedling emergence was verified, however, plants died even in the same soil with the lowest dose of aminocyclopyrachlor (10 g ha .…”

“…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…”

“…Strachan et al (2010) also reported a high sensitivity of soybean to this herbicide, reporting that the dose of 1.0 g ha -1…”

Evaluation of 2,4-D-Choline Based Herbicide Systems in 2,4-D Tolerant Soybean (<i>Glycine max</i> L.)

“…Tolerance was achieved through the insertion of bacterial genes into soybean that allows the plant to metabolize 2,4-D. [21]. Previous research has documented that up to 16% of spray solution can physically drift from the intended application area [22].…”

Palmer Amaranth (<i>Amaranthus palmeri</i> S. Wats.) and Pitted Morningglory (<i>Ipomoea lacunosa</i> L.) Control in Dicamba Tolerant Soybean (<i>Glycine max</i> L.)

“…Dicamba is a growth regulator that mimics the endogenous plant hormone indole-3-acetic acid (IAA) and causes the over-proliferation of plant cells at the meristematic regions, leading to death [13]. Auxin-like growth regulating herbicides, such as dicamba, are susceptible to off-target movement due to volatilization and subsequent vapor drift [14]. Several different salt formulations of dicamba have been developed to minimize the off-target damage to sensitive broadleaf crops due to volatilization and vapor drift [12].…”