Crop Response to Carryover of Mesotrione Residues in the Field

Abstract

Two field residue studies were conducted from 2005 to 2007 in Simcoe, Ontario, Canada, to evaluate the effects of mesotrione soil residues on injury, plant dry weight, and yield of sugar beet, cucumber, pea, green bean, and soybean and to verify the potential of reducing a 2-yr field-residue study (conventional residue carryover) to a 1-yr field study (simulated residue-carryover study) by growing these crops in soil treated with reduced rates of mesotrione applied in the same year. There was a significant difference in mesotrione carryover between 2006 and 2007 and differences between years can be explained by differences in soil pH and soil moisture. The conventional and the simulated residue-carryover studies successfully measured mesotrione persistence and rotational crop sensitivity. Both studies showed that sugar beet was the most-sensitive crop with injury, plant dry weight reduction, and yield loss because of mesotrione residues as high as 100%. Green bean was the next most-sensitive crop to mesotrione residues followed by pea, cucumber, and soybean. The simulated residue-carryover study provided a more-rigorous test of rotational crop sensitivity to mesotrione residues than the conventional residue-carryover study, especially at higher rates for the more-sensitive crops. For the other crops, responses to mesotrione residues were similar between the conventional and simulated residue-carryover studies.

Sensitivity of selected dry bean (Phaseolus vulgarisL.) cultivars to mesotrione in a simulated carry-over trial

“…However, Riddle et al (2013) noted that the dry mass of sugar beet, green bean and pea plants 40 d after planting was reduced at higher mesotrione application rates (>280 g ai ha −1 ) during the previous season, whereas that of soya bean was not affected, despite plants showing symptoms of phytotoxicity, and the mass of cucumber plants was only reduced at a rate of 560 g ai ha −1 , or four times the recommended application rate. Soya bean is extremely sensitive to this herbicide and can develop symptoms at rates as low as 4 g ai ha −1 (Mitchell et al 2001).…”

“…The symptoms of mesotrione toxicity are not always limited to the classical plant bleaching as described in the literature, but can vary appreciably, and some symptoms such as the crinkled leaves may even be confused with acetanilide damage (WSSA 2007). Riddle et al (2013) observed that symptoms in a carryover trial differed between plant species, with green bean and soya bean exhibiting mainly chlorosis followed by necrosis of the tissue, whereas pea, sugar beet and cucumber plants showed both these symptoms as well as the more characteristic bleaching symptoms. The severity of symptoms on all plant species decreased as the mesotrione application rates decreased (Felix et al 2007;Soltani et al 2007;Riddle et al 2013), a finding similar to that in the present study.…”

“…Both Soltani et al (2007) and Riddle et al (2013) indicated that stunting of plants was one of the symptoms of mesotrione injury. However, the extent of this stunting was not quantified in either study.…”

“…The formulations used in the USA and Canada are similar to that used in South Africa, i.e. 480 g ai L −1 suspension concentrate, whereas the formulation used in Europe is 100 g ai L −1 and contains a built-in wetting agent Riddle et al 2013). Application rates range from 100 to 225 g ai ha −1 when applied pre-emergence and 70 to 150 g ai ha −1 when used post-emergence (Mitchell et al 2001;WSSA 2007).…”

“…It is thus not possible to assume that the results of studies carried out in other countries can be extrapolated to local growing conditions, even though the crops and soils may be similar. Riddle et al (2013) estimated that more than 10.6 to 14 of the calculated half-lives from their trials would have to elapse prior to planting mesotrione-sensitive rotational crops, but could vary slightly according to soil and climatic conditions. Looking at the manner in which the residue concentrations in the soil were calculated (using the 9-day half-life) it is apparent that the time period during which phytotoxicity may be expected can vary.…”