Effects of Imazaquin Residues on Cotton (Gossypium hirsutum)

Abstract

Field and laboratory studies were conducted in 1987 and 1988 on several Arkansas soils to determine the effects of residual levels of imazaquin on cotton. Imazaquin concentrations ranging from 0.007 to 0.024 μg/g and 0.00 to 0.015 μg/g were found in soil samples taken 12 and 24 months, respectively, following preplant-incorporated applications at rates of 140 g/ha. Cotton yields were reduced from 7 to 42% in 1987 as the soil concentration of imazaquin increased from 0.007 to 0.024 μg/g. Imazaquin persistence was greater in clay soils than loams or sandy loams. Imazaquin was weakly adsorbed to a clay, loam, and sandy loam soil in laboratory studies; the adsorption isotherms did not differ significantly by soil texture. A bioassay utilizing cotton as the indicator species was developed to determine imazaquin concentrations in soils ranging from 0 to 0.06 μg/g. Imazaquin concentrations determined by the bioassay method were found to be 75, 77, and 80% of those determined by chemical extractions for a clay, loam, and sandy loam soil, respectively.

Cotton (Gossypium hirsutum) Response to Simulated Imazapic Residues1

“…Injury at both locations was concentration dependent. Cotton injury symptoms observed in all growing seasons included malformation and chlorosis of leaf tissue at rates from 2 to 9 g/ha at Plains, typical of imidazolinone herbicides (Barnes et al 1989;Johnson et al 1995;York et al 2000). These same symptoms were observed at Tifton for the 18 and 35 g/ha rates.…”

“…The Faceville sandy loam at Plains had 16% clay with 70% of that fraction composed of kaolinite and gibbsite (Grey et al 1996) and a cation-exchange capacity (CEC) of 11.87. These clay minerals can exhibit imidazolinone herbicide adsorption and then hysteresis (Barnes et al 1989;Goetz and Gbur 1990;Goetz et al 1986;Loux and Liebl 1989;Pusino and Gessa 1997), which can prolong carryover effects (Barnes et al 1989;Basham et al 1987;Johnson et al 1995). In contrast, Tifton loamy sand had a low clay content of 4% with 60% of that fraction composed of kaolinite and gibbsite (data not shown).…”

VA-mycorrhizae and mycorrhiza stimulating isoflavonoid compounds reduce plant herbicide injury

“…Crop phytotoxic symptoms include stunting, shortened internodes, deformed leaves, interveinal chlorosis, loss of apical dominance and premature senescence (Hess, 1989;Shaner, 1989b) and have been found to occur in double cropped soybeans and other crops (Barnes et al, 1989;Basham et al, 1987;Mills and Witt, 1989a, b;Renner et al, 1988). Under normal soil conditions these herbicides are degraded rapidly and do not reach the threshold concentrations for non-target phytotoxicity (Cantwell et al, 1989;Shaner, 1989a).…”

“…However, under unfavorable conditions for degradation, such as severe drought, high soil pH, low soil temperatures, and high clay content, residual herbicide levels may build up and adversely affect crop plants (Cantwell et al, 1989;Marking, 1988;Stougaard et al, 1990). Imazaquin persistence has been related to carryover injury in succeeding crops such as rice, wheat, corn, sorghum and cotton (Barnes et al, 1989;Barrett, 1989b;Basham et al, 1987;Basham and Lavy, 1987). Although the threshold level for imazaquin carryover is approximately 13 ppb, soil concentrations as low as 7ppb soil can affect crop growth (Basham et al, 1987;Basham and Lavy, 1987;Stougaard et al, 1990).…”

Effects of Soil-applied Imazapic on Pecan Production

“…One explanation as to the variable response of percentage of hollow kernels between the low and high rates of imazapic in the two orchards is soil type. The Fuquay soil on which the 2008 study was located is a deep sand with only 4% clay and a cation exchange capacity (CEC) of 5.27 meq/100 g. The 2009 orchard, situated on Tifton loamy sand, has 8% clay and a CEC of 10.48 meq/100 g. Imidazolinone herbicide adsorption and hysteresis can more readily occur with increasing clay content and CEC (Barnes et al, 1989;Goetz et al, 1986Goetz et al, , 1990Magels, 1991;Stougaard et al, 1990). The difference in the attributes of the two soils in this study may have prolonged exposure of the pecan feeder roots to imazapic in soils with high clay content, making the lower rate more damaging to the Fig.…”