Effect of ammonium sulfate on the phytotoxicity, foliar uptake, and translocation of imazamethabenz in wild oat
Experiments were conducted in greenhouse, growth chamber, and laboratory conditions to determine the effect of ammonium sulfate [(NH4)2SO4] on the phytotoxicity, foliar uptake, and translocation of imazamethabenz on wild oat. Rates of (NH4)2SO4 up to 5% (w/v) applied with a greenhouse sprayer did not affect the phytotoxicity of the herbicide when the mix was applied at the one- to two-leaf stage. However, inclusion of 1 and 2% (NH4)2SO4 increased the phytotoxicity of the herbicide when the mix was sprayed at the two- to three-leaf, or the three- to four-leaf stage. At 10%, (NH4)2SO4 decreased the phytotoxicity of the sublethal dosage of the herbicide. When the herbicide was applied as individual drops to the growth chamber-grown plants, inclusion of (NH4)2SO4 at 1% did not affect phytotoxicity as measured by shoot growth. The presence of (NH4)2SO4 did not affect the amount of imazamethabenz retained by wild oat foliage, but it decreased [14C]imazamethabenz absorption, slightly antagonized acropetal translocation, and increased the basipetal translocation of [14C]imazamethabenz. It was concluded that application methods greatly modify the effect of (NH4)2SO4 on imazamethabenz phytotoxicity. Herbicide absorption and translocation as determined by one method do not necessarily represent the absorption and translocation patterns when different application methods are used. Absorption and translocation were not the factors that were responsible for the observed effect of (NH4)2SO4 on the herbicide phytotoxicity.
Effects of sodium bisulphate, acidic buffers and ammonium sulphate on imazamethabenz phytotoxicity to wild oats
Abstract Greenhouse studies determined the effects of sodium bisulphate (NaB), acidic buffers and ammonium sulphate on the phytotoxicity of imazamethabenz, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H -imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2), applied to wild oat plants at the 2- to 3-leaf stage. At an equivalent dosage of imazamethabenz the liquid concentrate (LC) formulation had higher herbicidal activity and much lower pH than did the suspension concentrate (SC) formulation. NaB added to the SC formulation lowered solution pH by > 3 units to ∼ 2.2 and enhanced herbicidal activity at 200–300 g ha −1 active ingredient (a.i.), but not at 400 g a.i. ha −1 . NaB did not improve the activity of the LC formulation. Increasing the spray solution pH from 5.6 to ∼ 7.3 with 1 m KOH antagonized phytotoxicity of both LC and SC formulations of imazamethabenz alone, and imazamethabenz-SC plus NaB. Citric acid-phosphate buffers at pH 3–6, or HCl-KCl buffers at pH 1 and 2, either had no effect or antagonized the activity of the SC formulation of imazamethabenz. However, the same HCl-KCl buffers plus 1% (v/v) ammonium sulphate enhanced herbicidal activity at 250 g a.i. ha −1 , while 1% ammonium sulphate, alone, enhanced herbicidal activity at both 200 and 250 g ha −1 . NaB provided both bisulphate ion and low pH concurrently. Acidic buffers did not improve the activity of the SC formulation except in the presence of bisulphate or sulphate ions. It is suggested that at low pH the herbicide becomes cationic, forms the bisulphate or sulphate salt of the methyl ester of imazamethabenz, and enters true solution. In this form it readily penetrates the cuticle. High solution pH acts against this process.
A feasibility study of adolescent sex education: medical students as peer educators in Edinburgh schools
Objectives To determine the feasibility of medical students being involved in sex education in secondary schools, as lesson leaders in peer group discussions.