Physiological effect of clopyralid on corn as determined by bioassay and light-scattering spectroscopy

Abstract

The broadleaf auxinic herbicide clopyralid was applied to three varieties of corn (Pioneer 36B08, Pioneer 3730, and Pioneer 3559) to determine whether it was phytotoxic to this crop. The effects of clopyralid on the growth and development of corn were compared with those induced by the auxinic herbicides dicamba, 2,4-D, picloram, and fluroxypyr. When compared with the other auxinic herbicides, clopyralid, applied as a foliar spray at the three- and six-leaf stages of development, caused the least damage to all three varieties of corn. Among the auxinic herbicides tested, fluroxypyr and dicamba caused severe damage to the three varieties, whereas picloram and 2,4-D had significant detrimental effects on the growth and development of varieties 36B08 and 3730. Similar results were also obtained when corn seeds were germinated in petri dishes containing increasing concentrations of the auxinic herbicides. In addition to correlating these growth and development effects with auxinic herbicide–induced physiological changes in corn, we compared the effects of clopyralid and dicamba on proton efflux from isolated protoplasts of the three varieties. Results of these biophysical studies are consistent with those from our growth and developmental studies and confirm that clopyralid is least effective in eliciting a response in corn when compared with dicamba. We conclude that clopyralid does not cause the deleterious effects seen with other auxinic herbicides when sprayed under optimal environmental conditions, i.e., high humidity and temperature.

Genetic Engineering of Maize (Zea mays) for High-Level Tolerance to Treatment with the Herbicide Dicamba

“…The development of maize with complete tolerance to levels of dicamba employed in agriculture eliminates uncertainties regarding climatic conditions and application times that might lead to crop damage. [8][9][10][11][12] Our present studies with dicambatolerant maize indicate (as have studies with dicamba-tolerant broadleaf crops) that dicamba can be applied at recommended rates to DMO-containing crop plants either pre-or postemergence with no ill effects (Figure 2). Thus, dicamba-tolerant crops, in the future, may offer farmers the opportunity to use dicamba as a "burn down" herbicide, an option that may be particularly favorable in situations in which glyphosate-resistant broadleaf weeds are present in the area.…”

“…Although dicamba has been used for over 50 years for the effective control of most broadleaf weeds in maize, some crop damage can occur if dicamba is applied to corn crops outside the developmental window prescribed on the package label, in certain years with atypical climactic conditions, in certain soil types, and/or with maize production on certain types of soil. − Thus, development of maize that displays substantially enhanced tolerance to treatment with dicamba coupled with the ability to spray maize crops pre- or postemergence and under various climactic conditions may be appealing to farmers. Here we report the development of transgenic maize events expressing nuclear CTP-DMO genes that provide tolerance to treatments with high levels of dicamba applied either pre- or postemergence.…”

Sweet Corn Hybrid Sensitivity to Clopyralid

“…Clopyralid is a selective POST herbicide that is a member of the pyridinecarboxylic acid family that was originally registered for use in Ontario in 1989 for post-harvest renovation use in strawberries (Fragaria ananassa) (Vencill 2002;Vettakkorumakankav et al 2002). It has activity on a number of annual and perennial broadleaf weeds, including Canada thistle [Cirsium arvense (L.) Scop.…”

Effect of dicamba on reproductive development in corn and rice

“…Instead, injury on corn induced by dicamba was assessed by analyzing the total number of rows per ear and seeds per row of each ear, seeds per ear, and grain yield (Table 1). Often, visible injury to corn caused by dicamba occurs as a result of abnormal weather conditions, poorly timed applications, or misapplications (Vettakkorumakankav et al., 2002). Greater visible injury to corn is more likely to occur when dicamba is applied PRE and generally requires lower dicamba rates to express symptomology as opposed to higher rates when corn is more mature (Mingxia et al., 2011), possibly explaining the absence of injury symptomology from later applications.…”

“…Injury to corn has been observed with several synthetic auxin herbicides alongside dicamba, such as 2,4‐D and fluroxypyr (Vettakkorumakankav et al., 2002). Adverse consequences from dicamba applied to corn plants at 1, 2, or 4 kg ha −1 could be seen from applications made at the V3 growth stage, which were visually apparent from the various degrees of lodging that occurred 5 d after treatment.…”