Effect of Soil pH on Imazaquin and Imazethapyr Adsorption to Soil and Phytotoxicity to Corn (Zea mays)

Abstract

Adsorption of14C-imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} and imazethapyr [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-5-ethyl-3-pyridinecarboxylic acid] to soil increased as soil pH decreased from 8.0 to 3.0 in laboratory studies. Significantly more imazethapyr3(AC-263,499) than imazaquin was adsorbed at soil pH levels 3.0 and 5.5, while the greatest difference in adsorption behavior between the two herbicides was observed at a soil pH of 5.5. In greenhouse studies, phytotoxicity to corn (Zea maysL.) was greater for imazaquin than AC-263,499 applied at 26 and 53 g ai/ha. There were significant pH by herbicide and pH by rate interactions, but in trend analysis only a small proportion of the corn response (r2= 0.01 to 0.35) was attributed to increasing soil pH values. In field studies where imazaquin was applied to soil pH levels of 4.2 to 4.8, 5.4 to 5.5, and 5.8 to 6.2, injury to corn across all pH levels decreased as the time delay between herbicide application and corn planting increased. There was no significant effect of soil pH on imazaquin injury to corn planted in July or August. Decreased injury from imazaquin was observed in 1985 on corn planted in June on the soil pH of 5.8 to 6.2. Imazaquin injury was less for June-planted corn in 1984 than in 1985, across all soil pH levels.

Impact of rainfall and tillage systems on off‐site herbicide movement

“…Imazaquin is a relatively new herbicide in the imidazolinone family of herbicides, and is used for preemergence and postemergence weed control in soybean and warm-season turfgrasses. Imazaquin mobility in soil increases at high pH (Goetz et al, 1986;Renner et al, 1988) and is apparently inactivated more rapidly due to Downloaded by [University of Florida] at 15:20 25 June 2016 lower soil adsorption. High soil moisture and cool temperatures increase the mobility of imazaquin .…”

Adsorption and desorption variability of four herbicides used in paddy rice production

“…The pH effect on molinate adsorption, a non ionic pesticide, could be explained by variations in the chemical shift position on carboxyl and phenolic functional groups of HS [28] and the ionization in these functional groups. [29] Bentazon showed the lowest adsorption coefficients (Tables 2 and 3), presenting hysteresis in all soils, as the H values were below 0.7 which is indicative of this phenomenon according to Mamy et al [30] Although MCPA is an acidic herbicide as bentazon, hysteresis was not important, and its Kd values were in general greater than for bentazon (Table 3).…”

Interactions of ALS-Inhibiting Herbicide Residues in Three Prairie Soils

“…Imazamox and imazethapyr persisted for two seasons after application, resulting in significant root stunting with all imazamox and imazethapyr treatments compared with the untreated check. Lower soil pH increases the amount of imazethapyr that adsorbs to the soil colloids, also increasing persistence (Loux and Reese 1993;Renner et al 1988). Florasulam and sulfosulfuron did not result in a significant difference between imazamox-and imazethapyr-treated and untreated soil, and also were not different from the application of imazamox and imazethapyr alone.…”